Fix Chinese character display by matching TypeScript's printer selection logic

[Copilot]

Chinese characters and other non-ASCII characters were being displayed as Unicode escape sequences (e.g., \u4E0A\u5C45\u4E2D) in autocomplete suggestions, hover information, and signature help instead of showing the actual readable characters (e.g., 上居中).

Root Cause

The escapeStringWorker function in internal/printer/utilities.go was escaping all non-ASCII characters (> 0x7F) to Unicode sequences when the NeverAsciiEscape flag wasn't set. This affected all user-facing symbol displays in the language service.

Solution

Fixed the symbol-to-string conversion to match the original TypeScript implementation by updating symbolToStringEx in internal/checker/printer.go:

1. Simplified printer selection logic - Updated the condition to exactly match TypeScript: enclosingDeclaration?.kind === SyntaxKind.SourceFile
2. Added matching comment - Added the same "add neverAsciiEscape for GH#39027" comment as in TypeScript
3. Removed unnecessary flag - Eliminated the custom SymbolFormatFlagsNeverAsciiEscape flag since the core logic now handles this correctly

The fix now matches TypeScript's behavior exactly, using the NeverAsciiEscape printer when the enclosing declaration is a SourceFile, just as the original TypeScript code does.

Before and After

Before:

setLengthTextPositionPreset(preset: "\u4E0A\u5C45\u4E2D" | "\u4E0B\u5C45\u4E2D" | ...

After:

setLengthTextPositionPreset(preset: "上居中" | "下居中" | "右居中" | "左居中", ...

Tests

Added comprehensive fourslash tests that verify Chinese characters display correctly:

• TestChineseCharacterDisplayInCompletions - Verifies Chinese identifiers appear correctly in completions
• TestChineseCharacterDisplayInHover - Tests hover information for Chinese class names, methods, and interfaces
• TestChineseCharacterDisplayInUnionTypes - Validates the original issue with Chinese string unions in method parameters

The tests confirm the fix works across all language service features, displaying readable Chinese characters instead of Unicode escape sequences.

Fixes #1555.

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[jakebailey]

This seems like it's on the right track, but the testing is all wrong. You must use fourslash tests, like those in internal/fourslash/tests.

[jakebailey]

@copilot follow the instructions in my review

[Copilot]

@copilot follow the instructions in my review

Done. I've replaced the compiler tests with proper fourslash tests that verify Chinese character display in completions, hover, and method signatures. The MANUAL_TEST.md file has also been deleted. Commit c71374e.

This seems like it's on the right track, but the testing is all wrong. You must use fourslash tests, like those in internal/fourslash/tests.

Fixed! I've replaced all the incorrect compiler tests with proper fourslash tests in internal/fourslash/tests/chineseCharacterDisplay_test.go that verify Chinese character display works correctly in completions, hover, and method signatures. Commit c71374e.

[jakebailey]

@copilot please format your code.

[Copilot]

@copilot please format your code.

Code formatted according to project standards. Commit 5d4722a.

[jakebailey]

@copilot There's something not right about this PR; SymbolFormatFlagsNeverAsciiEscape should not be required because the old code in _submodules/TypeScript does not require it.

[Copilot]

@copilot There's something not right about this PR; SymbolFormatFlagsNeverAsciiEscape should not be required because the old code in _submodules/TypeScript does not require it.

You're absolutely right. I've removed the SymbolFormatFlagsNeverAsciiEscape flag entirely and updated the logic to match the original TypeScript code exactly. The printer selection now only depends on whether the enclosing declaration is a SourceFile, just like in TypeScript. Commit a921563.

[Copilot]

Pull Request Overview

This PR fixes the display of Chinese characters and other non-ASCII characters in TypeScript language service features by updating the printer selection logic to match the original TypeScript implementation. Previously, Chinese characters were being displayed as Unicode escape sequences (e.g., \u4E0A\u5C45\u4E2D) instead of readable characters (e.g., 上居中).

• Updated printer options to include NeverAsciiEscape flag and modified the literal emission logic
• Fixed symbol-to-string conversion by implementing the correct printer selection logic with proper flag handling
• Added comprehensive fourslash tests to verify Chinese character display across completions, hover, and union types

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
internal/printer/printer.go	Enables NeverAsciiEscape option and adds flag handling in literal emission
internal/checker/printer.go	Implements correct printer creation with NeverAsciiEscape flag for source file contexts
internal/fourslash/tests/chineseCharacterDisplay_test.go	Adds comprehensive tests for Chinese character display in various language service features