This would be even nicer if TypeScript added type inference for tagged template literals, like in this issue [1]. Then you could write:

    const schema = proto`
      syntax = "proto3";

      message Person { ... }
    `;

    type Person = typeof schema['Person'];

And you could get built-in schema validation with a sophisticated enough type definition for `proto`, nice syntax highlighting in many tools with a nested grammar.

We would love to see this feature in TypeScript to be able to have type-safe template in lit-html without an external tool.

The issue hasn't seen much activity lately, but it would be good to highlight this library as another use case.

[1]: https://github.com/microsoft/TypeScript/issues/33304