Make force-load-doc-strings work again

When load-force-doc-strings is true, read (#$ . POS) as the (unibyte)
string referred to.  This feature was lost by mistake in the recent
nonrecursive reader rewrite.

Noticed by Stefan Monnier.

* src/lread.c (get_lazy_string): New function (code mostly recycled
from an old version).
(read0): Detect (#$ . FIXNUM) and retrieve the string if appropriate.
* test/src/lread-resources/lazydoc.el:
* test/src/lread-tests.el (lread-force-load-doc-strings):
New test.

2 files changed, 17 insertions, 0 deletions

diff --git a/test/src/lread-resources/lazydoc.el b/test/src/lread-resources/lazydoc.el
new file mode 100644
index 00000000000..cb434c239b5
--- /dev/null
+++ b/test/src/lread-resources/lazydoc.el
diff --git a/test/src/lread-tests.el b/test/src/lread-tests.el
index f190f14781e..2f25de4cc39 100644
--- a/test/src/lread-tests.el
+++ b/test/src/lread-tests.el
@@ -322,4 +322,21 @@ literals (Bug#20852)."
   (should-error (read-from-string "?\\\n x"))
   (should (equal (read-from-string "\"a\\\nb\"") '("ab" . 6))))
 
+(ert-deftest lread-force-load-doc-strings ()
+  ;; Verify that lazy doc strings are loaded lazily by default,
+  ;; but eagerly with `force-load-doc-strings' set.
+  (let ((file (expand-file-name "lazydoc.el" (ert-resource-directory))))
+    (fmakunbound 'lazydoc-fun)
+    (load file)
+    (let ((f (symbol-function 'lazydoc-fun)))
+      (should (byte-code-function-p f))
+      (should (equal (aref f 4) (cons file 87))))
+
+    (fmakunbound 'lazydoc-fun)
+    (let ((load-force-doc-strings t))
+      (load file)
+      (let ((f (symbol-function 'lazydoc-fun)))
+        (should (byte-code-function-p f))
+        (should (equal (aref f 4) "My little\ndoc string\nhere"))))))
+
 ;;; lread-tests.el ends here