Parsing errors when dealing with TypeScript Generics in a type parameter.

[TylorS]

Hello there!

I'm running into an edge case that seems to be regarding the way esbuild is parsing TypeScript syntax. Here's the real example I was attempting to utilize.

The Code in Question

The conditions required to trip on this error

The error seems to arise under 2 specific conditions. 1.) The function being called must be an accessed method call on a Namespaced Import or Object/Class in the form of Foo.bar() and 2.) The first type parameter provided to that method must also have its own generics defined for it.

The Error

The Workaround

Changing the code to the following will allow things to continue working, which I've gone ahead to use as a workaround for this issue.

The Reproduction case

I've tried to boil this down to a smaller reproduction case, and this appears to trip up the same exact error.

export declare const Test: {
  readonly service: <F>() => <T extends string>(tag: T) => { service: F; tag: T }
}

export const Foo = Test.service<<A>() => A>()('Foo')

[evanw]

Thanks for the report. I haven't investigated yet but I bet it's due to the << token, which needs to sometimes be interpreted as two < tokens instead. Here's a quick workaround that's simpler if you'd like to use it instead:

 export declare const Test: {
   readonly service: <F>() => <T extends string>(tag: T) => { service: F; tag: T }
 }
 
-export const Foo = Test.service<<A>() => A>()('Foo')
+export const Foo = Test.service</**/<A>() => A>()('Foo')

[mnassabain]

Recently had a similar problem. Rewriting my functions with the "function" syntax instead of the arrow syntax solved the problem for me.