emitDecoratorMetadata does not preserve array types on fields

[arciisine]

TypeScript Version: 2.1.1 / nightly (2.2.0-dev.201xxxxx)
All Typescript Versions

Code

class Post {
     tags: string[];
}

Expected behavior:
There should be metadata added to indicate the type of array.

class Post {
   constructor() {}
}
__decorate([
    __metadata('design:type', [String])
], Post.prototype, "tags", void 0);

Actual behavior:

class Post {
   constructor() {}
}
__decorate([
    __metadata('design:type', Array)
], Post.prototype, "tags", void 0);

If you look at how rest parameters are handled, there is precedent for preserving array type:

Given:

class Post {
     tags: string[];
     constructor(...tags:string[]) {}
}

The output is:

class Post {
   constructor() {}
}
__decorate([
    __metadata('design:type', Array)
], Post.prototype, "tags", void 0);
Post = __decorate([    
    __metadata('design:paramtypes', [String])
], Post);

[arciisine]

@rbuckton It looks like you have done a great deal of the work on the file (src/compiler/transformers/ts.ts). Do you know if PRs would be accepted for this change, or if this change is even acceptable?

[arciisine]

So after thinking about this for a bit, I realized that the param types is actually reducing string[] to String to handle the variadic arguments. Would it be possible to treat the array as a generic class? Array<string>, and perhaps store all generic types in the metadata?

[DanielRosenwasser]

Closing as a duplicate of #3015.