Implement global/system file search paths

The goal of this work is to expose the search logic for "global",
"system", and "xdg" files through the git_libgit2_opts() interface.

Behind the scenes, I changed the logic for finding files to have a
notion of a git_strarray that represents a search path and to store
a separate search path for each of the three tiers of config file.
For each tier, I implemented a function to initialize it to default
values (generally based on environment variables), and then general
interfaces to get it, set it, reset it, and prepend new directories
to it.

Next, I exposed these interfaces through the git_libgit2_opts
interface, reusing the GIT_CONFIG_LEVEL_SYSTEM, etc., constants
for the user to control which search path they were modifying.
There are alternative designs for the opts interface / argument
ordering, so I'm putting this phase out for discussion.

Additionally, I ended up doing a little bit of clean up regarding
attr.h and attr_file.h, adding a new attrcache.h so the other two
files wouldn't have to be included in so many places.

1 files changed, 29 insertions, 59 deletions

diff --git a/src/config.c b/src/config.c
index d6aa3078c..85db0ab3c 100644
--- a/src/config.c
+++ b/src/config.c
@@ -510,62 +510,48 @@ int git_config_set_multivar(git_config *cfg, const char *name, const char *regex
 	return file->set_multivar(file, name, regexp, value);
 }
 
-int git_config_find_global_r(git_buf *path)
+static int git_config__find_file_to_path(
+	char *out, size_t outlen, int (*find)(git_buf *buf))
 {
-	int error = git_futils_find_global_file(path, GIT_CONFIG_FILENAME);
+	int error = 0;
+	git_buf path = GIT_BUF_INIT;
+
+	if ((error = find(&path)) < 0)
+		goto done;
+
+	if (path.size >= outlen) {
+		giterr_set(GITERR_NOMEMORY, "Buffer is too short for the path");
+		error = -1;
+		goto done;
+	}
 
+	git_buf_copy_cstr(out, outlen, &path);
+
+done:
+	git_buf_free(&path);
 	return error;
 }
 
-int git_config_find_xdg_r(git_buf *path)
+int git_config_find_global_r(git_buf *path)
 {
-	int error = git_futils_find_global_file(path, GIT_CONFIG_FILENAME_ALT);
-
-	return error;
+	return git_futils_find_global_file(path, GIT_CONFIG_FILENAME_GLOBAL);
 }
 
 int git_config_find_global(char *global_config_path, size_t length)
 {
-	git_buf path  = GIT_BUF_INIT;
-	int     ret = git_config_find_global_r(&path);
-
-	if (ret < 0) {
-		git_buf_free(&path);
-		return ret;
-	}
-
-	if (path.size >= length) {
-		git_buf_free(&path);
-		giterr_set(GITERR_NOMEMORY,
-			"Path is to long to fit on the given buffer");
-		return -1;
-	}
+	return git_config__find_file_to_path(
+		global_config_path, length, git_config_find_global_r);
+}
 
-	git_buf_copy_cstr(global_config_path, length, &path);
-	git_buf_free(&path);
-	return 0;
+int git_config_find_xdg_r(git_buf *path)
+{
+	return git_futils_find_xdg_file(path, GIT_CONFIG_FILENAME_XDG);
 }
 
 int git_config_find_xdg(char *xdg_config_path, size_t length)
 {
-	git_buf path  = GIT_BUF_INIT;
-	int ret = git_config_find_xdg_r(&path);
-
-	if (ret < 0) {
-		git_buf_free(&path);
-		return ret;
-	}
-
-	if (path.size >= length) {
-		git_buf_free(&path);
-		giterr_set(GITERR_NOMEMORY,
-			"Path is to long to fit on the given buffer");
-		return -1;
-	}
-
-	git_buf_copy_cstr(xdg_config_path, length, &path);
-	git_buf_free(&path);
-	return 0;
+	return git_config__find_file_to_path(
+		xdg_config_path, length, git_config_find_xdg_r);
 }
 
 int git_config_find_system_r(git_buf *path)
@@ -575,24 +561,8 @@ int git_config_find_system_r(git_buf *path)
 
 int git_config_find_system(char *system_config_path, size_t length)
 {
-	git_buf path  = GIT_BUF_INIT;
-	int     ret = git_config_find_system_r(&path);
-
-	if (ret < 0) {
-		git_buf_free(&path);
-		return ret;
-	}
-
-	if (path.size >= length) {
-		git_buf_free(&path);
-		giterr_set(GITERR_NOMEMORY,
-			"Path is to long to fit on the given buffer");
-		return -1;
-	}
-
-	git_buf_copy_cstr(system_config_path, length, &path);
-	git_buf_free(&path);
-	return 0;
+	return git_config__find_file_to_path(
+		system_config_path, length, git_config_find_system_r);
 }
 
 int git_config_open_default(git_config **out)