feat(attributes): expose ccRegisterBlockElements (#14)

Etherpad core's import-side content collector keeps its own
`_blockElems` set (`{div, p, pre, li}` by default), separate from
the editor's. `aceRegisterBlockElements` registers tags on the
editor side only -- so plugins built on `lineAttribute` /
`tagAttribute` (`ep_headings2`, `ep_subscript_and_superscript`,
etc.) tell the editor that `h1..h4` / `code` / `sub` / `sup` are
block elements but DON'T tell the importer.

Symptom: round-tripping a pad with `<h1>` / `<h2>` / `<code>` lines
through any HTML import path collapses adjacent heading-style
blocks into a single pad line. This just bit native DOCX export+
import in ether/etherpad#7568.

Fix: have `createLineAttribute` and `createTagAttribute` return a
`ccRegisterBlockElements` function with the same tag set as
`aceRegisterBlockElements`. Plugins re-export this from their
`ep.json` under `"ccRegisterBlockElements"` to register the same
tags on the import side.

Tests added for both factories.

Closes #13

Author: JohnMcLear

attributes.js

@@ -32,6 +32,16 @@ const createLineAttribute = (config) => {
 
   const aceRegisterBlockElements = () => tags;
 
+  // Server-side counterpart of aceRegisterBlockElements. Etherpad core's
+  // import-side content collector keeps its own `_blockElems` set
+  // separate from the editor's, so plugins that want their custom block
+  // tags treated as block elements on import (so adjacent ones don't
+  // merge into a single pad line) need to register them on the server
+  // side too. A plugin that uses `lineAttribute({tags: [...]})` should
+  // re-export this hook from its `ep.json` under
+  // `"ccRegisterBlockElements"`.
+  const ccRegisterBlockElements = () => tags;
+
   const collectContentPre = (hookName, context, cb) => {
     const tname = context.tname;
     const lineAttributes = context.state.lineAttributes;
@@ -60,6 +70,7 @@ const createLineAttribute = (config) => {
     aceDomLineProcessLineAttributes,
     aceRegisterBlockElements,
     aceRegisterLineAttributes,
+    ccRegisterBlockElements,
     collectContentPre,
     collectContentPost,
   };
@@ -122,6 +133,16 @@ const createTagAttribute = (config) => {
 
   const aceRegisterBlockElements = () => tags;
 
+  // Server-side counterpart of aceRegisterBlockElements. Etherpad core's
+  // import-side content collector keeps its own `_blockElems` set
+  // separate from the editor's, so plugins that want their custom block
+  // tags treated as block elements on import (so adjacent ones don't
+  // merge into a single pad line) need to register them on the server
+  // side too. A plugin that uses `lineAttribute({tags: [...]})` should
+  // re-export this hook from its `ep.json` under
+  // `"ccRegisterBlockElements"`.
+  const ccRegisterBlockElements = () => tags;
+
   const collectContentPre = (hookName, context, cb) => {
     const tname = context.tname;
     if (tags.includes(tname)) {
@@ -138,6 +159,7 @@ const createTagAttribute = (config) => {
     aceAttribClasses,
     aceAttribsToClasses,
     aceRegisterBlockElements,
+    ccRegisterBlockElements,
     collectContentPre,
     collectContentPost,
   };

test/attributes.js

@@ -56,6 +56,17 @@ describe('lineAttribute', () => {
     });
   });
 
+  describe('ccRegisterBlockElements', () => {
+    it('returns the tags array (server-side counterpart)', () => {
+      assert.deepStrictEqual(headings.ccRegisterBlockElements(), tags);
+    });
+
+    it('is exposed alongside aceRegisterBlockElements', () => {
+      assert.strictEqual(typeof headings.ccRegisterBlockElements, 'function');
+      assert.strictEqual(typeof headings.aceRegisterBlockElements, 'function');
+    });
+  });
+
   describe('collectContentPre', () => {
     it('sets line attribute for matching tag', () => {
       const state = {lineAttributes: {}};
@@ -198,6 +209,12 @@ describe('tagAttribute', () => {
     });
   });
 
+  describe('ccRegisterBlockElements', () => {
+    it('returns the tags array (server-side)', () => {
+      assert.deepStrictEqual(subSup.ccRegisterBlockElements(), ['sub', 'sup']);
+    });
+  });
+
   describe('collectContentPre', () => {
     it('calls doAttrib for matching tag', () => {
       let called = null;