stash: fix show referencing stash index

In the conversion of 'stash show' to C in dc7bd382b1 ("stash: convert
show to builtin", 2019-02-25), 'git stash show <n>', where n is the
index of a stash got broken, if n is not a file or a valid revision by
itself.

'stash show' accepts any flag 'git diff' accepts for changing the
output format.  Internally we use 'setup_revisions()' to parse these
command line flags.  Currently we pass the whole argv through to
'setup_revisions()', which includes the stash index.

As the stash index is not a valid revision or a file in the working
tree in most cases however, this 'setup_revisions()' call (and thus
the whole command) ends up failing if we use this form of 'git stash
show'.

Instead of passing the whole argv to 'setup_revisions()', only pass
the flags (and the command name) through, while excluding the stash
reference.  The stash reference is parsed (and validated) in
'get_stash_info()' already.

This separate parsing also means that we currently do produce the
correct output if the command succeeds.

Reported-by: Mike Hommey <mh@glandium.org>
Signed-off-by: Thomas Gummerer <t.gummerer@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 18 insertions, 0 deletions

diff --git a/t/t3903-stash.sh b/t/t3903-stash.sh
index ea30d5f..b22e671 100755
--- a/t/t3903-stash.sh
+++ b/t/t3903-stash.sh
@@ -708,6 +708,24 @@ test_expect_success 'invalid ref of the form "n", n >= N' '
 	git stash drop
 '
 
+test_expect_success 'valid ref of the form "n", n < N' '
+	git stash clear &&
+	echo bar5 >file &&
+	echo bar6 >file2 &&
+	git add file2 &&
+	git stash &&
+	git stash show 0 &&
+	git stash branch tmp 0 &&
+	git checkout master &&
+	git stash &&
+	git stash apply 0 &&
+	git reset --hard &&
+	git stash pop 0 &&
+	git stash &&
+	git stash drop 0 &&
+	test_must_fail git stash drop
+'
+
 test_expect_success 'branch: do not drop the stash if the branch exists' '
 	git stash clear &&
 	echo foo >file &&