Merge branch 'td/ref-filter-memoize-contains' into seen

'git branch --contains' and 'git for-each-ref --contains' have
been optimized to use the memoized commit traversal previously
used only by 'git tag --contains', significantly speeding up
connectivity checks across many candidate refs with shared
history.

* td/ref-filter-memoize-contains:
  commit-reach: die on contains walk errors
  ref-filter: memoize --contains with generations
  commit-reach: reject cycles in contains walk

commit-reach.c

@@ -757,7 +757,8 @@ static int in_commit_list(const struct commit_list *want, struct commit *c)
 
 /*
  * Test whether the candidate is contained in the list.
- * Do not recurse to find out, though, but return -1 if inconclusive.
+ * Do not recurse to find out, though, but return CONTAINS_UNKNOWN if
+ * inconclusive.
  */
 static enum contains_result contains_test(struct commit *candidate,
 					  const struct commit_list *want,
@@ -814,6 +815,7 @@ static enum contains_result contains_tag_algo(struct commit *candidate,
 	if (result != CONTAINS_UNKNOWN)
 		return result;
 
+	*contains_cache_at(cache, candidate) = CONTAINS_IN_PROGRESS;
 	push_to_contains_stack(candidate, &contains_stack);
 	while (contains_stack.nr) {
 		struct contains_stack_entry *entry = &contains_stack.contains_stack[contains_stack.nr - 1];
@@ -825,8 +827,8 @@ static enum contains_result contains_tag_algo(struct commit *candidate,
 			contains_stack.nr--;
 		}
 		/*
-		 * If we just popped the stack, parents->item has been marked,
-		 * therefore contains_test will return a meaningful yes/no.
+		 * A parent may have just been popped and marked, or may still
+		 * be active when replacement refs create a cycle.
 		 */
 		else switch (contains_test(parents->item, want, cache, cutoff)) {
 		case CONTAINS_YES:
@@ -836,7 +838,11 @@ static enum contains_result contains_tag_algo(struct commit *candidate,
 		case CONTAINS_NO:
 			entry->parents = parents->next;
 			break;
+		case CONTAINS_IN_PROGRESS:
+			die(_("commit ancestry contains a cycle"));
 		case CONTAINS_UNKNOWN:
+			*contains_cache_at(cache, parents->item) =
+				CONTAINS_IN_PROGRESS;
 			push_to_contains_stack(parents->item, &contains_stack);
 			break;
 		}
@@ -848,9 +854,16 @@ static enum contains_result contains_tag_algo(struct commit *candidate,
 int commit_contains(struct ref_filter *filter, struct commit *commit,
 		    struct commit_list *list, struct contains_cache *cache)
 {
-	if (filter->with_commit_tag_algo)
+	int result;
+
+	if (filter->with_commit_tag_algo ||
+	    generation_numbers_enabled(the_repository))
 		return contains_tag_algo(commit, list, cache) == CONTAINS_YES;
-	return repo_is_descendant_of(the_repository, commit, list);
+
+	result = repo_is_descendant_of(the_repository, commit, list);
+	if (result < 0)
+		die(_("failed to check reachability"));
+	return result;
 }
 
 int can_all_from_reach_with_flag(struct object_array *from,

commit-reach.h

@@ -73,7 +73,8 @@ int ref_newer(const struct object_id *new_oid, const struct object_id *old_oid);
 enum contains_result {
 	CONTAINS_UNKNOWN = 0,
 	CONTAINS_NO,
-	CONTAINS_YES
+	CONTAINS_YES,
+	CONTAINS_IN_PROGRESS
 };
 
 define_commit_slab(contains_cache, enum contains_result);

t/perf/p1500-graph-walks.sh

@@ -32,7 +32,16 @@ test_expect_success 'setup' '
 		echo "X:$line" >>test-tool-tags || return 1
 	done &&
 
-	commit=$(git commit-tree $(git rev-parse HEAD^{tree})) &&
+	git rev-list --first-parent --max-count=8192 HEAD >contains-commits &&
+	test_file_not_empty contains-commits &&
+	git update-ref refs/contains-perf-base "$(tail -n 1 contains-commits)" &&
+	awk "{
+		printf \"update refs/contains-perf/%04d %s\\n\", NR, \$1
+	}" contains-commits |
+		git update-ref --stdin &&
+	git pack-refs --include "refs/contains-perf/*" &&
+
+	commit=$(git commit-tree HEAD^{tree}) &&
 	git update-ref refs/heads/disjoint-base $commit &&
 
 	git commit-graph write --reachable
@@ -62,6 +71,23 @@ test_perf 'contains: git tag --merged' '
 	xargs git tag --merged=HEAD <tags
 '
 
+test_perf 'contains: git for-each-ref' '
+	git for-each-ref --contains=refs/contains-perf-base --stdin <refs
+'
+
+test_perf 'contains: git branch' '
+	xargs git branch --contains=refs/contains-perf-base <branches
+'
+
+test_perf 'contains: git tag' '
+	xargs git tag --contains=refs/contains-perf-base <tags
+'
+
+test_perf 'contains: synthetic shared history' '
+	git for-each-ref --contains=refs/contains-perf-base \
+		refs/contains-perf/ >/dev/null
+'
+
 test_perf 'is-base check: test-tool reach (refs)' '
 	test-tool reach get_branch_base_for_tip <test-tool-refs
 '

t/t6301-for-each-ref-errors.sh

@@ -52,6 +52,28 @@ test_expect_success 'Missing objects are reported correctly' '
 	test_must_be_empty brief-err
 '
 
+test_expect_success 'missing ancestors are reported by contains filters' '
+	test_when_finished "git update-ref -d refs/heads/missing-parent" &&
+	{
+		echo "tree $(git rev-parse HEAD^{tree})" &&
+		echo "parent $MISSING" &&
+		git cat-file commit HEAD |
+			sed -n -e "/^author /p" -e "/^committer /p" &&
+		echo &&
+		echo "missing parent"
+	} >commit &&
+	broken=$(git hash-object -t commit -w commit) &&
+	git update-ref refs/heads/missing-parent "$broken" &&
+	for option in --contains --no-contains
+	do
+		test_must_fail git for-each-ref "$option=HEAD" \
+			refs/heads/missing-parent >out 2>err &&
+		test_must_be_empty out &&
+		test_grep "parse commit $MISSING" err ||
+		return 1
+	done
+'
+
 test_expect_success 'ahead-behind requires an argument' '
 	test_must_fail git for-each-ref \
 		--format="%(ahead-behind)" 2>err &&

t/t7004-tag.sh

@@ -1611,6 +1611,24 @@ test_expect_success 'checking that first commit is in all tags (hash)' '
 	test_cmp expected actual
 '
 
+test_expect_success 'tag --contains rejects cyclic replacement histories' '
+	first=$(git rev-parse HEAD~2) &&
+	second=$(git rev-parse HEAD~) &&
+	third=$(git rev-parse HEAD) &&
+	test_when_finished "
+		git replace -d $first &&
+		git replace -d $third &&
+		git tag -d cycle-a cycle-b
+	" &&
+	git tag cycle-a "$first" &&
+	git tag cycle-b "$third" &&
+	git replace --graft "$first" "$third" "$second" &&
+	git replace --graft "$third" "$first" &&
+	test_must_fail git tag --contains="$second" --list "cycle-*" \
+		>/dev/null 2>err &&
+	test_grep "fatal: commit ancestry contains a cycle" err
+'
+
 # other ways of specifying the commit
 test_expect_success 'checking that first commit is in all tags (tag)' '
 	cat >expected <<-\EOF &&