Microsoft/TypeScript

Language Service: TypeParameter.constraint is lazily calculated, but does not have an accessor function

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#5,689 opened on Nov 16, 2015

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BugDomain: APIHelp Wanted

Description

Because of this, I have to go through this awkward motion every time:

function getConstraint( type: ts.TypeParameter ) {
  // This call will cause the typechecker to resolve properties, as well as a bunch of other information
  // about the type (such as generic constraints), but we don't actually need its result right now.
  type.getProperties(); 

  return type.constraint;
}

For some members (such as "properties" - above), there is an accessor function, which I can use to be sure the data is up to date. Another category of members don't need an accessor function, because they are calculated eagerly, and so are "always there".

But there is this third category of members, which fall through the gap. One example is TypeParameter.constraint. Another is InterfaceTypeWithDeclaredMembers.declaredProperties. There are probably more, but I haven't come across them yet.

Contributor guide

Tech stack
typescript
Domain
toolingdeveloper experience
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.
1-2 days
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.
mostly clear
Prerequisites
Understanding of TypeScript compiler internalsFamiliarity with lazy vs eager property computation
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
30
Research direction
Examine the TypeScript compiler source to identify other lazily calculated members like `TypeParameter.constraint` and `InterfaceTypeWithDeclaredMembers.declaredProperties`. Define an accessor pattern similar to `getProperties()` for each lazy member. Ensure the accessor triggers calculation and updates the property. Test with existing type checker code. The issue has no linked PRs or recent activity, so this is a design proposal.
Language Service: TypeParameter.constraint is lazily calculated, but does not have an accessor function · Microsoft/TypeScript#5689 | Good First Issue