Fix format selection deleting comments when selection ends inside comment trivia by Copilot · Pull Request #3159 · microsoft/typescript-go

Copilot · 2026-03-19T06:27:50Z

Write test for format selection deleting comments when selection ends inside a comment
Fix the bug in consumeTokenAndAdvanceScanner to cap previousRangeTriviaEnd before unprocessed comment trivia
Verify formatSelectionEditAtEndOfRange test still passes
Address review comments: strengthen assertions to exact equality, fix misleading comments, rename subtest

Original prompt

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

open a javascript or typescript file

create a block comment in such a way that a space will be inserted next to it when formatting
const test/* comment */=5;
select any part of the comment (except the ending /)

right click => Format Selection

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

✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.

…nside comment Co-authored-by: jakebailey <5341706+jakebailey@users.noreply.github.com>

…ment trivia When the selection range ends inside a block comment (e.g., selecting part of /* comment */ in const test/* comment */=5;), the trailing edit block's contiguity check would incorrectly pass because previousRangeTriviaEnd was set to the end of the comment (beyond the selection range). This caused processPair to generate edits that replaced the comment text between previousRange and the next token, effectively deleting the comment. The fix adds an additional guard: previousRangeTriviaEnd must not exceed originalRange.End() for the trailing edit to proceed. When trivia extends beyond the selection range, it was not actually processed, so any edit spanning that trivia would be bogus. Co-authored-by: jakebailey <5341706+jakebailey@users.noreply.github.com>

jakebailey · 2026-03-19T18:35:54Z

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

…ectionEditAtEndOfRange The previous fix added a bounds check in the trailing edit block that was too broad - it blocked legitimate trailing edits when non-comment trivia (like newlines) extended past the original range. The new fix is in consumeTokenAndAdvanceScanner: when setting previousRangeTriviaEnd, cap it before any comment trivia that extends past the original range. This way, the contiguity check in execute() correctly fails for unprocessed comments but still works for legitimate cases like semicolon removal where only newline trivia extends past. Co-authored-by: jakebailey <5341706+jakebailey@users.noreply.github.com>

Copilot · 2026-03-19T19:13:44Z

@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).

Copilot

Pull request overview

Fixes a formatter bug in the Go port’s format selection path where a selection ending inside trailing block-comment trivia could cause the comment to be deleted due to an incorrect “contiguous tokens” check.

Changes:

Adjust consumeTokenAndAdvanceScanner to cap previousRangeTriviaEnd before any trailing comment trivia that is not fully contained by the original selection range.
Add regression tests covering format-selection ranges that start/end inside a block comment, plus a sanity check for full-document formatting.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
internal/format/span.go	Prevents trailing-edit pairing across unprocessed (out-of-range) trailing comment trivia.
internal/format/comment_test.go	Adds regression coverage to ensure format selection doesn’t delete block comments.

Copilot · 2026-04-06T23:44:22Z

+		// Select a range that starts at the beginning of the line and ends inside the comment
+		// "const test/* comment" - selecting up to but not including the closing "*/"
+		// The comment "/* comment */" starts at position 10 and ends at position 24
+		// We select up to position 22 (inside the comment, before "*/)
+		commentStart := strings.Index(originalText, "/*")
+		selectionEnd := commentStart + len("/* comment") // ends inside the comment


The comment describing comment start/end positions appears incorrect for const test/* comment */=5; (and the quoted "*/) is missing a closing quote). This makes the test harder to trust/maintain; consider either removing the hard-coded positions or correcting them based on the actual string indices / ranges used in the test.

Suggested change

// Select a range that starts at the beginning of the line and ends inside the comment

// "const test/* comment" - selecting up to but not including the closing "*/"

// The comment "/* comment */" starts at position 10 and ends at position 24

// We select up to position 22 (inside the comment, before "*/)

commentStart := strings.Index(originalText, "/*")

selectionEnd := commentStart + len("/* comment") // ends inside the comment

// Select a range that starts at the beginning of the line and ends inside the block comment.

// This covers `const test/* comment`, stopping before the closing `*/`.

// Compute the comment start from the actual source text rather than relying on hard-coded positions.

commentStart := strings.Index(originalText, "/*")

selectionEnd := commentStart + len("/* comment") // ends inside the comment, before the closing `*/`

Copilot · 2026-04-06T23:44:22Z

+	t.Run("full document format should preserve block comment and add spaces", func(t *testing.T) {
+		t.Parallel()
+		ctx := format.WithFormatCodeSettings(t.Context(), &lsutil.FormatCodeSettings{
+			EditorSettings: lsutil.EditorSettings{
+				TabSize:                4,
+				IndentSize:             4,
+				BaseIndentSize:         0,
+				NewLineCharacter:       "\n",
+				ConvertTabsToSpaces:    true,
+				IndentStyle:            lsutil.IndentStyleSmart,
+				TrimTrailingWhitespace: true,
+			},
+		}, "\n")
+
+		originalText := `const test/* comment */=5;`
+
+		sourceFile := parser.ParseSourceFile(ast.SourceFileParseOptions{
+			FileName: "/test.ts",
+			Path:     "/test.ts",
+		}, originalText, core.ScriptKindTS)
+
+		edits := format.FormatDocument(ctx, sourceFile)
+		formatted := applyBulkEdits(originalText, edits)
+
+		// Full document format should preserve the comment and add proper spacing
+		assert.Check(t, strings.Contains(formatted, "/* comment */"), "full format should preserve the block comment")
+		assert.Check(t, strings.Contains(formatted, "test"), "should preserve identifier")
+	})


This subtest name says it verifies that formatting "adds spaces", but the assertions only check that the comment/identifier are preserved. Either assert the expected spacing (or exact output), or rename the subtest to reflect what it actually checks.

Copilot · 2026-04-06T23:44:22Z

+		edits := format.FormatSelection(ctx, sourceFile, 0, selectionEnd)
+		formatted := applyBulkEdits(originalText, edits)
+
+		// The comment should be preserved
+		assert.Check(t, strings.Contains(formatted, "/* comment */"), "format selection should not delete the block comment")
+		assert.Check(t, strings.Contains(formatted, "test"), "should preserve identifier")
+	})


The format-selection regression assertions are fairly loose (e.g., they only check that /* comment */ and sometimes test are present). This could still pass if other important parts of the statement (like =5;) are accidentally deleted or reordered. Consider strengthening the assertions to include the rest of the statement (or assert an exact expected result).

jakebailey · 2026-04-06T23:45:38Z

@copilot address review comments

- Replace loose Contains checks with exact assert.Equal for all three format-selection subtests, ensuring the entire statement is verified - Fix misleading comment about hard-coded positions; use computed positions from strings.Index (already done in code, fixed in comments) - Rename "full document format should preserve block comment and add spaces" to just "...preserve block comment" since no spaces are added Agent-Logs-Url: https://github.com/microsoft/typescript-go/sessions/9945b15e-7056-43e7-aacb-d12f4c1285e3 Co-authored-by: jakebailey <5341706+jakebailey@users.noreply.github.com>

Copilot · 2026-04-06T23:54:19Z

@copilot address review comments

Addressed all three review comments in 11fd998:

Fixed misleading hard-coded position comments — now describes what the computed strings.Index positions represent, with a clear note about stopping before */.
Renamed "full document format should preserve block comment and add spaces" → "...preserve block comment" since no spaces are actually added.
Replaced all loose strings.Contains assertions with exact assert.Equal checks against originalText, so any accidental deletion or reordering of statement parts (like =5;) will be caught.

Copilot

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Initial plan

7030a2a

Copilot AI assigned Copilot and jakebailey Mar 19, 2026

Copilot started work on behalf of jakebailey March 19, 2026 06:27 View session

Copilot AI and others added 2 commits March 19, 2026 06:43

Add test for format selection deleting comments when selection ends i…

63698dc

…nside comment Co-authored-by: jakebailey <5341706+jakebailey@users.noreply.github.com>

Copilot AI changed the title ~~[WIP] [bug] Fix JS/TS format selection deleting comments~~ Fix format selection deleting comments when selection ends inside comment trivia Mar 19, 2026

Copilot AI requested a review from jakebailey March 19, 2026 06:47

Copilot finished work on behalf of jakebailey March 19, 2026 06:47

Copilot started work on behalf of jakebailey March 19, 2026 18:36 View session

Copilot finished work on behalf of jakebailey March 19, 2026 19:15

jakebailey marked this pull request as ready for review April 6, 2026 23:40

Copilot AI review requested due to automatic review settings April 6, 2026 23:40

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Copilot started work on behalf of jakebailey April 6, 2026 23:45 View session

Copilot finished work on behalf of jakebailey April 6, 2026 23:54

jakebailey requested a review from Copilot April 16, 2026 23:25

Copilot started reviewing on behalf of jakebailey April 16, 2026 23:38 View session

Copilot AI reviewed Apr 16, 2026

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RyanCavanaugh added this to the TypeScript 7.0 RC milestone Apr 17, 2026

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Fix format selection deleting comments when selection ends inside comment trivia#3159

Fix format selection deleting comments when selection ends inside comment trivia#3159
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Copilot AI commented Mar 19, 2026 •

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