fix(lexical-html): $generateHtmlFromNodes should self-establish active-editor scope (back-compat for #8519)

[potatowagon]

Summary

PR #8519 (commit a6908ba) made $setTextContent in packages/lexical/src/nodes/LexicalTextNode.ts call $getEditor() at the top of the function. Because $generateHtmlFromNodes walks TextNode.createDOM/updateDOM → $setTextContent, it now throws inside any caller that uses the previously-idiomatic editor.getEditorState().read(cb) scope — getActiveEditor() returns null and the call dies with an opaque "getActiveEditor" invariant error.

Since $generateHtmlFromNodes already receives editor as its first argument, it can self-establish the active-editor scope.

Changes

• $generateHtmlFromNodes: wraps its body in editor.read(...), which is a no-op if an active editor scope already exists (nested reads are safe in Lexical).
• $generateDOMFromNodes: same treatment for consistency.
• $generateDOMFromRoot: same treatment for consistency.

This makes all three export functions work correctly regardless of whether the caller uses:

• editor.read(cb) (modern pattern — already sets active editor) ✅
• editor.getEditorState().read(cb, {editor}) (explicit editor option) ✅
• editor.getEditorState().read(cb) (legacy pattern — does NOT set active editor) ✅ ← previously broken after [Breaking Change][lexical][lexical-html][lexical-selection][lexical-utils][lexical-playground] Feature: Generalize DOMSlot and add DOMRenderExtension override surface #8519

Test Plan

Added LexicalHtmlBackwardCompat.test.ts with three tests:

1. Calls $generateHtmlFromNodes(editor) from inside editor.getEditorState().read(cb) (legacy pattern) — asserts it returns HTML without throwing.
2. Calls from inside editor.read(cb) (modern pattern) — asserts same behavior.
3. Asserts both patterns produce identical output (no behavioral divergence).

All 84 existing tests in packages/lexical-html continue to pass unchanged.

[vercel]

The latest updates on your projects. Learn more about Vercel for GitHub.

Project	Deployment	Actions	Updated (UTC)
lexical	Ready	Preview, Comment	May 29, 2026 2:28pm
lexical-playground	Ready	Preview, Comment	May 29, 2026 2:28pm

[zurfyx]

Stamping to unblock internal sync but would love to have @etrepum's thoughts here

[mayrang]

Thanks @potatowagon — will follow up after this lands to extend the same back-compat treatment to $generateDOMFromNodes / $generateDOMFromRoot.

[etrepum]

$generateDOMFromRoot and $generateDOMFromNodes are newer functions and don’t need this legacy workaround

[etrepum]

I think the best solution is a private LexicalUpdates API like this that we export through the lexical package for internal backwards compat use:

/** @internal */
export function $assumeActiveEditor(editor: LexicalEditor): void {
  // Throw if called outside of an update
  if (getActiveEditorState() !== null && activeEditor === null) {
    activeEditor = editor;
  }
  invariant(
    activeEditor === editor,
    'The given editor argument does not match $getEditor() in this context. Use editor.getEditorState().read(..., {editor}) if this cross-editor call is intentional.',
  );
}

Then you would just call $assumeActiveEditor(editor) in the $generateHtmlFromNodes call as the workaround (pushed an implementation)