make $compcontext more powerful and easier to use for simple cases

Completion/Core/_complete

@@ -12,10 +12,70 @@ oldcontext="$curcontext"
 # If we have a user-supplied context name, use only that.
 
 if [[ -n "$compcontext" ]]; then
-  ccarray[3]="$compcontext"
 
-  comp="$_comps[$compcontext]"
-  [[ -z "$comp" ]] || "$comp"
+  if [[ "${(t)compcontext}" = *(array|assoc)* ]]; then
+    local expl
+
+    _wanted values expl value compadd -a - compcontext
+
+  elif [[ "$compcontext" = *:*:* ]]; then
+    local tag="${${compcontext%%:*}:-values}"
+    local descr="${${${compcontext#${tag}:}%%:*}:-value}"
+    local action="${compcontext#${tag}:${descr}:}" expl ws ret=1
+
+    case "$action" in
+    \ #)
+      _message "$descr";;
+
+    \(\(*\)\))
+      eval ws\=\( "${action[3,-3]}" \)
+
+      _describe -t "$tag" "$descr" ws;;
+
+    \(*\))
+      eval ws\=\( "${action[2,-2]}" \)
+
+      _wanted "$tag" expl "$descr" compadd -a - ws;;
+
+    \{*\})
+      _tags "$tag"
+      while _tags; do
+        while _next_label "$tag" expl "$descr"; do
+          eval "$action[2,-2]" && ret=0
+	done
+	(( ret )) || break
+      done;;
+
+    \ *)
+      eval ws\=\( "$action" \)
+
+      _tags "$tag"
+      while _tags; do
+        while _next_label "$tag" expl "$descr"; do
+          "$ws[@]"
+	done
+	(( ret )) || break
+      done;;
+
+    *)
+      eval ws\=\( "$action" \)
+
+      _tags "$tag"
+      while _tags; do
+        while _next_label "$tag" expl "$descr"; do
+          "$ws[1]" "$expl[@]" "${(@)ws[2,-1]}"
+	done
+	(( ret )) || break
+      done;;
+
+    esac
+
+  else
+    ccarray[3]="$compcontext"
+
+    comp="$_comps[$compcontext]"
+    [[ -z "$comp" ]] || "$comp"
+  fi
 
   return
 fi

Doc/Zsh/compsys.yo

@@ -2313,13 +2313,21 @@ contexts, in most cases named after the context itself
 named `tt(_tilde)').
 
 Before trying to find a function for a specific context, tt(_complete) 
-checks if the parameter `tt(compcontext)' is set to a non-empty
-value.  If it is, the value is taken as the name of the context to use
-and the function defined for that context will be called.  For this
-purpose, there is a special context named tt(-command-line-) that
-completes whole command lines (commands and their arguments) and is
-not used by the completion system itself, but has a function handling
-completion for it.
+checks if the parameter `tt(compcontext)' is set.  If it is set to an
+array, the elements are taken to be the possible matches which will be
+completed using the tag `tt(values)' and the description `tt(value)'.
+If `tt(compcontext)' to a string containing colons, it should be of
+the form `var(tag)tt(:)var(descr)tt(:)var(action)'. In this case the
+var(tag) and var(descr) give the tag and description to use and the
+var(action) says what should be completed in one of the forms
+described for the tt(_arguments) utility function below.
+
+Finally, if `tt(compcontext)' is set a string without colons, the
+value is taken as the name of the context to use and the function
+defined for that context will be called.  For this purpose, there is a
+special context named tt(-command-line-) that completes whole command
+lines (commands and their arguments) and is not used by the completion
+system itself, but has a function handling completion for it.
 )
 findex(_correct)
 item(tt(_correct))(