Create empty directories and files on interactive startup (#7796)

Closes #7402

CHANGELOG.rst

@@ -19,6 +19,8 @@ Interactive improvements
 - Commands that wrap ``cd`` (using ``complete --wraps cd``) get the same completions as ``cd`` (:issue:`4693`).
 - Arguments longer than 1024 characters no longer trigger excessive CPU usage on Mac (:issue:`7837`).
 
+-  Fish now automatically creates ``config.fish`` and the configuration directories in ``$XDG_CONFIG_HOME/fish`` (by default ``~/.config/fish``) if they do not already exist.
+
 New or improved bindings
 ^^^^^^^^^^^^^^^^^^^^^^^^
 

share/functions/__fish_config_interactive.fish

@@ -266,6 +266,16 @@ function __fish_config_interactive -d "Initializations that should be performed
         __update_cwd_osc # Run once because we might have already inherited a PWD from an old tab
     end
 
+    # Create empty configuration directores if they do not already exist
+    test -e $__fish_config_dir/completions/ -a -e $__fish_config_dir/conf.d/ -a -e $__fish_config_dir/functions/ ||
+        mkdir -p $__fish_config_dir/{completions, conf.d, functions}
+
+    # Create config.fish with some boilerplate if it does not exist
+    test -e $__fish_config_dir/config.fish || echo "\
+if status is-interactive
+    # Commands to run in interactive sessions can go here
+end" >$__fish_config_dir/config.fish
+
     # Bump this whenever some code below needs to run once when upgrading to a new version.
     # The universal variable __fish_initialized is initialized in share/config.fish.
     set __fish_initialized 3100