Fix format selection deleting comments when selection ends inside comment trivia

[Copilot]

Format Selection deletes block comments when the selection range ends inside the comment. For example, selecting any part of the comment (except the closing /) in const test/* comment */=5; and formatting deletes the comment entirely, producing const test =5;.

Root cause

In consumeTokenAndAdvanceScanner, previousRangeTriviaEnd is set to the end of all trailing trivia unconditionally. When a block comment in the trailing trivia extends past originalRange.End(), processTrivia correctly skips it (not fully contained by the range), but previousRangeTriviaEnd still points past the comment. This makes the trailing edit contiguity check in execute() think previousRange and the next token are adjacent, causing processPair to emit an edit that spans—and deletes—the unprocessed comment.

Fix

In consumeTokenAndAdvanceScanner, after setting previousRangeTriviaEnd, cap it before any comment trivia that is not contained by originalRange. This prevents the contiguity check from pairing across unprocessed comment content, while still allowing legitimate trailing edits when only non-comment trivia (e.g., newlines) extends past the range.

// In consumeTokenAndAdvanceScanner, after setting previousRangeTriviaEnd:
for _, trivia := range currentTokenInfo.trailingTrivia {
    if isComment(trivia.Kind) && !trivia.Loc.ContainedBy(w.originalRange) {
        w.previousRangeTriviaEnd = trivia.Loc.Pos()
        break
    }
}

• internal/format/span.go: Cap previousRangeTriviaEnd before unprocessed comment trivia in consumeTokenAndAdvanceScanner
• internal/format/comment_test.go: Regression tests for format selection preserving block comments

Original prompt

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This section details on the original issue you should resolve

<issue_title>[bug] JS/TS Format Selection can delete comments</issue_title>
<issue_description>### Extension Version

0.20251214.1

VS Code Version

1.107.0

Operating system Version

Windows 11

Steps to reproduce

1. open a javascript or typescript file
2. create a block comment in such a way that a space will be inserted next to it when formatting

const test/* comment */=5;

3. select any part of the comment (except the ending /)
4. right click => Format Selection

5. comment gets deleted ❌

const test =5;

Issue

Format Selection can delete comments

• [bug] JS/TS Format Selection can delete comments TypeScript#57741</issue_description>

<agent_instructions>Write a test for this FIRST. COMMIT THAT! Then, fix the bug</agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes [bug] JS/TS Format Selection can delete comments #2382

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[jakebailey]

@copilot you must not have run the tests. you broke formatSelectionEditAtEndOfRange_test

[Copilot]

@copilot you must not have run the tests. you broke formatSelectionEditAtEndOfRange_test

Fixed in 82bec94. The previous fix was too broad — it blocked all trailing edits when any trivia extended past the range, including legitimate cases like newline trivia in the semicolon-removal test.

Moved the fix to consumeTokenAndAdvanceScanner instead: when setting previousRangeTriviaEnd, it now caps it before any comment trivia not contained by originalRange. This way newline trivia (like in formatSelectionEditAtEndOfRange) still allows the trailing edit, but unprocessed comment trivia blocks it. Verified all format selection gen tests pass (including formatSelectionEditAtEndOfRange).