multi-pack-index: define GIT_TEST_MULTI_PACK_INDEX

The multi-pack-index feature is tested in isolation by
t5319-multi-pack-index.sh, but there are many more interesting
scenarios in the test suite surrounding pack-file data shapes
and interactions. Since the multi-pack-index is an optional
data structure, it does not make sense to include it by default
in those tests.

Instead, add a new GIT_TEST_MULTI_PACK_INDEX environment variable
that enables core.multiPackIndex and writes a multi-pack-index
after each 'git repack' command. This adds extra test coverage
when needed.

There are a few spots in the test suite that need to react to this
change:

* t5319-multi-pack-index.sh: there is a test that checks that
  'git repack' deletes the multi-pack-index. Disable the environment
  variable to ensure this still happens.

* t5310-pack-bitmaps.sh: One test moves a pack-file from the object
  directory to an alternate. This breaks the multi-pack-index, so
  delete the multi-pack-index at this point, if it exists.

* t9300-fast-import.sh: One test verifies the number of files in
  the .git/objects/pack directory is exactly 8. Exclude the
  multi-pack-index from this count so it is still 8 in all cases.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/repack.c

@@ -553,6 +553,10 @@ int cmd_repack(int argc, const char **argv, const char *prefix)
 	if (!no_update_server_info)
 		update_server_info(0);
 	remove_temporary_files();
+
+	if (git_env_bool(GIT_TEST_MULTI_PACK_INDEX, 0))
+		write_midx_file(get_object_directory());
+
 	string_list_clear(&names, 0);
 	string_list_clear(&rollback, 0);
 	string_list_clear(&existing_packs, 0);

midx.c

@@ -338,9 +338,14 @@ int prepare_multi_pack_index_one(struct repository *r, const char *object_dir, i
 	struct multi_pack_index *m;
 	struct multi_pack_index *m_search;
 	int config_value;
+	static int env_value = -1;
 
-	if (repo_config_get_bool(r, "core.multipackindex", &config_value) ||
+	if (env_value < 0)
-	    !config_value)
+		env_value = git_env_bool(GIT_TEST_MULTI_PACK_INDEX, 0);
+
+	if (!env_value &&
+	    (repo_config_get_bool(r, "core.multipackindex", &config_value) ||
+	    !config_value))
 		return 0;
 
 	for (m_search = r->objects->multi_pack_index; m_search; m_search = m_search->next)

midx.h

@@ -3,6 +3,8 @@
 
 #include "repository.h"
 
+#define GIT_TEST_MULTI_PACK_INDEX "GIT_TEST_MULTI_PACK_INDEX"
+
 struct multi_pack_index {
 	struct multi_pack_index *next;
 

t/README

@@ -327,6 +327,10 @@ GIT_TEST_COMMIT_GRAPH=<boolean>, when true, forces the commit-graph to
 be written after every 'git commit' command, and overrides the
 'core.commitGraph' setting to true.
 
+GIT_TEST_MULTI_PACK_INDEX=<boolean>, when true, forces the multi-pack-
+index to be written after every 'git repack' command, and overrides the
+'core.multiPackIndex' setting to true.
+
 Naming Tests
 ------------
 

t/t5310-pack-bitmaps.sh

@@ -191,6 +191,7 @@ test_expect_success 'pack-objects respects --honor-pack-keep (local bitmapped pa
 
 test_expect_success 'pack-objects respects --local (non-local bitmapped pack)' '
 	mv .git/objects/pack/$packbitmap.* alt.git/objects/pack/ &&
+	rm -f .git/objects/pack/multi-pack-index &&
 	test_when_finished "mv alt.git/objects/pack/$packbitmap.* .git/objects/pack/" &&
 	echo HEAD | git pack-objects --local --stdout --revs >3b.pack &&
 	git index-pack 3b.pack &&

t/t5319-multi-pack-index.sh

@@ -152,7 +152,7 @@ compare_results_with_midx "twelve packs"
 
 test_expect_success 'repack removes multi-pack-index' '
 	test_path_is_file $objdir/pack/multi-pack-index &&
-	git repack -adf &&
+	GIT_TEST_MULTI_PACK_INDEX=0 git repack -adf &&
 	test_path_is_missing $objdir/pack/multi-pack-index
 '
 

t/t9300-fast-import.sh

@@ -1558,7 +1558,7 @@ test_expect_success 'O: blank lines not necessary after other commands' '
 	INPUT_END
 
 	git fast-import <input &&
-	test 8 = $(find .git/objects/pack -type f | wc -l) &&
+	test 8 = $(find .git/objects/pack -type f | grep -v multi-pack-index | wc -l) &&
 	test $(git rev-parse refs/tags/O3-2nd) = $(git rev-parse O3^) &&
 	git log --reverse --pretty=oneline O3 | sed s/^.*z// >actual &&
 	test_cmp expect actual