Add a autocompletation plugin for forgejo-cli

Fix #13909

plugins/fj/README.md

@@ -0,0 +1,23 @@
+# Forgejo CLI plugin
+
+This plugin adds completion for the [Forgejo CLI](https://codeberg.org/forgejo-contrib/forgejo-cli).
+
+To use it, add `fj` to the plugins array in your zshrc file:
+
+```zsh
+plugins=(... fj)
+```
+
+This plugin does not add any aliases.
+
+## Cache
+
+This plugin caches the completion script and is automatically updated when the
+plugin is loaded, which is usually when you start up a new terminal emulator.
+
+The cache is stored at:
+
+- `$ZSH/plugins/fj/_fj` completions script
+
+- `$ZSH_CACHE_DIR/fj_version` version of Forgejo CLI, used to invalidate
+  the cache.

plugins/fj/fj.plugin.zsh

@@ -0,0 +1,14 @@
+# Autocompletion for the Forgejo CLI (fj).
+if (( ! $+commands[fj] )); then
+  return
+fi
+
+# If the completion file doesn't exist yet, we need to autoload it and
+# bind it to `fj`. Otherwise, compinit will have already done that.
+if [[ ! -f "$ZSH_CACHE_DIR/completions/_fj" ]]; then
+  typeset -g -A _comps
+  autoload -Uz _fj
+  _comps[fj]=_fj
+fi
+
+fj completion --shell zsh >| "$ZSH_CACHE_DIR/completions/_fj" &|