[Flang] (Semantic check?) Incorrect error message when using the same name in interfaces and external statements

[UsmanNadeem]

The standard states:

Only one appearance of a name in all of the EXTERNAL statements in a scoping unit is permitted. A name that
appears in an EXTERNAL statement must not also appear as a specific procedure name in an interface block in
the scoping unit.

I was testing a piece of code (from NumPy) that works fine on Gfortran but did not compile with Flang. I have put a small test case here.
Consider the following two functions where we violate this constraint:

function foo1()
    external bar1

    interface
        function bar1(value) result (r)
            integer, intent(in) :: value
        end function bar1
    end interface
end function foo1

function foo2(bar2)
    external bar2

    interface
        function bar2(value) result (r)
            integer, intent(in) :: value
        end function bar2
    end interface
end function foo2

On flang the errors dont make much sense:

error: Semantic errors in /app/example.f90
/app/example.f90:5:18: error: 'bar1' was previously called as a subroutine
          function bar1(value) result (r)
                   ^^^^
/app/example.f90:2:14: Previous call of 'bar1'
      external bar1
               ^^^^
/app/example.f90:15:18: error: 'bar2' is already declared in this scoping unit
          function bar2(value) result (r)
                   ^^^^
/app/example.f90:11:15: Previous declaration of 'bar2'
  function foo2(bar2)
                ^^^^
Compiler returned: 1

Surprisingly, Gfortran is successfully able to compile the second file but we get an appropriate error Error: Duplicate EXTERNAL attribute specified for the first file: https://godbolt.org/z/oKq14a9Kz

Would it be possible to change the error message to something appropriate? Doing so will make debugging much easier.

[llvmbot]

@llvm/issue-subscribers-flang-frontend

[pscoro]

@UsmanNadeem Could I get this issue assigned to me? Thanks

[pscoro]

Complete and landed