grep: treat revs the same for --untracked as for --no-index

git-grep has always disallowed grepping in a tree (as
opposed to the working directory) with both --untracked
and --no-index. But we traditionally did so by first
collecting the revs, and then complaining when any were
provided.

The --no-index option recently learned to detect revs
much earlier. This has two user-visible effects:

  - we don't bother to resolve revision names at all. So
    when there's a rev/path ambiguity, we always choose to
    treat it as a path.

  - likewise, when you do specify a revision without "--",
    the error you get is "no such path" and not "--untracked
    cannot be used with revs".

The rationale for doing this with --no-index is that it is
meant to be used outside a repository, and so parsing revs
at all does not make sense.

This patch gives --untracked the same treatment. While it
_is_ meant to be used in a repository, it is explicitly
about grepping the non-repository contents. Telling the user
"we found a rev, but you are not allowed to use revs" is
not really helpful compared to "we treated your argument as
a path, and could not find it".

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/grep.c

@@ -967,6 +967,7 @@ int cmd_grep(int argc, const char **argv, const char *prefix)
 	int dummy;
 	int use_index = 1;
 	int pattern_type_arg = GREP_PATTERN_TYPE_UNSPECIFIED;
+	int allow_revs;
 
 	struct option options[] = {
 		OPT_BOOL(0, "cached", &cached,
@@ -1165,6 +1166,7 @@ int cmd_grep(int argc, const char **argv, const char *prefix)
 	 * to it must resolve as a rev. If not, then we stop at the first
 	 * non-rev and assume everything else is a path.
 	 */
+	allow_revs = use_index && !untracked;
 	for (i = 0; i < argc; i++) {
 		const char *arg = argv[i];
 		unsigned char sha1[20];
@@ -1176,9 +1178,9 @@ int cmd_grep(int argc, const char **argv, const char *prefix)
 			break;
 		}
 
-		if (!use_index) {
+		if (!allow_revs) {
 			if (seen_dashdash)
-				die(_("--no-index cannot be used with revs"));
+				die(_("--no-index or --untracked cannot be used with revs"));
 			break;
 		}
 
@@ -1201,7 +1203,7 @@ int cmd_grep(int argc, const char **argv, const char *prefix)
 	if (!seen_dashdash) {
 		int j;
 		for (j = i; j < argc; j++)
-			verify_filename(prefix, argv[j], j == i && use_index);
+			verify_filename(prefix, argv[j], j == i && allow_revs);
 	}
 
 	parse_pathspec(&pathspec, 0,
@@ -1273,8 +1275,6 @@ int cmd_grep(int argc, const char **argv, const char *prefix)
 
 	if (!use_index || untracked) {
 		int use_exclude = (opt_exclude < 0) ? use_index : !!opt_exclude;
-		if (list.nr)
-			die(_("--no-index or --untracked cannot be used with revs."));
 		hit = grep_directory(&opt, &pathspec, use_exclude, use_index);
 	} else if (0 <= opt_exclude) {
 		die(_("--[no-]exclude-standard cannot be used for tracked contents."));

t/t7810-grep.sh

@@ -1032,7 +1032,7 @@ test_expect_success 'grep --no-index pattern -- path' '
 
 test_expect_success 'grep --no-index complains of revs' '
 	test_must_fail git grep --no-index o master -- 2>err &&
-	test_i18ngrep "no-index cannot be used with revs" err
+	test_i18ngrep "cannot be used with revs" err
 '
 
 test_expect_success 'grep --no-index prefers paths to revs' '