rev-parse: correctly diagnose revision errors before "--"

Rev-parse understands that a "--" may separate revisions and
filenames, and that anything after the "--" is taken as-is.
However, it does not understand that anything before the
token must be a revision (which is the usual rule
implemented by the setup_revisions parser).

Since rev-parse prefers revisions to files when parsing
before the "--", we end up with the correct result (if such
an argument is a revision, we parse it as one, and if it is
not, it is an error either way).  However, we misdiagnose
the errors:

  $ git rev-parse foobar -- >/dev/null
  fatal: ambiguous argument 'foobar': unknown revision or path not in the working tree.
  Use '--' to separate paths from revisions, like this:
  'git <command> [<revision>...] -- [<file>...]'

  $ >foobar
  $ git rev-parse foobar -- >/dev/null
  fatal: bad flag '--' used after filename

In both cases, we should know that the real error is that
"foobar" is meant to be a revision, but could not be
resolved.

Signed-off-by: Jeff King <peff@peff.net>
Reviewed-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 24 insertions, 0 deletions

diff --git a/t/t1506-rev-parse-diagnosis.sh b/t/t1506-rev-parse-diagnosis.sh
index f950c1012..613d9bfe1 100755
--- a/t/t1506-rev-parse-diagnosis.sh
+++ b/t/t1506-rev-parse-diagnosis.sh
@@ -196,4 +196,28 @@ test_expect_success 'dotdot is not an empty set' '
 	test_cmp expect actual
 '
 
+test_expect_success 'arg before dashdash must be a revision (missing)' '
+	test_must_fail git rev-parse foobar -- 2>stderr &&
+	test_i18ngrep "bad revision" stderr
+'
+
+test_expect_success 'arg before dashdash must be a revision (file)' '
+	>foobar &&
+	test_must_fail git rev-parse foobar -- 2>stderr &&
+	test_i18ngrep "bad revision" stderr
+'
+
+test_expect_success 'arg before dashdash must be a revision (ambiguous)' '
+	>foobar &&
+	git update-ref refs/heads/foobar HEAD &&
+	{
+		# we do not want to use rev-parse here, because
+		# we are testing it
+		cat .git/refs/heads/foobar &&
+		printf "%s\n" --
+	} >expect &&
+	git rev-parse foobar -- >actual &&
+	test_cmp expect actual
+'
+
 test_done