commit-graph: define GIT_TEST_COMMIT_GRAPH

The commit-graph feature is tested in isolation by
t5318-commit-graph.sh and t6600-test-reach.sh, but there are many
more interesting scenarios involving commit walks. Many of these
scenarios are covered by the existing test suite, but we need to
maintain coverage when the optional commit-graph structure is not
present.

To allow running the full test suite with the commit-graph present,
add a new test environment variable, GIT_TEST_COMMIT_GRAPH. Similar
to GIT_TEST_SPLIT_INDEX, this variable makes every Git command try
to load the commit-graph when parsing commits, and writes the
commit-graph file after every 'git commit' command.

There are a few tests that rely on commits not existing in
pack-files to trigger important events, so manually set
GIT_TEST_COMMIT_GRAPH to false for the necessary commands.

There is one test in t6024-recursive-merge.sh that relies on the
merge-base algorithm picking one of two ambiguous merge-bases, and
the commit-graph feature changes which merge-base is picked.

Helped-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/commit.c

@@ -33,6 +33,7 @@
 #include "sequencer.h"
 #include "mailmap.h"
 #include "help.h"
+#include "commit-graph.h"
 
 static const char * const builtin_commit_usage[] = {
 	N_("git commit [<options>] [--] <pathspec>..."),
@@ -1651,6 +1652,9 @@ int cmd_commit(int argc, const char **argv, const char *prefix)
 		      "new_index file. Check that disk is not full and quota is\n"
 		      "not exceeded, and then \"git reset HEAD\" to recover."));
 
+	if (git_env_bool(GIT_TEST_COMMIT_GRAPH, 0))
+		write_commit_graph_reachable(get_object_directory(), 0);
+
 	rerere(0);
 	run_command_v_opt(argv_gc_auto, RUN_GIT_CMD);
 	run_commit_hook(use_editor, get_index_file(), "post-commit", NULL);

commit-graph.c

@@ -213,8 +213,9 @@ static int prepare_commit_graph(struct repository *r)
 		return !!r->objects->commit_graph;
 	r->objects->commit_graph_attempted = 1;
 
-	if (repo_config_get_bool(r, "core.commitgraph", &config_value) ||
-	    !config_value)
+	if (!git_env_bool(GIT_TEST_COMMIT_GRAPH, 0) &&
+	    (repo_config_get_bool(r, "core.commitgraph", &config_value) ||
+	    !config_value))
 		/*
 		 * This repository is not configured to use commit graphs, so
 		 * do not load one. (But report commit_graph_attempted anyway

commit-graph.h

@@ -6,6 +6,8 @@
 #include "string-list.h"
 #include "cache.h"
 
+#define GIT_TEST_COMMIT_GRAPH "GIT_TEST_COMMIT_GRAPH"
+
 struct commit;
 
 char *get_commit_graph_filename(const char *obj_dir);

t/README

@@ -319,6 +319,10 @@ GIT_TEST_OE_DELTA_SIZE=<n> exercises the uncomon pack-objects code
 path where deltas larger than this limit require extra memory
 allocation for bookkeeping.
 
+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.
+
 Naming Tests
 ------------
 

t/t0410-partial-clone.sh

@@ -181,7 +181,7 @@ test_expect_success 'rev-list stops traversal at missing and promised commit' '
 
 	git -C repo config core.repositoryformatversion 1 &&
 	git -C repo config extensions.partialclone "arbitrary string" &&
-	git -C repo rev-list --exclude-promisor-objects --objects bar >out &&
+	GIT_TEST_COMMIT_GRAPH=0 git -C repo rev-list --exclude-promisor-objects --objects bar >out &&
 	grep $(git -C repo rev-parse bar) out &&
 	! grep $FOO out
 '

t/t5307-pack-missing-commit.sh

@@ -24,11 +24,11 @@ test_expect_success 'check corruption' '
 '
 
 test_expect_success 'rev-list notices corruption (1)' '
-	test_must_fail git rev-list HEAD
+	test_must_fail env GIT_TEST_COMMIT_GRAPH=0 git rev-list HEAD
 '
 
 test_expect_success 'rev-list notices corruption (2)' '
-	test_must_fail git rev-list --objects HEAD
+	test_must_fail env GIT_TEST_COMMIT_GRAPH=0 git rev-list --objects HEAD
 '
 
 test_expect_success 'pack-objects notices corruption' '

t/t6011-rev-list-with-bad-commit.sh

@@ -41,10 +41,9 @@ test_expect_success 'corrupt second commit object' \
    test_must_fail git fsck --full
    '
 
-test_expect_success 'rev-list should fail' \
-   '
-   test_must_fail git rev-list --all > /dev/null
-   '
+test_expect_success 'rev-list should fail' '
+	test_must_fail env GIT_TEST_COMMIT_GRAPH=0 git rev-list --all > /dev/null
+'
 
 test_expect_success 'git repack _MUST_ fail' \
    '

t/t6024-recursive-merge.sh

@@ -60,9 +60,9 @@ git update-index a1 &&
 GIT_AUTHOR_DATE="2006-12-12 23:00:08" git commit -m F
 '
 
-test_expect_success "combined merge conflicts" "
-	test_must_fail git merge -m final G
-"
+test_expect_success 'combined merge conflicts' '
+	test_must_fail env GIT_TEST_COMMIT_GRAPH=0 git merge -m final G
+'
 
 cat > expect << EOF
 <<<<<<< HEAD