Adjust folding range end lines for lineFoldingOnly clients

[Copilot]

• Investigate the issue: VS Code folding ranges are different/worse with tsgo
• Root cause: The VS Code TypeScript extension applies adjustFoldingEnd when converting outlining spans to FoldingRange - it subtracts 1 from endLine when the range ends with a closing pair character (}, ], ), `, >). The Go LSP server returns FoldingRanges directly without this adjustment, causing VS Code (which hides endLine) to also hide the closing bracket line.
• Implement adjustFoldingEnd in internal/ls/folding.go that mirrors the VS Code TypeScript extension's behavior
• Apply the adjustment when client signals lineFoldingOnly: true
• Add VerifyFoldingRangeLines method to fourslash test framework
• Add integration test verifying the lineFoldingOnly adjustment
• Add integration test verifying #region folding works correctly with lineFoldingOnly
• Run existing tests to verify no regressions
• Run full test suite - all tests pass
• Run linter and formatter - no issues
• Code review and security check - no issues

Original prompt

---

This section details on the original issue you should resolve

<issue_title>VSCode: code folding ranges</issue_title>
<issue_description>The collapsible ranges in typescript-native w/ TypeScript (Native Preview) extension are different (and far worse) than the current stable versions

Steps to reproduce

if (EMPTY_TAGs.has(tag)) {
  output += "/>";
} else {
  output += ">";

  if (!html && kidcount > 0) {
    //
  }
}

export function use<T>(ctx: Value<T>): T | undefined {
  // 
}

Behavior with typescript@6.0

Behavior with tsgo

Versions

typescriptteam.native-preview @ 0.20260212.1
@typescript/native-preview @ 7.0.0-dev.20260212.1
```</issue_description>

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

<comments>
</comments>

• Fixes VSCode: code folding ranges #2771

---

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[jakebailey]

LGTM:

[Copilot]

Pull request overview

This PR aligns the Go language server’s folding range behavior with VS Code’s lineFoldingOnly semantics, preventing closing braces/brackets/tags from being hidden when a fold is applied (matching the stable TypeScript extension behavior referenced in vscode#47240).

Changes:

• Adjust folding range endLine for lineFoldingOnly clients when the fold ends on a closing pair character (}, ], ), `, >).
• Add fourslash helper VerifyFoldingRangeLines to assert folding behavior using only start/end lines.
• Add an integration test covering the reported reproduction case with lineFoldingOnly: true.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
internal/ls/folding.go	Applies lineFoldingOnly end-line adjustment to keep closing delimiters visible when folding.
internal/fourslash/fourslash.go	Adds a line-only folding range verifier for lineFoldingOnly scenarios.
internal/fourslash/tests/foldingRangeLineFoldingOnly_test.go	New fourslash integration test validating adjusted end lines for nested blocks/functions.

[DanielRosenwasser]

I guess I'll link to microsoft/vscode#281660 as well

[DanielRosenwasser]

Suggested change

	// When lineFoldingOnly is true, VS Code hides lines from startLine+1 to endLine. To keep closing
	// brackets/braces visible, we subtract 1 from endLine when the range ends with a closing pair character.
	// When lineFoldingOnly is true, we hide lines from startLine+1 to endLine. And to keep closing
	// brackets/braces visible, we subtract 1 from endLine when the range ends with a closing pair character.

[Copilot]

Applied in 0959ea3.

[DanielRosenwasser]

Did you test this out on #region comments?

[jakebailey]

I didn't, no. @copilot Address the above comments, including adding a test which uses regions too.

[Copilot]

I didn't, no. @copilot Address the above comments, including adding a test which uses regions too.

Added TestFoldingRangeLineFoldingOnlyWithRegions in 0959ea3. The #region/#endregion spans end with n (not a closing pair character), so adjustFoldingEnd correctly leaves them untouched. The test verifies that region spans keep their original end lines while code blocks within regions (like function foo() {}) still get adjusted.

[jakebailey]

Seems fine?

But, maybe you wanted it to leave the end?

[jakebailey]

Tested, and the above is what Strada in VS Code does, so this PR I think is fine. Note: https://github.com/microsoft/vscode/blob/b5f3937f1211ce4b8ee7f614645b88a6464a9cb0/extensions/typescript-language-features/src/languageFeatures/folding.ts#L58

[DanielRosenwasser]

I guess they can't intersect anyway, but it was probably good to have something here.

[DanielRosenwasser]

Needs a format I guess