support for traceResolution

[mprinc]

Desired Behavior

Would be great if ts-node would support tsconfig's traceResolution and provide resolution repport

Is this request related to a problem?

Kind of: I cannot trace and debug the mapping and resolution problems

[cspotcode]

Can this flag be specified in a tsconfig file?

[mprinc]

Hi, @cspotcode It can, but ts-node is not respecting/recognizing it.

[cspotcode]

This ticket is marked "help wanted" to indicate that we will accept a pull request implementing this feature. To help you get started, here is some information about how traceResolution works internally:

TypeScript communicates with your host environment through a Host. This Host implements filesystem access and other input-output functions. There is a trace function on the host. If implemented, TypeScript is able to output tracing information by calling this function. ts-node does not currently provide an implementation of the trace function.

So to add support for trace output, you'll need to add an implementation of the trace function, ensuring we pass it via both the LanguageService and CompilerHost codepaths. Should be simple enough: console.log.bind(console)

We'll also need a test case. Probably you can take one of our existing tests, add traceResolution to its tsconfig, and then use a regexp to verify that the stdout includes tracing messages.

[mprinc]

So to add support for trace output, you'll need to add an implementation of the trace function, ensuring we pass it via both the LanguageService and CompilerHost codepaths. Should be simple enough: console.log.bind(console)

Thanks @cspotcode, could you provide the references in the ts-node codebase, please?

[cspotcode]

Here is where we create the LanguageServiceHost: https://github.com/TypeStrong/ts-node/blob/master/src/index.ts#L652
Here is where we create the CompilerHost: https://github.com/TypeStrong/ts-node/blob/master/src/index.ts#L790

TypeScript uses the "host" we give it for all interaction with the host environment, so as long as these hosts have a trace implementation, TypeScript should be able to log tracing messages.

We'll need tests to verify that it works before we can merge.

Thanks!