Microsoft/TypeScript

Suggestion: output fewer errors for incorrectly implemented interface

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#10,077 opened on Aug 1, 2016

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 (1 comment) (0 reactions) (0 assignees)TypeScript (48,455 stars) (6,726 forks)batch import
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Description

TypeScript Version: nightly

Code

interface A {
    f(): void;
}
class B implements A {
    eff() {}
}

var b: B;
b.f();
b.f();
b.f();

Expected behavior:

src/a.ts(4,7): error TS2420: Class 'B' incorrectly implements interface 'A'.
  Property 'f' is missing in type 'B'.

Actual behavior:

src/a.ts(4,7): error TS2420: Class 'B' incorrectly implements interface 'A'.
  Property 'f' is missing in type 'B'.
src/a.ts(9,3): error TS2339: Property 'f' does not exist on type 'B'.
src/a.ts(10,3): error TS2339: Property 'f' does not exist on type 'B'.
src/a.ts(11,3): error TS2339: Property 'f' does not exist on type 'B'.

There can be an overwhelming number of missing-property errors if a commonly-used class mis-implements an interface it declares.

Contributor guide

Tech stack
typescript
Domain
developer experiencetooling
Issue type
feature
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.
half day
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
TypeScriptcompiler error handling
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
60
Research direction
Investigate the TypeScript compiler's error reporting mechanism for interface implementation. The relevant code is likely in the checker.ts file where type compatibility errors are generated. Focus on how the compiler can avoid reporting redundant property missing errors after the initial interface implementation error. Look at existing error suppression patterns in the compiler for similar cases.
Suggestion: output fewer errors for incorrectly implemented interface · Microsoft/TypeScript#10077 | Good First Issue