builtin/rev-parse: allow shortening to more than 40 hex characters

The `--short=` option for git-rev-parse(1) allows the user to specify
to how many characters object IDs should be shortened to. The option is
broken though for SHA256 repositories because we set the maximum allowed
hash size to `the_hash_algo->hexsz` before we have even set up the repo.
Consequently, `the_hash_algo` will always be SHA1 and thus we truncate
every hash after at most 40 characters.

Fix this by accessing `the_hash_algo` only after we have set up the
repo.

Signed-off-by: Patrick Steinhardt <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: pks-t

builtin/rev-parse.c

@@ -687,7 +687,6 @@ int cmd_rev_parse(int argc, const char **argv, const char *prefix)
 	const char *name = NULL;
 	struct object_context unused;
 	struct strbuf buf = STRBUF_INIT;
-	const int hexsz = the_hash_algo->hexsz;
 	int seen_end_of_options = 0;
 	enum format_type format = FORMAT_DEFAULT;
 
@@ -863,8 +862,8 @@ int cmd_rev_parse(int argc, const char **argv, const char *prefix)
 				abbrev = strtoul(arg, NULL, 10);
 				if (abbrev < MINIMUM_ABBREV)
 					abbrev = MINIMUM_ABBREV;
-				else if (hexsz <= abbrev)
-					abbrev = hexsz;
+				else if ((int)the_hash_algo->hexsz <= abbrev)
+					abbrev = the_hash_algo->hexsz;
 				continue;
 			}
 			if (!strcmp(arg, "--sq")) {

t/t1500-rev-parse.sh

@@ -304,4 +304,10 @@ test_expect_success 'rev-parse --bisect includes bad, excludes good' '
 	test_cmp expect actual
 '
 
+test_expect_success '--short= truncates to the actual hash length' '
+	git rev-parse HEAD >expect &&
+	git rev-parse --short=100 HEAD >actual &&
+	test_cmp expect actual
+'
+
 test_done