[PATCH 07/10] checkout: add -S to update sparse checkout

["Nguyễn Thái Ngọc Duy" <pclouds@gmail.com>]

The traditional way of updating sparse checkout is to open
$GIT_DIR/info/sparse-checkout manually, edit it, save, then run "git
checkout" or "git read-tree -m -u HEAD". That's not convenient.

"git checkout -S" is introduced to combine those steps in one. It also
provides some additional checks:

 - warn users if core.sparseCheckout is off
 - refuse to update sparse checkout if there is no valid sparse
   patterns (faulty sparse-checkout file for example)

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 Documentation/git-checkout.txt       |   16 +++++++++++++
 builtin/checkout.c                   |   42 +++++++++++++++++++++++++++++++++-
 t/t1011-read-tree-sparse-checkout.sh |   18 ++++++++++++++
 templates/info--sparse-checkout      |    1 +
 4 files changed, 76 insertions(+), 1 deletions(-)

diff --git a/Documentation/git-checkout.txt b/Documentation/git-checkout.txt
index 22d3611..478bfe7 100644
--- a/Documentation/git-checkout.txt
+++ b/Documentation/git-checkout.txt
@@ -12,6 +12,7 @@ SYNOPSIS
 'git checkout' [-q] [-f] [-m] [[-b|-B|--orphan] <new_branch>] [<start_point>]
 'git checkout' [-f|--ours|--theirs|-m|--conflict=<style>] [<tree-ish>] [--] <paths>...
 'git checkout' --patch [<tree-ish>] [--] [<paths>...]
+'git checkout' -S
 
 DESCRIPTION
 -----------
@@ -176,6 +177,13 @@ the conflicted merge in the specified paths.
 This means that you can use `git checkout -p` to selectively discard
 edits from your current working tree.
 
+-S::
+--update-sparse-checkout::
+	An editor is invoked to let you update your sparse checkout
+	patterns. The updated patterns will be saved in
+	$GIT_DIR/info/sparse-checkout. The working directory is also
+	updated. An empty file will abort the process.
+
 <branch>::
 	Branch to checkout; if it refers to a branch (i.e., a name that,
 	when prepended with "refs/heads/", is a valid ref), then that
@@ -316,6 +324,14 @@ $ git add frotz
 ------------
 
 
+ENVIRONMENT AND CONFIGURATION VARIABLES
+---------------------------------------
+The editor used to edit the commit log message will be chosen from the
+GIT_EDITOR environment variable, the core.editor configuration variable, the
+VISUAL environment variable, or the EDITOR environment variable (in that
+order).  See linkgit:git-var[1] for details.
+
+
 Author
 ------
 Written by Linus Torvalds <torvalds@osdl.org>
diff --git a/builtin/checkout.c b/builtin/checkout.c
index 9240faf..47847b3 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -675,6 +675,31 @@ static const char *unique_tracking_name(const char *name)
 	return NULL;
 }
 
+static void edit_info_sparse_checkout()
+{
+	char *tmpfile = xstrdup(git_path("sparse-checkout"));
+	struct exclude_list el;
+	int i;
+
+	copy_file(tmpfile, git_path("info/sparse-checkout"), 0666);
+
+	if (launch_editor(tmpfile, NULL, NULL))
+		exit(1);
+
+	memset(&el, 0, sizeof(el));
+	if (add_excludes_from_file_to_list(tmpfile, "", 0, NULL, &el, 0) < 0 ||
+	    el.nr == 0)
+		die("No valid sparse patterns. Abort.");
+	for (i = 0; i < el.nr; i++)
+		free(el.excludes[i]);
+	free(el.excludes);
+
+	if (rename(tmpfile, git_path("info/sparse-checkout")) < 0)
+		die_errno("Can't update %s", git_path("info/sparse-checkout"));
+
+	free(tmpfile);
+}
+
 int cmd_checkout(int argc, const char **argv, const char *prefix)
 {
 	struct checkout_opts opts;
@@ -685,6 +710,7 @@ int cmd_checkout(int argc, const char **argv, const char *prefix)
 	char *conflict_style = NULL;
 	int patch_mode = 0;
 	int dwim_new_local_branch = 1;
+	int update_sparse_checkout = 0;
 	struct option options[] = {
 		OPT__QUIET(&opts.quiet),
 		OPT_STRING('b', NULL, &opts.new_branch, "branch",
@@ -704,6 +730,8 @@ int cmd_checkout(int argc, const char **argv, const char *prefix)
 		OPT_STRING(0, "conflict", &conflict_style, "style",
 			   "conflict style (merge or diff3)"),
 		OPT_BOOLEAN('p', "patch", &patch_mode, "select hunks interactively"),
+		OPT_BOOLEAN('S', "update-sparse-checkout", &update_sparse_checkout,
+			    "open up editor to edit $GIT_DIR/info/sparse-checkout" ),
 		{ OPTION_BOOLEAN, 0, "guess", &dwim_new_local_branch, NULL,
 		  "second guess 'git checkout no-such-branch'",
 		  PARSE_OPT_NOARG | PARSE_OPT_HIDDEN },
@@ -722,6 +750,9 @@ int cmd_checkout(int argc, const char **argv, const char *prefix)
 	argc = parse_options(argc, argv, prefix, options, checkout_usage,
 			     PARSE_OPT_KEEP_DASHDASH);
 
+	if (update_sparse_checkout && !core_apply_sparse_checkout)
+		die("core.sparseCheckout needs to be turned on");
+
 	/* we can assume from now on new_branch = !new_branch_force */
 	if (opts.new_branch && opts.new_branch_force)
 		die("-B cannot be used with -b");
@@ -874,6 +905,9 @@ no_reference:
 		if (!pathspec)
 			die("invalid path specification");
 
+		if (update_sparse_checkout)
+			die("git checkout: update paths is incompatible with updating sparse checkout.");
+
 		if (patch_mode)
 			return interactive_checkout(new.name, pathspec, &opts);
 
@@ -892,8 +926,11 @@ no_reference:
 		return checkout_paths(source_tree, pathspec, &opts);
 	}
 
-	if (patch_mode)
+	if (patch_mode) {
+		if (update_sparse_checkout)
+			die("git checkout: interactive checkout is incompatible with updating sparse checkout.");
 		return interactive_checkout(new.name, NULL, &opts);
+	}
 
 	if (opts.new_branch) {
 		struct strbuf buf = STRBUF_INIT;
@@ -915,5 +952,8 @@ no_reference:
 	if (opts.writeout_stage)
 		die("--ours/--theirs is incompatible with switching branches.");
 
+	if (update_sparse_checkout)
+		edit_info_sparse_checkout();
+
 	return switch_branches(&opts, &new);
 }
diff --git a/t/t1011-read-tree-sparse-checkout.sh b/t/t1011-read-tree-sparse-checkout.sh
index 50f7dfe..fe4716c 100755
--- a/t/t1011-read-tree-sparse-checkout.sh
+++ b/t/t1011-read-tree-sparse-checkout.sh
@@ -184,4 +184,22 @@ test_expect_success 'read-tree --reset removes outside worktree' '
 	test_cmp empty result
 '
 
+test_expect_success 'git checkout -S fails to launch editor' '
+	GIT_EDITOR=/non-existent test_must_fail git checkout -S &&
+	grep init.t .git/info/sparse-checkout
+'
+
+test_expect_success 'git checkout -S' '
+	git checkout -f top &&
+	cat >editor.sh <<\EOF &&
+#!/bin/sh
+echo sub > "$1"
+EOF
+	chmod 755 editor.sh &&
+	GIT_EDITOR="./editor.sh" git checkout -S &&
+	grep sub .git/info/sparse-checkout &&
+	test -f sub/added &&
+	test ! -f init.t
+'
+
 test_done
diff --git a/templates/info--sparse-checkout b/templates/info--sparse-checkout
index 7426475..588008b 100644
--- a/templates/info--sparse-checkout
+++ b/templates/info--sparse-checkout
@@ -1,3 +1,4 @@
 # Specify what files are checked out in working directory
 # Run "git checkout" after updating this file to update working directory
+# If this is opened by "git checkout -S", empty this file will abort it.
 *
-- 
1.7.3.2.210.g045198