Hide plugin buttons when changing the parent object isn't allowed

Also, fall back to the readonly representation when determining the
region of plugins.

Closes feincms/feincms3#40

content_editor/admin.py

@@ -125,8 +125,11 @@ class ContentEditor(ModelAdmin):
 
     def _content_editor_context(self, request, context):
         instance = context.get("original")
-        if not instance:
+        show_plugins = True
+        if instance is None:
             instance = self.model()
+        else:
+            show_plugins = self.has_change_permission(request, instance)
 
         plugins = []
         adding_not_allowed = ["_adding_not_allowed"]
@@ -139,7 +142,7 @@ def _content_editor_context(self, request, context):
                     if callable(iaf.opts.regions)
                     else iaf.opts.regions
                 )
-                if iaf.opts.has_add_permission(request, instance)
+                if show_plugins and iaf.opts.has_add_permission(request, instance)
                 else adding_not_allowed
             )
             plugins.append(

content_editor/static/content_editor/content_editor.js

@@ -364,7 +364,10 @@ django.jQuery(function ($) {
   function assignRegionDataAttribute() {
     orderMachine.find(".inline-related:not(.empty-form)").each(function () {
       const $this = $(this)
-      let region = $this.find(".field-region input").val()
+      // Try input first and fall back to the readonly presentation
+      let region =
+        $this.find(".field-region input").val() ||
+        $this.find(".field-region .readonly").text()
 
       if (!ContentEditor.regionsByKey[region]) {
         const key = `_unknown_${region}`