Template literal types with decorator crashes in emit

[AdrianAbramczyk]

Bug Report

🔎 Search Terms

Template literal type annotation

🕗 Version & Regression Information

• This is a crash
• This is the behavior in every version I tried, and I reviewed the FAQ for entries about annotation / literal.

⏯ Playground Link

Playground link with relevant code (See console)

💻 Code

import "reflect-metadata";

const formatMetadataKey = Symbol("format");

function format(formatString: string) {
  return Reflect.metadata(formatMetadataKey, formatString);
}

class Greeter {
  // Here : Can't use a literal type with an annotation
  @format("Hello, %s")
  greeting: `${string}`;
  
  constructor() {
    this.greeting = '#XXXX';
    console.log('this.greeting', this.greeting);
  }
}

new Greeter();

🙁 Actual behavior

When using a template literal type with an annotation I get the following error in the console :

Error: Debug Failure. Unexpected node.
Node TemplateLiteralType was unexpected

Because the template literal type is not currently supported :

TypeScript/src/compiler/transformers/ts.ts

Line 1541 in 68ff738

return Debug.failBadSyntaxKind((node as LiteralTypeNode).literal);

🙂 Expected behavior

I should not get an error.

[a-tarasyuk]

@rbuckton How should the TemplateLiteralType be serialized?

__metadata("design:type", ????)

For instance union type serialized as Object

class A {
    @dec
    foo: string | number;
}

__metadata("design:type", Object)

/cc @RyanCavanaugh @andrewbranch

[rbuckton]

Probably as String, since it can only represent a string type.

[DanielRosenwasser]

Thanks @a-tarasyuk!