Extensions: show a dialog when dropping a URL while offline

The dialog notifies the user that online access is required with a
button to go to the system preferences.

See #120665.

scripts/addons_core/bl_pkg/bl_extension_ops.py

@@ -2349,14 +2349,44 @@ class BlPkgShowOnlinePreference(Operator):
         return True
 
     def execute(self, context):
-        wm = context.window_manager
-        prefs = context.preferences
-
         bpy.ops.screen.userpref_show('INVOKE_DEFAULT', section='SYSTEM')
-
         return {'FINISHED'}
 
 
+# NOTE: this is a wrapper for `bl_pkg.extensions_show_online_prefs`.
+# It exists *only* show a dialog.
+class BlPkgShowOnlinePreferencePopup(Operator):
+    """Show system preferences "Network" panel to allow online access"""
+    bl_idname = "bl_pkg.extensions_show_online_prefs_popup"
+    bl_label = ""
+    bl_options = {'INTERNAL'}
+
+    def execute(self, context):
+        bpy.ops.screen.userpref_show('INVOKE_DEFAULT', section='SYSTEM')
+        return {'FINISHED'}
+
+    def invoke(self, context, event):
+        wm = context.window_manager
+        wm.invoke_props_dialog(
+            self,
+            width=400,
+            confirm_text="Go to Settings",
+            title="Install Extension",
+        )
+        return {'RUNNING_MODAL'}
+
+    def draw(self, context):
+        layout = self.layout
+        col = layout.column()
+        lines = (
+            "Please turn Online Access on the System settings.",
+            "",
+            "Internet access is required to install extensions from the internet."
+        )
+        for line in lines:
+            col.label(text=line)
+
+
 class BlPkgEnableNotInstalled(Operator):
     """Turn on this extension"""
     bl_idname = "bl_pkg.extensions_enable_not_installed"
@@ -2407,6 +2437,7 @@ classes = (
 
     BlPkgShowUpgrade,
     BlPkgShowOnlinePreference,
+    BlPkgShowOnlinePreferencePopup,
 
     # Dummy, just shows a message.
     BlPkgEnableNotInstalled,

source/blender/editors/space_userpref/userpref_ops.cc

@@ -859,18 +859,28 @@ static void PREFERENCES_OT_extension_repo_upgrade(wmOperatorType *ot)
 static int preferences_extension_url_drop_invoke(bContext *C, wmOperator *op, const wmEvent *event)
 {
   char *url = RNA_string_get_alloc(op->ptr, "url", nullptr, 0, nullptr);
-  const bool url_is_remote = STRPREFIX(url, "http://") || STRPREFIX(url, "https://") ||
-                             STRPREFIX(url, "file://");
+  const bool url_is_file = STRPREFIX(url, "file://");
+  const bool url_is_online = STRPREFIX(url, "http://") || STRPREFIX(url, "https://");
+  const bool url_is_remote = url_is_file | url_is_online;
 
   /* NOTE: searching for hard-coded add-on name isn't great.
    * Needed since #WM_dropbox_add expects the operator to exist on startup. */
   const char *idname_external = url_is_remote ? "bl_pkg.pkg_install" : "bl_pkg.pkg_install_files";
+  bool use_url = true;
+
+  if (url_is_online && (G.f & G_FLAG_INTERNET_ALLOW) == 0) {
+    idname_external = "bl_pkg.extensions_show_online_prefs_popup";
+    use_url = false;
+  }
+
   wmOperatorType *ot = WM_operatortype_find(idname_external, true);
   int retval;
   if (ot) {
     PointerRNA props_ptr;
     WM_operator_properties_create_ptr(&props_ptr, ot);
-    RNA_string_set(&props_ptr, "url", url);
+    if (use_url) {
+      RNA_string_set(&props_ptr, "url", url);
+    }
     WM_operator_name_call_ptr(C, ot, WM_OP_INVOKE_DEFAULT, &props_ptr, event);
     WM_operator_properties_free(&props_ptr);
     retval = OPERATOR_FINISHED;