#Proposal
Current emitted decorator metadata, only contains minimal typing information. My suggestion is to provide detailed information. Such as, nested type (generic type).

Example

1. resolve nested typing.

class A {
    @Foo
    propA: Map<string, Promise<number>>;
    @Bar
    propA: Map<string, Map<List<number>, boolean>>;
    @Baz
    methodA(): Map<Promise<number>, string>;
}

both @Foo's deisng:type and @Foo's design:returntype and each design:paramtypes should be the same.

resulting metadata:

@Foo: [Map, [string, [Promise, [number] ] ] ];
@Bar: [Map, [string, [Map, [ [List, [number] ] , boolean] ] ];
@Baz: [Map, [ [Promise, [number] ] , string] ];

logic:
for any generic type.
Type<...Arguments> -> [Type, [...Arguments]], recursively.

2. Retrieve parameter names

new metadata design:paramnames, in the same order of design:paramtypes.

3. ParamTypes and ParamNames for class decorators

@Foo
class A {
	propA: string;
	methodA(): number;
}

similar to deisng:paramtypes and design:paramnames of a method decorator. It retrieves paramter types and paramnames of each property and function even props were not assigned with a initial value. param type for a method should be Function in this case.