config: learn the "onbranch:" includeIf condition

Currently, if a user wishes to have individual settings per branch, they
are required to manually keep track of the settings in their head and
manually set the options on the command-line or change the config at
each branch.

Teach config the "onbranch:" includeIf condition so that it can
conditionally include configuration files if the branch that is checked
out in the current worktree matches the pattern given.

Signed-off-by: Denton Liu <liu.denton@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/config.txt

@@ -144,6 +144,20 @@ refer to linkgit:gitignore[5] for details. For convenience:
 	This is the same as `gitdir` except that matching is done
 	case-insensitively (e.g. on case-insensitive file sytems)
 
+`onbranch`::
+	The data that follows the keyword `onbranch:` is taken to be a
+	pattern with standard globbing wildcards and two additional
+	ones, `**/` and `/**`, that can match multiple path components.
+	If we are in a worktree where the name of the branch that is
+	currently checked out matches the pattern, the include condition
+	is met.
++
+If the pattern ends with `/`, `**` will be automatically added. For
+example, the pattern `foo/` becomes `foo/**`. In other words, it matches
+all branches that begin with `foo/`. This is useful if your branches are
+organized hierarchically and you would like to apply a configuration to
+all the branches in that hierarchy.
+
 A few more notes on matching via `gitdir` and `gitdir/i`:
 
  * Symlinks in `$GIT_DIR` are not resolved before matching.
@@ -206,6 +220,11 @@ Example
 	[includeIf "gitdir:/path/to/group/"]
 		path = foo.inc
 
+	; include only if we are in a worktree where foo-branch is
+	; currently checked out
+	[includeIf "onbranch:foo-branch"]
+		path = foo.inc
+
 Values
 ~~~~~~
 

config.c

@@ -19,6 +19,7 @@
 #include "utf8.h"
 #include "dir.h"
 #include "color.h"
+#include "refs.h"
 
 struct config_source {
 	struct config_source *prev;
@@ -170,6 +171,12 @@ static int handle_path_include(const char *path, struct config_include_data *inc
 	return ret;
 }
 
+static void add_trailing_starstar_for_dir(struct strbuf *pat)
+{
+	if (pat->len && is_dir_sep(pat->buf[pat->len - 1]))
+		strbuf_addstr(pat, "**");
+}
+
 static int prepare_include_condition_pattern(struct strbuf *pat)
 {
 	struct strbuf path = STRBUF_INIT;
@@ -199,8 +206,7 @@ static int prepare_include_condition_pattern(struct strbuf *pat)
 	} else if (!is_absolute_path(pat->buf))
 		strbuf_insert(pat, 0, "**/", 3);
 
-	if (pat->len && is_dir_sep(pat->buf[pat->len - 1]))
-		strbuf_addstr(pat, "**");
+	add_trailing_starstar_for_dir(pat);
 
 	strbuf_release(&path);
 	return prefix;
@@ -264,6 +270,25 @@ done:
 	return ret;
 }
 
+static int include_by_branch(const char *cond, size_t cond_len)
+{
+	int flags;
+	int ret;
+	struct strbuf pattern = STRBUF_INIT;
+	const char *refname = resolve_ref_unsafe("HEAD", 0, NULL, &flags);
+	const char *shortname;
+
+	if (!refname || !(flags & REF_ISSYMREF)	||
+			!skip_prefix(refname, "refs/heads/", &shortname))
+		return 0;
+
+	strbuf_add(&pattern, cond, cond_len);
+	add_trailing_starstar_for_dir(&pattern);
+	ret = !wildmatch(pattern.buf, shortname, WM_PATHNAME);
+	strbuf_release(&pattern);
+	return ret;
+}
+
 static int include_condition_is_true(const struct config_options *opts,
 				     const char *cond, size_t cond_len)
 {
@@ -272,6 +297,8 @@ static int include_condition_is_true(const struct config_options *opts,
 		return include_by_gitdir(opts, cond, cond_len, 0);
 	else if (skip_prefix_mem(cond, cond_len, "gitdir/i:", &cond, &cond_len))
 		return include_by_gitdir(opts, cond, cond_len, 1);
+	else if (skip_prefix_mem(cond, cond_len, "onbranch:", &cond, &cond_len))
+		return include_by_branch(cond, cond_len);
 
 	/* unknown conditionals are always false */
 	return 0;

t/t1305-config-include.sh

@@ -309,6 +309,45 @@ test_expect_success SYMLINKS 'conditional include, gitdir matching symlink, icas
 	)
 '
 
+test_expect_success 'conditional include, onbranch' '
+	echo "[includeIf \"onbranch:foo-branch\"]path=bar9" >>.git/config &&
+	echo "[test]nine=9" >.git/bar9 &&
+	git checkout -b master &&
+	test_must_fail git config test.nine &&
+	git checkout -b foo-branch &&
+	echo 9 >expect &&
+	git config test.nine >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'conditional include, onbranch, wildcard' '
+	echo "[includeIf \"onbranch:?oo-*/**\"]path=bar10" >>.git/config &&
+	echo "[test]ten=10" >.git/bar10 &&
+	git checkout -b not-foo-branch/a &&
+	test_must_fail git config test.ten &&
+
+	echo 10 >expect &&
+	git checkout -b foo-branch/a/b/c &&
+	git config test.ten >actual &&
+	test_cmp expect actual &&
+
+	git checkout -b moo-bar/a &&
+	git config test.ten >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'conditional include, onbranch, implicit /** for /' '
+	echo "[includeIf \"onbranch:foo-dir/\"]path=bar11" >>.git/config &&
+	echo "[test]eleven=11" >.git/bar11 &&
+	git checkout -b not-foo-dir/a &&
+	test_must_fail git config test.eleven &&
+
+	echo 11 >expect &&
+	git checkout -b foo-dir/a/b/c &&
+	git config test.eleven >actual &&
+	test_cmp expect actual
+'
+
 test_expect_success 'include cycles are detected' '
 	cat >.gitconfig <<-\EOF &&
 	[test]value = gitconfig