Microsoft/TypeScript

[ID-Prep] Explicit type annotation of const replaced with initializer in declaration emit

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#57,442 opened on Feb 19, 2024

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Domain: flag: isolatedDeclarationsHelp WantedPossible Improvement

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Description

The [ID-prep] set of issues aligns Declaration Emit with the forthcoming Isolated Declarations feature.

🔎 Search Terms

declarations type annotation const not preserved

🕗 Version & Regression Information

  • This is the behavior in every version I tried

⏯ Playground Link

Playground Link

💻 Code

enum E { "some value" = 1 };
const e: typeof E["some value"] = E["some value"];

🙁 Actual behavior

e is emitted in declarations as declare const e = E["some value"];

🙂 Expected behavior

e should have in declarations the type that was manually declared

Additional information about the issue

No response

Contributor guide

Research direction
Examine the declaration emit logic in TypeScript's checker.ts or binder.ts to understand why the explicit type annotation for const is replaced by the initializer when the type is a computed enum member. Focus on how 'typeof E["some value"]' is handled in emit.
Tech stack
typescript
Domain
compilers
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.
Half day
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Fresh
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
TypeScriptGit
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
50