Fix various issues with the previewers

src/PanelCode.js

@@ -46,7 +46,14 @@ export default function PanelCode({ builder, previewer, settings }) {
   function switchLanguage() {
     panel.language = dropdown_code_lang.selected_item?.string;
     stack_code.visible_child_name = panel.language;
-    previewer.useInternal().catch(console.error);
+    if (panel.language === "JavaScript") {
+      previewer.useInternal().catch(console.error);
+    } else {
+      // If we switch language to anything other than JS,
+      // we need the user to hit "Run" first to compile the code and/or
+      // init the demo in the external previewer.
+      previewer.hideShowPreviewerButton().catch(console.error);
+    }
   }
   switchLanguage();
 

src/Previewer/External.js

@@ -46,7 +46,12 @@ export default function External({ output, builder, onWindowChange }) {
       console.debug(err);
       return;
     }
-    stack.set_visible_child_name("open_window");
+    // only do this, if we were previously on "close_window", because it's possible
+    // we have just been replaced with the internal previewer, which may have
+    // already switched tro "inline"
+    if (stack.get_visible_child_name() === "close_window") {
+      stack.set_visible_child_name("open_window");
+    }
   }
 
   function stop() {

src/Previewer/Previewer.js

@@ -74,7 +74,6 @@ export default function Previewer({
         stack.set_visible_child_name("close_window");
       } else {
         stack.set_visible_child_name("open_window");
-        useInternal().catch(console.error);
       }
     },
     output,
@@ -276,6 +275,7 @@ export default function Previewer({
 
     current = previewer;
 
+    button_open.show();
     handler_id_button_open = button_open.connect("clicked", async () => {
       try {
         await current.open();
@@ -301,6 +301,10 @@ export default function Previewer({
     }
   }
 
+  async function hideShowPreviewerButton() {
+    button_open.hide();
+  }
+
   builder.get_object("button_screenshot").connect("clicked", () => {
     screenshot({ application, window, current }).catch(console.error);
   });
@@ -323,6 +327,7 @@ export default function Previewer({
     },
     useExternal,
     useInternal,
+    hideShowPreviewerButton,
     setPanelCode(v) {
       panel_code = v;
     },

src/Previewer/previewer.vala

@@ -25,12 +25,12 @@ namespace Workbench {
         private void set_window (Gtk.Window window) {
             this.window?.destroy ();
             this.window = window;
+            this.window.hide_on_close = true;
             this.window.close_request.connect (this.on_window_closed);
         }
 
         private bool on_window_closed () {
             this.window_open (false);
-            this.window = null;
             return false;
         }
 

src/langs/python/python-previewer.py

@@ -216,11 +216,12 @@ def set_window(self, the_window: Gtk.Window):
         if self.window is not None:
             self.window.destroy()
         self.window = the_window
+        # Make sure the preview can be re-opened by using the "Show Preview Window" button.
+        self.window.set_hide_on_close(True)
         self.window.connect("close-request", self.on_window_closed)
 
     def on_window_closed(self, *args):
         self.window_open(False)
-        self.window = None
         return False
 
     def on_css_parsing_error(self, _css, section: Gtk.CssSection, error: GLib.Error):