rev-parse: handle --end-of-options

We taught rev-list a new way to separate options from revisions in
19e8789b23 (revision: allow --end-of-options to end option parsing,
2019-08-06), but rev-parse uses its own parser. It should know about
--end-of-options not only for consistency, but because it may be
presented with similarly ambiguous cases. E.g., if a caller does:

  git rev-parse "$rev" -- "$path"

to parse an untrusted input, then it will get confused if $rev contains
an option-like string like "--local-env-vars". Or even "--not-real",
which we'd keep as an option to pass along to rev-list.

Or even more importantly:

  git rev-parse --verify "$rev"

can be confused by options, even though its purpose is safely parsing
untrusted input. On the plus side, it will always fail the --verify
part, as it will not have parsed a revision, so the caller will
generally "fail closed" rather than continue to use the untrusted
string. But it will still trigger whatever option was in "$rev"; this
should be mostly harmless, since rev-parse options are all read-only,
but I didn't carefully audit all paths.

This patch lets callers write:

  git rev-parse --end-of-options "$rev" -- "$path"

and:

  git rev-parse --verify --end-of-options "$rev"

which will both treat "$rev" always as a revision parameter. The latter
is a bit clunky. It would be nicer if we had defined "--verify" to
require that its next argument be the revision. But we have not
historically done so, and:

  git rev-parse --verify -q "$rev"

does currently work. I added a test here to confirm that we didn't break
that.

A few implementation notes:

 - We don't document --end-of-options explicitly in commands, but rather
   in gitcli(7). So I didn't give it its own section in git-rev-parse(1).
   But I did call it out specifically in the --verify section, and
   include it in the examples, which should show best practices.

 - We don't have to re-indent the main option-parsing block, because we
   can combine our "did we see end of options" check with "does it start
   with a dash". The exception is the pre-setup options, which need
   their own block.

 - We do however have to pull the "--" parsing out of the "does it start
   with dash" block, because we want to parse it even if we've seen
   --end-of-options.

 - We'll leave "--end-of-options" in the output. This is probably not
   technically necessary, as a careful caller will do:

     git rev-parse --end-of-options $revs -- $paths

   and anything in $revs will be resolved to an object id. However, it
   does help a slightly less careful caller like:

     git rev-parse --end-of-options $revs_or_paths

   where a path "--foo" will remain in the output as long as it also
   exists on disk. In that case, it's helpful to retain --end-of-options
   to get passed along to rev-list, s it would otherwise see just
   "--foo".

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

Documentation/git-rev-parse.txt

@@ -109,6 +109,10 @@ names an existing object that is a commit-ish (i.e. a commit, or an
 annotated tag that points at a commit).  To make sure that `$VAR`
 names an existing object of any type, `git rev-parse "$VAR^{object}"`
 can be used.
++
+Note that if you are verifying a name from an untrusted source, it is
+wise to use `--end-of-options` so that the name argument is not mistaken
+for another option.
 
 -q::
 --quiet::
@@ -446,7 +450,7 @@ $ git rev-parse --verify HEAD
 * Print the commit object name from the revision in the $REV shell variable:
 +
 ------------
-$ git rev-parse --verify $REV^{commit}
+$ git rev-parse --verify --end-of-options $REV^{commit}
 ------------
 +
 This will error out if $REV is empty or not a valid revision.
@@ -454,7 +458,7 @@ This will error out if $REV is empty or not a valid revision.
 * Similar to above:
 +
 ------------
-$ git rev-parse --default master --verify $REV
+$ git rev-parse --default master --verify --end-of-options $REV
 ------------
 +
 but if $REV is empty, the commit object name from master will be printed.

builtin/rev-parse.c

@@ -595,6 +595,7 @@ int cmd_rev_parse(int argc, const char **argv, const char *prefix)
 	struct object_context unused;
 	struct strbuf buf = STRBUF_INIT;
 	const int hexsz = the_hash_algo->hexsz;
+	int seen_end_of_options = 0;
 
 	if (argc > 1 && !strcmp("--parseopt", argv[1]))
 		return cmd_parseopt(argc - 1, argv + 1, prefix);
@@ -628,6 +629,7 @@ int cmd_rev_parse(int argc, const char **argv, const char *prefix)
 			continue;
 		}
 
+		if (!seen_end_of_options) {
 			if (!strcmp(arg, "--local-env-vars")) {
 				int i;
 				for (i = 0; local_repo_env[i]; i++)
@@ -644,6 +646,7 @@ int cmd_rev_parse(int argc, const char **argv, const char *prefix)
 				puts(gitdir);
 				continue;
 			}
+		}
 
 		/* The rest of the options require a git repository. */
 		if (!did_repo_setup) {
@@ -652,7 +655,6 @@ int cmd_rev_parse(int argc, const char **argv, const char *prefix)
 			did_repo_setup = 1;
 		}
 
-		if (*arg == '-') {
 		if (!strcmp(arg, "--")) {
 			as_is = 2;
 			/* Pass on the "--" if we show anything but files.. */
@@ -660,6 +662,8 @@ int cmd_rev_parse(int argc, const char **argv, const char *prefix)
 				show_file(arg, 0);
 			continue;
 		}
+
+		if (!seen_end_of_options && *arg == '-') {
 			if (!strcmp(arg, "--git-path")) {
 				if (!argv[i + 1])
 					die("--git-path requires an argument");
@@ -937,6 +941,12 @@ int cmd_rev_parse(int argc, const char **argv, const char *prefix)
 				puts(the_hash_algo->name);
 				continue;
 			}
+			if (!strcmp(arg, "--end-of-options")) {
+				seen_end_of_options = 1;
+				if (filter & (DO_FLAGS | DO_REVS))
+					show_file(arg, 0);
+				continue;
+			}
 			if (show_flag(arg) && verify)
 				die_no_single_rev(quiet);
 			continue;

t/t1503-rev-parse-verify.sh

@@ -144,4 +144,17 @@ test_expect_success SYMLINKS 'ref resolution not confused by broken symlinks' '
 	test_must_fail git rev-parse --verify broken
 '
 
+test_expect_success 'options can appear after --verify' '
+	git rev-parse --verify HEAD >expect &&
+	git rev-parse --verify -q HEAD >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'verify respects --end-of-options' '
+	git update-ref refs/heads/-tricky HEAD &&
+	git rev-parse --verify HEAD >expect &&
+	git rev-parse --verify --end-of-options -tricky >actual &&
+	test_cmp expect actual
+'
+
 test_done

t/t1506-rev-parse-diagnosis.sh

@@ -263,4 +263,20 @@ test_expect_success 'arg after dashdash not interpreted as option' '
 	test_cmp expect actual
 '
 
+test_expect_success 'arg after end-of-options not interpreted as option' '
+	test_must_fail git rev-parse --end-of-options --not-real -- 2>err &&
+	test_i18ngrep bad.revision.*--not-real err
+'
+
+test_expect_success 'end-of-options still allows --' '
+	cat >expect <<-EOF &&
+	--end-of-options
+	$(git rev-parse --verify HEAD)
+	--
+	path
+	EOF
+	git rev-parse --end-of-options HEAD -- path >actual &&
+	test_cmp expect actual
+'
+
 test_done