[RFC 4/6] Add get_standard_config_dir function

[Tom Tromey]

This adds a new get_standard_config_dir, which returns the name of the
configuration directory.  In XDG, this is ~/.config/gdb/.  Future
patches will make use of this.

gdbsupport/ChangeLog
2020-03-28  Tom Tromey  <tom@tromey.com>

	* pathstuff.h (get_standard_config_dir): Declare.
	* pathstuff.cc (get_standard_config_dir): New function.
---
 gdbsupport/ChangeLog    |  5 +++++
 gdbsupport/pathstuff.cc | 32 ++++++++++++++++++++++++++++++++
 gdbsupport/pathstuff.h  | 14 ++++++++++++++
 3 files changed, 51 insertions(+)

diff --git a/gdbsupport/pathstuff.cc b/gdbsupport/pathstuff.cc
index 1f60fd0c986..9fb5e5cf614 100644
--- a/gdbsupport/pathstuff.cc
+++ b/gdbsupport/pathstuff.cc
@@ -266,6 +266,38 @@ get_standard_temp_dir ()
 #endif
 }
 
+/* See pathstuff.h.  */
+
+std::string
+get_standard_config_dir ()
+{
+#ifdef __APPLE__
+#define HOME_CONFIG_DIR "Library/Preferences"
+#else
+#define HOME_CONFIG_DIR ".config"
+#endif
+
+#ifndef __APPLE__
+  const char *xdg_config_home = getenv ("XDG_CONFIG_HOME");
+  if (xdg_config_home != NULL)
+    {
+      /* Make sure the path is absolute and tilde-expanded.  */
+      gdb::unique_xmalloc_ptr<char> abs (gdb_abspath (xdg_config_home));
+      return string_printf ("%s/gdb", abs.get ());
+    }
+#endif
+
+  const char *home = getenv ("HOME");
+  if (home != NULL)
+    {
+      /* Make sure the path is absolute and tilde-expanded.  */
+      gdb::unique_xmalloc_ptr<char> abs (gdb_abspath (home));
+      return string_printf ("%s/" HOME_CONFIG_DIR "/gdb", abs.get ());
+    }
+
+  return {};
+}
+
 /* See gdbsupport/pathstuff.h.  */
 
 const char *
diff --git a/gdbsupport/pathstuff.h b/gdbsupport/pathstuff.h
index 4bc0d892119..85241bc8c7c 100644
--- a/gdbsupport/pathstuff.h
+++ b/gdbsupport/pathstuff.h
@@ -85,6 +85,20 @@ extern std::string get_standard_cache_dir ();
 
 extern std::string get_standard_temp_dir ();
 
+/* Get the usual user config directory for the current platform.
+
+   On Linux, it follows the XDG Base Directory specification: use
+   $XDG_CONFIG_HOME/gdb if the XDG_CONFIG_HOME environment variable is
+   defined, otherwise $HOME/.config.
+
+   On macOS, it follows the local convention and uses
+   ~/Library/Preferences/gdb.
+
+  The return value is absolute and tilde-expanded.  Return an empty
+  string if neither XDG_CONFIG_HOME (on Linux) or HOME are defined.  */
+
+extern std::string get_standard_config_dir ();
+
 /* Return the file name of the user's shell.  Normally this comes from
    the SHELL environment variable.  */
 
-- 
2.17.2