completion: zsh: overhaul and sync to current flags

* List all current option flags
* Provide descriptions for every flag
* Pass the `task -l` descriptions as descriptions for the task completions
  + The prior logic had 4 invocations of sed and 1 of awk, and only kept the
    task name
  + Do all filtering in zsh without forking (except for `task` itself)
* When `--taskfile` is used, complete tasks from _that_ file
  + And otherwise, enable completions if only the `.dist` variant files are
    present
* Ensure mutually exclusive options preclude each other
  + the `+ '(groupname)'` clause defines this
* Fix `--dir` to take directories, not files

completion/zsh/_task

@@ -1,25 +1,60 @@
 #compdef task
 
-# Listing commands from Taskfile.yml
-function __list() {
-    local -a scripts
+local context state state_descr line
+typeset -A opt_args
 
-    if [ -f Taskfile.yml ] || [ -f Taskfile.yaml ]; then
-        scripts=($(task -l | sed '1d' | sed 's/^\* //' | awk '{ print $1 }' | sed 's/:$//' | sed 's/:/\\:/g'))
-        _describe 'script' scripts
+# Listing commands from Taskfile.yml
+function __task_list() {
+    local -a scripts cmd
+    local -i enabled=0
+    local taskfile item task desc
+
+    cmd=(task)
+    taskfile="${(v)opt_args[(i)-t|--taskfile]}"
+
+    if [[ -n "$taskfile" && -f "$taskfile" ]]; then
+        enabled=1
+        cmd+=(--taskfile "$taskfile")
+    else
+        for taskfile in Taskfile{,.dist}.{yaml,yml}; do
+            if [[ -f "$taskfile" ]]; then
+                enabled=1
+                break
+            fi
+        done
     fi
+
+    (( enabled )) || return 0
+
+    scripts=()
+    for item in "${(@)${(f)$("${cmd[@]}" --list)}[2,-1]#\* }"; do
+        task="${item%%:[[:space:]]*}"
+        desc="${item##[^[:space:]]##[[:space:]]##}"
+        scripts+=( "${task//:/\\:}:$desc" )
+    done
+    _describe 'Task to run' scripts
 }
 
 _arguments \
-    '(-d --dir)'{-d,--dir}': :_files' \
-    '(--dry)'--dry \
-    '(-f --force)'{-f,--force} \
-    '(-i --init)'{-i,--init} \
-    '(-l --list)'{-l,--list} \
-    '(-s --silent)'{-s,--silent} \
-    '(--status)'--status \
-    '(-v --verbose)'{-v,--verbose} \
-    '(--version)'--version \
-    '(-w --watch)'{-w,--watch} \
-    '(- *)'{-h,--help} \
-    '*: :__list' \
+    '(-C --concurrency)'{-C,--concurrency}'[limit number of concurrent tasks]: ' \
+    '(-p --parallel)'{-p,--parallel}'[run command-line tasks in parallel]' \
+    '(-f --force)'{-f,--force}'[run even if task is up-to-date]' \
+    '(-c --color)'{-c,--color}'[colored output]' \
+    '(-d --dir)'{-d,--dir}'[dir to run in]:execution dir:_dirs' \
+    '(--dry)--dry[dry-run mode, compile and print tasks only]' \
+    '(-o --output)'{-o,--output}'[set output style]:style:(interleaved group prefixed)' \
+    '(--output-group-begin)--output-group-begin[message template before grouped output]:template text: ' \
+    '(--output-group-end)--output-group-end[message template after grouped output]:template text: ' \
+    '(-s --silent)'{-s,--silent}'[disable echoing]' \
+    '(--status)--status[exit non-zero if supplied tasks not up-to-date]' \
+    '(--summary)--summary[show summary\: field from tasks instead of running them]' \
+    '(-t --taskfile)'{-t,--taskfile}'[specify a different taskfile]:taskfile:_files' \
+    '(-v --verbose)'{-v,--verbose}'[verbose mode]' \
+    '(-w --watch)'{-w,--watch}'[watch-mode for given tasks, re-run when inputs change]' \
+    + '(operation)' \
+        {-l,--list}'[list describable tasks]' \
+        {-a,--list-all}'[list all tasks]' \
+        {-i,--init}'[create new Taskfile.yaml]' \
+        '(-*)'{-h,--help}'[show help]' \
+        '(-*)--version[show version and exit]' \
+        '*: :__task_list'