[PATCH v5 1/1] config: add conditional include

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

This allows some more flexibility in managing configuration across
repositories. The most often seen use case on the mailing list is when
the user needs to use different email addresses on different
repositories. If these repositories share something that we can use to
group them up, then we can set the same configuration for groups
automatically.

In this patch, the only supported grouping is based on $GIT_DIR (in
absolute path), so you would need to group repositories by directory, or
something like that to take advantage of it.

We already have include.path for unconditional includes. This patch goes
with include-if.xxx.path to make it clearer that a condition is
required.

Similar to include.path, older git versions that don't understand
include-if will simply ignore them.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 Documentation/config.txt  |  54 +++++++++++++++++++++++++
 config.c                  | 100 ++++++++++++++++++++++++++++++++++++++++++++++
 t/t1305-config-include.sh |  56 ++++++++++++++++++++++++++
 3 files changed, 210 insertions(+)

diff --git a/Documentation/config.txt b/Documentation/config.txt
index 015346c417..8cadf2b776 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -91,6 +91,49 @@ found at the location of the include directive. If the value of the
 relative to the configuration file in which the include directive was
 found.  See below for examples.
 
+Conditional includes
+~~~~~~~~~~~~~~~~~~~~
+
+You can include one config file from another conditionally by setting
+a special `include-if.<condition>.path` variable to the name of the
+file to be included. The variable is treated the same way as
+`include.path`.
+
+The condition starts with a keyword, followed by a colon and a
+pattern. The interpretation of the pattern depends on the keyword.
+Supported keywords are:
+
+`gitdir`::
+	The environment variable `GIT_DIR` must match the following
+	pattern for files to be included. The pattern can contain
+	standard globbing wildcards and two additional ones, `**/` and
+	`/**`, that can match multiple path components. Please refer
+	to linkgit:gitignore[5] for details. For convenience:
+
+ * If the pattern starts with `~/`, `~` will be substituted with the
+   content of the environment variable `HOME`.
+
+ * If the pattern starts with `./`, it is replaced with the directory
+   containing the current config file.
+
+ * If the pattern does not start with either `~/`, `./` or `/`, `**/`
+   will be automatically prepended. For example, the pattern `foo/bar`
+   becomes `**/foo/bar` and would match `/any/path/to/foo/bar`.
+
+ * If the pattern ends with `/`, `**` will be automatically added. For
+   example, the pattern `foo/` becomes `foo/**`. In other words, it
+   matches "foo" and everything inside, recursively.
+
+`gitdir/i`::
+	This is the same as `gitdir` except that matching is done
+	case-insensitively (e.g. on case-insensitive file sytems)
+
+A few more notes on matching:
+
+ * Symlinks in `$GIT_DIR` are not resolved before matching.
+
+ * Note that "../" is not special and will match literally, which is
+   unlikely what you want.
 
 Example
 ~~~~~~~
@@ -119,6 +162,17 @@ Example
 		path = foo ; expand "foo" relative to the current file
 		path = ~/foo ; expand "foo" in your `$HOME` directory
 
+	; include if $GIT_DIR is /path/to/foo/.git
+	[include-if "gitdir:/path/to/foo/.git"]
+		path = /path/to/foo.inc
+
+	; include for all repositories inside /path/to/group
+	[include-if "gitdir:/path/to/group/"]
+		path = /path/to/foo.inc
+
+	; include for all repositories inside $HOME/to/group
+	[include-if "gitdir:~/to/group/"]
+		path = /path/to/foo.inc
 
 Values
 ~~~~~~
diff --git a/config.c b/config.c
index c6b874a7bf..3090fbf1a8 100644
--- a/config.c
+++ b/config.c
@@ -13,6 +13,7 @@
 #include "hashmap.h"
 #include "string-list.h"
 #include "utf8.h"
+#include "dir.h"
 
 struct config_source {
 	struct config_source *prev;
@@ -170,9 +171,101 @@ static int handle_path_include(const char *path, struct config_include_data *inc
 	return ret;
 }
 
+static int prepare_include_condition_pattern(struct strbuf *pat)
+{
+	struct strbuf path = STRBUF_INIT;
+	int prefix = 0;
+
+	/* TODO: maybe support ~user/ too */
+	if (pat->buf[0] == '~' && is_dir_sep(pat->buf[1])) {
+		const char *home = getenv("HOME");
+
+		if (!home)
+			return error(_("$HOME is not defined"));
+
+		strbuf_add_absolute_path(&path, home);
+		strbuf_splice(pat, 0, 1, path.buf, path.len);
+		prefix = path.len + 1 /*slash*/;
+	} else if (pat->buf[0] == '.' && is_dir_sep(pat->buf[1])) {
+		const char *slash;
+
+		if (!cf || !cf->path)
+			return error(_("relative config include "
+				       "conditionals must come from files"));
+
+		/* TODO: escape wildcards */
+		strbuf_add_absolute_path(&path, cf->path);
+		slash = find_last_dir_sep(path.buf);
+		if (!slash)
+			die("BUG: how is this possible?");
+		strbuf_splice(pat, 0, 1, path.buf, slash - path.buf);
+		prefix = slash - path.buf + 1 /* slash */;
+	} 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, "**");
+
+	strbuf_release(&path);
+	return prefix;
+}
+
+static int include_by_gitdir(const char *cond, size_t cond_len, int icase)
+{
+	struct strbuf text = STRBUF_INIT;
+	struct strbuf pattern = STRBUF_INIT;
+	int ret = 0, prefix;
+
+	strbuf_add_absolute_path(&text, get_git_dir());
+	strbuf_add(&pattern, cond, cond_len);
+	prefix = prepare_include_condition_pattern(&pattern);
+
+	if (prefix < 0)
+		goto done;
+
+	if (prefix > 0) {
+		/*
+		 * perform literal matching on the prefix part so that
+		 * any wildcard character in it can't create side effects.
+		 */
+		if (text.len < prefix)
+			goto done;
+		if (!icase && strncmp(pattern.buf, text.buf, prefix))
+			goto done;
+		if (icase && strncasecmp(pattern.buf, text.buf, prefix))
+			goto done;
+	}
+
+	ret = !wildmatch(pattern.buf + prefix, text.buf + prefix,
+			 icase ? WM_CASEFOLD : 0, NULL);
+
+done:
+	strbuf_release(&pattern);
+	strbuf_release(&text);
+	return ret;
+}
+
+static int include_condition_is_true(const char *cond, size_t cond_len)
+{
+	/* no condition (i.e., "include.path") is always true */
+	if (!cond)
+		return 1;
+
+	if (skip_prefix_mem(cond, cond_len, "gitdir:", &cond, &cond_len))
+		return include_by_gitdir(cond, cond_len, 0);
+	else if (skip_prefix_mem(cond, cond_len, "gitdir/i:", &cond, &cond_len))
+		return include_by_gitdir(cond, cond_len, 1);
+
+	error(_("unrecognized include condition: %.*s"), (int)cond_len, cond);
+	/* unknown conditionals are always false */
+	return 0;
+}
+
 int git_config_include(const char *var, const char *value, void *data)
 {
 	struct config_include_data *inc = data;
+	const char *cond, *key;
+	int cond_len;
 	int ret;
 
 	/*
@@ -185,6 +278,13 @@ int git_config_include(const char *var, const char *value, void *data)
 
 	if (!strcmp(var, "include.path"))
 		ret = handle_path_include(value, inc);
+
+	if (!parse_config_key(var, "include-if", &cond, &cond_len, &key) &&
+	    include_condition_is_true(cond, cond_len)) {
+		if (!strcmp(key, "path"))
+			ret = handle_path_include(value, inc);
+		/* else we do not know about this type of include; ignore */
+	}
 	return ret;
 }
 
diff --git a/t/t1305-config-include.sh b/t/t1305-config-include.sh
index 9ba2ba11c3..d5b586e270 100755
--- a/t/t1305-config-include.sh
+++ b/t/t1305-config-include.sh
@@ -152,6 +152,62 @@ test_expect_success 'relative includes from stdin line fail' '
 	test_must_fail git config --file - test.one
 '
 
+test_expect_success 'conditional include, both unanchored' '
+	git init foo &&
+	(
+		cd foo &&
+		echo "[include-if \"gitdir:foo/\"]path=bar" >>.git/config &&
+		echo "[test]one=1" >.git/bar &&
+		echo 1 >expect &&
+		git config test.one >actual &&
+		test_cmp expect actual
+	)
+'
+
+test_expect_success 'conditional include, $HOME expansion' '
+	(
+		cd foo &&
+		echo "[include-if \"gitdir:~/foo/\"]path=bar2" >>.git/config &&
+		echo "[test]two=2" >.git/bar2 &&
+		echo 2 >expect &&
+		git config test.two >actual &&
+		test_cmp expect actual
+	)
+'
+
+test_expect_success 'conditional include, full pattern' '
+	(
+		cd foo &&
+		echo "[include-if \"gitdir:**/foo/**\"]path=bar3" >>.git/config &&
+		echo "[test]three=3" >.git/bar3 &&
+		echo 3 >expect &&
+		git config test.three >actual &&
+		test_cmp expect actual
+	)
+'
+
+test_expect_success 'conditional include, relative path' '
+	echo "[include-if \"gitdir:./foo/.git\"]path=bar4" >>.gitconfig &&
+	echo "[test]four=4" >bar4 &&
+	(
+		cd foo &&
+		echo 4 >expect &&
+		git config test.four >actual &&
+		test_cmp expect actual
+	)
+'
+
+test_expect_success 'conditional include, both unanchored, icase' '
+	(
+		cd foo &&
+		echo "[include-if \"gitdir/i:FOO/\"]path=bar5" >>.git/config &&
+		echo "[test]five=5" >.git/bar5 &&
+		echo 5 >expect &&
+		git config test.five >actual &&
+		test_cmp expect actual
+	)
+'
+
 test_expect_success 'include cycles are detected' '
 	cat >.gitconfig <<-\EOF &&
 	[test]value = gitconfig
-- 
2.11.0.157.gd943d85