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 <redacted>
---

Thanks for taking a look, Johannes. I've modified the patch to match
with wildcards now.

Changes since v1:

* Allow onbranch: to specify a pattern instead of just a static
  comparison

Interdiff against v1:
  diff --git a/Documentation/config.txt b/Documentation/config.txt
  index 3b9fbe1860..93aa4323c6 100644
  --- a/Documentation/config.txt
  +++ b/Documentation/config.txt
  @@ -145,9 +145,11 @@ refer to linkgit:gitignore[5] for details. For convenience:
   	case-insensitively (e.g. on case-insensitive file sytems)
   
   `onbranch`::
  -	The data that follows the keyword `onbranch:` is taken to be a
  -	name of a local branch. If we are in a worktree where that
  -	branch is currently checked out, the include condition is met.
  +	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.
   
   A few more notes on matching via `gitdir` and `gitdir/i`:
   
  diff --git a/config.c b/config.c
  index 954e84e13a..48bb435739 100644
  --- a/config.c
  +++ b/config.c
  @@ -268,6 +268,8 @@ static int include_by_gitdir(const struct config_options *opts,
   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;
   
  @@ -275,7 +277,10 @@ static int include_by_branch(const char *cond, size_t cond_len)
   			!skip_prefix(refname, "refs/heads/", &shortname))
   		return 0;
   
  -	return !strncmp(cond, shortname, cond_len);
  +	strbuf_add(&pattern, cond, cond_len);
  +	ret = !wildmatch(pattern.buf, shortname, WM_PATHNAME);
  +	strbuf_release(&pattern);
  +	return ret;
   }
   
   static int include_condition_is_true(const struct config_options *opts,
  diff --git a/t/t1305-config-include.sh b/t/t1305-config-include.sh
  index 062db08ad9..05c7def1f2 100755
  --- a/t/t1305-config-include.sh
  +++ b/t/t1305-config-include.sh
  @@ -314,6 +314,7 @@ test_expect_success 'conditional include, onbranch' '
   		cd bar &&
   		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 &&
  @@ -322,6 +323,25 @@ test_expect_success 'conditional include, onbranch' '
   	)
   '
   
  +test_expect_success 'conditional include, onbranch, wildcard' '
  +	(
  +		cd bar &&
  +		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 'include cycles are detected' '
   	cat >.gitconfig <<-\EOF &&
   	[test]value = gitconfig

 Documentation/config.txt  | 12 ++++++++++++
 config.c                  | 21 +++++++++++++++++++++
 t/t1305-config-include.sh | 33 +++++++++++++++++++++++++++++++++
 3 files changed, 66 insertions(+)

diff --git a/Documentation/config.txt b/Documentation/config.txt
index 7e2a6f61f5..93aa4323c6 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt

@@ -144,6 +144,13 @@ 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.
+
 A few more notes on matching via `gitdir` and `gitdir/i`:
 
  * Symlinks in `$GIT_DIR` are not resolved before matching.

@@ -206,6 +213,11 @@ 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
 ~~~~~~
 

diff --git a/config.c b/config.c
index 296a6d9cc4..48bb435739 100644
--- a/config.c
+++ b/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;

@@ -264,6 +265,24 @@ static int include_by_gitdir(const struct config_options *opts,
 	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);
+	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 +291,8 @@ 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;

diff --git a/t/t1305-config-include.sh b/t/t1305-config-include.sh
index 579a86b7f8..05c7def1f2 100755
--- a/t/t1305-config-include.sh
+++ b/t/t1305-config-include.sh

@@ -309,6 +309,39 @@ test_expect_success SYMLINKS 'conditional include, gitdir matching symlink, icas
 	)
 '
 
+test_expect_success 'conditional include, onbranch' '
+	(
+		cd bar &&
+		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' '
+	(
+		cd bar &&
+		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 'include cycles are detected' '
 	cat >.gitconfig <<-\EOF &&
 	[test]value = gitconfig

-- 
2.22.0.rc1.169.g49223abbf8