parse-options-cb: only abbreviate hashes when hash algo is known

The `OPT__ABBREV()` option can be used to add an option that abbreviates
object IDs. When given a length longer than `the_hash_algo->hexsz`, then
it will instead set the length to that maximum length.

It may not always be guaranteed that we have `the_hash_algo` initialized
properly as the hash algorithm can only be set up after we have set up
`the_repository`. In that case, the hash would always be truncated to
the hex length of SHA1, which may not be what the user desires.

In practice it's not a problem as all commands that use `OPT__ABBREV()`
also have `RUN_SETUP` set and thus cannot work without a repository.
Consequently, both `the_repository` and `the_hash_algo` would be
properly set up.

Regardless of that, harden the code to not truncate the length when we
didn't set up a repository.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

parse-options-cb.c

@@ -7,6 +7,7 @@
 #include "environment.h"
 #include "gettext.h"
 #include "object-name.h"
+#include "setup.h"
 #include "string-list.h"
 #include "strvec.h"
 #include "oid-array.h"
@@ -29,7 +30,7 @@ int parse_opt_abbrev_cb(const struct option *opt, const char *arg, int unset)
 				     opt->long_name);
 		if (v && v < MINIMUM_ABBREV)
 			v = MINIMUM_ABBREV;
-		else if (v > the_hash_algo->hexsz)
+		else if (startup_info->have_repository && v > the_hash_algo->hexsz)
 			v = the_hash_algo->hexsz;
 	}
 	*(int *)(opt->value) = v;

t/t0040-parse-options.sh

@@ -176,6 +176,23 @@ test_expect_success 'long options' '
 	test_cmp expect output
 '
 
+test_expect_success 'abbreviate to something longer than SHA1 length' '
+	cat >expect <<-EOF &&
+	boolean: 0
+	integer: 0
+	magnitude: 0
+	timestamp: 0
+	string: (not set)
+	abbrev: 100
+	verbose: -1
+	quiet: 0
+	dry run: no
+	file: (not set)
+	EOF
+	test-tool parse-options --abbrev=100 >output &&
+	test_cmp expect output
+'
+
 test_expect_success 'missing required value' '
 	cat >expect <<-\EOF &&
 	error: switch `s'\'' requires a value