Re: [PATCH v4 1/4] cache.h: Introduce a generic "xdg_config_home_for(…)" function

Current implementation of `xdg_config_home(filename)` returns
`$XDG_CONFIG_HOME/git/$filename`, with the `git` subdirectory inserted
between the `XDG_CONFIG_HOME` environment variable and the parameter.

This patch introduces a `xdg_config_home_for(prog, filename)` function
which is more generic. It only concatenates "$XDG_CONFIG_HOME", or
"$HOME/.config" if the former isn’t defined, with the parameters,
without adding `git` in between.

`xdg_config_home(filename)` is now implemented by calling
`xdg_config_home_for("git", filename)` but this new generic function can
be used to compute the configuration directory of other programs.

Signed-off-by: Lénaïc Huard <redacted>
---
  cache.h |  7 +++++++
  path.c  | 13 ++++++++++---
  2 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/cache.h b/cache.h
index 148d9ab5f1..8a2969414a 100644
--- a/cache.h
+++ b/cache.h

@@ -1263,6 +1263,13 @@ int is_ntfs_dotgitattributes(const char *name);
   */
  int looks_like_command_line_option(const char *str);
  
+/**
+ * Return a newly allocated string with the evaluation of
+ * "$XDG_CONFIG_HOME/$prog/$filename" if $XDG_CONFIG_HOME is non-empty, otherwise
+ * "$HOME/.config/$prog/$filename". Return NULL upon error.
+ */
+char *xdg_config_home_for(const char *prog, const char *filename);
+
  /**
   * Return a newly allocated string with the evaluation of
   * "$XDG_CONFIG_HOME/git/$filename" if $XDG_CONFIG_HOME is non-empty, otherwise

diff --git a/path.c b/path.c
index 7b385e5eb2..3641d4c456 100644
--- a/path.c
+++ b/path.c

@@ -1498,21 +1498,28 @@ int looks_like_command_line_option(const char *str)
  	return str && str[0] == '-';
  }
  
-char *xdg_config_home(const char *filename)
+char *xdg_config_home_for(const char *prog, const char *filename)
  {
  	const char *home, *config_home;
  
+	assert(prog);
  	assert(filename);
  	config_home = getenv("XDG_CONFIG_HOME");
  	if (config_home && *config_home)
-		return mkpathdup("%s/git/%s", config_home, filename);
+		return mkpathdup("%s/%s/%s", config_home, prog, filename);
  
  	home = getenv("HOME");
  	if (home)
-		return mkpathdup("%s/.config/git/%s", home, filename);
+		return mkpathdup("%s/.config/%s/%s", home, prog, filename);
+
  	return NULL;
  }
  
+char *xdg_config_home(const char *filename)
+{
+	return xdg_config_home_for("git", filename);
+}
+
  char *xdg_cache_home(const char *filename)
  {
  	const char *home, *cache_home;