summaryrefslogtreecommitdiff
path: root/lisp/vc.el
blob: d8605b9fa12ef52e132543240da1d19544c9b50c (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
1899
1900
1901
1902
1903
1904
1905
1906
1907
1908
1909
1910
1911
1912
1913
1914
1915
1916
1917
1918
1919
1920
1921
1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
2024
2025
2026
2027
2028
2029
2030
2031
2032
2033
2034
2035
2036
2037
2038
2039
2040
2041
2042
2043
2044
2045
2046
2047
2048
2049
2050
2051
2052
2053
2054
2055
2056
2057
2058
2059
2060
2061
2062
2063
2064
2065
2066
2067
2068
2069
2070
2071
2072
2073
2074
2075
2076
2077
2078
2079
2080
2081
2082
2083
2084
2085
2086
2087
2088
2089
2090
2091
2092
2093
2094
2095
2096
2097
2098
2099
2100
2101
2102
2103
2104
2105
2106
2107
2108
2109
2110
2111
2112
2113
2114
2115
2116
2117
2118
2119
2120
2121
2122
2123
2124
2125
2126
2127
2128
2129
2130
2131
2132
2133
2134
2135
2136
2137
2138
2139
2140
2141
2142
2143
2144
2145
2146
2147
2148
2149
2150
2151
2152
2153
2154
2155
2156
2157
2158
2159
2160
2161
2162
2163
2164
2165
2166
2167
2168
2169
2170
2171
2172
2173
2174
2175
2176
2177
2178
2179
2180
2181
2182
2183
2184
2185
2186
2187
2188
2189
2190
2191
2192
2193
2194
2195
2196
2197
2198
2199
2200
2201
2202
2203
2204
2205
2206
2207
2208
2209
2210
2211
2212
2213
2214
2215
2216
2217
2218
2219
2220
2221
2222
2223
2224
2225
2226
2227
2228
2229
2230
2231
2232
2233
2234
2235
2236
2237
2238
2239
2240
2241
2242
2243
2244
2245
2246
2247
2248
2249
2250
2251
2252
2253
2254
2255
2256
2257
2258
2259
2260
2261
2262
2263
2264
2265
2266
2267
2268
2269
2270
2271
2272
2273
2274
2275
2276
2277
2278
2279
2280
2281
2282
2283
2284
2285
2286
2287
2288
2289
2290
2291
2292
2293
2294
2295
2296
2297
2298
2299
2300
2301
2302
2303
2304
2305
2306
2307
2308
2309
2310
2311
2312
2313
2314
2315
2316
2317
2318
2319
2320
2321
2322
2323
2324
2325
2326
2327
2328
2329
2330
2331
2332
2333
2334
2335
2336
2337
2338
2339
2340
2341
2342
2343
2344
2345
2346
2347
2348
2349
2350
2351
2352
2353
2354
2355
2356
2357
2358
2359
2360
2361
2362
2363
2364
2365
2366
2367
2368
2369
2370
2371
2372
2373
2374
2375
2376
2377
2378
2379
2380
2381
2382
2383
2384
2385
2386
2387
2388
2389
2390
2391
2392
2393
2394
2395
2396
2397
2398
2399
2400
2401
2402
2403
2404
2405
2406
2407
2408
2409
2410
2411
2412
2413
2414
2415
2416
2417
2418
2419
2420
2421
2422
2423
2424
2425
2426
2427
2428
2429
2430
2431
2432
2433
2434
2435
2436
2437
2438
2439
2440
2441
2442
2443
2444
2445
2446
2447
2448
2449
2450
2451
2452
2453
2454
2455
2456
2457
2458
2459
2460
2461
2462
2463
2464
2465
2466
2467
2468
2469
2470
2471
2472
2473
2474
2475
2476
2477
2478
2479
2480
2481
2482
2483
2484
2485
2486
2487
2488
2489
2490
2491
2492
2493
2494
2495
2496
2497
2498
2499
2500
2501
2502
2503
2504
2505
2506
2507
2508
2509
2510
2511
2512
2513
2514
2515
2516
2517
2518
2519
2520
2521
2522
2523
2524
2525
2526
2527
2528
2529
2530
2531
2532
2533
2534
2535
2536
2537
2538
2539
2540
2541
2542
2543
2544
2545
2546
2547
2548
2549
2550
2551
2552
2553
2554
2555
2556
2557
2558
2559
2560
2561
2562
2563
2564
2565
2566
2567
2568
2569
2570
2571
2572
2573
2574
2575
2576
2577
2578
2579
2580
2581
2582
2583
2584
2585
2586
2587
2588
2589
2590
2591
2592
2593
2594
2595
2596
2597
2598
2599
2600
2601
2602
2603
2604
2605
2606
2607
2608
2609
2610
2611
2612
2613
2614
2615
2616
2617
2618
2619
2620
2621
2622
2623
2624
2625
2626
2627
2628
2629
2630
2631
2632
2633
2634
2635
2636
2637
2638
2639
2640
2641
2642
2643
2644
2645
2646
2647
2648
2649
2650
2651
2652
2653
2654
2655
2656
2657
2658
2659
2660
2661
2662
2663
2664
2665
2666
2667
2668
2669
2670
2671
2672
2673
2674
2675
2676
2677
2678
2679
2680
2681
2682
2683
2684
2685
2686
2687
2688
2689
2690
2691
2692
2693
2694
2695
2696
2697
2698
2699
2700
2701
2702
2703
2704
2705
2706
2707
2708
2709
2710
2711
2712
2713
2714
2715
2716
2717
2718
2719
2720
2721
2722
2723
2724
2725
2726
2727
2728
2729
2730
2731
2732
2733
2734
2735
2736
2737
2738
2739
2740
2741
2742
2743
2744
2745
2746
2747
2748
2749
2750
2751
2752
2753
2754
2755
2756
;;; vc.el --- drive a version-control system from within Emacs

;; Copyright (C) 1992, 93, 94, 95, 96 Free Software Foundation, Inc.

;; Author: Eric S. Raymond <esr@snark.thyrsus.com>
;; Modified by:
;;   ttn@netcom.com
;;   Per Cederqvist <ceder@lysator.liu.edu>
;;   Andre Spiegel <spiegel@berlin.informatik.uni-stuttgart.de>

;; This file is part of GNU Emacs.

;; GNU Emacs is free software; you can redistribute it and/or modify
;; it under the terms of the GNU General Public License as published by
;; the Free Software Foundation; either version 2, or (at your option)
;; any later version.

;; GNU Emacs is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;; GNU General Public License for more details.

;; You should have received a copy of the GNU General Public License
;; along with GNU Emacs; see the file COPYING.  If not, write to the
;; Free Software Foundation, Inc., 59 Temple Place - Suite 330,
;; Boston, MA 02111-1307, USA.

;;; Commentary:

;; This mode is fully documented in the Emacs user's manual.
;;
;; This was designed and implemented by Eric Raymond <esr@snark.thyrsus.com>.
;; Paul Eggert <eggert@twinsun.com>, Sebastian Kremer <sk@thp.uni-koeln.de>,
;; and Richard Stallman contributed valuable criticism, support, and testing.
;; CVS support was added by Per Cederqvist <ceder@lysator.liu.se>
;; in Jan-Feb 1994.
;;
;; Supported version-control systems presently include SCCS, RCS, and CVS.
;;
;; Some features will not work with old RCS versions.  Where
;; appropriate, VC finds out which version you have, and allows or
;; disallows those features (stealing locks, for example, works only 
;; from 5.6.2 onwards).
;; Even initial checkins will fail if your RCS version is so old that ci
;; doesn't understand -t-; this has been known to happen to people running
;; NExTSTEP 3.0. 
;;
;; You can support the RCS -x option by adding pairs to the 
;; vc-master-templates list.
;;
;; Proper function of the SCCS diff commands requires the shellscript vcdiff
;; to be installed somewhere on Emacs's path for executables.
;;
;; If your site uses the ChangeLog convention supported by Emacs, the
;; function vc-comment-to-change-log should prove a useful checkin hook.
;;
;; This code depends on call-process passing back the subprocess exit
;; status.  Thus, you need Emacs 18.58 or later to run it.  For the
;; vc-directory command to work properly as documented, you need 19.
;; You also need Emacs 19's ring.el.
;;
;; The vc code maintains some internal state in order to reduce expensive
;; version-control operations to a minimum.  Some names are only computed
;; once.  If you perform version control operations with RCS/SCCS/CVS while
;; vc's back is turned, or move/rename master files while vc is running,
;; vc may get seriously confused.  Don't do these things!
;;
;; Developer's notes on some concurrency issues are included at the end of
;; the file.

;;; Code:

(require 'vc-hooks)
(require 'ring)
(eval-when-compile (require 'dired))	; for dired-map-over-marks macro

(if (not (assoc 'vc-parent-buffer minor-mode-alist))
    (setq minor-mode-alist
	  (cons '(vc-parent-buffer vc-parent-buffer-name)
		minor-mode-alist)))

;; To implement support for a new version-control system, add another
;; branch to the vc-backend-dispatch macro and fill it in in each
;; call.  The variable vc-master-templates in vc-hooks.el will also
;; have to change.

(defmacro vc-backend-dispatch (f s r c)
  "Execute FORM1, FORM2 or FORM3 for SCCS, RCS or CVS respectively.
If FORM3 is `RCS', use FORM2 for CVS as well as RCS.
\(CVS shares some code with RCS)."
  (list 'let (list (list 'type (list 'vc-backend f)))
	(list 'cond
	      (list (list 'eq 'type (quote 'SCCS)) s)	;; SCCS
	      (list (list 'eq 'type (quote 'RCS)) r)	;; RCS
	      (list (list 'eq 'type (quote 'CVS)) 	;; CVS
		    (if (eq c 'RCS) r c))
	      )))

;; General customization

(defvar vc-suppress-confirm nil
  "*If non-nil, treat user as expert; suppress yes-no prompts on some things.")
(defvar vc-initial-comment nil
  "*If non-nil, prompt for initial comment when a file is registered.")
(defvar vc-command-messages nil
  "*If non-nil, display run messages from back-end commands.")
(defvar vc-checkin-switches nil
  "*A string or list of strings specifying extra switches passed 
to the checkin program by \\[vc-checkin].")
(defvar vc-checkout-switches nil
  "*A string or list of strings specifying extra switches passed 
to the checkout program by \\[vc-checkout].")
(defvar vc-directory-exclusion-list '("SCCS" "RCS" "CVS")
  "*A list of directory names ignored by functions that recursively 
walk file trees.")

(defconst vc-maximum-comment-ring-size 32
  "Maximum number of saved comments in the comment ring.")

;;; This is duplicated in diff.el.
(defvar diff-switches "-c"
  "*A string or list of strings specifying switches to be be passed to diff.")

;;;###autoload
(defvar vc-checkin-hook nil
  "*List of functions called after a checkin is done.  See `run-hooks'.")

(defvar vc-make-buffer-writable-hook nil
  "*List of functions called when a buffer is made writable.  See `run-hooks.'
This hook is only used when the version control system is CVS.  It
might be useful for sites who uses locking with CVS, or who uses link
farms to gold trees.")

;; Header-insertion hair

(defvar vc-header-alist
  '((SCCS "\%W\%") (RCS "\$Id\$") (CVS "\$Id\$"))
  "*Header keywords to be inserted by `vc-insert-headers'.
Must be a list of two-element lists, the first element of each must
be `RCS', `CVS', or `SCCS'.  The second element is the string to
be inserted for this particular backend.")
(defvar vc-static-header-alist
  '(("\\.c$" .
     "\n#ifndef lint\nstatic char vcid[] = \"\%s\";\n#endif /* lint */\n"))
  "*Associate static header string templates with file types.  A \%s in the
template is replaced with the first string associated with the file's
version-control type in `vc-header-alist'.")

(defvar vc-comment-alist
  '((nroff-mode ".\\\"" ""))
  "*Special comment delimiters to be used in generating vc headers only.
Add an entry in this list if you need to override the normal comment-start
and comment-end variables.  This will only be necessary if the mode language
is sensitive to blank lines.")

;; Default is to be extra careful for super-user.
(defvar vc-checkout-carefully (= (user-uid) 0)
  "*Non-nil means be extra-careful in checkout.
Verify that the file really is not locked
and that its contents match what the master file says.")

(defvar vc-rcs-release nil
  "*The release number of your RCS installation, as a string.
If nil, VC itself computes this value when it is first needed.")

(defvar vc-sccs-release nil
  "*The release number of your SCCS installation, as a string.
If nil, VC itself computes this value when it is first needed.")

(defvar vc-cvs-release nil
  "*The release number of your CVS installation, as a string.
If nil, VC itself computes this value when it is first needed.")

;; Variables the user doesn't need to know about.
(defvar vc-log-entry-mode nil)
(defvar vc-log-operation nil)
(defvar vc-log-after-operation-hook nil)
(defvar vc-checkout-writable-buffer-hook 'vc-checkout-writable-buffer)
;; In a log entry buffer, this is a local variable
;; that points to the buffer for which it was made
;; (either a file, or a VC dired buffer).
(defvar vc-parent-buffer nil)
(defvar vc-parent-buffer-name nil)

(defvar vc-log-file)
(defvar vc-log-version)

(defconst vc-name-assoc-file "VC-names")

(defvar vc-dired-mode nil)
(make-variable-buffer-local 'vc-dired-mode)

(defvar vc-comment-ring nil)
(defvar vc-comment-ring-index nil)
(defvar vc-last-comment-match nil)

;; Back-portability to Emacs 18

(defun file-executable-p-18 (f)
  (let ((modes (file-modes f)))
    (and modes (not (zerop (logand 292))))))

(defun file-regular-p-18 (f)
  (let ((attributes (file-attributes f)))
    (and attributes (not (car attributes)))))

; Conditionally rebind some things for Emacs 18 compatibility
(if (not (boundp 'minor-mode-map-alist))
    (progn
      (setq compilation-old-error-list nil)
      (fset 'file-executable-p 'file-executable-p-18)
      (fset 'shrink-window-if-larger-than-buffer 'beginning-of-buffer)
      ))

(if (not (fboundp 'file-regular-p))
    (fset 'file-regular-p 'file-regular-p-18))

;;; Find and compare backend releases

(defun vc-backend-release (backend)
  ;; Returns which backend release is installed on this system.
  (cond
   ((eq backend 'RCS)
    (or vc-rcs-release
	(and (zerop (vc-do-command nil 2 "rcs" nil nil "-V"))
	     (save-excursion
	       (set-buffer (get-buffer "*vc*"))
	       (setq vc-rcs-release
		     (car (vc-parse-buffer
			   '(("^RCS version \\([0-9.]+ *.*\\)" 1)))))))
	(setq vc-rcs-release 'unknown)))
   ((eq backend 'CVS)
    (or vc-cvs-release
	(and (zerop (vc-do-command nil 1 "cvs" nil nil "-v"))
	     (save-excursion
	       (set-buffer (get-buffer "*vc*"))
	       (setq vc-cvs-release
		     (car (vc-parse-buffer
			   '(("^Concurrent Versions System (CVS) \\([0-9.]+\\)"
			      1)))))))
	(setq vc-cvs-release 'unknown)))
     ((eq backend 'SCCS)
      vc-sccs-release)))

(defun vc-release-greater-or-equal (r1 r2)
  ;; Compare release numbers, represented as strings.
  ;; Release components are assumed cardinal numbers, not decimal
  ;; fractions (5.10 is a higher release than 5.9).  Omitted fields
  ;; are considered lower (5.6.7 is earlier than 5.6.7.1).
  ;; Comparison runs till the end of the string is found, or a
  ;; non-numeric component shows up (5.6.7 is earlier than "5.6.7 beta",
  ;; which is probably not what you want in some cases).
  ;;   This code is suitable for existing RCS release numbers.  
  ;; CVS releases are handled reasonably, too (1.3 < 1.4* < 1.5).
  (let (v1 v2 i1 i2)
    (catch 'done
      (or (and (string-match "^\\.?\\([0-9]+\\)" r1)
	       (setq i1 (match-end 0))
	       (setq v1 (string-to-number (match-string 1 r1)))
	       (or (and (string-match "^\\.?\\([0-9]+\\)" r2)
			(setq i2 (match-end 0))
			(setq v2 (string-to-number (match-string 1 r2)))
			(if (> v1 v2) (throw 'done t)
			  (if (< v1 v2) (throw 'done nil)
			    (throw 'done
				   (vc-release-greater-or-equal
				    (substring r1 i1)
				    (substring r2 i2)))))))
		   (throw 'done t)))
	  (or (and (string-match "^\\.?\\([0-9]+\\)" r2)
		   (throw 'done nil))
	      (throw 'done t)))))

(defun vc-backend-release-p (backend release)
  ;; Return t if we have RELEASE of BACKEND or better
  (let (i r (ri 0) (ii 0) is rs (installation (vc-backend-release backend)))
    (if (not (eq installation 'unknown))
	(cond
	 ((or (eq backend 'RCS) (eq backend 'CVS))
	  (vc-release-greater-or-equal installation release))))))

;;; functions that operate on RCS revision numbers

(defun vc-trunk-p (rev)
  ;; return t if REV is a revision on the trunk
  (not (eq nil (string-match "\\`[0-9]+\\.[0-9]+\\'" rev))))

(defun vc-branch-part (rev)
  ;; return the branch part of a revision number REV
  (substring rev 0 (string-match "\\.[0-9]+\\'" rev)))

;; File property caching

(defun vc-clear-context ()
  "Clear all cached file properties and the comment ring."
  (interactive)
  (fillarray vc-file-prop-obarray nil)
  ;; Note: there is potential for minor lossage here if there is an open
  ;; log buffer with a nonzero local value of vc-comment-ring-index.
  (setq vc-comment-ring nil))

(defun vc-file-clear-masterprops (file)
  ;; clear all properties of FILE that were retrieved
  ;; from the master file
  (vc-file-setprop file 'vc-latest-version nil)
  (vc-file-setprop file 'vc-your-latest-version nil)
  (vc-backend-dispatch file
     (progn   ;; SCCS
       (vc-file-setprop file 'vc-master-locks nil))
     (progn   ;; RCS
       (vc-file-setprop file 'vc-default-branch nil)
       (vc-file-setprop file 'vc-head-version nil)
       (vc-file-setprop file 'vc-master-workfile-version nil)
       (vc-file-setprop file 'vc-master-locks nil))
     (progn
       (vc-file-setprop file 'vc-cvs-status nil))))

(defun vc-head-version (file)
  ;; Return the RCS head version of FILE 
  (cond ((vc-file-getprop file 'vc-head-version))
	(t (vc-fetch-master-properties file)
	   (vc-file-getprop file 'vc-head-version))))

;; Random helper functions

(defun vc-latest-on-branch-p (file)
  ;; return t iff the current workfile version of FILE is
  ;; the latest on its branch.
  (vc-backend-dispatch file
     ;; SCCS
     (string= (vc-workfile-version file) (vc-latest-version file)) 
     ;; RCS
     (let ((workfile-version (vc-workfile-version file)) tip-version)
       (if (vc-trunk-p workfile-version) 
	   (progn 
	     ;; Re-fetch the head version number.  This is to make
             ;; sure that no-one has checked in a new version behind
	     ;; our back.
	     (vc-fetch-master-properties file)
	     (string= (vc-file-getprop file 'vc-head-version)
		      workfile-version))
	 ;; If we are not on the trunk, we need to examine the
	 ;; whole current branch.  (vc-master-workfile-version 
         ;; is not what we need.)
	 (save-excursion
	   (set-buffer (get-buffer-create "*vc-info*"))
	   (vc-insert-file (vc-name file) "^desc")
	   (setq tip-version (car (vc-parse-buffer (list (list 
             (concat "^\\(" (regexp-quote (vc-branch-part workfile-version))
		     "\\.[0-9]+\\)\ndate[ \t]+\\([0-9.]+\\);") 1 2)))))
	   (if (get-buffer "*vc-info*") 
	       (kill-buffer (get-buffer "*vc-info*")))
	   (string= tip-version workfile-version))))
     ;; CVS
     t))

(defun vc-registration-error (file)
  (if file
      (error "File %s is not under version control" file)
    (error "Buffer %s is not associated with a file" (buffer-name))))

(defvar vc-binary-assoc nil)

(defun vc-find-binary (name)
  "Look for a command anywhere on the subprocess-command search path."
  (or (cdr (assoc name vc-binary-assoc))
      (catch 'found
	(mapcar
	 (function 
	  (lambda (s)
	    (if s
		(let ((full (concat s "/" name)))
		  (if (file-executable-p full)
		      (progn
			(setq vc-binary-assoc
			      (cons (cons name full) vc-binary-assoc))
			(throw 'found full)))))))
	 exec-path)
	nil)))

(defun vc-do-command (buffer okstatus command file last &rest flags)
  "Execute a version-control command, notifying user and checking for errors.
Output from COMMAND goes to BUFFER, or *vc* if BUFFER is nil.  
The command is successful if its exit status does not exceed OKSTATUS.
The last argument of the command is the master name of FILE if LAST is 
`MASTER', or the workfile of FILE if LAST is `WORKFILE'; this is appended 
to an optional list of FLAGS."
  (and file (setq file (expand-file-name file)))
  (if (not buffer) (setq buffer "*vc*"))
  (if vc-command-messages
      (message "Running %s on %s..." command file))
  (let ((obuf (current-buffer)) (camefrom (current-buffer))
	(squeezed nil)
	(vc-file (and file (vc-name file)))
	(olddir default-directory)
	status)
    (set-buffer (get-buffer-create buffer))
    (set (make-local-variable 'vc-parent-buffer) camefrom)
    (set (make-local-variable 'vc-parent-buffer-name)
	 (concat " from " (buffer-name camefrom)))
    (setq default-directory olddir)
    
    (erase-buffer)

    (mapcar
     (function (lambda (s) (and s (setq squeezed (append squeezed (list s))))))
     flags)
    (if (and vc-file (eq last 'MASTER))
	(setq squeezed (append squeezed (list vc-file))))
    (if (eq last 'WORKFILE)
	(progn
	  (let* ((pwd (expand-file-name default-directory))
		 (preflen (length pwd)))
	    (if (string= (substring file 0 preflen) pwd)
		(setq file (substring file preflen))))
	  (setq squeezed (append squeezed (list file)))))
    (let ((exec-path (append vc-path exec-path))
	  ;; Add vc-path to PATH for the execution of this command.
	  (process-environment
	   (cons (concat "PATH=" (getenv "PATH")
			 path-separator
			 (mapconcat 'identity vc-path path-separator))
		 process-environment)))
      (setq status (apply 'call-process command nil t nil squeezed)))
    (goto-char (point-max))
    (set-buffer-modified-p nil)
    (forward-line -1)
    (if (or (not (integerp status)) (< okstatus status))
	(progn
	  (pop-to-buffer buffer)
	  (goto-char (point-min))
	  (shrink-window-if-larger-than-buffer)
	  (error "Running %s...FAILED (%s)" command
		 (if (integerp status)
		     (format "status %d" status)
		   status))
	  )
      (if vc-command-messages
	  (message "Running %s...OK" command))
      )
    (set-buffer obuf)
    status)
  )

;;; Save a bit of the text around POSN in the current buffer, to help
;;; us find the corresponding position again later.  This works even
;;; if all markers are destroyed or corrupted.
;;; A lot of this was shamelessly lifted from Sebastian Kremer's rcs.el mode.
(defun vc-position-context (posn)
  (list posn
	(buffer-size)
	(buffer-substring posn
			  (min (point-max) (+ posn 100)))))

;;; Return the position of CONTEXT in the current buffer, or nil if we
;;; couldn't find it.
(defun vc-find-position-by-context (context)
  (let ((context-string (nth 2 context)))
    (if (equal "" context-string)
	(point-max)
      (save-excursion
	(let ((diff (- (nth 1 context) (buffer-size))))
	  (if (< diff 0) (setq diff (- diff)))
	  (goto-char (nth 0 context))
	  (if (or (search-forward context-string nil t)
		  ;; Can't use search-backward since the match may continue
		  ;; after point.
		  (progn (goto-char (- (point) diff (length context-string)))
			 ;; goto-char doesn't signal an error at
			 ;; beginning of buffer like backward-char would
			 (search-forward context-string nil t)))
	      ;; to beginning of OSTRING
	      (- (point) (length context-string))))))))

(defun vc-buffer-context ()
  ;; Return a list '(point-context mark-context reparse); from which
  ;; vc-restore-buffer-context can later restore the context.
  (let ((point-context (vc-position-context (point)))
	;; Use mark-marker to avoid confusion in transient-mark-mode.
	(mark-context  (if (eq (marker-buffer (mark-marker)) (current-buffer))
			   (vc-position-context (mark-marker))))
	;; Make the right thing happen in transient-mark-mode.
	(mark-active nil)
	;; We may want to reparse the compilation buffer after revert
	(reparse (and (boundp 'compilation-error-list) ;compile loaded
		      (let ((curbuf (current-buffer)))
			;; Construct a list; each elt is nil or a buffer
			;; iff that buffer is a compilation output buffer
			;; that contains markers into the current buffer.
			(save-excursion
			  (mapcar (function
				   (lambda (buffer)
				    (set-buffer buffer)
				    (let ((errors (or
						   compilation-old-error-list
						   compilation-error-list))
					  (buffer-error-marked-p nil))
				      (while (and (consp errors)
						  (not buffer-error-marked-p))
					(and (markerp (cdr (car errors)))
					     (eq buffer
						 (marker-buffer
						  (cdr (car errors))))
					     (setq buffer-error-marked-p t))
					(setq errors (cdr errors)))
				      (if buffer-error-marked-p buffer))))
				  (buffer-list)))))))
    (list point-context mark-context reparse)))

(defun vc-restore-buffer-context (context)
  ;; Restore point/mark, and reparse any affected compilation buffers.
  ;; CONTEXT is that which vc-buffer-context returns.
  (let ((point-context (nth 0 context))
	(mark-context (nth 1 context))
	(reparse (nth 2 context)))
    ;; Reparse affected compilation buffers.
    (while reparse
      (if (car reparse)
	  (save-excursion
	    (set-buffer (car reparse))
	    (let ((compilation-last-buffer (current-buffer)) ;select buffer
		  ;; Record the position in the compilation buffer of
		  ;; the last error next-error went to.
		  (error-pos (marker-position
			      (car (car-safe compilation-error-list)))))
	      ;; Reparse the error messages as far as they were parsed before.
	      (compile-reinitialize-errors '(4) compilation-parsing-end)
	      ;; Move the pointer up to find the error we were at before
	      ;; reparsing.  Now next-error should properly go to the next one.
	      (while (and compilation-error-list
			  (/= error-pos (car (car compilation-error-list))))
		(setq compilation-error-list (cdr compilation-error-list))))))
      (setq reparse (cdr reparse)))

    ;; Restore point and mark
    (let ((new-point (vc-find-position-by-context point-context)))
      (if new-point (goto-char new-point)))
    (if mark-context
	(let ((new-mark (vc-find-position-by-context mark-context)))
	  (if new-mark (set-mark new-mark))))))

(defun vc-revert-buffer1 (&optional arg no-confirm)
  ;; Revert buffer, try to keep point and mark where user expects them in spite
  ;; of changes because of expanded version-control key words.
  ;; This is quite important since otherwise typeahead won't work as expected.
  (interactive "P")
  (widen)
  (let ((context (vc-buffer-context)))
    ;; t means don't call normal-mode; that's to preserve various minor modes.
    (revert-buffer arg no-confirm t)
    (vc-restore-buffer-context context)))


(defun vc-buffer-sync (&optional not-urgent)
  ;; Make sure the current buffer and its working file are in sync
  ;; NOT-URGENT means it is ok to continue if the user says not to save.
  (if (buffer-modified-p)
      (if (or vc-suppress-confirm
	      (y-or-n-p (format "Buffer %s modified; save it? " (buffer-name))))
	  (save-buffer)
	(if not-urgent
	    nil
	  (error "Aborted")))))


(defun vc-workfile-unchanged-p (file &optional want-differences-if-changed)
  ;; Has the given workfile changed since last checkout?
  (let ((checkout-time (vc-file-getprop file 'vc-checkout-time))
	(lastmod (nth 5 (file-attributes file))))
    (or (equal checkout-time lastmod)
	(and (or (not checkout-time) want-differences-if-changed)
	     (let ((unchanged (zerop (vc-backend-diff file nil nil
					  (not want-differences-if-changed)))))
	       ;; 0 stands for an unknown time; it can't match any mod time.
	       (vc-file-setprop file 'vc-checkout-time (if unchanged lastmod 0))
	       unchanged)))))

(defun vc-next-action-on-file (file verbose &optional comment)
  ;;; If comment is specified, it will be used as an admin or checkin comment.
  (let ((vc-file (vc-name file))
	(vc-type (vc-backend file))
	owner version buffer)
    (cond

     ;; if there is no master file corresponding, create one
     ((not vc-file)
      (vc-register verbose comment)
      (if vc-initial-comment
	  (setq vc-log-after-operation-hook
		'vc-checkout-writable-buffer-hook)
	(vc-checkout-writable-buffer file)))

     ;; CVS: changes to the master file need to be 
     ;; merged back into the working file
     ((and (eq vc-type 'CVS)
	   (or (eq (vc-cvs-status file) 'needs-checkout)
	       (eq (vc-cvs-status file) 'needs-merge)))
      (if (or vc-dired-mode
	      (yes-or-no-p 
	       (format "%s is not up-to-date.  Merge in changes now? "
		       (buffer-name))))
	  (progn
	    (if vc-dired-mode
		(and (setq buffer (get-file-buffer file))
		     (buffer-modified-p buffer)
		     (switch-to-buffer-other-window buffer)
		     (vc-buffer-sync t))
	      (setq buffer (current-buffer))
	      (vc-buffer-sync t))
	    (if (and buffer (buffer-modified-p buffer)
		     (not (yes-or-no-p 
			   (format 
			    "Buffer %s modified; merge file on disc anyhow? " 
			    (buffer-name buffer)))))
		(error "Merge aborted"))
	    (if (not (zerop (vc-backend-merge-news file)))
		;; Overlaps detected - what now?  Should use some
		;; fancy RCS conflict resolving package, or maybe
		;; emerge, but for now, simply warn the user with a
		;; message.
		(message "Conflicts detected!"))
	    (and buffer
		 (vc-resynch-buffer file t (not (buffer-modified-p buffer)))))
	(error "%s needs update" (buffer-name))))

     ;; if there is no lock on the file, assert one and get it
     ((not (setq owner (vc-locking-user file)))
      (if (and vc-checkout-carefully
	       (not (vc-workfile-unchanged-p file t)))
	  (if (save-window-excursion
		(pop-to-buffer "*vc-diff*")
		(goto-char (point-min))
		(insert-string (format "Changes to %s since last lock:\n\n"
				       file))
		(not (beep))
		(yes-or-no-p
		      (concat "File has unlocked changes, "
		       "claim lock retaining changes? ")))
	      (progn (vc-backend-steal file)
		     (vc-mode-line file))
	    (if (not (yes-or-no-p "Revert to checked-in version, instead? "))
		(error "Checkout aborted")
	      (vc-revert-buffer1 t t)
	      (vc-checkout-writable-buffer file))
	    )
	(if verbose 
	    (if (not (eq vc-type 'SCCS))
		(vc-checkout file nil 
		   (read-string "Branch or version to move to: "))
	      (error "Sorry, this is not implemented for SCCS"))
	  (if (vc-latest-on-branch-p file)
	      (vc-checkout-writable-buffer file)
	    (if (yes-or-no-p 
		 "This is not the latest version.  Really lock it?  ")
		(vc-checkout-writable-buffer file)
	      (if (yes-or-no-p "Lock the latest version instead? ")
		  (vc-checkout-writable-buffer file
		     (if (vc-trunk-p (vc-workfile-version file)) 
                         ""  ;; this means check out latest on trunk
                       (vc-branch-part (vc-workfile-version file)))))))
	  )))

     ;; a checked-out version exists, but the user may not own the lock
     ((and (not (eq vc-type 'CVS))
	   (not (string-equal owner (user-login-name))))
      (if comment
	  (error "Sorry, you can't steal the lock on %s this way" file))
      (and (eq vc-type 'RCS)
	   (not (vc-backend-release-p 'RCS "5.6.2"))
	   (error "File is locked by %s" owner))
      (vc-steal-lock
       file
       (if verbose (read-string "Version to steal: ")
	 (vc-workfile-version file))
       owner))

     ;; OK, user owns the lock on the file
     (t
	  (if vc-dired-mode 
	      (find-file-other-window file) 
	    (find-file file))

	  ;; give luser a chance to save before checking in.
	  (vc-buffer-sync)

	  ;; Revert if file is unchanged and buffer is too.
	  ;; If buffer is modified, that means the user just said no
	  ;; to saving it; in that case, don't revert,
	  ;; because the user might intend to save
	  ;; after finishing the log entry.
	  (if (and (vc-workfile-unchanged-p file) 
		   (not (buffer-modified-p)))
	       ;; DO NOT revert the file without asking the user!
	      (cond 
	       ((yes-or-no-p "Revert to master version? ")
		(vc-backend-revert file)
		(vc-resynch-window file t t)))

	    ;; user may want to set nonstandard parameters
	    (if verbose
		(setq version (read-string "New version level: ")))

	    ;; OK, let's do the checkin
	    (vc-checkin file version comment)
	    )))))

(defun vc-next-action-dired (file rev comment)
  ;; Do a vc-next-action-on-file on all the marked files, possibly 
  ;; passing on the log comment we've just entered.
  (let ((configuration (current-window-configuration))
	(dired-buffer (current-buffer))
	(dired-dir default-directory))
    (dired-map-over-marks
     (let ((file (dired-get-filename)) p
	   (default-directory default-directory))
       (message "Processing %s..." file)
       ;; Adjust the default directory so that checkouts
       ;; go to the right place.
       (setq default-directory (file-name-directory file))
       (vc-next-action-on-file file nil comment)
       (set-buffer dired-buffer)
       (setq default-directory dired-dir)
       (vc-dired-update-line file)
       (set-window-configuration configuration)
       (message "Processing %s...done" file))
    nil t)))

;; Here's the major entry point.

;;;###autoload
(defun vc-next-action (verbose)
  "Do the next logical checkin or checkout operation on the current file.
   If you call this from within a VC dired buffer with no files marked,
it will operate on the file in the current line.
   If you call this from within a VC dired buffer, and one or more
files are marked, it will accept a log message and then operate on
each one.  The log message will be used as a comment for any register
or checkin operations, but ignored when doing checkouts.  Attempted
lock steals will raise an error.
   A prefix argument lets you specify the version number to use.

For RCS and SCCS files:
   If the file is not already registered, this registers it for version
control and then retrieves a writable, locked copy for editing.
   If the file is registered and not locked by anyone, this checks out
a writable and locked file ready for editing.
   If the file is checked out and locked by the calling user, this
first checks to see if the file has changed since checkout.  If not,
it performs a revert.
   If the file has been changed, this pops up a buffer for entry
of a log message; when the message has been entered, it checks in the
resulting changes along with the log message as change commentary.  If
the variable `vc-keep-workfiles' is non-nil (which is its default), a
read-only copy of the changed file is left in place afterwards.
   If the file is registered and locked by someone else, you are given
the option to steal the lock.

For CVS files:
   If the file is not already registered, this registers it for version
control.  This does a \"cvs add\", but no \"cvs commit\".
   If the file is added but not committed, it is committed.
   If your working file is changed, but the repository file is
unchanged, this pops up a buffer for entry of a log message; when the
message has been entered, it checks in the resulting changes along
with the logmessage as change commentary.  A writable file is retained.
   If the repository file is changed, you are asked if you want to
merge in the changes into your working copy."

  (interactive "P")
  (catch 'nogo
    (if vc-dired-mode
	(let ((files (dired-get-marked-files)))
	  (if (string= "" 
		 (mapconcat
	             (function (lambda (f)
			 (if (eq (vc-backend f) 'CVS)
			     (if (or (eq (vc-cvs-status f) 'locally-modified)
				     (eq (vc-cvs-status f) 'locally-added))
				 "@" "")
			   (if (vc-locking-user f) "@" ""))))
		     files ""))
		(vc-next-action-dired nil nil "dummy")
	      (vc-start-entry nil nil nil
			      "Enter a change comment for the marked files."
			      'vc-next-action-dired))
	    (throw 'nogo nil)))
    (while vc-parent-buffer
      (pop-to-buffer vc-parent-buffer))
    (if buffer-file-name
	(vc-next-action-on-file buffer-file-name verbose)
      (vc-registration-error nil))))

;;; These functions help the vc-next-action entry point

(defun vc-checkout-writable-buffer (&optional file rev)
  "Retrieve a writable copy of the latest version of the current buffer's file."
  (vc-checkout (or file (buffer-file-name)) t rev)
  )

;;;###autoload
(defun vc-register (&optional override comment)
  "Register the current file into your version-control system."
  (interactive "P")
  (or buffer-file-name
      (error "No visited file"))
  (let ((master (vc-name buffer-file-name)))
    (and master (file-exists-p master)
	 (error "This file is already registered"))
    (and master
	 (not (y-or-n-p "Previous master file has vanished.  Make a new one? "))
	 (error "This file is already registered")))
  ;; Watch out for new buffers of size 0: the corresponding file
  ;; does not exist yet, even though buffer-modified-p is nil.
  (if (and (not (buffer-modified-p))
	   (zerop (buffer-size))
	   (not (file-exists-p buffer-file-name)))
      (set-buffer-modified-p t))
  (vc-buffer-sync)
  (cond ((not vc-make-backup-files)
	 ;; inhibit backup for this buffer
	 (make-local-variable 'backup-inhibited)
	 (setq backup-inhibited t)))
  (vc-admin
   buffer-file-name
   (and override
	(read-string
	 (format "Initial version level for %s: " buffer-file-name))))
  )

(defun vc-resynch-window (file &optional keep noquery)
  ;; If the given file is in the current buffer,
  ;; either revert on it so we see expanded keywords,
  ;; or unvisit it (depending on vc-keep-workfiles)
  ;; NOQUERY if non-nil inhibits confirmation for reverting.
  ;; NOQUERY should be t *only* if it is known the only difference
  ;; between the buffer and the file is due to RCS rather than user editing!
  (and (string= buffer-file-name file)
       (if keep
	   (progn
	     ;; temporarily remove vc-find-file-hook, so that
             ;; we don't lose the properties
	     (remove-hook 'find-file-hooks 'vc-find-file-hook)
	     (vc-revert-buffer1 t noquery)
	     (add-hook 'find-file-hooks 'vc-find-file-hook)
	     (vc-mode-line buffer-file-name))
	 (kill-buffer (current-buffer)))))

(defun vc-resynch-buffer (file &optional keep noquery)
  ;; if FILE is currently visited, resynch its buffer
  (let ((buffer (get-file-buffer file)))
    (if buffer
	(save-excursion
	  (set-buffer buffer)
	  (vc-resynch-window file keep noquery)))))

(defun vc-start-entry (file rev comment msg action &optional after-hook)
  ;; Accept a comment for an operation on FILE revision REV.  If COMMENT
  ;; is nil, pop up a VC-log buffer, emit MSG, and set the
  ;; action on close to ACTION; otherwise, do action immediately.
  ;; Remember the file's buffer in vc-parent-buffer (current one if no file).
  ;; AFTER-HOOK specifies the local value for vc-log-operation-hook.
  (let ((parent (if file (find-file-noselect file) (current-buffer))))
    (if comment
	(set-buffer (get-buffer-create "*VC-log*"))
      (pop-to-buffer (get-buffer-create "*VC-log*")))
    (set (make-local-variable 'vc-parent-buffer) parent)
    (set (make-local-variable 'vc-parent-buffer-name)
	 (concat " from " (buffer-name vc-parent-buffer)))
    (if file (vc-mode-line file))
    (vc-log-mode)
    (make-local-variable 'vc-log-after-operation-hook)
    (if after-hook
	(setq vc-log-after-operation-hook after-hook))
    (setq vc-log-operation action)
    (setq vc-log-file file)
    (setq vc-log-version rev)
    (if comment
	(progn
	  (erase-buffer)
	  (if (eq comment t)
	      (vc-finish-logentry t)
	    (insert comment)
	    (vc-finish-logentry nil)))
      (message "%s  Type C-c C-c when done." msg))))

(defun vc-admin (file rev &optional comment)
  "Check a file into your version-control system.
FILE is the unmodified name of the file.  REV should be the base version
level to check it in under.  COMMENT, if specified, is the checkin comment."
  (vc-start-entry file rev
		  (or comment (not vc-initial-comment))
		  "Enter initial comment." 'vc-backend-admin
		  nil))

(defun vc-checkout (file &optional writable rev)
  "Retrieve a copy of the latest version of the given file."
  ;; If ftp is on this system and the name matches the ange-ftp format
  ;; for a remote file, the user is trying something that won't work.
  (if (and (string-match "^/[^/:]+:" file) (vc-find-binary "ftp"))
      (error "Sorry, you can't check out files over FTP"))
  (vc-backend-checkout file writable rev)
  (vc-resynch-buffer file t t))

(defun vc-steal-lock (file rev &optional owner)
  "Steal the lock on the current workfile."
  (let (file-description)
    (if (not owner)
	(setq owner (vc-locking-user file)))
    (if rev
	(setq file-description (format "%s:%s" file rev))
      (setq file-description file))
    (if (not (y-or-n-p (format "Take the lock on %s from %s? "
			       file-description owner)))
	(error "Steal cancelled"))
    (pop-to-buffer (get-buffer-create "*VC-mail*"))
    (setq default-directory (expand-file-name "~/"))
    (auto-save-mode auto-save-default)
    (mail-mode)
    (erase-buffer)
    (mail-setup owner (format "Stolen lock on %s" file-description) nil nil nil
		(list (list 'vc-finish-steal file rev)))
    (goto-char (point-max))
    (insert
     (format "I stole the lock on %s, " file-description)
     (current-time-string)
     ".\n")
    (message "Please explain why you stole the lock.  Type C-c C-c when done.")))

;; This is called when the notification has been sent.
(defun vc-finish-steal (file version)
  (vc-backend-steal file version)
  (if (get-file-buffer file)
      (save-excursion
	(set-buffer (get-file-buffer file))
	(vc-resynch-window file t t))))

(defun vc-checkin (file &optional rev comment)
  "Check in the file specified by FILE.
The optional argument REV may be a string specifying the new version level
\(if nil increment the current level).  The file is either retained with write
permissions zeroed, or deleted (according to the value of `vc-keep-workfiles').
If the back-end is CVS, a writable workfile is always kept.
COMMENT is a comment string; if omitted, a buffer is
popped up to accept a comment."
  (vc-start-entry file rev comment
		  "Enter a change comment." 'vc-backend-checkin
		  'vc-checkin-hook))

;;; Here is a checkin hook that may prove useful to sites using the
;;; ChangeLog facility supported by Emacs.
(defun vc-comment-to-change-log (&optional whoami file-name)
  "Enter last VC comment into change log file for current buffer's file.
Optional arg (interactive prefix) non-nil means prompt for user name and site.
Second arg is file name of change log.  \
If nil, uses `change-log-default-name'."
  (interactive (if current-prefix-arg
		   (list current-prefix-arg
			 (prompt-for-change-log-name))))
  ;; Make sure the defvar for add-log-current-defun-function has been executed
  ;; before binding it.
  (require 'add-log)
  (let (;; Extract the comment first so we get any error before doing anything.
	(comment (ring-ref vc-comment-ring 0))
	;; Don't let add-change-log-entry insert a defun name.
	(add-log-current-defun-function 'ignore)
	end)
    ;; Call add-log to do half the work.
    (add-change-log-entry whoami file-name t t)
    ;; Insert the VC comment, leaving point before it.
    (setq end (save-excursion (insert comment) (point-marker)))
    (if (looking-at "\\s *\\s(")
	;; It starts with an open-paren, as in "(foo): Frobbed."
	;; So remove the ": " add-log inserted.
	(delete-char -2))
    ;; Canonicalize the white space between the file name and comment.
    (just-one-space)
    ;; Indent rest of the text the same way add-log indented the first line.
    (let ((indentation (current-indentation)))
      (save-excursion
	(while (< (point) end)
	  (forward-line 1)
	  (indent-to indentation))
	(setq end (point))))
    ;; Fill the inserted text, preserving open-parens at bol.
    (let ((paragraph-separate (concat paragraph-separate "\\|\\s *\\s("))
	  (paragraph-start (concat paragraph-start "\\|\\s *\\s(")))
      (beginning-of-line)
      (fill-region (point) end))
    ;; Canonicalize the white space at the end of the entry so it is
    ;; separated from the next entry by a single blank line.
    (skip-syntax-forward " " end)
    (delete-char (- (skip-syntax-backward " ")))
    (or (eobp) (looking-at "\n\n")
	(insert "\n"))))


(defun vc-finish-logentry (&optional nocomment)
  "Complete the operation implied by the current log entry."
  (interactive)
  ;; Check and record the comment, if any.
  (if (not nocomment)
      (progn
	(goto-char (point-max))
	(if (not (bolp))
	    (newline))
	;; Comment too long?
	(vc-backend-logentry-check vc-log-file)
	;; Record the comment in the comment ring
	(if (null vc-comment-ring)
	    (setq vc-comment-ring (make-ring vc-maximum-comment-ring-size)))
	(ring-insert vc-comment-ring (buffer-string))
	))
  ;; Sync parent buffer in case the user modified it while editing the comment.
  ;; But not if it is a vc-dired buffer.
  (save-excursion
    (set-buffer vc-parent-buffer)
    (or vc-dired-mode
	(vc-buffer-sync)))
  (if (not vc-log-operation) (error "No log operation is pending"))
  ;; save the parameters held in buffer-local variables
  (let ((log-operation vc-log-operation)
	(log-file vc-log-file)
	(log-version vc-log-version)
	(log-entry (buffer-string))
	(after-hook vc-log-after-operation-hook))
    ;; Return to "parent" buffer of this checkin and remove checkin window
    (pop-to-buffer vc-parent-buffer)
    (let ((logbuf (get-buffer "*VC-log*")))
      (delete-windows-on logbuf)
      (kill-buffer logbuf))
    ;; OK, do it to it
    (save-excursion
      (funcall log-operation 
	       log-file
	       log-version
	       log-entry))
    ;; Now make sure we see the expanded headers
    (if buffer-file-name
	(vc-resynch-window buffer-file-name vc-keep-workfiles t))
    (run-hooks after-hook)))

;; Code for access to the comment ring

(defun vc-previous-comment (arg)
  "Cycle backwards through comment history."
  (interactive "*p")
  (let ((len (ring-length vc-comment-ring)))
    (cond ((<= len 0)
	   (message "Empty comment ring")
	   (ding))
	  (t
	   (erase-buffer)
	   ;; Initialize the index on the first use of this command
	   ;; so that the first M-p gets index 0, and the first M-n gets
	   ;; index -1.
	   (if (null vc-comment-ring-index)
	       (setq vc-comment-ring-index
		     (if (> arg 0) -1
			 (if (< arg 0) 1 0))))
	   (setq vc-comment-ring-index
		 (mod (+ vc-comment-ring-index arg) len))
	   (message "%d" (1+ vc-comment-ring-index))
	   (insert (ring-ref vc-comment-ring vc-comment-ring-index))))))

(defun vc-next-comment (arg)
  "Cycle forwards through comment history."
  (interactive "*p")
  (vc-previous-comment (- arg)))

(defun vc-comment-search-reverse (str)
  "Searches backwards through comment history for substring match."
  (interactive "sComment substring: ")
  (if (string= str "")
      (setq str vc-last-comment-match)
    (setq vc-last-comment-match str))
  (if (null vc-comment-ring-index)
      (setq vc-comment-ring-index -1))
  (let ((str (regexp-quote str))
        (len (ring-length vc-comment-ring))
	(n (1+ vc-comment-ring-index)))
    (while (and (< n len) (not (string-match str (ring-ref vc-comment-ring n))))
      (setq n (+ n 1)))
    (cond ((< n len)
	   (vc-previous-comment (- n vc-comment-ring-index)))
	  (t (error "Not found")))))

(defun vc-comment-search-forward (str)
  "Searches forwards through comment history for substring match."
  (interactive "sComment substring: ")
  (if (string= str "")
      (setq str vc-last-comment-match)
    (setq vc-last-comment-match str))
  (if (null vc-comment-ring-index)
      (setq vc-comment-ring-index 0))
  (let ((str (regexp-quote str))
        (len (ring-length vc-comment-ring))
	(n vc-comment-ring-index))
    (while (and (>= n 0) (not (string-match str (ring-ref vc-comment-ring n))))
      (setq n (- n 1)))
    (cond ((>= n 0)
	   (vc-next-comment (- n vc-comment-ring-index)))
	  (t (error "Not found")))))

;; Additional entry points for examining version histories

;;;###autoload
(defun vc-diff (historic &optional not-urgent)
  "Display diffs between file versions.
Normally this compares the current file and buffer with the most recent 
checked in version of that file.  This uses no arguments.
With a prefix argument, it reads the file name to use
and two version designators specifying which versions to compare."
  (interactive (list current-prefix-arg t))
  (if vc-dired-mode
      (set-buffer (find-file-noselect (dired-get-filename))))
  (while vc-parent-buffer
      (pop-to-buffer vc-parent-buffer))
  (if historic
      (call-interactively 'vc-version-diff)
    (if (or (null buffer-file-name) (null (vc-name buffer-file-name)))
	(error
	 "There is no version-control master associated with this buffer"))
    (let ((file buffer-file-name)
	  unchanged)
      (or (and file (vc-name file))
	  (vc-registration-error file))
      (vc-buffer-sync not-urgent)
      (setq unchanged (vc-workfile-unchanged-p buffer-file-name))
      (if unchanged
	  (message "No changes to %s since latest version" file)
	(vc-backend-diff file)
	;; Ideally, we'd like at this point to parse the diff so that
	;; the buffer effectively goes into compilation mode and we
	;; can visit the old and new change locations via next-error.
	;; Unfortunately, this is just too painful to do.  The basic
	;; problem is that the `old' file doesn't exist to be
	;; visited.  This plays hell with numerous assumptions in
	;; the diff.el and compile.el machinery.
	(set-buffer "*vc-diff*")
	(setq default-directory (file-name-directory file))
	(if (= 0 (buffer-size))
	    (progn
	      (setq unchanged t)
	      (message "No changes to %s since latest version" file))
          (pop-to-buffer "*vc-diff*")
	  (goto-char (point-min))
	  (shrink-window-if-larger-than-buffer)))
      (not unchanged))))

(defun vc-version-diff (file rel1 rel2)
  "For FILE, report diffs between two stored versions REL1 and REL2 of it.
If FILE is a directory, generate diffs between versions for all registered
files in or below it."
  (interactive "FFile or directory to diff: \nsOlder version: \nsNewer version: ")
  (if (string-equal rel1 "") (setq rel1 nil))
  (if (string-equal rel2 "") (setq rel2 nil))
  (if (file-directory-p file)
      (let ((camefrom (current-buffer)))
	(set-buffer (get-buffer-create "*vc-status*"))
	(set (make-local-variable 'vc-parent-buffer) camefrom)
	(set (make-local-variable 'vc-parent-buffer-name)
	     (concat " from " (buffer-name camefrom)))
	(erase-buffer)
	(insert "Diffs between "
		(or rel1 "last version checked in")
		" and "
		(or rel2 "current workfile(s)")
		":\n\n")
	(set-buffer (get-buffer-create "*vc-diff*"))
	(cd file)
	(vc-file-tree-walk
	 default-directory
	 (function (lambda (f)
		     (message "Looking at %s" f)
		     (and
		      (not (file-directory-p f))
		      (vc-registered f)
		      (vc-backend-diff f rel1 rel2)
		      (append-to-buffer "*vc-status*" (point-min) (point-max)))
		     )))
	(pop-to-buffer "*vc-status*")
	(insert "\nEnd of diffs.\n")
	(goto-char (point-min))
	(set-buffer-modified-p nil)
	)
    (if (zerop (vc-backend-diff file rel1 rel2))
	(message "No changes to %s between %s and %s." file rel1 rel2)
      (pop-to-buffer "*vc-diff*"))))

;;;###autoload
(defun vc-version-other-window (rev)
  "Visit version REV of the current buffer in another window.
If the current buffer is named `F', the version is named `F.~REV~'.
If `F.~REV~' already exists, it is used instead of being re-created."
  (interactive "sVersion to visit (default is latest version): ")
  (if vc-dired-mode
      (set-buffer (find-file-noselect (dired-get-filename))))
  (while vc-parent-buffer
      (pop-to-buffer vc-parent-buffer))
  (if (and buffer-file-name (vc-name buffer-file-name))
      (let* ((version (if (string-equal rev "")
			  (vc-latest-version buffer-file-name)
			rev))
	     (filename (concat buffer-file-name ".~" version "~")))
	 (or (file-exists-p filename)
	     (vc-backend-checkout buffer-file-name nil version filename))
	 (find-file-other-window filename))
    (vc-registration-error buffer-file-name)))

;; Header-insertion code

;;;###autoload
(defun vc-insert-headers ()
  "Insert headers in a file for use with your version-control system.
Headers desired are inserted at the start of the buffer, and are pulled from
the variable `vc-header-alist'."
  (interactive)
  (if vc-dired-mode
      (find-file-other-window (dired-get-filename)))
  (while vc-parent-buffer
      (pop-to-buffer vc-parent-buffer))
  (save-excursion
    (save-restriction
      (widen)
      (if (or (not (vc-check-headers))
	      (y-or-n-p "Version headers already exist.  Insert another set? "))
	  (progn
	    (let* ((delims (cdr (assq major-mode vc-comment-alist)))
		   (comment-start-vc (or (car delims) comment-start "#"))
		   (comment-end-vc (or (car (cdr delims)) comment-end ""))
		   (hdstrings (cdr (assoc (vc-backend (buffer-file-name)) vc-header-alist))))
	      (mapcar (function (lambda (s)
				  (insert comment-start-vc "\t" s "\t"
					  comment-end-vc "\n")))
		      hdstrings)
	      (if vc-static-header-alist
		  (mapcar (function (lambda (f)
				      (if (string-match (car f) buffer-file-name)
					  (insert (format (cdr f) (car hdstrings))))))
			  vc-static-header-alist))
	      )
	    )))))

(defun vc-clear-headers ()
  ;; Clear all version headers in the current buffer, i.e. reset them 
  ;; to the nonexpanded form.  Only implemented for RCS, yet.
  ;; Don't lose point and mark during this.
  (let ((context (vc-buffer-context)))
    (goto-char (point-min))
    (while (re-search-forward "\\$\\([A-Za-z]+\\): [^\\$]+\\$" nil t)
      (replace-match "$\\1$"))
    (vc-restore-buffer-context context)))

;; The VC directory major mode.  Coopt Dired for this.
;; All VC commands get mapped into logical equivalents.

(define-derived-mode vc-dired-mode dired-mode "Dired under VC"
  "The major mode used in VC directory buffers.  It is derived from Dired.
All Dired commands operate normally.  Users currently locking listed files
are listed in place of the file's owner and group.
Keystrokes bound to VC commands will execute as though they had been called
on a buffer attached to the file named in the current Dired buffer line."
  (setq vc-dired-mode t))

(define-key vc-dired-mode-map "\C-xv" vc-prefix-map)
(define-key vc-dired-mode-map "g" 'vc-dired-update)
(define-key vc-dired-mode-map "=" 'vc-diff)

(defun vc-dired-state-info (file)
  ;; Return the string that indicates the version control status
  ;; on a VC dired line.
  (let ((cvs-state (and (eq (vc-backend file) 'CVS)
			(vc-cvs-status file))))
    (if cvs-state
	(cond ((eq cvs-state 'up-to-date) nil)
	      ((eq cvs-state 'needs-checkout)      "patch")
	      ((eq cvs-state 'locally-modified)    "modified")
	      ((eq cvs-state 'needs-merge)         "merge")
	      ((eq cvs-state 'unresolved-conflict) "conflict")
	      ((eq cvs-state 'locally-added)       "added"))
      (vc-locking-user file))))

(defun vc-dired-reformat-line (x)
  ;; Hack a directory-listing line, plugging in locking-user info in
  ;; place of the user and group info.  Should have the beneficial
  ;; side-effect of shortening the listing line.  Each call starts with
  ;; point immediately following the dired mark area on the line to be
  ;; hacked.
  ;;
  ;; Simplest possible one:
  ;; (insert (concat x "\t")))
  ;;
  ;; This code, like dired, assumes UNIX -l format.
  (let ((pos (point)) limit perm owner date-and-file)
    (end-of-line)
    (setq limit (point))
    (goto-char pos)
    (cond
     ((or
       (re-search-forward  ;; owner and group
"\\([drwxlts-]+ \\) *[0-9]+ \\([^ ]+\\) +[^ ]+ +[0-9]+\\( [^ 0-9]+ [0-9 ][0-9] .*\\)"
	  limit t)       
       (re-search-forward  ;; only owner displayed
"\\([drwxlts-]+ \\) *[0-9]+ \\([^ ]+\\) +[0-9]+\\( [^ 0-9]+ [0-9 ][0-9] .*\\)" 
	  limit t))
      (setq perm          (match-string 1)
	    owner         (match-string 2)
	    date-and-file (match-string 3)))
     ((re-search-forward  ;; OS/2 -l format, no links, owner, group
"\\([drwxlts-]+ \\) *[0-9]+\\( [^ 0-9]+ [0-9 ][0-9] .*\\)"
         limit t)
      (setq perm          (match-string 1)
	    date-and-file (match-string 2))))
    (if (numberp x) (setq x (or owner (number-to-string x))))
    (if x (setq x (concat "(" x ")")))
    (let ((rep (substring (concat x "                 ") 0 10)))
      (replace-match (concat perm rep date-and-file)))))
       
(defun vc-dired-update-line (file)
  ;; Update the vc-dired listing line of file -- it is assumed 
  ;; that point is already on this line.  Don't use dired-do-redisplay
  ;; for this, because it cannot handle the way vc-dired deals with 
  ;; subdirectories.
  (beginning-of-line)
  (forward-char 2)
  (let ((start (point)))
    (forward-line 1)
    (beginning-of-line)
    (delete-region start (point))
    (insert-directory file dired-listing-switches)
    (forward-line -1)
    (end-of-line)
    (delete-char (- (length file)))
    (insert (substring file (length (expand-file-name default-directory))))
    (goto-char start))
  (vc-dired-reformat-line (vc-dired-state-info file)))

(defun vc-dired-update (verbose)
  (interactive "P")
  (vc-directory default-directory verbose))

;;; Note in Emacs 18 the following defun gets overridden
;;; with the symbol 'vc-directory-18.  See below.
;;;###autoload
(defun vc-directory (dirname verbose)
  "Show version-control status of the current directory and subdirectories.
Normally it creates a Dired buffer that lists only the locked files
in all these directories.  With a prefix argument, it lists all files."
  (interactive "DDired under VC (directory): \nP")
  (require 'dired)
  (setq dirname (expand-file-name dirname))
  ;; force a trailing slash
  (if (not (eq (elt dirname (1- (length dirname))) ?/))
      (setq dirname (concat dirname "/")))
  (let (nonempty
	(dl (length dirname))
	(filelist nil) (statelist nil)
	(old-dir default-directory)
	dired-buf
	dired-buf-mod-count)
    (vc-file-tree-walk
     dirname
     (function 
      (lambda (f)
	(if (vc-registered f)
	    (let ((state (vc-dired-state-info f)))
	      (and (or verbose state)
		   (setq filelist (cons (substring f dl) filelist))
		   (setq statelist (cons state statelist))))))))
    (save-window-excursion
      (save-excursion
	;; This uses a semi-documented feature of dired; giving a switch
	;; argument forces the buffer to refresh each time.
	(setq dired-buf
	      (dired-internal-noselect
	       (cons dirname (nreverse filelist))
	       dired-listing-switches 'vc-dired-mode))
	(setq nonempty (not (eq 0 (length filelist))))))
    (switch-to-buffer dired-buf)
    ;; Make a few modifications to the header
    (setq buffer-read-only nil)
    (goto-char (point-min))
    (forward-line 1)	      ;; Skip header line
    (let ((start (point)))    ;; Erase (but don't remove) the 
      (end-of-line)           ;; "wildcard" line.
      (delete-region start (point)))
    (beginning-of-line)
    (if nonempty
	(progn
	  ;; Plug the version information into the individual lines
	  (mapcar
	   (function
	    (lambda (x)
	     (forward-char 2)	;; skip dired's mark area
	     (vc-dired-reformat-line x)
	     (forward-line 1)))	;; go to next line
	   (nreverse statelist))
	  (setq buffer-read-only t)
	  (goto-char (point-min))
	  (dired-next-line 2)
	  )
      (dired-next-line 1) 
      (insert "  ")
      (setq buffer-read-only t)
      (message "No files are currently %s under %s"
	       (if verbose "registered" "locked") dirname))
    ))

;; Emacs 18 version
(defun vc-directory-18 (verbose)
  "Show version-control status of all files under the current directory."
  (interactive "P")
  (let (nonempty (dir default-directory))
    (save-excursion
      (set-buffer (get-buffer-create "*vc-status*"))
      (erase-buffer)
      (cd dir)
      (vc-file-tree-walk
       default-directory
       (function (lambda (f)
		   (if (vc-registered f)
		       (let ((user (vc-locking-user f)))
			 (if (or user verbose)
			     (insert (format
				      "%s	%s\n"
				      (concat user) f))))))))
      (setq nonempty (not (zerop (buffer-size)))))

    (if nonempty
	(progn
	  (pop-to-buffer "*vc-status*" t)
	  (goto-char (point-min))
	  (shrink-window-if-larger-than-buffer)))
      (message "No files are currently %s under %s"
	       (if verbose "registered" "locked") default-directory))
    )

(or (boundp 'minor-mode-map-alist)
    (fset 'vc-directory 'vc-directory-18))

;; Named-configuration support for SCCS

(defun vc-add-triple (name file rev)
  (save-excursion
    (find-file (expand-file-name
		vc-name-assoc-file
		(file-name-as-directory
		 (expand-file-name (vc-backend-subdirectory-name file) 
				   (file-name-directory file)))))
    (goto-char (point-max))
    (insert name "\t:\t" file "\t" rev "\n")
    (basic-save-buffer)
    (kill-buffer (current-buffer))
    ))

(defun vc-record-rename (file newname)
  (save-excursion
    (find-file
     (expand-file-name
      vc-name-assoc-file
      (file-name-as-directory
       (expand-file-name (vc-backend-subdirectory-name file) 
			 (file-name-directory file)))))
    (goto-char (point-min))
    ;; (replace-regexp (concat ":" (regexp-quote file) "$") (concat ":" newname))
    (while (re-search-forward (concat ":" (regexp-quote file) "$") nil t)
      (replace-match (concat ":" newname) nil nil))
    (basic-save-buffer)
    (kill-buffer (current-buffer))
    ))

(defun vc-lookup-triple (file name)
  ;; Return the numeric version corresponding to a named snapshot of file
  ;; If name is nil or a version number string it's just passed through
  (cond ((null name) name)
	((let ((firstchar (aref name 0)))
	   (and (>= firstchar ?0) (<= firstchar ?9)))
	 name)
	(t
	 (save-excursion
	   (set-buffer (get-buffer-create "*vc-info*"))
	   (vc-insert-file
	    (expand-file-name
	     vc-name-assoc-file
	     (file-name-as-directory
	      (expand-file-name (vc-backend-subdirectory-name file) 
				(file-name-directory file)))))
	   (prog1
	       (car (vc-parse-buffer
		     (list (list (concat name "\t:\t" file "\t\\(.+\\)") 1))))
	     (kill-buffer "*vc-info*"))))
	 ))

;; Named-configuration entry points

(defun vc-snapshot-precondition ()
  ;; Scan the tree below the current directory.
  ;; If any files are locked, return the name of the first such file.
  ;; (This means, neither snapshot creation nor retrieval is allowed.)
  ;; If one or more of the files are currently visited, return `visited'.
  ;; Otherwise, return nil.
  (let ((status nil))
    (catch 'vc-locked-example
      (vc-file-tree-walk
       default-directory
       (function (lambda (f)
		   (and (vc-registered f)
			(if (vc-locking-user f) (throw 'vc-locked-example f)
			  (if (get-file-buffer f) (setq status 'visited)))))))
      status)))

;;;###autoload
(defun vc-create-snapshot (name)
  "Make a snapshot called NAME.
The snapshot is made from all registered files at or below the current
directory.  For each file, the version level of its latest
version becomes part of the named configuration."
  (interactive "sNew snapshot name: ")
  (let ((result (vc-snapshot-precondition)))
    (if (stringp result)
	(error "File %s is locked" result)
      (vc-file-tree-walk
       default-directory
       (function (lambda (f) (and
			      (vc-name f)
			      (vc-backend-assign-name f name)))))
      )))

;;;###autoload
(defun vc-retrieve-snapshot (name)
  "Retrieve the snapshot called NAME.
This function fails if any files are locked at or below the current directory
Otherwise, all registered files are checked out (unlocked) at their version
levels in the snapshot."
  (interactive "sSnapshot name to retrieve: ")
  (let ((result (vc-snapshot-precondition))
	(update nil))
    (if (stringp result)
	(error "File %s is locked" result)
      (if (eq result 'visited)
	  (setq update (yes-or-no-p "Update the affected buffers? ")))
      (vc-file-tree-walk
       default-directory
       (function (lambda (f) (and
			      (vc-name f)
			      (vc-error-occurred
			       (vc-backend-checkout f nil name)
			       (if update (vc-resynch-buffer f t t)))))))
      )))

;; Miscellaneous other entry points

;;;###autoload
(defun vc-print-log ()
  "List the change log of the current buffer in a window."
  (interactive)
  (if vc-dired-mode
      (set-buffer (find-file-noselect (dired-get-filename))))
  (while vc-parent-buffer
      (pop-to-buffer vc-parent-buffer))
  (if (and buffer-file-name (vc-name buffer-file-name))
      (let ((file buffer-file-name))
	(vc-backend-print-log file)
	(pop-to-buffer (get-buffer-create "*vc*"))
	(setq default-directory (file-name-directory file))
	(while (looking-at "=*\n")
	  (delete-char (- (match-end 0) (match-beginning 0)))
	  (forward-line -1))
	(goto-char (point-min))
	(if (looking-at "[\b\t\n\v\f\r ]+")
	    (delete-char (- (match-end 0) (match-beginning 0))))
	(shrink-window-if-larger-than-buffer)
	)
    (vc-registration-error buffer-file-name)
    )
  )

;;;###autoload
(defun vc-revert-buffer ()
  "Revert the current buffer's file back to the latest checked-in version.
This asks for confirmation if the buffer contents are not identical
to that version.
If the back-end is CVS, this will give you the most recent revision of
the file on the branch you are editing."
  (interactive)
  (if vc-dired-mode
      (find-file-other-window (dired-get-filename)))
  (while vc-parent-buffer
      (pop-to-buffer vc-parent-buffer))
  (let ((file buffer-file-name)
	;; This operation should always ask for confirmation.
	(vc-suppress-confirm nil)
	(obuf (current-buffer)) (changed (vc-diff nil t)))
    (if (and changed (not (yes-or-no-p "Discard changes? ")))
	(progn
	  (if (and (window-dedicated-p (selected-window))
		   (one-window-p t 'selected-frame))
	      (make-frame-invisible (selected-frame))
	    (delete-window))
	  (error "Revert cancelled"))
      (set-buffer obuf))
    (if changed
	(if (and (window-dedicated-p (selected-window))
		 (one-window-p t 'selected-frame))
	    (make-frame-invisible (selected-frame))
	  (delete-window)))
    (vc-backend-revert file)
    (vc-resynch-window file t t)
    )
  )

;;;###autoload
(defun vc-cancel-version (norevert)
  "Get rid of most recently checked in version of this file.
A prefix argument means do not revert the buffer afterwards."
  (interactive "P")
  (if vc-dired-mode
      (find-file-other-window (dired-get-filename)))
  (while vc-parent-buffer
    (pop-to-buffer vc-parent-buffer))
  (cond 
   ((not (vc-registered (buffer-file-name)))
    (vc-registration-error (buffer-file-name))
    (eq (vc-backend (buffer-file-name)) 'CVS)
    (error "Unchecking files under CVS is dangerous and not supported in VC"))
   ((vc-locking-user (buffer-file-name))
    (error "This version is locked; use vc-revert-buffer to discard changes"))
   ((not (vc-latest-on-branch-p (buffer-file-name)))
    (error "This is not the latest version--VC cannot cancel it")))
  (let* ((target (vc-workfile-version (buffer-file-name)))
         (recent (if (vc-trunk-p target) "" (vc-branch-part target)))
         (config (current-window-configuration)) done)
    (if (null (yes-or-no-p (format "Remove version %s from master? " target)))
	nil
      (setq norevert (or norevert (not 
           (yes-or-no-p "Revert buffer to most recent remaining version? "))))
      (vc-backend-uncheck (buffer-file-name) target)
      ;; Check out the most recent remaining version.  If it fails, because
      ;; the whole branch got deleted, do a double-take and check out the
      ;; version where the branch started.
      (while (not done)
        (condition-case err
            (progn
              (if norevert
                  ;; Check out locked, but only to disc, and keep 
                  ;; modifications in the buffer.
                  (vc-backend-checkout (buffer-file-name) t recent)
                ;; Check out unlocked, and revert buffer.
                (vc-checkout (buffer-file-name) nil recent))
              (setq done t))
          ;; If the checkout fails, vc-do-command signals an error.
          ;; We catch this error, check the reason, correct the
          ;; version number, and try a second time.
          (error (set-buffer "*vc*")
                 (goto-char (point-min))
                 (if (search-forward "no side branches present for" nil t)
                     (progn (setq recent (vc-branch-part recent))
                            ;; vc-do-command popped up a window with
                            ;; the error message.  Get rid of it, by
                            ;; restoring the old window configuration.
                            (set-window-configuration config))
                   ;; No, it was some other error: re-signal it.
                   (signal (car err) (cdr err))))))
      ;; If norevert, clear version headers and mark the buffer modified.
      (if norevert
          (progn
            (set-visited-file-name (buffer-file-name))
            (if (not vc-make-backup-files)
                ;; inhibit backup for this buffer
                (progn (make-local-variable 'backup-inhibited)
                       (setq backup-inhibited t)))
            (if (eq (vc-backend (buffer-file-name)) 'RCS)
                (progn (setq buffer-read-only nil)
                       (vc-clear-headers)))
            (vc-mode-line (buffer-file-name))))
      (message "Version %s has been removed from the master" target)
      )))

;;;###autoload
(defun vc-rename-file (old new)
  "Rename file OLD to NEW, and rename its master file likewise."
  (interactive "fVC rename file: \nFRename to: ")
  ;; There are several ways of renaming files under CVS 1.3, but they all
  ;; have serious disadvantages.  See the FAQ (available from think.com in
  ;; pub/cvs/).  I'd rather send the user an error, than do something he might
  ;; consider to be wrong.  When the famous, long-awaited rename database is
  ;; implemented things might change for the better.  This is unlikely to occur
  ;; until CVS 2.0 is released.  --ceder 1994-01-23 21:27:51
  (if (eq (vc-backend old) 'CVS)
      (error "Renaming files under CVS is dangerous and not supported in VC"))
  (let ((oldbuf (get-file-buffer old)))
    (if (and oldbuf (buffer-modified-p oldbuf))
	(error "Please save files before moving them"))
    (if (get-file-buffer new)
	(error "Already editing new file name"))
    (if (file-exists-p new)
	(error "New file already exists"))
    (let ((oldmaster (vc-name old)))
      (if oldmaster
	  (progn
	    (if (vc-locking-user old)
		(error "Please check in files before moving them"))
	    (if (or (file-symlink-p oldmaster)
		    ;; This had FILE, I changed it to OLD. -- rms.
		    (file-symlink-p (vc-backend-subdirectory-name old)))
		(error "This is not a safe thing to do in the presence of symbolic links"))
	    (rename-file
	     oldmaster
	     (let ((backend (vc-backend old))
		   (newdir (or (file-name-directory new) ""))
		   (newbase (file-name-nondirectory new)))
	       (catch 'found
		 (mapcar
		  (function
		   (lambda (s)
		     (if (eq backend (cdr s))
			 (let* ((newmaster (format (car s) newdir newbase))
				(newmasterdir (file-name-directory newmaster)))
			   (if (or (not newmasterdir)
				   (file-directory-p newmasterdir))
			       (throw 'found newmaster))))))
		  vc-master-templates)
		 (error "New file lacks a version control directory"))))))
      (if (or (not oldmaster) (file-exists-p old))
	  (rename-file old new)))
; ?? Renaming a file might change its contents due to keyword expansion.
; We should really check out a new copy if the old copy was precisely equal
; to some checked in version.  However, testing for this is tricky....
    (if oldbuf
	(save-excursion
	  (set-buffer oldbuf)
	  (set-visited-file-name new)
	  (set-buffer-modified-p nil))))
  ;; This had FILE, I changed it to OLD. -- rms.
  (vc-backend-dispatch old
		       (vc-record-rename old new) ;SCCS
		       nil		;RCS
		       nil		;CVS
		       )
  )

;;;###autoload
(defun vc-update-change-log (&rest args)
  "Find change log file and add entries from recent RCS logs.
The mark is left at the end of the text prepended to the change log.
With prefix arg of C-u, only find log entries for the current buffer's file.
With any numeric prefix arg, find log entries for all files currently visited.
Otherwise, find log entries for all registered files in the default directory.
From a program, any arguments are passed to the `rcs2log' script."
  (interactive
   (cond ((consp current-prefix-arg)	;C-u
	  (list buffer-file-name))
	 (current-prefix-arg		;Numeric argument.
	  (let ((files nil)
		(buffers (buffer-list))
		file)
	    (while buffers
	      (setq file (buffer-file-name (car buffers)))
	      (and file (vc-backend file)
		   (setq files (cons file files)))
	      (setq buffers (cdr buffers)))
	    files))
	 (t
	  (let ((RCS (concat default-directory "RCS")))
	    (and (file-directory-p RCS)
		 (mapcar (function
			  (lambda (f)
			    (if (string-match "\\(.*\\),v$" f)
				(substring f 0 (match-end 1))
			      f)))
			 (directory-files RCS nil "...\\|^[^.]\\|^.[^.]")))))))
  (let ((odefault default-directory)
	(full-name (if (boundp 'add-log-full-name)
		       add-log-full-name
		     (user-full-name)))
	(mailing-address (if (boundp 'add-log-mailing-address)
			     add-log-mailing-address
			   user-mail-address)))
    (find-file-other-window (find-change-log))
    (barf-if-buffer-read-only)
    (vc-buffer-sync)
    (undo-boundary)
    (goto-char (point-min))
    (push-mark)
    (message "Computing change log entries...")
    (message "Computing change log entries... %s"
	     (if (or (null args)
		     (eq 0 (apply 'call-process "rcs2log" nil t nil
				  "-u"
				  (concat (user-login-name)
					  "\t"
					  full-name
					  "\t"
					  mailing-address)
				  (mapcar (function
					   (lambda (f)
					     (file-relative-name
					      (if (file-name-absolute-p f)
						  f
						(concat odefault f)))))
					  args))))
		 "done" "failed"))))

;; Collect back-end-dependent stuff here

(defun vc-backend-admin (file &optional rev comment)
  ;; Register a file into the version-control system
  ;; Automatically retrieves a read-only version of the file with
  ;; keywords expanded if vc-keep-workfiles is non-nil, otherwise
  ;; it deletes the workfile.
  (vc-file-clearprops file)
  (or vc-default-back-end
      (setq vc-default-back-end (if (vc-find-binary "rcs") 'RCS 'SCCS)))
  (message "Registering %s..." file)
  (let ((backend
	 (cond
	  ((file-exists-p (vc-backend-subdirectory-name)) vc-default-back-end)
	  ((file-exists-p "RCS") 'RCS)
	  ((file-exists-p "SCCS") 'SCCS)
	  ((file-exists-p "CVS") 'CVS)
	  (t vc-default-back-end))))
    (cond ((eq backend 'SCCS)
	   (vc-do-command nil 0 "admin" file 'MASTER	;; SCCS
			  (and rev (concat "-r" rev))
			  "-fb"
			  (concat "-i" file)
			  (and comment (concat "-y" comment))
			  (format
			   (car (rassq 'SCCS vc-master-templates))
			   (or (file-name-directory file) "")
			   (file-name-nondirectory file)))
	   (delete-file file)
	   (if vc-keep-workfiles
	       (vc-do-command nil 0 "get" file 'MASTER)))
	  ((eq backend 'RCS)
	   (vc-do-command nil 0 "ci" file 'MASTER	;; RCS
                          ;; if available, use the secure registering option
			  (and (vc-backend-release-p 'RCS "5.6.4") "-i")
			  (concat (if vc-keep-workfiles "-u" "-r") rev)
			  (and comment (concat "-t-" comment))
			  file))
	  ((eq backend 'CVS)
	   (vc-do-command nil 0 "cvs" file 'WORKFILE ;; CVS
			  "add"
			  (and comment (string-match "[^\t\n ]" comment)
			       (concat "-m" comment)))
	   )))
  (message "Registering %s...done" file)
  )

(defun vc-backend-checkout (file &optional writable rev workfile)
  ;; Retrieve a copy of a saved version into a workfile
  (let ((filename (or workfile file))
	(file-buffer (get-file-buffer file))
	switches)
    (message "Checking out %s..." filename)
    (save-excursion
      ;; Change buffers to get local value of vc-checkout-switches.
      (if file-buffer (set-buffer file-buffer))
      (setq switches (if (stringp vc-checkout-switches)
			 (list vc-checkout-switches)
		       vc-checkout-switches))
      ;; Save this buffer's default-directory
      ;; and use save-excursion to make sure it is restored
      ;; in the same buffer it was saved in.
      (let ((default-directory default-directory))
	(save-excursion
	  ;; Adjust the default-directory so that the check-out creates 
	  ;; the file in the right place.
	  (setq default-directory (file-name-directory filename))
	  (vc-backend-dispatch file
	    (progn  ;; SCCS
	      (and rev (string= rev "") (setq rev nil))
	      (if workfile  
		  ;; Some SCCS implementations allow checking out directly to a
		  ;; file using the -G option, but then some don't so use the
		  ;; least common denominator approach and use the -p option
		  ;; ala RCS.
		  (let ((vc-modes (logior (file-modes (vc-name file))
					  (if writable 128 0)))
			(failed t))
		    (unwind-protect
			(progn
			  (apply 'vc-do-command
				 nil 0 "/bin/sh" file 'MASTER "-c"
				 ;; Some shells make the "" dummy argument into $0
				 ;; while others use the shell's name as $0 and
				 ;; use the "" as $1.  The if-statement
				 ;; converts the latter case to the former.
				 (format "if [ x\"$1\" = x ]; then shift; fi; \
			       umask %o; exec >\"$1\" || exit; \
			       shift; umask %o; exec get \"$@\""
				       (logand 511 (lognot vc-modes))
				       (logand 511 (lognot (default-file-modes))))
				 ""		; dummy argument for shell's $0
				 filename 
				 (if writable "-e")
				 "-p" 
				 (and rev
				      (concat "-r" (vc-lookup-triple file rev)))
				 switches)
			  (setq failed nil))
		      (and failed (file-exists-p filename) 
			   (delete-file filename))))
		(apply 'vc-do-command nil 0 "get" file 'MASTER   ;; SCCS
		       (if writable "-e")
		       (and rev (concat "-r" (vc-lookup-triple file rev)))
		       switches)
		(vc-file-setprop file 'vc-workfile-version nil)))
	    (if workfile  ;; RCS
		;; RCS doesn't let us check out into arbitrary file names directly.
		;; Use `co -p' and make stdout point to the correct file.
		(let ((vc-modes (logior (file-modes (vc-name file))
					(if writable 128 0)))
		      (failed t))
		  (unwind-protect
		      (progn
			(apply 'vc-do-command
			       nil 0 "/bin/sh" file 'MASTER "-c"
			       ;; See the SCCS case, above, regarding the
			       ;; if-statement.
			       (format "if [ x\"$1\" = x ]; then shift; fi; \
			       umask %o; exec >\"$1\" || exit; \
			       shift; umask %o; exec co \"$@\""
				       (logand 511 (lognot vc-modes))
				       (logand 511 (lognot (default-file-modes))))
			       ""		; dummy argument for shell's $0
			       filename
			       (if writable "-l")
			       (concat "-p" rev)
			       switches)
			(setq failed nil))
		    (and failed (file-exists-p filename) (delete-file filename))))
	      (let (new-version)
		;; if we should go to the head of the trunk, 
		;; clear the default branch first
		(and rev (string= rev "") 
		     (vc-do-command nil 0 "rcs" file 'MASTER "-b"))
		;; now do the checkout
		(apply 'vc-do-command
		       nil 0 "co" file 'MASTER
		       ;; If locking is not strict, force to overwrite
		       ;; the writable workfile.
		       (if (eq (vc-checkout-model file) 'implicit) "-f")
		       (if writable "-l")
		       (if rev (concat "-r" rev)
			 ;; if no explicit revision was specified,
			 ;; check out that of the working file
			 (let ((workrev (vc-workfile-version file)))
			   (if workrev (concat "-r" workrev)
			     nil)))
		       switches)
		;; determine the new workfile version
		(save-excursion
		  (set-buffer "*vc*")
		  (goto-char (point-min))
		  (setq new-version 
			(if (re-search-forward "^revision \\([0-9.]+\\).*\n" nil t)
			    (buffer-substring (match-beginning 1) (match-end 1)))))
		(vc-file-setprop file 'vc-workfile-version new-version)
		;; if necessary, adjust the default branch
		(and rev (not (string= rev ""))
		     (vc-do-command nil 0 "rcs" file 'MASTER 
			(concat "-b" (if (vc-latest-on-branch-p file)
					 (if (vc-trunk-p new-version) nil
					   (vc-branch-part new-version))
				       new-version))))))
	    (if workfile  ;; CVS
		;; CVS is much like RCS
		(let ((failed t))
		  (unwind-protect
		      (progn
			(apply 'vc-do-command
			       nil 0 "/bin/sh" file 'WORKFILE "-c"
			       "exec >\"$1\" || exit; shift; exec cvs update \"$@\""
			       ""		; dummy argument for shell's $0
			       workfile
			       (concat "-r" rev)
			       "-p"
			       switches)
			(setq failed nil))
		    (and failed (file-exists-p filename) (delete-file filename))))
	      ;; default for verbose checkout: clear the sticky tag
	      ;; so that the actual update will get the head of the trunk
	      (and rev (string= rev "")
		   (vc-do-command nil 0 "cvs" file 'WORKFILE "update" "-A"))
	      ;; If a revision was specified, check that out.
	      (if rev
		  (apply 'vc-do-command nil 0 "cvs" file 'WORKFILE 
			 (and writable (eq (vc-checkout-model file) 'manual) "-w")
			 "update"
			 (and rev (not (string= rev ""))
			      (concat "-r" rev))
			 switches)
		;; If no revision was specified, simply make the file writable.
		(and writable 
		     (or (eq (vc-checkout-model file) 'manual)
			 (zerop (logand 128 (file-modes file))))
		     (set-file-modes file (logior 128 (file-modes file)))))
	      (if rev (vc-file-setprop file 'vc-workfile-version nil))))
	  (cond 
	   ((not workfile)
	    (vc-file-clear-masterprops file)
	    (if writable 
		(vc-file-setprop file 'vc-locking-user (user-login-name)))
	    (vc-file-setprop file
			     'vc-checkout-time (nth 5 (file-attributes file)))))
	  (message "Checking out %s...done" filename))))))

(defun vc-backend-logentry-check (file)
  (vc-backend-dispatch file
   (if (>= (buffer-size) 512)	;; SCCS
       (progn
	 (goto-char 512)
	 (error
	  "Log must be less than 512 characters; point is now at pos 512")))
   nil    ;; RCS
   nil)   ;; CVS
  )

(defun vc-backend-checkin (file rev comment)
  ;; Register changes to FILE as level REV with explanatory COMMENT.
  ;; Automatically retrieves a read-only version of the file with
  ;; keywords expanded if vc-keep-workfiles is non-nil, otherwise
  ;; it deletes the workfile.
  ;;   Adaptation for RCS branch support: if this is an explicit checkin,
  ;; or if the checkin creates a new branch, set the master file branch
  ;; accordingly.
  (message "Checking in %s..." file)
  ;; "This log message intentionally left almost blank".
  ;; RCS 5.7 gripes about white-space-only comments too.
  (or (and comment (string-match "[^\t\n ]" comment))
      (setq comment "*** empty log message ***"))
  (save-excursion
    ;; Change buffers to get local value of vc-checkin-switches.
    (set-buffer (or (get-file-buffer file) (current-buffer)))
    (let ((switches
	   (if (stringp vc-checkin-switches)
	       (list vc-checkin-switches)
	     vc-checkin-switches)))
      ;; Clear the master-properties.  Do that here, not at the
      ;; end, because if the check-in fails we want them to get
      ;; re-computed before the next try.
      (vc-file-clear-masterprops file)
      (vc-backend-dispatch file
	;; SCCS
	(progn
	  (apply 'vc-do-command nil 0 "delta" file 'MASTER
		 (if rev (concat "-r" rev))
		 (concat "-y" comment)
		 switches)
	  (vc-file-setprop file 'vc-locking-user 'none)
	  (vc-file-setprop file 'vc-workfile-version nil)
	  (if vc-keep-workfiles
	      (vc-do-command nil 0 "get" file 'MASTER))
	  )
	;; RCS
	(let ((old-version (vc-workfile-version file)) new-version)
	  (apply 'vc-do-command nil 0 "ci" file 'MASTER
		 ;; if available, use the secure check-in option
		 (and (vc-backend-release-p 'RCS "5.6.4") "-j")
		 (concat (if vc-keep-workfiles "-u" "-r") rev)
		 (concat "-m" comment)
		 switches)
	  (vc-file-setprop file 'vc-locking-user 'none)
	  (vc-file-setprop file 'vc-workfile-version nil)

	  ;; determine the new workfile version
	  (set-buffer "*vc*")
	  (goto-char (point-min))
	  (if (or (re-search-forward 
		   "new revision: \\([0-9.]+\\);" nil t)
		  (re-search-forward 
		   "reverting to previous revision \\([0-9.]+\\)" nil t))
	      (progn (setq new-version (buffer-substring (match-beginning 1)
							 (match-end 1)))
		     (vc-file-setprop file 'vc-workfile-version new-version)))

	  ;; if we got to a different branch, adjust the default
	  ;; branch accordingly
	  (cond 
	   ((and old-version new-version
		 (not (string= (vc-branch-part old-version)
			       (vc-branch-part new-version))))
	    (vc-do-command nil 0 "rcs" file 'MASTER 
			   (if (vc-trunk-p new-version) "-b"
			     (concat "-b" (vc-branch-part new-version))))
	    ;; If this is an old RCS release, we might have 
	    ;; to remove a remaining lock.
	    (if (not (vc-backend-release-p 'RCS "5.6.2"))
		;; exit status of 1 is also accepted.
		;; It means that the lock was removed before.
		(vc-do-command nil 1 "rcs" file 'MASTER 
			       (concat "-u" old-version))))))
	;; CVS
	(progn
	  ;; explicit check-in to the trunk requires a 
	  ;; double check-in (first unexplicit) (CVS-1.3)
	  (condition-case nil
	      (progn
		(if (and rev (vc-trunk-p rev))
		    (apply 'vc-do-command nil 0 "cvs" file 'WORKFILE 
			   "ci" "-m" "intermediate"
			   switches))
		(apply 'vc-do-command nil 0 "cvs" file 'WORKFILE 
		       "ci" (if rev (concat "-r" rev))
		       (concat "-m" comment)
		       switches))
	    (error (if (eq (vc-cvs-status file) 'needs-merge)
		       ;; The CVS output will be on top of this message.
		       (error "Type C-x 0 C-x C-q to merge in changes")
		     (error "Check-in failed"))))
	  ;; determine and store the new workfile version
	  (set-buffer "*vc*")
	  (goto-char (point-min))
	  (if (re-search-forward 
	       "^\\(new\\|initial\\) revision: \\([0-9.]+\\)" nil t)
	      (vc-file-setprop file 'vc-workfile-version 
			       (buffer-substring (match-beginning 2)
						 (match-end 2)))
	    (vc-file-setprop file 'vc-workfile-version nil))
	  ;; if this was an explicit check-in, remove the sticky tag
	  (if rev
	      (vc-do-command nil 0 "cvs" file 'WORKFILE "update" "-A"))
	  (vc-file-setprop file 'vc-locking-user 'none)
	  (vc-file-setprop file 'vc-checkout-time 
			   (nth 5 (file-attributes file)))))))
  (message "Checking in %s...done" file))

(defun vc-backend-revert (file)
  ;; Revert file to latest checked-in version.
  ;; (for RCS, to workfile version)
  (message "Reverting %s..." file)
  (vc-file-clear-masterprops file)
  (vc-backend-dispatch
   file
   ;; SCCS
   (progn
     (vc-do-command nil 0 "unget" file 'MASTER nil)
     (vc-do-command nil 0 "get" file 'MASTER nil))
   ;; RCS
   (vc-do-command nil 0 "co" file 'MASTER
		  "-f" (concat "-u" (vc-workfile-version file)))
   ;; CVS
   (progn
     (delete-file file)
     (vc-do-command nil 0 "cvs" file 'WORKFILE "update")))
  (vc-file-setprop file 'vc-locking-user 'none)
  (vc-file-setprop file 'vc-checkout-time (nth 5 (file-attributes file)))
  (message "Reverting %s...done" file)
  )

(defun vc-backend-steal (file &optional rev)
  ;; Steal the lock on the current workfile.  Needs RCS 5.6.2 or later for -M.
  (message "Stealing lock on %s..." file)
  (vc-backend-dispatch file
   (progn				;SCCS
     (vc-do-command nil 0 "unget" file 'MASTER "-n" (if rev (concat "-r" rev)))
     (vc-do-command nil 0 "get" file 'MASTER "-g" (if rev (concat "-r" rev)))
     )
   (vc-do-command nil 0 "rcs" file 'MASTER	;RCS
		  "-M" (concat "-u" rev) (concat "-l" rev))
   (error "You cannot steal a CVS lock; there are no CVS locks to steal") ;CVS
   )
  (vc-file-setprop file 'vc-locking-user (user-login-name))
  (message "Stealing lock on %s...done" file)
  )  

(defun vc-backend-uncheck (file target)
  ;; Undo the latest checkin.
  (message "Removing last change from %s..." file)
  (vc-backend-dispatch file
   (vc-do-command nil 0 "rmdel" file 'MASTER (concat "-r" target))
   (vc-do-command nil 0 "rcs" file 'MASTER (concat "-o" target))
   nil  ;; this is never reached under CVS
   )
  (message "Removing last change from %s...done" file)
  )

(defun vc-backend-print-log (file)
  ;; Get change log associated with FILE.
  (vc-backend-dispatch 
   file
   (vc-do-command nil 0 "prs" file 'MASTER)
   (vc-do-command nil 0 "rlog" file 'MASTER)
   (vc-do-command nil 0 "cvs" file 'WORKFILE "rlog")))

(defun vc-backend-assign-name (file name)
  ;; Assign to a FILE's latest version a given NAME.
  (vc-backend-dispatch file
   (vc-add-triple name file (vc-latest-version file))              ;; SCCS
   (vc-do-command nil 0 "rcs" file 'MASTER (concat "-n" name ":")) ;; RCS
   (vc-do-command nil 0 "cvs" file 'WORKFILE "tag" name)	   ;; CVS
   )
  )

(defun vc-backend-diff (file &optional oldvers newvers cmp)
  ;; Get a difference report between two versions of FILE.
  ;; Get only a brief comparison report if CMP, a difference report otherwise.
  (let ((backend (vc-backend file)))
    (cond
     ((eq backend 'SCCS)
      (setq oldvers (vc-lookup-triple file oldvers))
      (setq newvers (vc-lookup-triple file newvers)))
     ((eq backend 'RCS)
      (if (not oldvers) (setq oldvers (vc-workfile-version file)))
      ;; If we know that --brief is not supported, don't try it.
      (setq cmp (and cmp (not (eq vc-rcsdiff-knows-brief 'no))))))
     ;; SCCS and RCS shares a lot of code.
    (cond
     ((or (eq backend 'SCCS) (eq backend 'RCS))
      (let* ((command (if (eq backend 'SCCS) "vcdiff" "rcsdiff"))
	     (mode (if (eq backend 'RCS) 'WORKFILE 'MASTER))
	     (options (append (list (and cmp "--brief")
				    "-q"
				    (and oldvers (concat "-r" oldvers))
				    (and newvers (concat "-r" newvers)))
			      (and (not cmp)
				   (if (listp diff-switches)
				       diff-switches
				     (list diff-switches)))))
	     (status (apply 'vc-do-command "*vc-diff*" 2 
			    command file mode options)))
	;; If --brief didn't work, do a double-take and remember it 
        ;; for the future.
	(if (eq status 2)
            (prog1
                (apply 'vc-do-command "*vc-diff*" 1 command file 'WORKFILE
                       (if cmp (cdr options) options))
              (if cmp (setq vc-rcsdiff-knows-brief 'no)))
          ;; If --brief DID work, remember that, too.
	  (and cmp (not vc-rcsdiff-knows-brief)
               (setq vc-rcsdiff-knows-brief 'yes))
          status)))
     ;; CVS is different.  
     ((eq backend 'CVS)
      (if (string= (vc-workfile-version file) "0") ;CVS
	  ;; This file is added but not yet committed; there is no master file.
	  (if (or oldvers newvers)
	      (error "No revisions of %s exist" file)
	    (if cmp 1 ;; file is added but not committed, 
	              ;; we regard this as "changed".
	      ;; diff it against /dev/null.
	      (apply 'vc-do-command
		     "*vc-diff*" 1 "diff" file 'WORKFILE
		     (append (if (listp diff-switches) 
				 diff-switches
			       (list diff-switches)) '("/dev/null")))))
	;; cmp is not yet implemented -- we always do a full diff.
	(apply 'vc-do-command
	       "*vc-diff*" 1 "cvs" file 'WORKFILE "diff"
	       (and oldvers (concat "-r" oldvers))
	       (and newvers (concat "-r" newvers))
	       (if (listp diff-switches)
		   diff-switches
		 (list diff-switches)))))
     (t
      (vc-registration-error file)))))

(defun vc-backend-merge-news (file)
  ;; Merge in any new changes made to FILE.
  (message "Merging changes into %s..." file)
  (prog1
      (vc-backend-dispatch 
       file
       (error "vc-backend-merge-news not meaningful for SCCS files") ;SCCS
       (error "vc-backend-merge-news not meaningful for RCS files")	;RCS
       (save-excursion  ; CVS
	 (vc-file-clear-masterprops file)
	 (vc-file-setprop file 'vc-workfile-version nil)
	 (vc-file-setprop file 'vc-locking-user nil)
	 (vc-do-command nil 0 "cvs" file 'WORKFILE "update")
	 ;; CVS doesn't return an error code if conflicts are detected.
	 ;; Since we want to warn the user about it (and possibly start
	 ;; emerge later), scan the output and see if this occurred.
	 (set-buffer (get-buffer "*vc*"))
	 (goto-char (point-min))
	 (if (re-search-forward "^cvs update: conflicts found in .*" nil t)
	     1  ;; error code for caller
	   0  ;; no conflict detected
	   )))
    (message "Merging changes into %s...done" file)))

(defun vc-check-headers ()
  "Check if the current file has any headers in it."
  (interactive)
  (save-excursion
    (goto-char (point-min))
    (vc-backend-dispatch buffer-file-name
     (re-search-forward  "%[MIRLBSDHTEGUYFPQCZWA]%" nil t)	;; SCCS
     (re-search-forward "\\$[A-Za-z\300-\326\330-\366\370-\377]+\\(: [\t -#%-\176\240-\377]*\\)?\\$" nil t)		;; RCS
     'RCS				;; CVS works like RCS in this regard.
     )
    ))

;; Back-end-dependent stuff ends here.

;; Set up key bindings for use while editing log messages

(defun vc-log-mode ()
  "Minor mode for driving version-control tools.
These bindings are added to the global keymap when you enter this mode:
\\[vc-next-action]		perform next logical version-control operation on current file
\\[vc-register]			register current file
\\[vc-toggle-read-only]		like next-action, but won't register files
\\[vc-insert-headers]		insert version-control headers in current file
\\[vc-print-log]		display change history of current file
\\[vc-revert-buffer]		revert buffer to latest version
\\[vc-cancel-version]		undo latest checkin
\\[vc-diff]		show diffs between file versions
\\[vc-version-other-window]		visit old version in another window
\\[vc-directory]		show all files locked by any user in or below .
\\[vc-update-change-log]		add change log entry from recent checkins

While you are entering a change log message for a version, the following
additional bindings will be in effect.

\\[vc-finish-logentry]	proceed with check in, ending log message entry

Whenever you do a checkin, your log comment is added to a ring of
saved comments.  These can be recalled as follows:

\\[vc-next-comment]	replace region with next message in comment ring
\\[vc-previous-comment]	replace region with previous message in comment ring
\\[vc-comment-search-reverse]	search backward for regexp in the comment ring
\\[vc-comment-search-forward]	search backward for regexp in the comment ring

Entry to the change-log submode calls the value of text-mode-hook, then
the value of vc-log-mode-hook.

Global user options:
	vc-initial-comment	If non-nil, require user to enter a change
				comment upon first checkin of the file.

	vc-keep-workfiles	Non-nil value prevents workfiles from being
				deleted when changes are checked in

        vc-suppress-confirm     Suppresses some confirmation prompts,
				notably for reversions.

	vc-header-alist		Which keywords to insert when adding headers
				with \\[vc-insert-headers].  Defaults to
				'(\"\%\W\%\") under SCCS, '(\"\$Id\$\") under 
				RCS and CVS.

	vc-static-header-alist	By default, version headers inserted in C files
				get stuffed in a static string area so that
				ident(RCS/CVS) or what(SCCS) can see them in
				the compiled object code.  You can override
				this by setting this variable to nil, or change
				the header template by changing it.

	vc-command-messages	if non-nil, display run messages from the
				actual version-control utilities (this is
				intended primarily for people hacking vc
				itself).
"
  (interactive)
  (set-syntax-table text-mode-syntax-table)
  (use-local-map vc-log-entry-mode)
  (setq local-abbrev-table text-mode-abbrev-table)
  (setq major-mode 'vc-log-mode)
  (setq mode-name "VC-Log")
  (make-local-variable 'vc-log-file)
  (make-local-variable 'vc-log-version)
  (make-local-variable 'vc-comment-ring-index)
  (set-buffer-modified-p nil)
  (setq buffer-file-name nil)
  (run-hooks 'text-mode-hook 'vc-log-mode-hook)
)

;; Initialization code, to be done just once at load-time
(if vc-log-entry-mode
    nil
  (setq vc-log-entry-mode (make-sparse-keymap))
  (define-key vc-log-entry-mode "\M-n" 'vc-next-comment)
  (define-key vc-log-entry-mode "\M-p" 'vc-previous-comment)
  (define-key vc-log-entry-mode "\M-r" 'vc-comment-search-reverse)
  (define-key vc-log-entry-mode "\M-s" 'vc-comment-search-forward)
  (define-key vc-log-entry-mode "\C-c\C-c" 'vc-finish-logentry)
  )

;;; These things should probably be generally available

(defun vc-file-tree-walk (dirname func &rest args)
  "Walk recursively through DIRNAME.
Invoke FUNC f ARGS on each non-directory file f underneath it."
  (vc-file-tree-walk-internal (expand-file-name dirname) func args)
  (message "Traversing directory %s...done" dirname))

(defun vc-file-tree-walk-internal (file func args)
  (if (not (file-directory-p file))
      (apply func file args)
    (message "Traversing directory %s..." (abbreviate-file-name file))
    (let ((dir (file-name-as-directory file)))
      (mapcar
       (function
	(lambda (f) (or
		     (string-equal f ".")
		     (string-equal f "..")
		     (member f vc-directory-exclusion-list)
		     (let ((dirf (concat dir f)))
			(or
			 (file-symlink-p dirf) ;; Avoid possible loops
			 (vc-file-tree-walk-internal dirf func args))))))
       (directory-files dir)))))

(provide 'vc)

;;; DEVELOPER'S NOTES ON CONCURRENCY PROBLEMS IN THIS CODE
;;;
;;; These may be useful to anyone who has to debug or extend the package.
;;; (Note that this information corresponds to versions 5.x. Some of it
;;; might have been invalidated by the additions to support branching
;;; and RCS keyword lookup. AS, 1995/03/24)
;;; 
;;; A fundamental problem in VC is that there are time windows between
;;; vc-next-action's computations of the file's version-control state and
;;; the actions that change it.  This is a window open to lossage in a
;;; multi-user environment; someone else could nip in and change the state
;;; of the master during it.
;;; 
;;; The performance problem is that rlog/prs calls are very expensive; we want
;;; to avoid them as much as possible.
;;; 
;;; ANALYSIS:
;;; 
;;; The performance problem, it turns out, simplifies in practice to the
;;; problem of making vc-locking-user fast.  The two other functions that call
;;; prs/rlog will not be so commonly used that the slowdown is a problem; one
;;; makes snapshots, the other deletes the calling user's last change in the
;;; master.
;;; 
;;; The race condition implies that we have to either (a) lock the master
;;; during the entire execution of vc-next-action, or (b) detect and
;;; recover from errors resulting from dispatch on an out-of-date state.
;;; 
;;; Alternative (a) appears to be infeasible.  The problem is that we can't
;;; guarantee that the lock will ever be removed.  Suppose a user starts a
;;; checkin, the change message buffer pops up, and the user, having wandered
;;; off to do something else, simply forgets about it?
;;; 
;;; Alternative (b), on the other hand, works well with a cheap way to speed up
;;; vc-locking-user.  Usually, if a file is registered, we can read its locked/
;;; unlocked state and its current owner from its permissions.
;;; 
;;; This shortcut will fail if someone has manually changed the workfile's
;;; permissions; also if developers are munging the workfile in several
;;; directories, with symlinks to a master (in this latter case, the
;;; permissions shortcut will fail to detect a lock asserted from another
;;; directory).
;;; 
;;; Note that these cases correspond exactly to the errors which could happen
;;; because of a competing checkin/checkout race in between two instances of
;;; vc-next-action.
;;; 
;;; For VC's purposes, a workfile/master pair may have the following states:
;;; 
;;; A. Unregistered.  There is a workfile, there is no master.
;;; 
;;; B. Registered and not locked by anyone.
;;; 
;;; C. Locked by calling user and unchanged.
;;; 
;;; D. Locked by the calling user and changed.
;;; 
;;; E. Locked by someone other than the calling user.
;;; 
;;; This makes for 25 states and 20 error conditions.  Here's the matrix:
;;; 
;;; VC's idea of state
;;;  |
;;;  V  Actual state   RCS action              SCCS action          Effect
;;;    A  B  C  D  E
;;;  A .  1  2  3  4   ci -u -t-          admin -fb -i<file>      initial admin
;;;  B 5  .  6  7  8   co -l              get -e                  checkout
;;;  C 9  10 .  11 12  co -u              unget; get              revert
;;;  D 13 14 15 .  16  ci -u -m<comment>  delta -y<comment>; get  checkin
;;;  E 17 18 19 20 .   rcs -u -M -l       unget -n ; get -g       steal lock
;;; 
;;; All commands take the master file name as a last argument (not shown).
;;; 
;;; In the discussion below, a "self-race" is a pathological situation in
;;; which VC operations are being attempted simultaneously by two or more
;;; Emacsen running under the same username.
;;; 
;;; The vc-next-action code has the following windows:
;;; 
;;; Window P:
;;;    Between the check for existence of a master file and the call to
;;; admin/checkin in vc-buffer-admin (apparent state A).  This window may
;;; never close if the initial-comment feature is on.
;;; 
;;; Window Q:
;;;    Between the call to vc-workfile-unchanged-p in and the immediately
;;; following revert (apparent state C).
;;; 
;;; Window R:
;;;    Between the call to vc-workfile-unchanged-p in and the following
;;; checkin (apparent state D).  This window may never close.
;;; 
;;; Window S:
;;;    Between the unlock and the immediately following checkout during a
;;; revert operation (apparent state C).  Included in window Q.
;;; 
;;; Window T:
;;;    Between vc-locking-user and the following checkout (apparent state B).
;;; 
;;; Window U:
;;;    Between vc-locking-user and the following revert (apparent state C).
;;; Includes windows Q and S.
;;; 
;;; Window V:
;;;    Between vc-locking-user and the following checkin (apparent state
;;; D).  This window may never be closed if the user fails to complete the
;;; checkin message.  Includes window R.
;;; 
;;; Window W:
;;;    Between vc-locking-user and the following steal-lock (apparent
;;; state E).  This window may never close if the user fails to complete
;;; the steal-lock message.  Includes window X.
;;; 
;;; Window X:
;;;    Between the unlock and the immediately following re-lock during a
;;; steal-lock operation (apparent state E).  This window may never cloce
;;; if the user fails to complete the steal-lock message.
;;; 
;;; Errors:
;;; 
;;; Apparent state A ---
;;;
;;; 1. File looked unregistered but is actually registered and not locked.
;;; 
;;;    Potential cause: someone else's admin during window P, with
;;; caller's admin happening before their checkout.
;;; 
;;;    RCS: Prior to version 5.6.4, ci fails with message
;;;         "no lock set by <user>".  From 5.6.4 onwards, VC uses the new
;;;         ci -i option and the message is "<file>,v: already exists".
;;;    SCCS: admin will fail with error (ad19).
;;; 
;;;    We can let these errors be passed up to the user.
;;; 
;;; 2. File looked unregistered but is actually locked by caller, unchanged.
;;; 
;;;    Potential cause: self-race during window P.
;;; 
;;;    RCS: Prior to version 5.6.4, reverts the file to the last saved
;;;         version and unlocks it.  From 5.6.4 onwards, VC uses the new
;;;         ci -i option, failing with message "<file>,v: already exists".
;;;    SCCS: will fail with error (ad19).
;;; 
;;;    Either of these consequences is acceptable.
;;; 
;;; 3. File looked unregistered but is actually locked by caller, changed.
;;; 
;;;    Potential cause: self-race during window P.
;;; 
;;;    RCS: Prior to version 5.6.4, VC registers the caller's workfile as 
;;;         a delta with a null change comment (the -t- switch will be 
;;;         ignored). From 5.6.4 onwards, VC uses the new ci -i option,
;;;         failing with message "<file>,v: already exists".
;;;    SCCS: will fail with error (ad19).
;;; 
;;; 4. File looked unregistered but is locked by someone else.
;;; 
;;;    Potential cause: someone else's admin during window P, with
;;; caller's admin happening *after* their checkout.
;;; 
;;;    RCS: Prior to version 5.6.4, ci fails with a 
;;;         "no lock set by <user>" message.  From 5.6.4 onwards, 
;;;         VC uses the new ci -i option, failing with message 
;;;         "<file>,v: already exists".
;;;    SCCS: will fail with error (ad19).
;;; 
;;;    We can let these errors be passed up to the user.
;;; 
;;; Apparent state B ---
;;;
;;; 5. File looked registered and not locked, but is actually unregistered.
;;; 
;;;    Potential cause: master file got nuked during window P.
;;; 
;;;    RCS: will fail with "RCS/<file>: No such file or directory"
;;;    SCCS: will fail with error ut4.
;;; 
;;;    We can let these errors be passed up to the user.
;;; 
;;; 6. File looked registered and not locked, but is actually locked by the
;;; calling user and unchanged.
;;; 
;;;    Potential cause: self-race during window T.
;;; 
;;;    RCS: in the same directory as the previous workfile, co -l will fail
;;; with "co error: writable foo exists; checkout aborted".  In any other
;;; directory, checkout will succeed.
;;;    SCCS: will fail with ge17.
;;; 
;;;    Either of these consequences is acceptable.
;;; 
;;; 7. File looked registered and not locked, but is actually locked by the
;;; calling user and changed.
;;; 
;;;    As case 6.
;;; 
;;; 8. File looked registered and not locked, but is actually locked by another
;;; user.
;;; 
;;;    Potential cause: someone else checks it out during window T.
;;; 
;;;    RCS: co error: revision 1.3 already locked by <user>
;;;    SCCS: fails with ge4 (in directory) or ut7 (outside it).
;;; 
;;;    We can let these errors be passed up to the user.
;;; 
;;; Apparent state C ---
;;;
;;; 9. File looks locked by calling user and unchanged, but is unregistered.
;;; 
;;;    As case 5.
;;; 
;;; 10. File looks locked by calling user and unchanged, but is actually not
;;; locked.
;;; 
;;;    Potential cause: a self-race in window U, or by the revert's
;;; landing during window X of some other user's steal-lock or window S
;;; of another user's revert.
;;; 
;;;    RCS: succeeds, refreshing the file from the identical version in
;;; the master.
;;;    SCCS: fails with error ut4 (p file nonexistent).
;;;
;;;    Either of these consequences is acceptable.
;;; 
;;; 11. File is locked by calling user.  It looks unchanged, but is actually
;;; changed.
;;; 
;;;    Potential cause: the file would have to be touched by a self-race
;;; during window Q.
;;; 
;;;    The revert will succeed, removing whatever changes came with
;;; the touch.  It is theoretically possible that work could be lost.
;;; 
;;; 12. File looks like it's locked by the calling user and unchanged, but
;;; it's actually locked by someone else.
;;; 
;;;    Potential cause: a steal-lock in window V.
;;; 
;;;    RCS: co error: revision <rev> locked by <user>; use co -r or rcs -u
;;;    SCCS: fails with error un2
;;; 
;;;    We can pass these errors up to the user.
;;; 
;;; Apparent state D ---
;;;
;;; 13. File looks like it's locked by the calling user and changed, but it's
;;; actually unregistered.
;;; 
;;;    Potential cause: master file got nuked during window P.
;;; 
;;;    RCS: Prior to version 5.6.4, checks in the user's version as an 
;;;         initial delta.  From 5.6.4 onwards, VC uses the new ci -j
;;;         option, failing with message "no such file or directory".
;;;    SCCS: will fail with error ut4.
;;;
;;;    This case is kind of nasty.  Under RCS prior to version 5.6.4,
;;; VC may fail to detect the loss of previous version information.
;;; 
;;; 14. File looks like it's locked by the calling user and changed, but it's
;;; actually unlocked.
;;; 
;;;    Potential cause: self-race in window V, or the checkin happening
;;; during the window X of someone else's steal-lock or window S of
;;; someone else's revert.
;;; 
;;;    RCS: ci will fail with "no lock set by <user>".
;;;    SCCS: delta will fail with error ut4.
;;; 
;;; 15. File looks like it's locked by the calling user and changed, but it's
;;; actually locked by the calling user and unchanged.
;;; 
;;;    Potential cause: another self-race --- a whole checkin/checkout
;;; sequence by the calling user would have to land in window R.
;;; 
;;;    SCCS: checks in a redundant delta and leaves the file unlocked as usual.
;;;    RCS: reverts to the file state as of the second user's checkin, leaving
;;; the file unlocked.
;;;
;;;    It is theoretically possible that work could be lost under RCS.
;;; 
;;; 16. File looks like it's locked by the calling user and changed, but it's
;;; actually locked by a different user.
;;; 
;;;    RCS: ci error: no lock set by <user>
;;;    SCCS: unget will fail with error un2
;;; 
;;;    We can pass these errors up to the user.
;;; 
;;; Apparent state E ---
;;;
;;; 17. File looks like it's locked by some other user, but it's actually
;;; unregistered.
;;; 
;;;    As case 13.
;;; 
;;; 18. File looks like it's locked by some other user, but it's actually
;;; unlocked.
;;; 
;;;    Potential cause: someone released a lock during window W.
;;; 
;;;    RCS: The calling user will get the lock on the file.
;;;    SCCS: unget -n will fail with cm4.
;;; 
;;;    Either of these consequences will be OK.
;;; 
;;; 19. File looks like it's locked by some other user, but it's actually
;;; locked by the calling user and unchanged.
;;; 
;;;    Potential cause: the other user relinquishing a lock followed by
;;; a self-race, both in window W.
;;; 
;;;     Under both RCS and SCCS, both unlock and lock will succeed, making
;;; the sequence a no-op.
;;; 
;;; 20. File looks like it's locked by some other user, but it's actually
;;; locked by the calling user and changed.
;;; 
;;;     As case 19.
;;; 
;;; PROBLEM CASES:
;;; 
;;;    In order of decreasing severity:
;;; 
;;;    Cases 11 and 15 are the only ones that potentially lose work.
;;; They would require a self-race for this to happen.
;;; 
;;;    Case 13 in RCS loses information about previous deltas, retaining
;;; only the information in the current workfile.  This can only happen
;;; if the master file gets nuked in window P.
;;; 
;;;    Case 3 in RCS and case 15 under SCCS insert a redundant delta with
;;; no change comment in the master.  This would require a self-race in
;;; window P or R respectively.
;;; 
;;;    Cases 2, 10, 19 and 20 do extra work, but make no changes.
;;; 
;;;    Unfortunately, it appears to me that no recovery is possible in these
;;; cases.  They don't yield error messages, so there's no way to tell that
;;; a race condition has occurred.
;;; 
;;;    All other cases don't change either the workfile or the master, and
;;; trigger command errors which the user will see.
;;; 
;;;    Thus, there is no explicit recovery code.

;;; vc.el ends here