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Compiler API - Type parameter constraint and default always undefined #20137
Description
TypeScript Version: 2.7.0-dev.2011118
Code
Test code:
let t: <T extends string = string>() => void;Compiler code:
const type = ...; // get type of VariableDeclaration
const signature = type.getCallSignatures()[0];
const typeParam = signature.getTypeParameters()[0];
typeParam.constraint; // undefined
typeParam.default; // undefinedExpected behavior: A string type will be returned for both.
Actual behavior: Always returns undefined.
typescript.d.ts says the following:
interface TypeParameter extends TypeVariable {
/** Retrieve using getConstraintFromTypeParameter */
constraint: Type;
default?: Type;
}Problems
- Both properties are always undefined (from why I've tried).
getConstraintFromTypeParameterdoes not exist anywhere in the compiler api.constraint: Typeshould have a question token.
Workaround
- Get type's symbol.
- Get symbol's type parameter declaration.
- Get type via type checker from type parameter declaration's constraint and default nodes (if they exist).
Activity
mhegazy commentedon Nov 20, 2017
We need to make these internal and instead expose
getDefaultandgetConstrainton aTypeObject.[-]Compiler API - Signature constraint and default always undefined[/-][+]Compiler API - Type parameter constraint and default always undefined[/+]dsherret commentedon Nov 29, 2017
Thanks guys!