examples: add merge

examples/merge.c

+/*
+ * libgit2 "merge" example - shows how to perform merges
+ *
+ * Written by the libgit2 contributors
+ *
+ * To the extent possible under law, the author(s) have dedicated all copyright
+ * and related and neighboring rights to this software to the public domain
+ * worldwide. This software is distributed without any warranty.
+ *
+ * You should have received a copy of the CC0 Public Domain Dedication along
+ * with this software. If not, see
+ * <http://creativecommons.org/publicdomain/zero/1.0/>.
+ */
+
+#include "common.h"
+#include <assert.h>
+
+#ifdef _MSC_VER
+#define snprintf sprintf_s
+#endif
+
+/** The following example demonstrates how to do merges with libgit2.
+ *
+ * It will merge whatever commit-ish you pass in into the current branch.
+ *
+ * Recognized options are :
+ *  --no-commit: don't actually commit the merge.
+ *
+ */
+
+typedef struct {
+	const char **heads;
+	size_t heads_count;
+
+	git_annotated_commit **annotated;
+	size_t annotated_count;
+
+	int no_commit : 1;
+	int did_merge : 1;
+} merge_options;
+
+static void print_usage(void)
+{
+	fprintf(stderr, "usage: merge [--no-commit] <commit...>\n");
+	exit(1);
+}
+
+static void merge_options_init(merge_options *opts)
+{
+	opts->heads = NULL;
+	opts->heads_count = 0;
+	opts->annotated = NULL;
+	opts->annotated_count = 0;
+}
+
+static void opts_add_refish(merge_options *opts, const char *refish)
+{
+	size_t sz;
+
+	assert(opts != NULL);
+
+	sz = ++opts->heads_count * sizeof(opts->heads[0]);
+	opts->heads = xrealloc(opts->heads, sz);
+	opts->heads[opts->heads_count - 1] = refish;
+}
+
+static void parse_options(const char **repo_path, merge_options *opts, int argc, char **argv)
+{
+	struct args_info args = ARGS_INFO_INIT;
+
+	if (argc <= 1)
+		print_usage();
+
+	for (args.pos = 1; args.pos < argc; ++args.pos) {
+		const char *curr = argv[args.pos];
+
+		if (curr[0] != '-') {
+			opts_add_refish(opts, curr);
+		} else if (!strcmp(curr, "--no-commit")) {
+			opts->no_commit = 1;
+		} else if (match_str_arg(repo_path, &args, "--git-dir")) {
+		} else {
+			print_usage();
+		}
+	}
+}
+
+static int resolve_refish(git_annotated_commit **commit, git_repository *repo, const char *refish)
+{
+	git_reference *ref;
+	int err = 0;
+	git_oid oid;
+
+	assert(commit != NULL);
+
+	err = git_reference_dwim(&ref, repo, refish);
+	if (err == GIT_OK) {
+		git_annotated_commit_from_ref(commit, repo, ref);
+		git_reference_free(ref);
+		return 0;
+	}
+
+	err = git_oid_fromstr(&oid, refish);
+	if (err == GIT_OK) {
+		err = git_annotated_commit_lookup(commit, repo, &oid);
+	}
+
+	return err;
+}
+
+static int resolve_heads(git_repository *repo, merge_options *opts) {
+	git_annotated_commit **annotated = calloc(opts->heads_count, sizeof(git_annotated_commit *));
+	size_t annotated_count = 0, i;
+	int err = 0;
+
+	for (i = 0; i < opts->heads_count; i++) {
+		err = resolve_refish((git_annotated_commit **)&annotated[annotated_count++], repo, opts->heads[i]);
+		if (err != 0) {
+			fprintf(stderr, "failed to resolve refish %s (%d)\n", opts->heads[i], err);
+			annotated_count--;
+			continue;
+		}
+	}
+
+	if (annotated_count <= 0) {
+		fprintf(stderr, "unable to parse any refish\n");
+		free(annotated);
+		return -1;
+	}
+
+	opts->annotated = annotated;
+	opts->annotated_count = annotated_count;
+	return 0;
+}
+
+static int perform_fastforward(git_repository *repo, const git_oid *target_oid, int is_unborn)
+{
+	git_checkout_options ff_checkout_options = GIT_CHECKOUT_OPTIONS_INIT;
+	git_reference *target_ref;
+	git_reference *new_target_ref;
+	git_object *target = NULL;
+	int err = 0;
+
+	if (is_unborn) {
+		const char *symbolic_ref;
+		git_reference *head_ref;
+
+		/* HEAD reference is unborn, lookup manually so we don't try to resolve it */
+		err = git_reference_lookup(&head_ref, repo, "HEAD");
+		if (err != 0) {
+			fprintf(stderr, "failed to lookup HEAD ref\n");
+			return -1;
+		}
+
+		/* Grab the reference HEAD should be pointing to */
+		symbolic_ref = git_reference_symbolic_target(head_ref);
+
+		/* Force-create that reference on the target OID */
+		err = git_reference_create(&target_ref, repo, symbolic_ref, target_oid, 1, NULL);
+		if (err != 0) {
+			fprintf(stderr, "failed to create master reference\n");
+			return -1;
+		}
+
+		git_reference_free(head_ref);
+	} else {
+		/* HEAD exists, just lookup and resolve */
+		err = git_repository_head(&target_ref, repo);
+		if (err != 0) {
+			fprintf(stderr, "failed to get HEAD reference\n");
+			return -1;
+		}
+	}
+
+	/* Lookup the target object */
+	err = git_object_lookup(&target, repo, target_oid, GIT_OBJ_COMMIT);
+	if (err != 0) {
+		fprintf(stderr, "failed to lookup OID %s\n", git_oid_tostr_s(target_oid));
+		return -1;
+	}
+
+	/* Force-checkout the result so the workdir is in the expected state */
+	ff_checkout_options.checkout_strategy = GIT_CHECKOUT_FORCE;
+	err = git_checkout_tree(repo, target, &ff_checkout_options);
+	if (err != 0) {
+		fprintf(stderr, "failed to checkout HEAD reference\n");
+		return -1;
+	}
+
+	/* Move the target reference to the target OID */
+	err = git_reference_set_target(&new_target_ref, target_ref, target_oid, NULL);
+	if (err != 0) {
+		fprintf(stderr, "failed to move HEAD reference\n");
+		return -1;
+	}
+
+	git_reference_free(target_ref);
+	git_reference_free(new_target_ref);
+	git_object_free(target);
+
+	return 0;
+}
+
+static int analyze_merge(git_repository *repo, merge_options *opts)
+{
+	git_merge_options merge_opts = GIT_MERGE_OPTIONS_INIT;
+	git_checkout_options checkout_opts = GIT_CHECKOUT_OPTIONS_INIT;
+	git_merge_analysis_t analysis;
+	git_merge_preference_t preference;
+	int err = 0;
+
+	merge_opts.flags = 0; // GIT_MERGE_FIND_RENAMES;
+	merge_opts.file_flags = GIT_MERGE_FILE_STYLE_DIFF3;
+
+	checkout_opts.checkout_strategy = GIT_CHECKOUT_FORCE|GIT_CHECKOUT_ALLOW_CONFLICTS;
+
+	err = git_merge_analysis(&analysis, &preference,
+	                         repo,
+	                         (const git_annotated_commit **)opts->annotated,
+	                         opts->annotated_count);
+	check_lg2(err, "merge analysis failed", NULL);
+
+	if (analysis & GIT_MERGE_ANALYSIS_UP_TO_DATE) {
+		printf("Already up-to-date\n");
+		return 0;
+	} else if (analysis & GIT_MERGE_ANALYSIS_UNBORN ||
+	          (analysis & GIT_MERGE_ANALYSIS_FASTFORWARD &&
+	          !(preference & GIT_MERGE_PREFERENCE_NO_FASTFORWARD))) {
+		const git_oid *target_oid;
+		if (analysis & GIT_MERGE_ANALYSIS_UNBORN) {
+			printf("Unborn\n");
+		} else {
+			printf("Fast-forward\n");
+		}
+
+		/* Since this is a fast-forward, there can be only one merge head */
+		target_oid = git_annotated_commit_id(opts->annotated[0]);
+
+		return perform_fastforward(repo, target_oid, (analysis & GIT_MERGE_ANALYSIS_UNBORN));
+	} else if (analysis & GIT_MERGE_ANALYSIS_NORMAL) {
+		if (preference & GIT_MERGE_PREFERENCE_FASTFORWARD_ONLY) {
+			printf("Fast-forward is preferred, but only a merge is possible\n");
+			return -1;
+		}
+
+		err = git_merge(repo,
+		                (const git_annotated_commit **)opts->annotated, opts->annotated_count,
+		                &merge_opts, &checkout_opts);
+		if (err != 0)
+			return -1;
+
+		/* Inform that a merge was done */
+		opts->did_merge = 1;
+
+		return 0;
+	}
+
+	return -1;
+}
+
+int main(int argc, char **argv)
+{
+	git_repository *repo = NULL;
+	merge_options opts;
+	git_index *index;
+	git_repository_state_t state;
+	const char *path = ".";
+	int err = 0;
+
+	merge_options_init(&opts);
+	parse_options(&path, &opts, argc, argv);
+
+	git_libgit2_init();
+
+	check_lg2(git_repository_open_ext(&repo, path, 0, NULL),
+	          "Could not open repository", NULL);
+
+	state = git_repository_state(repo);
+	if (state != GIT_REPOSITORY_STATE_NONE) {
+		fprintf(stderr, "repository is in unexpected state %d\n", state);
+		goto cleanup;
+	}
+
+	err = resolve_heads(repo, &opts);
+	if (err != 0)
+		goto cleanup;
+
+	err = analyze_merge(repo, &opts);
+	if (err != 0) {
+		fprintf(stderr, "merge failed\n");
+		goto cleanup;
+	}
+
+	if (!opts.did_merge) {
+		/* Was either up-to-date, unborn, or a fast-forward, nothing left to do */
+		goto cleanup;
+	}
+
+	check_lg2(git_repository_index(&index, repo), "failed to get repository index", NULL);
+
+	if (git_index_has_conflicts(index)) {
+		/* Handle conflicts */
+		git_index_conflict_iterator *conflicts;
+		const git_index_entry *ancestor;
+		const git_index_entry *our;
+		const git_index_entry *their;
+
+		check_lg2(git_index_conflict_iterator_new(&conflicts, index), "failed to create conflict iterator", NULL);
+
+		while ((err = git_index_conflict_next(&ancestor, &our, &their, conflicts)) == 0) {
+			fprintf(stderr, "conflict: a:%s o:%s t:%s\n",
+			        ancestor ? ancestor->path : "", our->path, their->path);
+		}
+
+		if (err != GIT_ITEROVER) {
+			fprintf(stderr, "error iterating conflicts\n");
+		}
+
+		git_index_conflict_iterator_free(conflicts);
+	} else if (!opts.no_commit) {
+		git_oid tree_oid, commit_oid;
+		git_tree *tree;
+		git_signature *sign;
+		git_reference *merge_ref = NULL;
+		git_annotated_commit *merge_commit;
+		git_reference *head_ref;
+		git_commit **parents = calloc(opts.annotated_count + 1, sizeof(git_commit *));
+		const char *msg_target = NULL;
+		size_t msglen = 0;
+		char *msg;
+		size_t i;
+		int err;
+
+		/* Grab our needed references */
+		check_lg2(git_repository_head(&head_ref, repo), "failed to get repo HEAD", NULL);
+		if (resolve_refish(&merge_commit, repo, opts.heads[0])) {
+			fprintf(stderr, "failed to resolve refish %s", opts.heads[0]);
+		}
+
+		/* Maybe that's a ref, so DWIM it */
+		git_reference_dwim(&merge_ref, repo, opts.heads[0]);
+
+		/* Grab a signature */
+		check_lg2(git_signature_now(&sign, "Me", "me@example.com"), "failed to create signature", NULL);
+
+#define MERGE_COMMIT_MSG "Merge %s '%s'\n"
+		/* Prepare a standard merge commit message */
+		if (merge_ref != NULL) {
+			check_lg2(git_branch_name(&msg_target, merge_ref), "failed to get branch name of merged ref", NULL);
+		} else {
+			msg_target = git_oid_tostr_s(git_annotated_commit_id(merge_commit));
+		}
+
+		msglen = snprintf(NULL, 0, MERGE_COMMIT_MSG, (merge_ref ? "branch" : "commit"), msg_target);
+		if (msglen > 0) msglen++;
+		msg = malloc(msglen);
+		err = snprintf(msg, msglen, MERGE_COMMIT_MSG, (merge_ref ? "branch" : "commit"), msg_target);
+
+		/* This is only to silence the compiler */
+		if (err < 0) goto cleanup;
+
+		/* Setup our parent commits */
+		check_lg2(git_reference_peel((git_object **)&parents[0], head_ref, GIT_OBJ_COMMIT), "failed to peel head reference", NULL);
+		for (i = 0; i < opts.annotated_count; i++) {
+			git_commit_lookup(&parents[i + 1], repo, git_annotated_commit_id(opts.annotated[i]));
+		}
+
+		/* Prepare our commit tree */
+		check_lg2(git_index_write_tree(&tree_oid, index), "failed to write merged tree", NULL);
+		check_lg2(git_tree_lookup(&tree, repo, &tree_oid), "failed to lookup tree", NULL);
+
+		/* Commit time ! */
+		err = git_commit_create(&commit_oid,
+		                        repo, git_reference_name(head_ref),
+		                        sign, sign,
+		                        NULL, msg,
+		                        tree,
+		                        opts.annotated_count + 1, (const git_commit **)parents);
+		check_lg2(err, "failed to create commit", NULL);
+
+		/* We're done merging, cleanup the repository state */
+		git_repository_state_cleanup(repo);
+	}
+cleanup:
+	free(opts.heads);
+	free(opts.annotated);
+	git_repository_free(repo);
+	git_libgit2_shutdown();
+
+	return 0;
+}