1 files changed, 165 insertions, 26 deletions

diff --git a/builtin/checkout.c b/builtin/checkout.c
index 28627650cd..acdafc6e4c 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -23,6 +23,9 @@
 #include "resolve-undo.h"
 #include "submodule-config.h"
 #include "submodule.h"
+#include "advice.h"
+
+static int checkout_optimize_new_branch;
 
 static const char * const checkout_usage[] = {
 	N_("git checkout [<options>] <branch>"),
@@ -41,6 +44,10 @@ struct checkout_opts {
 	int ignore_skipworktree;
 	int ignore_other_worktrees;
 	int show_progress;
+	/*
+	 * If new checkout options are added, skip_merge_working_tree
+	 * should be updated accordingly.
+	 */
 
 	const char *new_branch;
 	const char *new_branch_force;
@@ -78,7 +85,7 @@ static int update_some(const struct object_id *oid, struct strbuf *base,
 		return READ_TREE_RECURSIVE;
 
 	len = base->len + strlen(pathname);
-	ce = xcalloc(1, cache_entry_size(len));
+	ce = make_empty_cache_entry(&the_index, len);
 	oidcpy(&ce->oid, oid);
 	memcpy(ce->name, base->buf, base->len);
 	memcpy(ce->name + base->len, pathname, len - base->len);
@@ -95,9 +102,9 @@ static int update_some(const struct object_id *oid, struct strbuf *base,
 	if (pos >= 0) {
 		struct cache_entry *old = active_cache[pos];
 		if (ce->ce_mode == old->ce_mode &&
-		    !oidcmp(&ce->oid, &old->oid)) {
+		    oideq(&ce->oid, &old->oid)) {
 			old->ce_flags |= CE_UPDATE;
-			free(ce);
+			discard_cache_entry(ce);
 			return 0;
 		}
 	}
@@ -207,7 +214,8 @@ static int checkout_merged(int pos, const struct checkout *state)
 	 * merge.renormalize set, too
 	 */
 	status = ll_merge(&result_buf, path, &ancestor, "base",
-			  &ours, "ours", &theirs, "theirs", NULL);
+			  &ours, "ours", &theirs, "theirs",
+			  state->istate, NULL);
 	free(ancestor.ptr);
 	free(ours.ptr);
 	free(theirs.ptr);
@@ -231,11 +239,11 @@ static int checkout_merged(int pos, const struct checkout *state)
 	if (write_object_file(result_buf.ptr, result_buf.size, blob_type, &oid))
 		die(_("Unable to add merge result for '%s'"), path);
 	free(result_buf.ptr);
-	ce = make_cache_entry(mode, oid.hash, path, 2, 0);
+	ce = make_transient_cache_entry(mode, &oid, path, 2);
 	if (!ce)
 		die(_("make_cache_entry failed for path '%s'"), path);
 	status = checkout_entry(ce, state, NULL);
-	free(ce);
+	discard_cache_entry(ce);
 	return status;
 }
 
@@ -317,7 +325,7 @@ static int checkout_paths(const struct checkout_opts *opts,
 		 * match_pathspec() for _all_ entries when
 		 * opts->source_tree != NULL.
 		 */
-		if (ce_path_match(ce, &opts->pathspec, ps_matched))
+		if (ce_path_match(&the_index, ce, &opts->pathspec, ps_matched))
 			ce->ce_flags |= CE_MATCHED;
 	}
 
@@ -379,7 +387,7 @@ static int checkout_paths(const struct checkout_opts *opts,
 		die(_("unable to write new index file"));
 
 	read_ref_full("HEAD", 0, &rev, NULL);
-	head = lookup_commit_reference_gently(&rev, 1);
+	head = lookup_commit_reference_gently(the_repository, &rev, 1);
 
 	errs |= post_checkout_hook(head, head, 0);
 	return errs;
@@ -390,7 +398,7 @@ static void show_local_changes(struct object *head,
 {
 	struct rev_info rev;
 	/* I think we want full paths, even if we're in a subdirectory. */
-	init_revisions(&rev, NULL);
+	repo_init_revisions(the_repository, &rev, NULL);
 	rev.diffopt.flags = opts->flags;
 	rev.diffopt.output_format |= DIFF_FORMAT_NAME_STATUS;
 	diff_setup_done(&rev.diffopt);
@@ -471,6 +479,99 @@ static void setup_branch_path(struct branch_info *branch)
 	branch->path = strbuf_detach(&buf, NULL);
 }
 
+/*
+ * Skip merging the trees, updating the index and working directory if and
+ * only if we are creating a new branch via "git checkout -b <new_branch>."
+ */
+static int skip_merge_working_tree(const struct checkout_opts *opts,
+	const struct branch_info *old_branch_info,
+	const struct branch_info *new_branch_info)
+{
+	/*
+	 * Do the merge if sparse checkout is on and the user has not opted in
+	 * to the optimized behavior
+	 */
+	if (core_apply_sparse_checkout && !checkout_optimize_new_branch)
+		return 0;
+
+	/*
+	 * We must do the merge if we are actually moving to a new commit.
+	 */
+	if (!old_branch_info->commit || !new_branch_info->commit ||
+		!oideq(&old_branch_info->commit->object.oid,
+		       &new_branch_info->commit->object.oid))
+		return 0;
+
+	/*
+	 * opts->patch_mode cannot be used with switching branches so is
+	 * not tested here
+	 */
+
+	/*
+	 * opts->quiet only impacts output so doesn't require a merge
+	 */
+
+	/*
+	 * Honor the explicit request for a three-way merge or to throw away
+	 * local changes
+	 */
+	if (opts->merge || opts->force)
+		return 0;
+
+	/*
+	 * --detach is documented as "updating the index and the files in the
+	 * working tree" but this optimization skips those steps so fall through
+	 * to the regular code path.
+	 */
+	if (opts->force_detach)
+		return 0;
+
+	/*
+	 * opts->writeout_stage cannot be used with switching branches so is
+	 * not tested here
+	 */
+
+	/*
+	 * Honor the explicit ignore requests
+	 */
+	if (!opts->overwrite_ignore || opts->ignore_skipworktree ||
+		opts->ignore_other_worktrees)
+		return 0;
+
+	/*
+	 * opts->show_progress only impacts output so doesn't require a merge
+	 */
+
+	/*
+	 * If we aren't creating a new branch any changes or updates will
+	 * happen in the existing branch.  Since that could only be updating
+	 * the index and working directory, we don't want to skip those steps
+	 * or we've defeated any purpose in running the command.
+	 */
+	if (!opts->new_branch)
+		return 0;
+
+	/*
+	 * new_branch_force is defined to "create/reset and checkout a branch"
+	 * so needs to go through the merge to do the reset
+	 */
+	if (opts->new_branch_force)
+		return 0;
+
+	/*
+	 * A new orphaned branch requrires the index and the working tree to be
+	 * adjusted to <start_point>
+	 */
+	if (opts->new_orphan_branch)
+		return 0;
+
+	/*
+	 * Remaining variables are not checkout options but used to track state
+	 */
+
+	return 1;
+}
+
 static int merge_working_tree(const struct checkout_opts *opts,
 			      struct branch_info *old_branch_info,
 			      struct branch_info *new_branch_info,
@@ -799,7 +900,7 @@ static void orphaned_commit_warning(struct commit *old_commit, struct commit *ne
 	struct rev_info revs;
 	struct object *object = &old_commit->object;
 
-	init_revisions(&revs, NULL);
+	repo_init_revisions(the_repository, &revs, NULL);
 	setup_revisions(0, NULL, &revs, NULL);
 
 	object->flags &= ~UNINTERESTING;
@@ -830,7 +931,7 @@ static int switch_branches(const struct checkout_opts *opts,
 	memset(&old_branch_info, 0, sizeof(old_branch_info));
 	old_branch_info.path = path_to_free = resolve_refdup("HEAD", 0, &rev, &flag);
 	if (old_branch_info.path)
-		old_branch_info.commit = lookup_commit_reference_gently(&rev, 1);
+		old_branch_info.commit = lookup_commit_reference_gently(the_repository, &rev, 1);
 	if (!(flag & REF_ISSYMREF))
 		old_branch_info.path = NULL;
 
@@ -845,10 +946,19 @@ static int switch_branches(const struct checkout_opts *opts,
 		parse_commit_or_die(new_branch_info->commit);
 	}
 
-	ret = merge_working_tree(opts, &old_branch_info, new_branch_info, &writeout_error);
-	if (ret) {
-		free(path_to_free);
-		return ret;
+	/* optimize the "checkout -b <new_branch> path */
+	if (skip_merge_working_tree(opts, &old_branch_info, new_branch_info)) {
+		if (!checkout_optimize_new_branch && !opts->quiet) {
+			if (read_cache_preload(NULL) < 0)
+				return error(_("index file corrupt"));
+			show_local_changes(&new_branch_info->commit->object, &opts->diff_options);
+		}
+	} else {
+		ret = merge_working_tree(opts, &old_branch_info, new_branch_info, &writeout_error);
+		if (ret) {
+			free(path_to_free);
+			return ret;
+		}
 	}
 
 	if (!opts->quiet && !old_branch_info.path && old_branch_info.commit && new_branch_info->commit != old_branch_info.commit)
@@ -863,6 +973,11 @@ static int switch_branches(const struct checkout_opts *opts,
 
 static int git_checkout_config(const char *var, const char *value, void *cb)
 {
+	if (!strcmp(var, "checkout.optimizenewbranch")) {
+		checkout_optimize_new_branch = git_config_bool(var, value);
+		return 0;
+	}
+
 	if (!strcmp(var, "diff.ignoresubmodules")) {
 		struct checkout_opts *opts = cb;
 		handle_ignore_submodules_arg(&opts->diff_options, value);
@@ -879,7 +994,8 @@ static int parse_branchname_arg(int argc, const char **argv,
 				int dwim_new_local_branch_ok,
 				struct branch_info *new_branch_info,
 				struct checkout_opts *opts,
-				struct object_id *rev)
+				struct object_id *rev,
+				int *dwim_remotes_matched)
 {
 	struct tree **source_tree = &opts->source_tree;
 	const char **new_branch = &opts->new_branch;
@@ -911,8 +1027,10 @@ static int parse_branchname_arg(int argc, const char **argv,
 	 *   (b) If <something> is _not_ a commit, either "--" is present
 	 *       or <something> is not a path, no -t or -b was given, and
 	 *       and there is a tracking branch whose name is <something>
-	 *       in one and only one remote, then this is a short-hand to
-	 *       fork local <something> from that remote-tracking branch.
+	 *       in one and only one remote (or if the branch exists on the
+	 *       remote named in checkout.defaultRemote), then this is a
+	 *       short-hand to fork local <something> from that
+	 *       remote-tracking branch.
 	 *
 	 *   (c) Otherwise, if "--" is present, treat it like case (1).
 	 *
@@ -973,7 +1091,8 @@ static int parse_branchname_arg(int argc, const char **argv,
 			recover_with_dwim = 0;
 
 		if (recover_with_dwim) {
-			const char *remote = unique_tracking_name(arg, rev);
+			const char *remote = unique_tracking_name(arg, rev,
+								  dwim_remotes_matched);
 			if (remote) {
 				*new_branch = arg;
 				arg = remote;
@@ -1004,7 +1123,7 @@ static int parse_branchname_arg(int argc, const char **argv,
 	else
 		new_branch_info->path = NULL; /* not an existing branch */
 
-	new_branch_info->commit = lookup_commit_reference_gently(rev, 1);
+	new_branch_info->commit = lookup_commit_reference_gently(the_repository, rev, 1);
 	if (!new_branch_info->commit) {
 		/* not a commit */
 		*source_tree = parse_tree_indirect(rev);
@@ -1110,6 +1229,7 @@ int cmd_checkout(int argc, const char **argv, const char *prefix)
 	struct branch_info new_branch_info;
 	char *conflict_style = NULL;
 	int dwim_new_local_branch = 1;
+	int dwim_remotes_matched = 0;
 	struct option options[] = {
 		OPT__QUIET(&opts.quiet, N_("suppress progress reporting")),
 		OPT_STRING('b', NULL, &opts.new_branch, N_("branch"),
@@ -1192,12 +1312,12 @@ int cmd_checkout(int argc, const char **argv, const char *prefix)
 	if (opts.track != BRANCH_TRACK_UNSPECIFIED && !opts.new_branch) {
 		const char *argv0 = argv[0];
 		if (!argc || !strcmp(argv0, "--"))
-			die (_("--track needs a branch name"));
+			die(_("--track needs a branch name"));
 		skip_prefix(argv0, "refs/", &argv0);
 		skip_prefix(argv0, "remotes/", &argv0);
 		argv0 = strchr(argv0, '/');
 		if (!argv0 || !argv0[1])
-			die (_("Missing branch name; try -b"));
+			die(_("missing branch name; try -b"));
 		opts.new_branch = argv0 + 1;
 	}
 
@@ -1222,7 +1342,8 @@ int cmd_checkout(int argc, const char **argv, const char *prefix)
 			opts.track == BRANCH_TRACK_UNSPECIFIED &&
 			!opts.new_branch;
 		int n = parse_branchname_arg(argc, argv, dwim_ok,
-					     &new_branch_info, &opts, &rev);
+					     &new_branch_info, &opts, &rev,
+					     &dwim_remotes_matched);
 		argv += n;
 		argc -= n;
 	}
@@ -1264,8 +1385,26 @@ int cmd_checkout(int argc, const char **argv, const char *prefix)
 	}
 
 	UNLEAK(opts);
-	if (opts.patch_mode || opts.pathspec.nr)
-		return checkout_paths(&opts, new_branch_info.name);
-	else
+	if (opts.patch_mode || opts.pathspec.nr) {
+		int ret = checkout_paths(&opts, new_branch_info.name);
+		if (ret && dwim_remotes_matched > 1 &&
+		    advice_checkout_ambiguous_remote_branch_name)
+			advise(_("'%s' matched more than one remote tracking branch.\n"
+				 "We found %d remotes with a reference that matched. So we fell back\n"
+				 "on trying to resolve the argument as a path, but failed there too!\n"
+				 "\n"
+				 "If you meant to check out a remote tracking branch on, e.g. 'origin',\n"
+				 "you can do so by fully qualifying the name with the --track option:\n"
+				 "\n"
+				 "    git checkout --track origin/<name>\n"
+				 "\n"
+				 "If you'd like to always have checkouts of an ambiguous <name> prefer\n"
+				 "one remote, e.g. the 'origin' remote, consider setting\n"
+				 "checkout.defaultRemote=origin in your config."),
+			       argv[0],
+			       dwim_remotes_matched);
+		return ret;
+	} else {
 		return checkout_branch(&opts, &new_branch_info);
+	}
 }