Microsoft/TypeScript

Incorrect type declarations for a constant inside a namespace merged with an enum

Open

#61,944 opened on Jun 25, 2025

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 (1 comment) (2 reactions) (1 assignee)TypeScript (48,455 stars) (6,726 forks)batch import
BugDomain: Declaration EmitFix AvailableHelp Wanted

Description

🔎 Search Terms

"enum", "namespace", "declaration", "d.ts", "const"

🕗 Version & Regression Information

  • This changed between versions 3.1.0-dev.20180906 and 3.1.0-dev.20180907

⏯ Playground Link

https://www.typescriptlang.org/play/?#code/KYOwrgtgBAYg9nKBvAUFdUBGBDATigXxRGwmAGcAHbAY2FgWTQ2AA9K5cAXKGuEcjxwAvKAF4GcAHQ5cAbkIogA

💻 Code

enum Foo {
    bar
}
namespace Foo {
    export const baz = Foo.bar;
}

🙁 Actual behavior

Typescript generates invalid d.ts for the enum value assigned to the constant (in all versions starting 3.1.0-dev.20180907)

declare enum Foo {
    bar = 0
}
declare namespace Foo {
    const baz = bar; // <-- unknown `bar` identifier, `baz` type is `any`
}

In versions before 3.1.0-dev.20180906 the constant is declared as const baz: Foo;

🙂 Expected behavior

Typescript generates a valid declaration of the constant

declare enum Foo {
    bar = 0
}
declare namespace Foo {
    const baz = Foo.bar;
}

or

declare enum Foo {
    bar = 0
}
declare namespace Foo {
    const baz: Foo;
}

Additional information about the issue

No response

Contributor guide

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.
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.
active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
TypeScript declaration emissionenum and namespace merging
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
40
Research direction
Investigate the declaration emitter in TypeScript's compiler (likely src/compiler/emitter.ts or declarationEmitter.ts). The bug was introduced between versions 3.1.0 dev.20180906 and 3.1.0 dev.20180907, so examine the changes in declaration emission for enum+namespace merging. The expected behavior is that the constant 'baz' should reference 'Foo.bar' or have type 'Foo'. The current output references an unresolved 'bar'. Look for where the declaration emitter handles namespaced constants that reference enum members, and ensure the namespace qualifier is included.