releng: add fish completions

If you use fish shell, you can run `bash -c 'source ./setup.sh Debug; exec fish'` or with Nix `nix-shell --run fish`. Unfortunately, we cannot get away with using direnv for now.

direnv/direnv#443
fish-shell/fish-shell#8261

releng/tools/fish/vendor_completions.d/rcfg.fish

@@ -0,0 +1,28 @@
+function _external_completion
+    # Get the current command up to a cursor.
+    # - Behaves correctly even with pipes and nested in commands like env.
+    # - Note that it returns the command verbatim (does not interpolate variables).
+    set -l fixed_args (commandline --current-process --tokenize --cut-at-cursor)
+    # --cut-at-cursor with --tokenize removes the current token so we need to add it separately.
+    # https://github.com/fish-shell/fish-shell/issues/7375
+    # Can be an empty string.
+    set -l current_token (commandline --current-token --cut-at-cursor)
+
+    # The completion scripts also want the index of the argv item to complete
+    # but the $fixed_args variable contains the program name (argv[0]) so we would need to subtract 1.
+    # But the variable also misses the current token so it cancels out.
+    set -l arg_to_complete (count $fixed_args)
+
+    env $ROFI_ROOT/releng/tools/$argv[1] $arg_to_complete $fixed_args $current_token
+end
+
+function _rcfg_completion
+    _external_completion _rcfg.completion.py $arguments
+end
+
+function _rmake_completion
+    _external_completion _rmake.completion.py $arguments
+end
+
+set util (basename (status filename) .fish)
+complete --path $ROFI_ROOT/releng/tools/$util --no-files --arguments '(_'$util'_completion)'

releng/tools/fish/vendor_completions.d/rmake.fish

@@ -0,0 +1 @@
+rcfg.fish

setup.sh

@@ -194,6 +194,11 @@ run() {
         autoload bashcompinit
         bashcompinit
     fi
+
+    ## For fish completions
+    backup XDG_DATA_DIRS
+    export XDG_DATA_DIRS="$XDG_DATA_DIRS:$ROFI_ROOT/releng/tools"
+
     source releng/tools/_registerCompletion.sh
 }