Microsoft/TypeScript

Template string literal highlighting breaks on ternary operator with typeof

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#42,793 opened on Feb 13, 2021

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 (0 comments) (0 reactions) (0 assignees)TypeScript (48,455 stars) (6,726 forks)batch import
BugDomain: Something ElseHelp Wanted

Description

Bug Report

🔎 Search Terms

template string literal highlighting

🕗 Version & Regression Information

VSCode 1.53.2 + TypeScript 4.1.5

⏯ Playground Link

Workbench Repro

Workbench Repro

💻 Code

function HighlightingWorksFineHere(): void {}
`${0 ? typeof 0 ? 0 : 0 : 0}`;
function ButHereItIsBroken(): void {}

function HighlightingWorksFineHere(): void {}
`${0 ? typeof 0 : 0}`;
function ButHereItIsBroken(): void {}

🙁 Actual behavior

Highlighting breaks after template literal with ternary operator and typeof in VSCode (seems fine in playground though), looks like the closing backtick is not recognized or treated as opening backtick.

1 2

Contributor guide

Tech stack
typescript
Domain
developer experiencetooling
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
tokenizationsyntax highlightingTypeScript language service
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
30
Research direction
The bug is in template literal string highlighting when a ternary operator with typeof is used. Likely the issue is in the TypeScript language service's tokenizer or scanner. Start by examining the scanner code in `src/services/scanner.ts` or `src/compiler/scanner.ts` to see how template literals are tokenized. Look for handling of ternary expressions inside template substitutions. There are no linked PRs or comments. Add a test case reproducing the broken highlighting to the language service's test suite.