[FIX] web_editor, website: allow links to unreachable pages

Since commit [1] removed `legacyRejectPromiseHandler()`, trying to edit
a link leading to an HTTP error triggers an "Uncaught Promise" error.
This commit makes sure such links do not cause a traceback: the link
popover is just less detailed (no title, favicon).

[1]: https://github.com/odoo/odoo/commit/fcb16a3b1bd373726ffb54f0fbe41fb6d1784769

task-3584686

closes odoo/odoo#141225

Signed-off-by: Quentin Smetz (qsm) <qsm@odoo.com>

addons/web_editor/static/src/js/wysiwyg/widgets/link_popover_widget.js

@@ -261,6 +261,13 @@ export class LinkPopoverWidget {
                     this.$urlLink.text(ogTitle ? ogTitle.getAttribute('content') : title.text.trim());
                 }
                 this.$fullUrl.removeClass('d-none').addClass('o_we_webkit_box');
+            }).catch(error => {
+                // HTML error codes should not prevent to edit the links, so we
+                // only check for proper instances of Error.
+                if (error instanceof Error) {
+                    return Promise.reject(error);
+                }
+            }).finally(() => {
                 this.$target.popover('update');
             });
         }

addons/website/static/tests/tours/link_tools.js

@@ -305,9 +305,24 @@ wTourUtils.registerWebsitePreviewTour('link_tools', {
         trigger: "iframe .s_text_image p a[href='/contactus']:contains('/contactus')",
         run: () => null,
     },
+    // 11. Add a link leading to a 404 page
+    {
+        content: "Enter a non-existent URL",
+        trigger: "#o_link_dialog_url_input",
+        run: "text /this-address-does-not-exist",
+    },
+    {
+        content: "Check that the link's href was updated and click on it",
+        trigger: "iframe .s_text_image p a[href='/this-address-does-not-exist']",
+    },
+    {
+        content: "Check popover content is up-to-date",
+        trigger: "iframe .popover div a:contains('/this-address-does-not-exist')",
+        isCheck: true,
+    },
     ...wTourUtils.clickOnSave(),
     ...wTourUtils.clickOnEditAndWaitEditMode(),
-    // 11. Add mega menu with Cards template and edit URL on text-selected card.
+    // 12. Add mega menu with Cards template and edit URL on text-selected card.
     wTourUtils.clickOnElement("menu link", "iframe header .nav-item a"),
     wTourUtils.clickOnElement("'Edit menu' icon", "iframe .o_edit_menu_popover .fa-sitemap"),
     {