[flang-commits] [flang] [flang] Safer hermetic module file reading (PR #121002)

[via flang-commits]

jeanPerier wrote:

The patch removed the ambiguous error about the module, but more advanced scenarios where subroutine/variable are referred are still causing semantic errors.

Example:

```
! my_mpi.f90

module my_mpi
! version 1.0
implicit none
integer :: my_mpi_var = 1
contains
subroutine some_mpi_subroutine
  print *, my_mpi_var
end subroutine
end module
```

```
! my_lib.f90 
module my_lib
  use my_mpi
  implicit none
contains
subroutine some_lib_subroutine
  print *, my_mpi_var
  call some_mpi_subroutine()
end subroutine
end module
```

```
my_mpi_v2.f90 
module my_mpi
! version 2.0 that is backward compatible (only adding things).
implicit none
integer :: my_mpi_var = 1
integer :: my_mpi_new_var
contains
subroutine some_mpi_subroutine
  print *, my_mpi_var
end subroutine
end module
```

```
! main.f90
main.f90 
  use my_mpi
  use my_lib
  implicit none
  print *, my_mpi_var
  call some_lib_subroutine()
  call some_mpi_subroutine()
end
```

build script:
```
FC=flang

# Build library with MY_MPI version 1.
rm -rf my_mpi.o my_mpi.mod
$FC -c my_mpi.f90
rm -rf my_lib.o my_lib.mod
$FC -c -fhermetic-module-files my_lib.f90

# Build application with MY_MPI version 2.
rm -rf my_mpi.o my_mpi.mod
$FC -c my_mpi.f90
$FC -c my_mpi_v2.f90 -o my_mpi.o

$FC main.f90 my_lib.o my_mpi.o
```

With this patch, I am getting the following semantic errors:
```
error: Semantic errors in main.f90
./main.f90:4:12: error: Reference to 'my_mpi_var' is ambiguous
    print *, my_mpi_var
             ^^^^^^^^^^
./main.f90:1:7: 'my_mpi_var' was use-associated from module 'my_mpi'
    use my_mpi
        ^^^^^^
./main.f90:2:7: 'my_mpi_var' was use-associated from module 'my_lib'
    use my_lib
        ^^^^^^
./main.f90:6:8: error: Reference to 'some_mpi_subroutine' is ambiguous
    call some_mpi_subroutine()
         ^^^^^^^^^^^^^^^^^^^
./main.f90:1:7: 'some_mpi_subroutine' was use-associated from module 'my_mpi'
    use my_mpi
        ^^^^^^
./main.f90:2:7: 'some_mpi_subroutine' was use-associated from module 'my_lib'
    use my_lib
```

https://github.com/llvm/llvm-project/pull/121002