sha1_name: Suggest commit:./file for path in subdir

Currently, the "Did you mean..." message suggests "commit:fullpath"
only. Extend this to show the more convenient "commit:./file" form also.

Signed-off-by: Michael J Gruber <git@drmicha.warpmail.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

sha1_name.c

@@ -1012,11 +1012,13 @@ static void diagnose_invalid_sha1_path(const char *prefix,
 		if (!get_tree_entry(tree_sha1, fullname,
 				    sha1, &mode)) {
 			die("Path '%s' exists, but not '%s'.\n"
-			    "Did you mean '%s:%s'?",
+			    "Did you mean '%s:%s' aka '%s:./%s'?",
 			    fullname,
 			    filename,
 			    object_name,
-			    fullname);
+			    fullname,
+			    object_name,
+			    filename);
 		}
 		die("Path '%s' does not exist in '%s'",
 		    filename, object_name);
@@ -1065,9 +1067,10 @@ static void diagnose_invalid_index_path(int stage,
 		if (ce_namelen(ce) == fullnamelen &&
 		    !memcmp(ce->name, fullname, fullnamelen))
 			die("Path '%s' is in the index, but not '%s'.\n"
-			    "Did you mean ':%d:%s'?",
+			    "Did you mean ':%d:%s' aka ':%d:./%s'?",
 			    fullname, filename,
-			    ce_stage(ce), fullname);
+			    ce_stage(ce), fullname,
+			    ce_stage(ce), filename);
 	}
 
 	if (!lstat(filename, &st))

t/t1506-rev-parse-diagnosis.sh

@@ -9,7 +9,7 @@ exec </dev/null
 test_did_you_mean ()
 {
 	printf "fatal: Path '$2$3' $4, but not ${5:-'$3'}.\n" >expected &&
-	printf "Did you mean '$1:$2$3'?\n" >>expected &&
+	printf "Did you mean '$1:$2$3'${2:+ aka '$1:./$3'}?\n" >>expected &&
 	test_cmp expected error
 }