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, 38 insertions, 8 deletions

diff --git a/include/git2/common.h b/include/git2/common.h
index 7066d5ea3..137ffa0a4 100644
--- a/include/git2/common.h
+++ b/include/git2/common.h
@@ -128,7 +128,10 @@ enum {
 	GIT_OPT_GET_MWINDOW_SIZE,
 	GIT_OPT_SET_MWINDOW_SIZE,
 	GIT_OPT_GET_MWINDOW_MAPPED_LIMIT,
-	GIT_OPT_SET_MWINDOW_MAPPED_LIMIT
+	GIT_OPT_SET_MWINDOW_MAPPED_LIMIT,
+	GIT_OPT_GET_SEARCH_PATH,
+	GIT_OPT_SET_SEARCH_PATH,
+	GIT_OPT_PREPEND_SEARCH_PATH,
 };
 
 /**
@@ -136,17 +139,44 @@ enum {
  *
  * Available options:
  *
- *	opts(GIT_OPT_MWINDOW_SIZE, size_t):
- *		set the maximum mmap window size
+ *	opts(GIT_OPT_GET_MWINDOW_SIZE, size_t *):
+ *		Get the maximum mmap window size
  *
- *	opts(GIT_OPT_MWINDOW_MAPPED_LIMIT, size_t):
- *		set the maximum amount of memory that can be mapped at any time
+ *	opts(GIT_OPT_SET_MWINDOW_SIZE, size_t):
+ *		Set the maximum mmap window size
+ *
+ *	opts(GIT_OPT_GET_MWINDOW_MAPPED_LIMIT, size_t *):
+ *		Get the maximum memory that will be mapped in total by the library
+ *
+ *	opts(GIT_OPT_SET_MWINDOW_MAPPED_LIMIT, size_t):
+ *		Set the maximum amount of memory that can be mapped at any time
  *		by the library
  *
- *	@param option Option key
- *	@param ... value to set the option
+ *	opts(GIT_OPT_GET_SEARCH_PATH, const git_strarray **, int level)
+ *		Get a strarray of the search path for a given level of config
+ *		data.  "level" must be one of GIT_CONFIG_LEVEL_SYSTEM,
+ *		GIT_CONFIG_LEVEL_GLOBAL, or GIT_CONFIG_LEVEL_XDG.  The search
+ *		path applies to shared attributes and ignore files, too.
+ *
+ *	opts(GIT_OPT_SET_SEARCH_PATH, int level, const git_strarray *)
+ *		Set the search path for a given level of config data.  Passing
+ *		NULL for the git_strarray pointer resets the search path to the
+ *		default (which is generally based on environment variables).
+ *		"level" must be one of GIT_CONFIG_LEVEL_SYSTEM,
+ *		GIT_CONFIG_LEVEL_GLOBAL, or GIT_CONFIG_LEVEL_XDG.  The search
+ *		path applies to shared attributes and ignore files, too.
+ *
+ *	opts(GIT_OPT_PREPEND_SEARCH_PATH, int level, const git_strarray *)
+ *		Prepend new directories to the search path for a given level of
+ *		config data.  "level" must be one of GIT_CONFIG_LEVEL_SYSTEM,
+ *		GIT_CONFIG_LEVEL_GLOBAL, or GIT_CONFIG_LEVEL_XDG.  The search
+ *		path applies to shared attributes and ignore files, too.
+ *
+ * @param option Option key
+ * @param ... value to set the option
+ * @return 0 on success, <0 on failure
  */
-GIT_EXTERN(void) git_libgit2_opts(int option, ...);
+GIT_EXTERN(int) git_libgit2_opts(int option, ...);
 
 /** @} */
 GIT_END_DECL