diff: handle --no-abbrev in no-index case

There are two different places where the --no-abbrev option is parsed,
and two different places where SHA-1s are abbreviated. We normally parse
--no-abbrev with setup_revisions(), but in the no-index case, "git diff"
calls diff_opt_parse() directly, and diff_opt_parse() didn't handle
--no-abbrev until now. (It did handle --abbrev, however.) We normally
abbreviate SHA-1s with find_unique_abbrev(), but commit 4f03666 ("diff:
handle sha1 abbreviations outside of repository, 2016-10-20) recently
introduced a special case when you run "git diff" outside of a
repository.

setup_revisions() does also call diff_opt_parse(), but not for --abbrev
or --no-abbrev, which it handles itself. setup_revisions() sets
rev_info->abbrev, and later copies that to diff_options->abbrev. It
handles --no-abbrev by setting abbrev to zero. (This change doesn't
touch that.)

Setting abbrev to zero was broken in the outside-of-a-repository special
case, which until now resulted in a truly zero-length SHA-1, rather than
taking zero to mean do not abbreviate. The only way to trigger this bug,
however, was by running "git diff --raw" without either the --abbrev or
--no-abbrev options, because 1) without --raw it doesn't respect abbrev
(which is bizarre, but has been that way forever), 2) we silently clamp
--abbrev=0 to MINIMUM_ABBREV, and 3) --no-abbrev wasn't handled until
now.

The outside-of-a-repository case is one of three no-index cases. The
other two are when one of the files you're comparing is outside of the
repository you're in, and the --no-index option.

Signed-off-by: Jack Bates <jack@nottheoilrig.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 5 insertions, 1 deletions

diff --git a/diff.c b/diff.c
index ec87283..84dba60 100644
--- a/diff.c
+++ b/diff.c
@@ -3106,7 +3106,8 @@ static const char *diff_abbrev_oid(const struct object_id *oid, int abbrev)
 			abbrev = FALLBACK_DEFAULT_ABBREV;
 		if (abbrev > GIT_SHA1_HEXSZ)
 			die("BUG: oid abbreviation out of range: %d", abbrev);
-		hex[abbrev] = '\0';
+		if (abbrev)
+			hex[abbrev] = '\0';
 		return hex;
 	}
 }
@@ -3364,6 +3365,7 @@ void diff_setup(struct diff_options *options)
 
 	options->file = stdout;
 
+	options->abbrev = DEFAULT_ABBREV;
 	options->line_termination = '\n';
 	options->break_opt = -1;
 	options->rename_limit = -1;
@@ -4024,6 +4026,8 @@ int diff_opt_parse(struct diff_options *options,
 			    offending, optarg);
 		return argcount;
 	}
+	else if (!strcmp(arg, "--no-abbrev"))
+		options->abbrev = 0;
 	else if (!strcmp(arg, "--abbrev"))
 		options->abbrev = DEFAULT_ABBREV;
 	else if (skip_prefix(arg, "--abbrev=", &arg)) {