UX: prosemirror rich editor nodes cleanup / slightly better UX (#32361)

We don't want "ghost" `content` within mention/hashtag, as they're
already rendering their non-editable content on `toDOM`.

`atom: true` is not necessary for content-less nodes

Re-use existing heading node spec instead of re-creating.

A UX improvement from these changes is a better Cmd-Left/Home navigation
when these nodes begin a paragraph and the caret is after them.

app/assets/javascripts/discourse/app/static/prosemirror/extensions/hashtag.js

@@ -7,8 +7,6 @@ const extension = {
       attrs: { name: {} },
       inline: true,
       group: "inline",
-      content: "text*",
-      atom: true,
       draggable: true,
       selectable: false,
       parseDOM: [
@@ -53,7 +51,9 @@ const extension = {
     span_open(state, token, tokens, i) {
       if (token.attrGet("class") === "hashtag-raw") {
         state.openNode(state.schema.nodes.hashtag, {
-          name: tokens[i + 1].content.slice(1),
+          // this is not ideal, but working around the span_open/close structure
+          // a text is expected just after the span_open token
+          name: tokens.splice(i + 1, 1)[0].content.slice(1),
         });
         return true;
       }

app/assets/javascripts/discourse/app/static/prosemirror/extensions/heading.js

@@ -1,23 +1,11 @@
+import { schema } from "prosemirror-markdown";
+
 /** @type {RichEditorExtension} */
 const extension = {
   nodeSpec: {
     heading: {
-      attrs: { level: { default: 1 } },
+      ...schema.nodes.heading.spec,
-      // Overriding ProseMirror's default to allow inline content
       content: "inline*",
-      group: "block",
-      defining: true,
-      parseDOM: [
-        { tag: "h1", attrs: { level: 1 } },
-        { tag: "h2", attrs: { level: 2 } },
-        { tag: "h3", attrs: { level: 3 } },
-        { tag: "h4", attrs: { level: 4 } },
-        { tag: "h5", attrs: { level: 5 } },
-        { tag: "h6", attrs: { level: 6 } },
-      ],
-      toDOM(node) {
-        return ["h" + node.attrs.level, 0];
-      },
     },
   },
 };

app/assets/javascripts/discourse/app/static/prosemirror/extensions/mention.js

@@ -8,8 +8,6 @@ const extension = {
       attrs: { name: {} },
       inline: true,
       group: "inline",
-      content: "text*",
-      atom: true,
       draggable: true,
       selectable: false,
       parseDOM: [
@@ -55,7 +53,7 @@ const extension = {
       getAttrs: (token, tokens, i) => ({
         // this is not ideal, but working around the mention_open/close structure
         // a text is expected just after the mention_open token
-        name: tokens[i + 1].content.slice(1),
+        name: tokens.splice(i + 1, 1)[0].content.slice(1),
       }),
     },
   },

app/assets/javascripts/discourse/app/static/prosemirror/extensions/onebox.js

@@ -15,7 +15,6 @@ const extension = {
       attrs: { url: {}, html: {} },
       selectable: true,
       group: "block",
-      atom: true,
       draggable: true,
       parseDOM: [
         {
@@ -44,7 +43,6 @@ const extension = {
       inline: true,
       group: "inline",
       selectable: true,
-      atom: true,
       draggable: true,
       parseDOM: [
         {

plugins/discourse-local-dates/assets/javascripts/lib/rich-editor-extension.js

@@ -5,7 +5,6 @@ const extension = {
     local_date: {
       attrs: { date: {}, time: {}, timezone: { default: null } },
       group: "inline",
-      atom: true,
       inline: true,
       parseDOM: [
         {
@@ -42,7 +41,6 @@ const extension = {
         timezone: { default: null },
       },
       group: "inline",
-      atom: true,
       inline: true,
       parseDOM: [
         {