config: add include directive

It can be useful to split your ~/.gitconfig across multiple
files. For example, you might have a "main" file which is
used on many machines, but a small set of per-machine
tweaks. Or you may want to make some of your config public
(e.g., clever aliases) while keeping other data back (e.g.,
your name or other identifying information). Or you may want
to include a number of config options in some subset of your
repos without copying and pasting (e.g., you want to
reference them from the .git/config of participating repos).

This patch introduces an include directive for config files.
It looks like:

  [include]
    path = /path/to/file

This is syntactically backwards-compatible with existing git
config parsers (i.e., they will see it as another config
entry and ignore it unless you are looking up include.path).

The implementation provides a "git_config_include" callback
which wraps regular config callbacks. Callers can pass it to
git_config_from_file, and it will transparently follow any
include directives, passing all of the discovered options to
the real callback.

Include directives are turned on automatically for "regular"
git config parsing. This includes calls to git_config, as
well as calls to the "git config" program that do not
specify a single file (e.g., using "-f", "--global", etc).
They are not turned on in other cases, including:

  1. Parsing of other config-like files, like .gitmodules.
     There isn't a real need, and I'd rather be conservative
     and avoid unnecessary incompatibility or confusion.

  2. Reading single files via "git config". This is for two
     reasons:

       a. backwards compatibility with scripts looking at
          config-like files.

       b. inspection of a specific file probably means you
	  care about just what's in that file, not a general
          lookup for "do we have this value anywhere at
	  all". If that is not the case, the caller can
	  always specify "--includes".

  3. Writing files via "git config"; we want to treat
     include.* variables as literal items to be copied (or
     modified), and not expand them. So "git config
     --unset-all foo.bar" would operate _only_ on
     .git/config, not any of its included files (just as it
     also does not operate on ~/.gitconfig).

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 73 insertions, 2 deletions

diff --git a/config.c b/config.c
index 1e30ad9d18..ad0390819d 100644
--- a/config.c
+++ b/config.c
@@ -26,6 +26,69 @@ static config_file *cf;
 
 static int zlib_compression_seen;
 
+#define MAX_INCLUDE_DEPTH 10
+static const char include_depth_advice[] =
+"exceeded maximum include depth (%d) while including\n"
+"	%s\n"
+"from\n"
+"	%s\n"
+"Do you have circular includes?";
+static int handle_path_include(const char *path, struct config_include_data *inc)
+{
+	int ret = 0;
+	struct strbuf buf = STRBUF_INIT;
+
+	/*
+	 * Use an absolute path as-is, but interpret relative paths
+	 * based on the including config file.
+	 */
+	if (!is_absolute_path(path)) {
+		char *slash;
+
+		if (!cf || !cf->name)
+			return error("relative config includes must come from files");
+
+		slash = find_last_dir_sep(cf->name);
+		if (slash)
+			strbuf_add(&buf, cf->name, slash - cf->name + 1);
+		strbuf_addstr(&buf, path);
+		path = buf.buf;
+	}
+
+	if (!access(path, R_OK)) {
+		if (++inc->depth > MAX_INCLUDE_DEPTH)
+			die(include_depth_advice, MAX_INCLUDE_DEPTH, path,
+			    cf && cf->name ? cf->name : "the command line");
+		ret = git_config_from_file(git_config_include, path, inc);
+		inc->depth--;
+	}
+	strbuf_release(&buf);
+	return ret;
+}
+
+int git_config_include(const char *var, const char *value, void *data)
+{
+	struct config_include_data *inc = data;
+	const char *type;
+	int ret;
+
+	/*
+	 * Pass along all values, including "include" directives; this makes it
+	 * possible to query information on the includes themselves.
+	 */
+	ret = inc->fn(var, value, inc->data);
+	if (ret < 0)
+		return ret;
+
+	type = skip_prefix(var, "include.");
+	if (!type)
+		return ret;
+
+	if (!strcmp(type, "path"))
+		ret = handle_path_include(value, inc);
+	return ret;
+}
+
 static void lowercase(char *p)
 {
 	for (; *p; p++)
@@ -913,10 +976,18 @@ int git_config_early(config_fn_t fn, void *data, const char *repo_config)
 }
 
 int git_config_with_options(config_fn_t fn, void *data,
-			    const char *filename)
+			    const char *filename, int respect_includes)
 {
 	char *repo_config = NULL;
 	int ret;
+	struct config_include_data inc = CONFIG_INCLUDE_INIT;
+
+	if (respect_includes) {
+		inc.fn = fn;
+		inc.data = data;
+		fn = git_config_include;
+		data = &inc;
+	}
 
 	/*
 	 * If we have a specific filename, use it. Otherwise, follow the
@@ -934,7 +1005,7 @@ int git_config_with_options(config_fn_t fn, void *data,
 
 int git_config(config_fn_t fn, void *data)
 {
-	return git_config_with_options(fn, data, NULL);
+	return git_config_with_options(fn, data, NULL, 1);
 }
 
 /*