commit: introduce git_commit_create_from_stage

Provide a simple helper method that allows users to create a commit from
the current index with minimal information.

include/git2/commit.h

@@ -394,6 +394,36 @@ GIT_EXTERN(int) git_commit_create_v(
 	size_t parent_count,
 	...);
 
+typedef struct {
+	unsigned int version;
+
+	unsigned int allow_empty_commit : 1;
+
+	const git_signature *author;
+	const git_signature *committer;
+} git_commit_create_options;
+
+#define GIT_COMMIT_CREATE_OPTIONS_VERSION 1
+#define GIT_COMMIT_CREATE_OPTIONS_INIT { GIT_COMMIT_CREATE_OPTIONS_VERSION }
+
+/**
+ * Commits the staged changes in the repository; this is a near analog to
+ * `git commit -m message`.
+ *
+ * By default, empty commits are not allowed.
+ *
+ * @param id pointer to store the new commit's object id
+ * @param repo repository to commit changes in
+ * @param message the commit message
+ * @param opts options for creating the commit
+ * @return 0 on success, GIT_EUNCHANGED if there were no changes to commit, or an error code
+ */
+GIT_EXTERN(int) git_commit_create_from_stage(
+	git_oid *id,
+	git_repository *repo,
+	const char *message,
+	const git_commit_create_options *opts);
+
 /**
  * Amend an existing commit by replacing only non-NULL values.
  *

include/git2/errors.h

@@ -59,7 +59,8 @@ typedef enum {
 	GIT_EINDEXDIRTY     = -34,	/**< Unsaved changes in the index would be overwritten */
 	GIT_EAPPLYFAIL      = -35,	/**< Patch application failed */
 	GIT_EOWNER          = -36,	/**< The object is not owned by the current user */
-	GIT_TIMEOUT         = -37	/**< The operation timed out */
+	GIT_TIMEOUT         = -37,	/**< The operation timed out */
+	GIT_EUNCHANGED      = -38	/**< There were no changes */
 } git_error_code;
 
 /**

src/libgit2/commit.c

@@ -1086,6 +1086,79 @@ cleanup:
 	return error;
 }
 
+int git_commit_create_from_stage(
+	git_oid *out,
+	git_repository *repo,
+	const char *message,
+	const git_commit_create_options *given_opts)
+{
+	git_commit_create_options opts = GIT_COMMIT_CREATE_OPTIONS_INIT;
+	git_signature *default_signature = NULL;
+	const git_signature *author, *committer;
+	git_index *index = NULL;
+	git_diff *diff = NULL;
+	git_oid tree_id;
+	git_tree *head_tree = NULL, *tree = NULL;
+	git_commitarray parents = { 0 };
+	int error = -1;
+
+	GIT_ASSERT_ARG(out && repo);
+
+	if (given_opts)
+		memcpy(&opts, given_opts, sizeof(git_commit_create_options));
+
+	if ((author = opts.author) == NULL ||
+	    (committer = opts.committer) == NULL) {
+		if (git_signature_default(&default_signature, repo) < 0)
+			goto done;
+
+		if (!author)
+			author = default_signature;
+
+		if (!committer)
+			committer = default_signature;
+	}
+
+	if (git_repository_index(&index, repo) < 0)
+		goto done;
+
+	if (!opts.allow_empty_commit) {
+		error = git_repository_head_tree(&head_tree, repo);
+
+		if (error && error != GIT_EUNBORNBRANCH)
+			goto done;
+
+		error = -1;
+
+		if (git_diff_tree_to_index(&diff, repo, head_tree, index, NULL) < 0)
+			goto done;
+
+		if (git_diff_num_deltas(diff) == 0) {
+			git_error_set(GIT_ERROR_REPOSITORY,
+				"no changes are staged for commit");
+			error = GIT_EUNCHANGED;
+			goto done;
+		}
+	}
+
+	if (git_index_write_tree(&tree_id, index) < 0 ||
+	    git_tree_lookup(&tree, repo, &tree_id) < 0 ||
+	    git_repository_commit_parents(&parents, repo) < 0)
+		goto done;
+
+	error = git_commit_create(out, repo, "HEAD", author, committer,
+			NULL, message, tree, parents.count, parents.commits);
+
+done:
+	git_commitarray_dispose(&parents);
+	git_signature_free(default_signature);
+	git_tree_free(tree);
+	git_tree_free(head_tree);
+	git_diff_free(diff);
+	git_index_free(index);
+	return error;
+}
+
 int git_commit_committer_with_mailmap(
 	git_signature **out, const git_commit *commit, const git_mailmap *mailmap)
 {

tests/libgit2/commit/create.c

@@ -0,0 +1,112 @@
+#include "clar_libgit2.h"
+#include "repository.h"
+
+/* Fixture setup */
+static git_repository *g_repo;
+static git_signature *g_author, *g_committer;
+
+void test_commit_create__initialize(void)
+{
+	g_repo = cl_git_sandbox_init("testrepo2");
+	cl_git_pass(git_signature_new(&g_author, "Edward Thomson", "ethomson@edwardthomson.com", 123456789, 60));
+	cl_git_pass(git_signature_new(&g_committer, "libgit2 user", "nobody@noreply.libgit2.org", 987654321, 90));
+}
+
+void test_commit_create__cleanup(void)
+{
+	git_signature_free(g_committer);
+	git_signature_free(g_author);
+	cl_git_sandbox_cleanup();
+}
+
+
+void test_commit_create__from_stage_simple(void)
+{
+	git_commit_create_options opts = GIT_COMMIT_CREATE_OPTIONS_INIT;
+	git_index *index;
+	git_oid commit_id;
+	git_tree *tree;
+
+	opts.author = g_author;
+	opts.committer = g_committer;
+
+	cl_git_rewritefile("testrepo2/newfile.txt", "This is a new file.\n");
+	cl_git_rewritefile("testrepo2/newfile2.txt", "This is a new file.\n");
+	cl_git_rewritefile("testrepo2/README", "hello, world.\n");
+	cl_git_rewritefile("testrepo2/new.txt", "hi there.\n");
+
+	cl_git_pass(git_repository_index(&index, g_repo));
+	cl_git_pass(git_index_add_bypath(index, "newfile2.txt"));
+	cl_git_pass(git_index_add_bypath(index, "README"));
+	cl_git_pass(git_index_write(index));
+
+	cl_git_pass(git_commit_create_from_stage(&commit_id, g_repo, "This is the message.", &opts));
+
+	cl_git_pass(git_repository_head_tree(&tree, g_repo));
+
+	cl_assert_equal_oidstr("241b5b04e847bc38dd7b4b9f49f21e55da40f3a6", &commit_id);
+	cl_assert_equal_oidstr("b27210772d0633870b4f486d04ed3eb5ebbef5e7", git_tree_id(tree));
+
+	git_index_free(index);
+	git_tree_free(tree);
+}
+
+void test_commit_create__from_stage_nochanges(void)
+{
+	git_commit_create_options opts = GIT_COMMIT_CREATE_OPTIONS_INIT;
+	git_oid commit_id;
+	git_tree *tree;
+
+	opts.author = g_author;
+	opts.committer = g_committer;
+
+	cl_git_fail_with(GIT_EUNCHANGED, git_commit_create_from_stage(&commit_id, g_repo, "Message goes here.", &opts));
+
+	opts.allow_empty_commit = 1;
+
+	cl_git_pass(git_commit_create_from_stage(&commit_id, g_repo, "Message goes here.", &opts));
+
+	cl_git_pass(git_repository_head_tree(&tree, g_repo));
+
+	cl_assert_equal_oidstr("f776dc4c7fd8164b7127dc8e4f9b44421cb01b56", &commit_id);
+	cl_assert_equal_oidstr("c4dc1555e4d4fa0e0c9c3fc46734c7c35b3ce90b", git_tree_id(tree));
+
+	git_tree_free(tree);
+}
+
+void test_commit_create__from_stage_newrepo(void)
+{
+	git_commit_create_options opts = GIT_COMMIT_CREATE_OPTIONS_INIT;
+	git_repository *newrepo;
+	git_index *index;
+	git_commit *commit;
+	git_tree *tree;
+	git_oid commit_id;
+
+	opts.author = g_author;
+	opts.committer = g_committer;
+
+	git_repository_init(&newrepo, "newrepo", false);
+	cl_git_pass(git_repository_index(&index, newrepo));
+
+	cl_git_rewritefile("newrepo/hello.txt", "hello, world.\n");
+	cl_git_rewritefile("newrepo/hi.txt", "hi there.\n");
+	cl_git_rewritefile("newrepo/foo.txt", "bar.\n");
+
+	cl_git_pass(git_index_add_bypath(index, "hello.txt"));
+	cl_git_pass(git_index_add_bypath(index, "foo.txt"));
+	cl_git_pass(git_index_write(index));
+
+	cl_git_pass(git_commit_create_from_stage(&commit_id, newrepo, "Initial commit.", &opts));
+	cl_git_pass(git_repository_head_commit(&commit, newrepo));
+	cl_git_pass(git_repository_head_tree(&tree, newrepo));
+
+	cl_assert_equal_oid(&commit_id, git_commit_id(commit));
+	cl_assert_equal_oidstr("b2fa96a4f191c76eb172437281c66aa29609dcaa", git_commit_tree_id(commit));
+
+	git_tree_free(tree);
+	git_commit_free(commit);
+	git_index_free(index);
+	git_repository_free(newrepo);
+	cl_fixture_cleanup("newrepo");
+}