Microsoft/TypeScript

Middle operand in comma operator list not properly checked for side-effect-freeness

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#33,646 opened on Sep 27, 2019

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BugDomain: Error MessagesHelp Wanted

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Description

TypeScript Version: master at f304b81fa54285f Search Terms: comma side effects

Code

declare const obj: any;
console.log(`${JSON.stringify(obj), undefined, 2}`);

Expected behavior: error TS2695: Left side of comma operator is unused and has no side effects.

Actual behavior: No errors

Playground Link: http://www.typescriptlang.org/play/#code/CYUwxgNghgTiAEYD2A7AzgF3kgRgKwC54oUBPAbgChl0kIQA6CJAcwAoADAEgG8ApAMoB5AHINMMAJYoWkgGak2uPAEoANPACuKUHOkhgGgEwBfDiqpA

Related Issues: #10814

Contributor guide

Research direction
Inspect the comma operator side effect checking logic in the TypeScript checker (checker.ts). The issue reports that the middle operand in a comma list is not checked for side effect freeness. Look for where comma operator expressions are validated and ensure all operands except the last are checked.
Tech stack
typescript
Domain
backenddeveloper experience
Issue type
Bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
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.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
TypeScript
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
70