rename: Break filepairs with different types.

When we consider if a path has been totally rewritten, we did not
touch changes from symlinks to files or vice versa.  But a change
that modifies even the type of a blob surely should count as a
complete rewrite.

While we are at it, modernise diffcore-break to be aware of gitlinks (we
do not want to touch them).

Signed-off-by: Junio C Hamano <gitster@pobox.com>

2 files changed, 89 insertions, 3 deletions

diff --git a/t/t4008-diff-break-rewrite.sh b/t/t4008-diff-break-rewrite.sh
index 1287d2ad17..26c2e4aa65 100755
--- a/t/t4008-diff-break-rewrite.sh
+++ b/t/t4008-diff-break-rewrite.sh
@@ -122,11 +122,11 @@ test_expect_success \
     'run diff with -B -M' \
     'git diff-index -B -M "$tree" >current'
 
-# This should not mistake file0 as the copy source of new file1
-# due to type differences.
+# file0 changed from regular to symlink.  file1 is very close to the preimage of file0.
+# because we break file0, file1 can become a rename of it.
 cat >expected <<\EOF
 :100644 120000 f5deac7be59e7eeab8657fd9ae706fd6a57daed2 67be421f88824578857624f7b3dc75e99a8a1481 T	file0
-:100644 100644 6ff87c4664981e4397625791c8ea3bbb5f2279a3 f5deac7be59e7eeab8657fd9ae706fd6a57daed2 M100	file1
+:100644 100644 6ff87c4664981e4397625791c8ea3bbb5f2279a3 f5deac7be59e7eeab8657fd9ae706fd6a57daed2 R	file0	file1
 EOF
 
 test_expect_success \
diff --git a/t/t4023-diff-rename-typechange.sh b/t/t4023-diff-rename-typechange.sh
new file mode 100755
index 0000000000..255604effd
--- /dev/null
+++ b/t/t4023-diff-rename-typechange.sh
@@ -0,0 +1,86 @@
+#!/bin/sh
+
+test_description='typechange rename detection'
+
+. ./test-lib.sh
+
+test_expect_success setup '
+
+	rm -f foo bar &&
+	cat ../../COPYING >foo &&
+	ln -s linklink bar &&
+	git add foo bar &&
+	git commit -a -m Initial &&
+	git tag one &&
+
+	rm -f foo bar &&
+	cat ../../COPYING >bar &&
+	ln -s linklink foo &&
+	git add foo bar &&
+	git commit -a -m Second &&
+	git tag two &&
+
+	rm -f foo bar &&
+	cat ../../COPYING >foo &&
+	git add foo &&
+	git commit -a -m Third &&
+	git tag three &&
+
+	mv foo bar &&
+	ln -s linklink foo &&
+	git add foo bar &&
+	git commit -a -m Fourth &&
+	git tag four &&
+
+	# This is purely for sanity check
+
+	rm -f foo bar &&
+	cat ../../COPYING >foo &&
+	cat ../../Makefile >bar &&
+	git add foo bar &&
+	git commit -a -m Fifth &&
+	git tag five &&
+
+	rm -f foo bar &&
+	cat ../../Makefile >foo &&
+	cat ../../COPYING >bar &&
+	git add foo bar &&
+	git commit -a -m Sixth &&
+	git tag six
+
+'
+
+test_expect_success 'cross renames to be detected for regular files' '
+
+	git diff-tree five six -r --name-status -B -M | sort >actual &&
+	{
+		echo "R100	foo	bar"
+		echo "R100	bar	foo"
+	} | sort >expect &&
+	diff -u expect actual
+
+'
+
+test_expect_success 'cross renames to be detected for typechange' '
+
+	git diff-tree one two -r --name-status -B -M | sort >actual &&
+	{
+		echo "R100	foo	bar"
+		echo "R100	bar	foo"
+	} | sort >expect &&
+	diff -u expect actual
+
+'
+
+test_expect_success 'moves and renames' '
+
+	git diff-tree three four -r --name-status -B -M | sort >actual &&
+	{
+		echo "R100	foo	bar"
+		echo "T100	foo"
+	} | sort >expect &&
+	diff -u expect actual
+
+'
+
+test_done