[lexical-extension] Bug Fix: Use maybeFromEditor in getPeerDependencyFromEditor

[potatowagon]

Summary

Fixes a crash introduced by #8360, which moved code block escape logic into CodeNode.insertNewAfter() with a backward-compat fallback that calls getPeerDependencyFromEditor(). The fallback was intended to gracefully handle editors not built with buildEditorFromExtensions(), but getPeerDependencyFromEditor itself called LexicalBuilder.fromEditor(editor) — which throws when no builder is attached to the editor. This means the fallback path could never be reached, and pressing Enter inside a code block crashed the editor.

This affects every editor created with createEditor() directly, which includes all editors on www today.

Call chain before this fix

1. User presses Enter in a code block
2. Lexical calls CodeNode.insertNewAfter()
3. insertNewAfter calls getPeerDependencyFromEditor(editor, 'LexicalCode') to check if CodeExtension is registered
4. getPeerDependencyFromEditor calls LexicalBuilder.fromEditor(editor)
5. fromEditor internally calls maybeFromEditor(editor) which returns undefined (no builder attached)
6. fromEditor sees undefined and throws: "The given editor was not created with LexicalBuilder"
7. insertNewAfter never gets to evaluate the ! check or run the fallback — it has already crashed

With this fix

• Step 4 now calls LexicalBuilder.maybeFromEditor(editor) directly, which returns undefined instead of throwing
• The new if (!builder) return undefined early-returns gracefully
• Back in insertNewAfter, !undefined is truthy, so it enters the fallback branch and runs the old code block exit logic
• No crash

This aligns with the function's own JSDoc, which documents the editor parameter as one that "may have been built using extension" and the return type as | undefined.

Test plan

• Verified on www: the MLCShortcuts-e2e.js test that was failing now passes
• TypeScript type check passes (pnpm run tsc)

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Project	Deployment	Actions	Updated (UTC)
lexical	Ready	Preview, Comment	Apr 27, 2026 10:46am
lexical-playground	Ready	Preview, Comment	Apr 27, 2026 10:46am