Merge pull request git-for-windows#193: Update to include 'checkout -b' fix

In git-for-windows#183, we quickly fixed a performance problem around `git checkout -b` and added a deprecation waning. After submitting that upstream, we found instead the commit 3136776, which just puts a simple performance hack in to `git checkout` to check for exactly `checkout -b <branch>` and then use the `git switch -c <branch>` logic.

This PR reverts the commits from git-for-windows#183 as fixups and merges in the commit from upstream instead.

Author: derrickstolee

Documentation/config/checkout.txt

@@ -16,11 +16,3 @@ will checkout the '<something>' branch on another remote,
 and by linkgit:git-worktree[1] when 'git worktree add' refers to a
 remote branch. This setting might be used for other checkout-like
 commands or functionality in the future.
-
-checkout.optimizeNewBranch::
-	Optimizes the performance of "git checkout -b <new_branch>" when
-	using sparse-checkout.  When set to true, git will not update the
-	repo based on the current sparse-checkout settings.  This means it
-	will not update the skip-worktree bit in the index nor add/remove
-	files in the working directory to reflect the current sparse checkout
-	settings nor will it show the local changes.

builtin/checkout.c

@@ -28,8 +28,6 @@
 #include "xdiff-interface.h"
 #include "packfile.h"
 
-static int checkout_optimize_new_branch;
-
 static const char * const checkout_usage[] = {
 	N_("git checkout [<options>] <branch>"),
 	N_("git checkout [<options>] [<branch>] -- <file>..."),
@@ -74,11 +72,6 @@ struct checkout_opts {
 	const char *ignore_unmerged_opt;
 	int ignore_unmerged;
 
-	/*
-	 * If new checkout options are added, skip_merge_working_tree
-	 * should be updated accordingly.
-	 */
-
 	const char *new_branch;
 	const char *new_branch_force;
 	const char *new_orphan_branch;
@@ -647,112 +640,6 @@ 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_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
-	 */
-
-	/*
-	 * opts->overlay_mode cannot be used with switching branches so is
-	 * not tested here
-	 */
-
-	/*
-	 * 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
-	 */
-
-	 /*
-	  * Do the merge if this is the initial checkout. We cannot use
-	  * is_cache_unborn() here because the index hasn't been loaded yet
-	  * so cache_nr and timestamp.sec are always zero.
-	  */
-	if (!file_exists(get_index_file()))
-		return 0;
-
-	return 1;
-}
-
 static int merge_working_tree(const struct checkout_opts *opts,
 			      struct branch_info *old_branch_info,
 			      struct branch_info *new_branch_info,
@@ -1163,6 +1050,7 @@ static int switch_branches(const struct checkout_opts *opts,
 			BUG("'switch --orphan' should never accept a commit as starting point");
 		new_branch_info->commit = NULL;
 		new_branch_info->name = "(empty)";
+		do_merge = 1;
 	}
 
 	if (!new_branch_info->name) {
@@ -1176,16 +1064,7 @@ static int switch_branches(const struct checkout_opts *opts,
 			do_merge = 0;
 	}
 
-	/* optimize the "checkout -b <new_branch> path */
-	if (!do_merge || 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);
-		}
-		if (!opts->only_merge_on_switching_branches)
-			warning(_("'git checkout -b <new-branch>' is being deprecated in favor of 'git switch -c <new-branch>'. Please adjust your workflow accordingly."));
-	} else {
+	if (do_merge) {
 		ret = merge_working_tree(opts, &old_branch_info, new_branch_info, &writeout_error);
 		if (ret) {
 			free(path_to_free);
@@ -1205,11 +1084,6 @@ 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);
@@ -1851,6 +1725,15 @@ int cmd_checkout(int argc, const char **argv, const char *prefix)
 	opts.checkout_index = -2;    /* default on */
 	opts.checkout_worktree = -2; /* default on */
 
+	if (argc == 3 && !strcmp(argv[1], "-b")) {
+		/*
+		 * User ran 'git checkout -b <branch>' and expects
+		 * the same behavior as 'git switch -c <branch>'.
+		 */
+		opts.switch_branch_doing_nothing_is_ok = 0;
+		opts.only_merge_on_switching_branches = 1;
+	}
+
 	options = parse_options_dup(checkout_options);
 	options = add_common_options(&opts, options);
 	options = add_common_switch_branch_options(&opts, options);

t/t1090-sparse-checkout-scope.sh

@@ -31,20 +31,6 @@ test_expect_success 'perform sparse checkout of master' '
 	test_path_is_file c
 '
 
-test_expect_success 'checkout -b checkout.optimizeNewBranch interaction' '
-	cp .git/info/sparse-checkout .git/info/sparse-checkout.bak &&
-	test_when_finished "
-		mv -f .git/info/sparse-checkout.bak .git/info/sparse-checkout
-		git checkout master
-	" &&
-	echo "/b" >>.git/info/sparse-checkout &&
-	test "$(git ls-files -t b)" = "S b" &&
-	git -c checkout.optimizeNewBranch=true checkout -b fast &&
-	test "$(git ls-files -t b)" = "S b" &&
-	git checkout -b slow &&
-	test "$(git ls-files -t b)" = "H b"
-'
-
 test_expect_success 'merge feature branch into sparse checkout of master' '
 	git merge feature &&
 	test_path_is_file a &&

t/t7114-reset-sparse-checkout.sh

@@ -24,7 +24,7 @@ test_expect_success 'setup' '
 test_expect_success 'reset when there is a sparse-checkout' '
 	echo "/c" >.git/info/sparse-checkout &&
 	test_config core.sparsecheckout true &&
-	git checkout -b resetBranch &&
+	git checkout -B resetBranch &&
 	test_path_is_missing m &&
 	test_path_is_missing a &&
 	test_path_is_missing d &&
@@ -41,7 +41,7 @@ test_expect_success 'reset after deleting file without skip-worktree bit' '
 	echo "/c
 /m" >.git/info/sparse-checkout &&
 	test_config core.sparsecheckout true &&
-	git checkout -b resetAfterDelete &&
+	git checkout -B resetAfterDelete &&
 	test_path_is_file m &&
 	test_path_is_missing a &&
 	test_path_is_missing d &&