https://issues.dlang.org/show_bug.cgi?id=24255

          Issue ID: 24255
           Summary: Can't deduce parameter type of function literal used
                    as argument in IFTI
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: normal
          Priority: P1
         Component: dmd
          Assignee: nobody@puremagic.com
          Reporter: snarwin+bugzilla@gmail.com

As of DMD 2.105.3, the following program fails to compile:

---
void fun(T)(T t, void function(T) f) {}

void main()
{
    fun(123, (x) {});
}
---

The error message is:

---
bug.d(5): Error: template `bug.fun` is not callable using argument types
`!()(int, void)`
bug.d(1):        Candidate is: `fun(T)(T t, void function(T) f)`
---

Since the compiler can deduce that T is int from the argument 123, it should be
able to further deduce that the argument (x) {} has type void function(int).

--