Add option to always inline .json type import

[maxpatiiuk]

🔍 Search Terms

json type import inline library resolveJsonModule

✅ Viability Checklist

• This wouldn't be a breaking change in existing TypeScript/JavaScript code
• This wouldn't change the runtime behavior of existing JavaScript code
• This could be implemented without emitting different JS based on the types of the expressions
• This isn't a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, new syntax sugar for JS, etc.)
• This isn't a request to add a new utility type: https://github.com/microsoft/TypeScript/wiki/No-New-Utility-Types
• This feature would agree with the rest of our Design Goals: https://github.com/Microsoft/TypeScript/wiki/TypeScript-Design-Goals

⭐ Suggestion

Add a tsconfig.json option to force .json type imports to inline the inferred .json type, rather than preserve .json import inside emitted .d.ts

or always inline without introducing a new option

or enable #resolveJsonModule by default

📃 Motivating Example

JSON type imports are a very convenient feature for getting a type of localization strings to get intellisense when dealing with translation strings:

// The .json for correct locale will be loaded at runtime - but we need a type at compile time
import type T9nStrings from "../assets/t9n/messages.en.json";

However, as a library author, that presents two issues because TypeScript may preserve the above type import in the .d.ts file:

• Unless every consumer has #resolveJsonModule enabled, their typescript will error out when trying to resolve the .json type import from my .d.ts
• I need to make sure the above .json file is also accessible relative to the final .d.ts file I distribute in dist/

💻 Use Cases

1. What do you want to use this for?
   • I want to use .json type imports for getting types of translation files and configuration files
2. What shortcomings exist with current approaches?
   • the .json type import is inlined some of the time only. when not inlined, it can break my consumers
3. What workarounds are you using in the meantime?
   • the following hack seems to trigger typescript to always inline the .json file rather than preserve the type import:

import type T9nStrings from "./assets/t9n/messages.en.json";
const identity = <T>(value: T): T => value;
const messages = identity<typeof T9nStrings>;
type Messages = ReturnType<typeof messages>;

related issues:

• Flattening types in generated .d.ts files for libraries #60647
• resolveJsonModule doesn't copy source file when located within node_modules subdirectory #43940

[MartinJohns]

• This feature would agree with the rest of our Design Goals: https://github.com/Microsoft/TypeScript/wiki/TypeScript-Design-Goals

Technically it goes against goal 7:

Preserve runtime behavior of all JavaScript code.

And one could argue non-goal 4:

Provide an end-to-end build pipeline. Instead, make the system extensible so that external tools can use the compiler for more complex build workflows.