blame: handle --no-abbrev

You can already ask blame for full sha1s with "-l" or with
"--abbrev=40". But for consistency with other parts of Git,
we should support "--no-abbrev".

Worse, blame already accepts --no-abbrev, but it's totally
broken. When we see --no-abbrev, the abbrev variable is set
to 0, which is then used as a printf precision. For regular
sha1s, that means we print nothing at all (which is very
wrong). For boundary commits we decrement it to "-1", which
printf interprets as "no limit" (which is almost correct,
except it misses the 39-length magic explained in the
previous commit).

Let's detect --no-abbrev and behave as if --abbrev=40 was
given.

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

builtin/blame.c

@@ -2609,6 +2609,8 @@ parse_done:
 	if (0 < abbrev && abbrev < GIT_SHA1_HEXSZ)
 		/* one more abbrev length is needed for the boundary commit */
 		abbrev++;
+	else if (!abbrev)
+		abbrev = GIT_SHA1_HEXSZ;
 
 	if (revs_file && read_ancestry(revs_file))
 		die_errno("reading graft file '%s' failed", revs_file);

t/t8002-blame.sh

@@ -114,4 +114,8 @@ test_expect_success 'blame --abbrev=40 behaves like -l' '
 	check_abbrev 39 --abbrev=40 ^HEAD
 '
 
+test_expect_success '--no-abbrev works like --abbrev=40' '
+	check_abbrev 40 --no-abbrev
+'
+
 test_done