Better handling for manually created source files and compiler APIs

Search Terms

type checker source file cannot ready property 'members' of undefined

Suggestion

When a user of the compiler API manually creates a source file with ts.createSourceFile instead of retrieving it from their program, and then asks the program for type inference on a contained node, this can crash. See https://github.com/Microsoft/TypeScript/issues/8136 / https://github.com/vuejs/vue-cli/issues/2712 / https://github.com/angular/tsickle/issues/151 / https://github.com/general-language-syntax/TS-GLS/issues/39.

It seems like one of three interpretations might be best:

• This is explicitly unsupported behavior, but for the sake of performance & simplicity, no checks should happen
• This is explicitly unsupported behavior, and a more explicit error should be thrown
• This should become supported behavior, and the program should dynamically create source files as requested

Use Cases

Auto-generated TypeScript files, such as .vue snippets, still want access to a type checker, such as for TSLint rules.

Examples

https://github.com/palantir/tslint/issues/4273

Checklist

My suggestion meets these guidelines:

• 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. new expression-level syntax)

Start by reproducing the crash with ts.createSourceFile and a program type-checker query on a node from the manually created file. Review the linked issues and determine whether this behavior should be unsupported, fail explicitly, or be supported dynamically. Done requires a decided API behavior and corresponding implementation and validation.