Added reflection support

[realglebivanov]

Hello! Currently i'm writing a library which uses properties custom reflection metadata.

The problem is that the metadata is lost due to prototype of prototype extension and I don't have a way to solve that problem except creating class decorator instead of property decorators.

I think there should be some possibility to clone that metadata in newly created class or so.
I will provide you a brief example.

@WithRender
@Component
export class TestComponent extends Vue {
    @Inject
    public service?: Service;
}

Metadata defined by @Inject decorator is lost. Possible solution is:

@Inject({service: Service})
@WithRender
@Component
export class TestComponent extends Vue {
    public service?: Service;
}

But I don't like it because idea is a property injection. Also, I'm thinking of lifecycle methods DI, but I'm not sure if it's useful.

[ktsn]

Thanks for your contribution!
Can we revert all changes to files under dist/ directly since it should only updated during publishing process?

[ktsn]

I'm not a fan of adding dependency that some users may not need as it bloats the lib size. Can we remove the dep and make this feature be optional?
I think only forwarding metadata when Reflect metadata is supported would work.

[realglebivanov]

That's reasonable, I'll fix it.

[ktsn]

Why do we need such temporary object and to process for it in different functions? Why don't we just directly assign the original metadata to component properties?

[realglebivanov]

Do you mean ComponentOptions? If you mean that, it's a tricky way because i don't want to change options interface and expose internal work of Component decorator.

[ktsn]

No, I don't mean that.
I mean why we need to store metadata in temporary object rather than just forward them directly on the place.
https://github.com/vuejs/vue-class-component/pull/227/files#diff-7db1d7c8dc88ce00d1aa236fa0c128ccR40
https://github.com/vuejs/vue-class-component/pull/227/files#diff-7db1d7c8dc88ce00d1aa236fa0c128ccR118

[realglebivanov]

Because forwarding code will be duplicated. If you okay with that, I'll do it in the way you are asking. Also, we don't have a new class object until almost the end of function.

[ktsn]

Well, then we can extract the logic as a function. I believe we can remove reflectionMap without duplication.

something like:

function forwardMetadata(to: typeof Vue, from: typeof Vue, propertyKey: string): void {
  Reflect.getOwnMetadataKeys(from, propertyKey).forEach(metaKey => {
    const metadata = Reflect.getOwnMetadata(metaKey, from, propertyKey)
    Reflect.defineMetadata(metaKey, metadata, to, propertyKey)
  })
}

Then we just call it inline:

  Object.getOwnPropertyNames(Original).forEach(key => {
     // `prototype` should not be overwritten
     if (key === 'prototype') {
       return
     }
 	 
-    reflectionMap.static[key] = Reflect.getOwnMetadataKeys(Original, key);
+    forwardMetadata(Extended, Original, key)

     // Some browsers does not allow reconfigure built-in properties
     const extendedDescriptor = Object.getOwnPropertyDescriptor(Extended, key)
     if (extendedDescriptor && !extendedDescriptor.configurable) {

  forwardStaticMembersAndCollectReflection(Extended, Component, Super, reflectionMap)
-  copyReflectionMetadata(Component, Extended, reflectionMap)
+  Object.getOwnPropertyNames(proto).forEach(key => {
+    forwardMetadata(Extended.prototype, proto, key)
+  })

[ktsn]

I think we don't need this if we directly forward metadata and remove reflectionMap.

[ktsn]

Sorry, I overlooked somethings. Can you fix the code format to follow the existing one (indent space 2, and no-semicolons)?

[realglebivanov]

Thank you for your quick responses. Of course i can fix codestyle.

[realglebivanov]

Done.

Review this PR, please.

[304NotModified]

Done.

bump @ktsn

[ktsn]

Thank you for your contribution.