Mangled (unbound) type-parameter names in merged declarations

[chocolateboy]

keywords: alias, dollar, dollars, interface, mangle, mangled, mangling, name, naming, parameter, rename, undeclared

System

• rollup-plugin-ts: 1.3.8
• typescript: 4.1.3
• node: v14.15.4
• OS: Linux (Arch)

Description

I'm getting unbound type-parameters in a declaration file generated for an index.ts entry which exports types from two modules. The exports have overlapping parameter names but don't reference each other or conflict in any way. Rather than preserving the original type-parameter names, new (undeclared) names are used in the body of the declaration, which results in the following error:

Cannot find name 'T$0'.

The unbound parameter names are of the form <letter><dollar><number>, e.g. T$0, R$0. These names aren't used in the code, and aren't generated for the standalone modules, only for the merged index declaration. I can't reproduce this with tsc, but then it doesn't merge the declarations.

Reproduction

• https://github.com/chocolateboy/rollup-plugin-ts-issue

Expected Behavior

interface Foo {
    <T, R>(value: T, fn: (value: T) => R): R;
}

declare const foo: Foo;

interface Bar {
    <T, R>(value: T, fn: (value: T) => R): R;
}

declare const bar: Bar;

export { foo, bar };

Actual Behavior

interface Foo {
    <T, R>(value: T, fn: (value: T) => R): R;
}

declare const foo: Foo;

interface Bar {
    // XXX error: Cannot find name 'T$0'.
    // XXX error: Cannot find name 'R$0'.
    <T, R>(value: T$0, fn: (value: T$0) => R$0): R$0;
}

declare const bar: Bar;

export { foo, bar };

See Also

• May be related to wrong d.ts generated when importing same name classes with alias #136.

[wessberg]

Hey there. Thanks for the repro, and sorry for the late follow-up. This problem was caused by the deconflicting layer of the declaration bundler that didn't handle CallSignatureDeclarations. I've added support for nodes of that kind in this commit and it will be published to npm as soon as possible.