update comment and documentation for :/foo syntax

The documentation in revisions.txt did not match the implementation, and
the comment in sha1_name.c was incomplete.

Signed-off-by: Matthieu Moy <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: moy

Documentation/revisions.txt

@@ -107,11 +107,13 @@ the `$GIT_DIR/refs` directory or from the `$GIT_DIR/packed-refs` file.
   found.
 
 * A colon, followed by a slash, followed by a text (e.g. `:/fix nasty bug`): this names
-  a commit whose commit message starts with the specified text.
+  a commit whose commit message matches the specified regular expression.
   This name returns the youngest matching commit which is
   reachable from any ref.  If the commit message starts with a
   '!', you have to repeat that;  the special sequence ':/!',
   followed by something else than '!' is reserved for now.
+  The regular expression can match any part of the commit message. To
+  match messages starting with a string, one can use e.g. `:/^foo`.
 
 * A suffix ':' followed by a path (e.g. `HEAD:README`); this names the blob or tree
   at the given path in the tree-ish object named by the part

sha1_name.c

@@ -1062,6 +1062,7 @@ int get_sha1_with_context_1(const char *name, unsigned char *sha1,
 	/* sha1:path --> object name of path in ent sha1
 	 * :path -> object name of path in index
 	 * :[0-3]:path -> object name of path in index at stage
+	 * :/foo -> recent commit matching foo
 	 */
 	if (name[0] == ':') {
 		int stage = 0;