[PATCH v4 0/3] config: allow overriding global/system config

Hi,

this is the fourth version of my patch series to provide a way of overriding the global system configuration.

Compared to v3, I only dropped the special-casing of `/dev/null`. As Junio rightly pointed out, the special-casing was incomplete and would have required more work to do the right thing for all cases. It can still be re-added at a later point if the usecase actually comes up.

Patrick

Patrick Steinhardt (3):
  config: rename `git_etc_config()`
  config: unify code paths to get global config paths
  config: allow overriding of global and system configuration

 Documentation/git-config.txt |  5 +++
 Documentation/git.txt        | 10 +++++
 builtin/config.c             |  6 +--
 config.c                     | 41 +++++++++++++++------
 config.h                     |  4 +-
 t/t1300-config.sh            | 71 ++++++++++++++++++++++++++++++++++++
 6 files changed, 121 insertions(+), 16 deletions(-)

Range-diff against v3:
1:  34bdbc27d6 = 1:  34bdbc27d6 config: rename `git_etc_config()`
2:  30f18679bd = 2:  30f18679bd config: unify code paths to get global config paths
3:  af663640ae ! 3:  d27efc0aa8 config: allow overriding of global and system configuration
    @@ Commit message
             - If unset, git continues to use the usual locations.
     
             - If set to a specific path, we skip reading the normal
    -          configuration files and instead take the path.
    -
    -        - If set to `/dev/null`, we do not load either global- or
    -          system-level configuration at all.
    +          configuration files and instead take the path. By setting the path
    +          to `/dev/null`, no configuration will be loaded for the respective
    +          level.
     
         This implements the usecase where we want to execute code in a sanitized
         environment without any potential misconfigurations via `/dev/null`, but
    @@ Documentation/git.txt: for further details.
      	Whether to skip reading settings from the system-wide
      	`$(prefix)/etc/gitconfig` file.  This environment variable can
     
    - ## builtin/config.c ##
    -@@ builtin/config.c: int cmd_config(int argc, const char **argv, const char *prefix)
    - 		char *user_config, *xdg_config;
    - 
    - 		git_global_config(&user_config, &xdg_config);
    --		if (!user_config)
    -+		if (!user_config) {
    -+			if (getenv("GIT_CONFIG_GLOBAL"))
    -+				die(_("GIT_CONFIG_GLOBAL=/dev/null set"));
    -+
    - 			/*
    - 			 * It is unknown if HOME/.gitconfig exists, so
    - 			 * we do not know if we should write to XDG
    -@@ builtin/config.c: int cmd_config(int argc, const char **argv, const char *prefix)
    - 			 * is set and points at a sane location.
    - 			 */
    - 			die(_("$HOME not set"));
    -+		}
    - 
    - 		given_config_source.scope = CONFIG_SCOPE_GLOBAL;
    - 
    -
      ## config.c ##
     @@ config.c: static int git_config_from_blob_ref(config_fn_t fn,
      
      char *git_system_config(void)
      {
     +	char *system_config = xstrdup_or_null(getenv("GIT_CONFIG_SYSTEM"));
    -+	if (system_config) {
    -+		if (!strcmp(system_config, "/dev/null"))
    -+			FREE_AND_NULL(system_config);
    ++	if (system_config)
     +		return system_config;
    -+	}
      	return system_path(ETC_GITCONFIG);
      }
      
    @@ config.c: static int git_config_from_blob_ref(config_fn_t fn,
     +	char *user_config = xstrdup_or_null(getenv("GIT_CONFIG_GLOBAL"));
     +	char *xdg_config = NULL;
     +
    -+	if (user_config) {
    -+		if (!strcmp(user_config, "/dev/null"))
    -+			FREE_AND_NULL(user_config);
    -+		xdg_config = NULL;
    -+	} else {
    ++	if (!user_config) {
     +		user_config = expand_user_path("~/.gitconfig", 0);
     +		xdg_config = xdg_config_home("config");
     +	}