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import*asreflectfrom'jsii-reflect';// Version ^1.5.0exporttypeApiElement=reflect.Type|reflect.TypeMember|reflect.EnumMember;exportinterfaceData{readonlyelement: ApiElement;}// Note: reflect.Method and reflect.Initializer both directly or indirectly implement reflect.TypeMemberexportfunctiondoSomething<Textends(reflect.Method|reflect.Initializer)>(element: T): Data{if(reflect.Method.isMethod(element)){// Type 'T & Method' is not assignable to type 'Type'.return{ element };}if(reflect.Initializer.isInitializer(element)){// Type 'T & Initializer' is not assignable to type 'Type'.return{ element };}// Type checking absolutely fine - why'd previous ones not?return{ element };}
Expected behavior:
It should work like it did in TypeScript 3.8
Actual behavior:
$ tsc --build
lib/index.ts:13:14 - error TS2322: Type 'T & Method' is not assignable to type 'ApiElement'.
Type 'T & Method' is not assignable to type 'Type'.
12 return { element };
~~~~~~~
lib/index.ts:6:12
6 readonly element: ApiElement;
~~~~~~~
The expected type comes from property 'element' which is declared here on type 'Data'
lib/index.ts:17:14 - error TS2322: Type 'T & Initializer' is not assignable to type 'ApiElement'.
Type 'T & Initializer' is not assignable to type 'Type'.
16 return { element };
~~~~~~~
lib/index.ts:6:12
6 readonly element: ApiElement;
~~~~~~~
The expected type comes from property 'element' which is declared here on type 'Data'
TypeScript Version: 3.9.2, 4.0.0-dev.20200512
Search Terms: TS2322, "is not assignable to type"
Code
Expected behavior:
It should work like it did in TypeScript 3.8
Actual behavior:
Playground Link: I stored my repro at https://github.com/RomainMuller/TypeScript39-Bug (public)
Related Issues: It appears likely related to the breaking change in #37195 (but not certain)