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ahejlsberg avatar ahejlsberg commented on March 29, 2024

Changing to spec issue. The new compiler supports merging of all module declarations, including ambient external module declarations. I see no reason why we should only allow merging of internal modules and specifically disallow merging of ambient external modules. In particular, declaration files sometimes extend existing internal modules and may want to do exactly that for ambient external modules.

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sophiajt avatar sophiajt commented on March 29, 2024

From design meeting: agreed this should merge just like internal modules.

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sophiajt avatar sophiajt commented on March 29, 2024

Leaving open so we can make the text change to the spec

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iislucas avatar iislucas commented on March 29, 2024

When I run this code in typescript I get

ldixon/foo.ts(4,16): error TS2000: Duplicate identifier '"fs"'. Additional locations:
    ldixon/foo.ts(1,16)
ldixon/foo.ts(4,16): error TS2191: Ambient external module declaration cannot be reopened.

Sounds like the correct behaviour is no errors. Would be great to have an npm publish of a version with this fixed :)

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basarat avatar basarat commented on March 29, 2024

agreed this should merge just like internal modules.

DT actually needs this. Thanks guys (/cc @Bartvds @vvakame will possibly make non-instantiated modules less necessary)

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spion avatar spion commented on March 29, 2024

It seems like this doesn't work if the module is exported by assignment?

declare module "m" {
  function inner(s: string);
  module inner { export interface Test {t: string;} }
  export = inner //error here
}

declare module "m" {
  // even though we're only extending already existing submodule
  module inner { export interface Other { t: number; } }
}

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RyanCavanaugh avatar RyanCavanaugh commented on March 29, 2024

@spion The name inner is not "shared" between declarations here -- when there's an export =, all other declarations inside that module declaration are considered to not be visible at all

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spion avatar spion commented on March 29, 2024

@RyanCavanaugh I see. The original problem is express.d.ts

https://github.com/DefinitelyTyped/DefinitelyTyped/blob/master/express/express.d.ts

Here, express exposes a namespace Express to let us extend Request. Unfortunately those extensions cannot contain types imported from ambient external modules, which means they're of limited use. However, since express-the-module is also a function, the only way to declare the module is to use declaration merging then write export = module at the end, so we can't use declaration merging for ambient external modules either.

I'll open a separate issue.

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