Microsoft/TypeScript

Enum types are not checked in binary operators

Open

#3,845 opened on Jul 13, 2015

View on GitHub
 (5 comments) (0 reactions) (0 assignees)TypeScript (48,455 stars) (6,726 forks)batch import
Breaking ChangeBugDomain: enumHelp Wanted

Description

I ran into this for real while trying to fix a bug in the compiler. We disallow assigning one enum to another if you use the = operator. But we do not disallow it for any of the compound assignment operators. Nor do we disallow for bitwise operators. I think we should disallow all of them.

enum E { }
enum F { }

var e: E;
var f: F;

e = f; // Error
e |= f; // No error
var g = e | f; // No error, g is number

Contributor guide

Tech stack
typescript
Domain
tooling
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
Basic understanding of TypeScript's type systemFamiliarity with compiler source code
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
30
Research direction
The issue describes that enum type checking is missing for compound assignment operators (e.g., |=) and bitwise operators. To fix this, locate the type checking logic for binary operators in the TypeScript compiler, likely in checker.ts. Study how the '=' operator checks enum types and extend that logic to other operators. Check for any existing test cases for enum assignment to ensure consistency.