[Flang] Incorrect diagnostic on procedure pointer actual argument

[DanielCChen]

Consider the following code:

module m
    contains

    function genF1 (i)
        procedure (real), pointer :: genF1
        integer :: i
    end function
end module

program fmisc043a
use m
    call test1(genF1(1))

    contains
    subroutine test1 (p)
        procedure(real), pointer :: p
    end subroutine
end

Flang is currently issue an error as

error: Semantic errors in t3.f
./t3.f:12:16: error: Actual argument associated with procedure pointer dummy argument 'p=' must be a pointer unless INTENT(IN)
      call test1(genF1(1))
                 ^^^^^^^^

The standard explicitly allows such a usage as [24-007: 15.5.2.10]

If a dummy argument is a procedure pointer, the corresponding actual argument shall be a procedure pointer, a
reference to a function that returns a procedure pointer, a reference to the intrinsic function NULL, or a valid
target for the dummy pointer in a pointer assignment statement.

[llvmbot]

@llvm/issue-subscribers-flang-frontend

Author: Daniel Chen (DanielCChen)

Consider the following code: ``` module m contains

function genF1 (i)
    procedure (real), pointer :: genF1
    integer :: i
end function

end module

program fmisc043a
use m
call test1(genF1(1))

contains
subroutine test1 (p)
    procedure(real), pointer :: p
end subroutine

end

Flang is currently issue an error as

error: Semantic errors in t3.f
./t3.f:12:16: error: Actual argument associated with procedure pointer dummy argument 'p=' must be a pointer unless INTENT(IN)
call test1(genF1(1))
^^^^^^^^

The standard explicitly allows such a usage as [24-007: 15.5.2.10]

If a dummy argument is a procedure pointer, the corresponding actual argument shall be a procedure pointer, a
reference to a function that returns a procedure pointer, a reference to the intrinsic function NULL, or a valid
target for the dummy pointer in a pointer assignment statement.

</details>

[eugeneepshteyn]

Yes, seems to be a bug. The very next sentence of the standard's quote above says "If the actual argument is not a pointer, the dummy argument shall have INTENT (IN)", which may explain where INTENT(IN) in the error message came from, but it doesn't apply here.

[klausler]

F'2023 15.5.2.10 p5: "If a dummy argument is a procedure pointer, the corresponding actual argument shall be a procedure pointer, a reference to a function that returns a procedure pointer, a reference to the intrinsic function NULL, or a valid
target for the dummy pointer in a pointer assignment statement. If the actual argument is not a pointer, the
dummy argument shall have INTENT (IN); if the actual argument is not a dummy argument it becomes pointer
associated with the actual argument, otherwise it becomes pointer associated with the ultimate argument of the
actual argument."

The text that I emphasized in the above quote is ambiguous. Does a reference to a function qualify as a pointer in this context? I suspect that it does, and that the requirement of INTENT(IN) applies only to actual arguments that are valid targets, but I think that it could also be read as applying to anything that is not a proper procedure pointer.

I'll change this to apply only to the last case (targets), but I am not confident that this is clearly correct.

[DanielCChen]

F'2023 15.5.2.10 p5: "If a dummy argument is a procedure pointer, the corresponding actual argument shall be a procedure pointer, a reference to a function that returns a procedure pointer, a reference to the intrinsic function NULL, or a valid target for the dummy pointer in a pointer assignment statement. If the actual argument is not a pointer, the dummy argument shall have INTENT (IN); if the actual argument is not a dummy argument it becomes pointer associated with the actual argument, otherwise it becomes pointer associated with the ultimate argument of the actual argument."

The text that I emphasized in the above quote is ambiguous. Does a reference to a function qualify as a pointer in this context? I suspect that it does, and that the requirement of INTENT(IN) applies only to actual arguments that are valid targets, but I think that it could also be read as applying to anything that is not a proper procedure pointer.

I'll change this to apply only to the last case (targets), but I am not confident that this is clearly correct.

Right, I see your point.
The standard does say the following for INTENT(OUT) and INTENT(INOUT)

Any actual argument that corresponds to such a dummy pointer shall
be a pointer variable or a procedure pointer that is not the result of a function reference.

So I think it should be the same for all non-definable actual argument, the check should be on the presence of those two intents rather than missing INTENT(IN).