graph: Create git_graph_reachable_from_any()

This change introduces a new API function
`git_graph_reachable_from_any()`, that answers the question whether a
commit is reachable from any of the provided commits through following
parent edges.

This function can take advantage of optimizations provided by the
existence of a `commit-graph` file, since it makes it faster to know
whether, given two commits X and Y, X cannot possibly be an reachable
from Y.

Part of: libgit2#5757

Author: lhchavez

include/git2/graph.h

@@ -43,8 +43,9 @@ GIT_EXTERN(int) git_graph_ahead_behind(size_t *ahead, size_t *behind, git_reposi
  * Note that a commit is not considered a descendant of itself, in contrast
  * to `git merge-base --is-ancestor`.
  *
- * @param commit a previously loaded commit.
- * @param ancestor a potential ancestor commit.
+ * @param repo the repository where the commits exist
+ * @param commit a previously loaded commit
+ * @param ancestor a potential ancestor commit
  * @return 1 if the given commit is a descendant of the potential ancestor,
  * 0 if not, error code otherwise.
  */
@@ -53,6 +54,23 @@ GIT_EXTERN(int) git_graph_descendant_of(
 	const git_oid *commit,
 	const git_oid *ancestor);
 
+/**
+ * Determine if a commit is reachable from any of a list of commits by
+ * following parent edges.
+ *
+ * @param repo the repository where the commits exist
+ * @param commit a previously loaded commit
+ * @param length the number of commits in the provided `descendant_array`
+ * @param descendant_array oids of the commits
+ * @return 1 if the given commit is an ancestor of any of the given potential
+ * descendants, 0 if not, error code otherwise.
+ */
+GIT_EXTERN(int) git_graph_reachable_from_any(
+	git_repository *repo,
+	const git_oid *commit,
+	size_t length,
+	const git_oid descendant_array[]);
+
 /** @} */
 GIT_END_DECL
 #endif

src/graph.c

@@ -176,19 +176,74 @@ int git_graph_ahead_behind(size_t *ahead, size_t *behind, git_repository *repo,
 
 int git_graph_descendant_of(git_repository *repo, const git_oid *commit, const git_oid *ancestor)
 {
-	git_oid merge_base;
-	int error;
-
 	if (git_oid_equal(commit, ancestor))
 		return 0;
 
-	error = git_merge_base(&merge_base, repo, commit, ancestor);
-	/* No merge-base found, it's not a descendant */
-	if (error == GIT_ENOTFOUND)
+	return git_graph_reachable_from_any(repo, ancestor, 1, commit);
+}
+
+int git_graph_reachable_from_any(
+		git_repository *repo,
+		const git_oid *commit_id,
+		size_t length,
+		const git_oid descendant_array[])
+{
+	git_revwalk *walk = NULL;
+	git_vector list;
+	git_commit_list *result = NULL;
+	git_commit_list_node *commit;
+	size_t i;
+	uint32_t minimum_generation = 0xffffffff;
+	int error = 0;
+
+	if (!length)
 		return 0;
 
-	if (error < 0)
+	for (i = 0; i < length; ++i) {
+		if (git_oid_equal(commit_id, &descendant_array[i]))
+			return 1;
+	}
+
+	if ((error = git_vector_init(&list, length + 1, NULL)) < 0)
 		return error;
 
-	return git_oid_equal(&merge_base, ancestor);
+	if ((error = git_revwalk_new(&walk, repo)) < 0)
+		goto done;
+
+	for (i = 0; i < length; i++) {
+		commit = git_revwalk__commit_lookup(walk, &descendant_array[i]);
+		if (commit == NULL) {
+			error = -1;
+			goto done;
+		}
+
+		git_vector_insert(&list, commit);
+		if (minimum_generation > commit->generation)
+			minimum_generation = commit->generation;
+	}
+
+	commit = git_revwalk__commit_lookup(walk, commit_id);
+	if (commit == NULL) {
+		error = -1;
+		goto done;
+	}
+
+	if (minimum_generation > commit->generation)
+		minimum_generation = commit->generation;
+
+	if ((error = git_merge__bases_many(&result, walk, commit, &list, minimum_generation)) < 0)
+		goto done;
+
+	if (result) {
+		error = git_oid_equal(commit_id, &result->item->oid);
+	} else {
+		/* No merge-base found, it's not a descendant */
+		error = 0;
+	}
+
+done:
+	git_commit_list_free(&result);
+	git_vector_free(&list);
+	git_revwalk_free(walk);
+	return error;
 }

src/merge.c

@@ -112,7 +112,7 @@ static int merge_bases_many(git_commit_list **out, git_revwalk **walk_out, git_r
 	if (commit == NULL)
 		goto on_error;
 
-	if (git_merge__bases_many(&result, walk, commit, &list) < 0)
+	if (git_merge__bases_many(&result, walk, commit, &list, 0) < 0)
 		goto on_error;
 
 	if (!result) {
@@ -243,7 +243,7 @@ static int merge_bases(git_commit_list **out, git_revwalk **walk_out, git_reposi
 	if (commit == NULL)
 		goto on_error;
 
-	if (git_merge__bases_many(&result, walk, commit, &list) < 0)
+	if (git_merge__bases_many(&result, walk, commit, &list, 0) < 0)
 		goto on_error;
 
 	if (!result) {
@@ -378,7 +378,11 @@ static int clear_commit_marks(git_commit_list_node *commit, unsigned int mark)
 }
 
 static int paint_down_to_common(
-	git_commit_list **out, git_revwalk *walk, git_commit_list_node *one, git_vector *twos)
+		git_commit_list **out,
+		git_revwalk *walk,
+		git_commit_list_node *one,
+		git_vector *twos,
+		uint32_t minimum_generation)
 {
 	git_pqueue list;
 	git_commit_list *result = NULL;
@@ -399,7 +403,6 @@ static int paint_down_to_common(
 			return -1;
 
 		two->flags |= PARENT2;
-
 		if (git_pqueue_insert(&list, two) < 0)
 			return -1;
 	}
@@ -427,6 +430,8 @@ static int paint_down_to_common(
 			git_commit_list_node *p = commit->parents[i];
 			if ((p->flags & flags) == flags)
 				continue;
+			if (p->generation < minimum_generation)
+				continue;
 
 			if ((error = git_commit_list_parse(walk, p)) < 0)
 				return error;
@@ -442,7 +447,7 @@ static int paint_down_to_common(
 	return 0;
 }
 
-static int remove_redundant(git_revwalk *walk, git_vector *commits)
+static int remove_redundant(git_revwalk *walk, git_vector *commits, uint32_t minimum_generation)
 {
 	git_vector work = GIT_VECTOR_INIT;
 	unsigned char *redundant;
@@ -478,7 +483,7 @@ static int remove_redundant(git_revwalk *walk, git_vector *commits)
 				goto done;
 		}
 
-		error = paint_down_to_common(&common, walk, commit, &work);
+		error = paint_down_to_common(&common, walk, commit, &work, minimum_generation);
 		if (error < 0)
 			goto done;
 
@@ -510,7 +515,12 @@ static int remove_redundant(git_revwalk *walk, git_vector *commits)
 	return error;
 }
 
-int git_merge__bases_many(git_commit_list **out, git_revwalk *walk, git_commit_list_node *one, git_vector *twos)
+int git_merge__bases_many(
+		git_commit_list **out,
+		git_revwalk *walk,
+		git_commit_list_node *one,
+		git_vector *twos,
+		uint32_t minimum_generation)
 {
 	int error;
 	unsigned int i;
@@ -532,7 +542,7 @@ int git_merge__bases_many(git_commit_list **out, git_revwalk *walk, git_commit_l
 	if (git_commit_list_parse(walk, one) < 0)
 		return -1;
 
-	error = paint_down_to_common(&result, walk, one, twos);
+	error = paint_down_to_common(&result, walk, one, twos, minimum_generation);
 	if (error < 0)
 		return error;
 
@@ -559,7 +569,7 @@ int git_merge__bases_many(git_commit_list **out, git_revwalk *walk, git_commit_l
 
 		if ((error = clear_commit_marks(one, ALL_FLAGS)) < 0 ||
 		    (error = clear_commit_marks_many(twos, ALL_FLAGS)) < 0 ||
-		    (error = remove_redundant(walk, &redundant)) < 0) {
+		    (error = remove_redundant(walk, &redundant, minimum_generation)) < 0) {
 			git_vector_free(&redundant);
 			return error;
 		}

src/merge.h

@@ -129,7 +129,8 @@ int git_merge__bases_many(
 	git_commit_list **out,
 	git_revwalk *walk,
 	git_commit_list_node *one,
-	git_vector *twos);
+	git_vector *twos,
+	uint32_t minimum_generation);
 
 /*
  * Three-way tree differencing