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, 27 insertions, 1 deletions

diff --git a/Documentation/technical/api-config.txt b/Documentation/technical/api-config.txt
index b0aeb2e..edf8dfb 100644
--- a/Documentation/technical/api-config.txt
+++ b/Documentation/technical/api-config.txt
@@ -52,13 +52,17 @@ while adjusting some of the default behavior of `git_config`. It should
 almost never be used by "regular" git code that is looking up
 configuration variables. It is intended for advanced callers like
 `git-config`, which are intentionally tweaking the normal config-lookup
-process. It takes one extra parameter:
+process. It takes two extra parameters:
 
 `filename`::
 If this parameter is non-NULL, it specifies the name of a file to
 parse for configuration, rather than looking in the usual files. Regular
 `git_config` defaults to `NULL`.
 
+`respect_includes`::
+Specify whether include directives should be followed in parsed files.
+Regular `git_config` defaults to `1`.
+
 There is a special version of `git_config` called `git_config_early`.
 This version takes an additional parameter to specify the repository
 config, instead of having it looked up via `git_path`. This is useful
@@ -108,6 +112,28 @@ string is given, prints an error message and returns -1.
 Similar to `git_config_string`, but expands `~` or `~user` into the
 user's home directory when found at the beginning of the path.
 
+Include Directives
+------------------
+
+By default, the config parser does not respect include directives.
+However, a caller can use the special `git_config_include` wrapper
+callback to support them. To do so, you simply wrap your "real" callback
+function and data pointer in a `struct config_include_data`, and pass
+the wrapper to the regular config-reading functions. For example:
+
+-------------------------------------------
+int read_file_with_include(const char *file, config_fn_t fn, void *data)
+{
+	struct config_include_data inc = CONFIG_INCLUDE_INIT;
+	inc.fn = fn;
+	inc.data = data;
+	return git_config_from_file(git_config_include, file, &inc);
+}
+-------------------------------------------
+
+`git_config` respects includes automatically. The lower-level
+`git_config_from_file` does not.
+
 Writing Config Files
 --------------------