[flang] Allocate object must be conformable with the `SOURCE=` in an ALLOCATE statement

[DanielCChen]

Consider the following code

    type base
        real      :: r1
    end type

    type (base), allocatable :: b1(:)
    type (base) :: b2 (10)

    b2 = base(10.0)

    allocate (b1(5), source=(/(b2(j),j=10,6)/))  !<-- this is illegal
end

The shape of the SOURCE= expr is 0 while the shape of the allocate object is 5.
It is not conforming to the standard. All ifort, gfortran and XLF issues an error.
Is this an intentional extension for Flang?

[llvmbot]

@llvm/issue-subscribers-flang-frontend

Author: Daniel Chen (DanielCChen)

Consider the following code ``` type base real :: r1 end type

type (base), allocatable :: b1(:)
type (base) :: b2 (10)

b2 = base(10.0)

allocate (b1(5), source=(/(b2(j),j=10,6)/))  !<-- this is illegal

end

The shape of the `SOURCE=` expr is 0 while the shape of the allocate object is `5`.
It is not conforming to the standard. All ifort, gfortran and XLF issues an error.
Is this an intentional extension for Flang?
</details>

[klausler]

It is not an extension; will add code to check at runtime.