Questions: check if type is assignable to other

[lazarljubenovic]

Need a bit of help here: how do I check if types assignable to one other?

Scenario 1: I have two nodes, I can get their types via getType(). How do I check if A is assignable to B and if B is assignable to A?

Scenario 2: I have one node, and I want to check if it's assignable to custom type that I will conclude based on a string (template in a framework). To give context, user does something like (let's assume Angular syntax for familiarity) *ngIf="foo". In my framework, ngIf doesn't exist runtime and there's no boolean type anywhere where I can getType it -- so how can I create it? What about more complex cases?

I was expecting some Type constructors, but browsing through .d.ts files gives me nothing. Also assignable gives no results. I see the docs mention the type checker but I don't see anything useful there either based on method names.

Any pointers would be appreciated. 😄

[dsherret]

Yeah, this would be very useful. We probably have to wait for this issue to be resolved in the TypeScript compiler API: microsoft/TypeScript#9879

In the meantime, you might have to roll with your own implementation :(

[lazarljubenovic]

Wow, I was almost sure there was something in the TS API for this. How crazy would it to be to print two types, create a project with a single file, try the assignment and then type check the file? Do you think it would work?

[dsherret]

Haha! That would work. You could just create some temporary dummy file within your existing project then call dummyFile.delete() when you're done with it.

[cancerberoSgx]

@dsherret @lazarljubenovic I'm doing just that to test a type utility library where I need to check for failures . With tools like tsd-check that run at compile time you cannot make the test fail (cannot leave compile errors in the project)... so I did basically what you mention:

https://github.com/cancerberoSgx/tsd-check-runtime/

BTW is based on ts-simple-ast, sorry, ts-morph. I added lots of features but still its execution time is acceptable ... and I'm creating a new project for each test and emitting diagnostics, each time,