[lexical-markdown] Bug Fix: don't emit a dangling closing tag when a selection slices a format to whitespace

[luantaraschi]

Description

exportTextFormat decides two different things from two different strings, and a selection export can make them disagree.

Whether the node carries a format comes from checkHasFormat, which reads the node's whole text and rejects nodes that are entirely whitespace:

if (n && /^\s*$/.test(n.getTextContent())) {
  return false;
}

Whether the tags are actually emitted comes from isWhitespaceOnly, computed from the textContent argument, which on the selection path is the node sliced down to the selected range:

if (isWhitespaceOnly && !node.hasFormat('code')) {
  return closingTagsBefore + output;
}

When a selection slices a formatted node down to whitespace, the first check passes and the second one fires. The tag is pushed onto unclosedTags but the opening tag is thrown away by the early return, so the next node closes a tag that was never opened.

Two bold text nodes, 'a ' and 'b', with the selection running from offset 1 of the first through the second:

$convertSelectionToMarkdownString(TRANSFORMERS, $getSelection())
// '  b**', expected '  **b**'

The ** at the end has no opener, so the output is not valid markdown.

The opening-tag registration is now skipped when the exported text is whitespace-only. The early return already discards those tags, so registering them had no effect other than corrupting the shared unclosedTags list. The following node then sees no pending **, opens its own, and closes it.

This does not change the full-document path: there textContent is the node's whole text, so isWhitespaceOnly can only be true when checkHasFormat already returned false for every format.

Test plan

Before

FAIL packages/lexical-markdown/src/__tests__/unit/LexicalMarkdown.test.ts
  > $convertSelectionToMarkdownString whitespace slices
    > does not emit a dangling closing tag when the selection slices a format down to whitespace

AssertionError: expected '  b**' to be '  **b**'

After

Test Files  1 passed (1)
     Tests  417 passed (417)

Full vitest run: 5251 passed, 2 skipped. The two failures are in scripts/__tests__/unit/childProcess.test.ts and are about shell env forwarding on Windows. They reproduce on a clean main with this change stashed, so they are not related to it.

pnpm run prettier and pnpm run tsc are clean.

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Project	Deployment	Actions	Updated (UTC)
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