Contextual typing is wrong in nested function calls.

[dpeter99]

🔎 Search Terms

I have run into the following issue while working on a schema lib.
https://tsplay.dev/w1eekw
The type of varaible d is any for some reason, at line 78.
On the discord it was suggested that this is a compiler bug.
https://discord.com/channels/508357248330760243/1428318052205854720/1432271574689517660

🕗 Version & Regression Information

• This is the behavior in every version I tried: 5.9.3, 5.8.3, 5.7.3

⏯ Playground Link

https://tsplay.dev/w1eekw

💻 Code

// Your code here

🙁 Actual behavior

The type of the d param in the lambda is any.

🙂 Expected behavior

It should be of type User

Additional information about the issue

No response

[RyanCavanaugh]

Please reduce this to something minimal

[Andarist]

The repro ain't that bad if we just drop the irrelevant runtime code: TS playground

It is a design limitation. It boils down to what is described in this comment:

        // When a call to a generic function is an argument to an outer call to a generic function for which
        // inference is in process, we have a choice to make. If the inner call relies on inferences made from
        // its contextual type to its return type, deferring the inner call processing allows the best possible
        // contextual type to accumulate. But if the outer call relies on inferences made from the return type of
        // the inner call, the inner call should be processed early. There's no sure way to know which choice is
        // right (only a full unification algorithm can determine that), so we resort to the following heuristic:
        // If no type arguments are specified in the inner call and at least one call signature is generic and
        // returns a function type, we choose to defer processing. This narrowly permits function composition
        // operators to flow inferences through return types, but otherwise processes calls right away. We
        // use the resolvingSignature singleton to indicate that we deferred processing. This result will be
        // propagated out and eventually turned into silentNeverType (a type that is assignable to anything and
        // from which we never make inferences).
        if (checkMode & CheckMode.SkipGenericFunctions && !node.typeArguments && callSignatures.some(isGenericFunctionReturningFunction)) {
            skippedGenericFunction(node, checkMode);
            return resolvingSignature;
        }

We can somewhat easily verify this is relevant because the issue gets "fixed" if we add a dummy signature to MTypeBase (TS playground):

interface MTypeBase<TSource, TValue> {
  id: string;
  getter: Getter<TSource, TValue>;
+(...args: never): unknown
}

This makes the code defer resolving this inner call (as described in the comment)

[typescript-bot]

This issue has been marked as "Design Limitation" and has seen no recent activity. It has been automatically closed for house-keeping purposes.