[Flang] Compile error when an ancestor module is referenced within submodule via USE statement

[ohno-fj]

Version of flang : 22.0.0(7761a89e1230d8ccbb8e6ee15dc14ea74792a53c)/AArch64

The attached program (test01.f90) contains module (mod) and submodule (smod) that extends this module (mod). Within module subroutine sub section following CONTAINS statement in submodule (smod), the ancestor module (mod) is referenced via USE statement.

According to Fortran Standard 2023 14.2.2 The USE statement and use association, it states: A module shall not reference itself, either directly or indirectly.
and according to Fortran Standard 2023 5.2.1 Program units and scoping units, it states: The module or submodule containing a module subprogram is the host scoping unit of the module subprogram.

I believe this program does not fall under the above specification.
The scope extends only to the definitions of declared procedures, which is separate from the module's program unit, and I do not believe it falls under the above.
Therefore, the compilation error of Flang appears to be incorrect.
Is my interpretation of this specification incorrect?

The following are the test program, Flang-new, Gfortran and ifx compilation/execution result.

test01.f90:

module mod
  integer:: var=1
  interface
    module subroutine sub
    end
  end interface
end

submodule (mod) smod
  integer:: var=100
  contains
  module subroutine sub
  use mod
   print *,var
  end
end

use mod
call sub
print *,'pass'
end

$ flang test01.f90
error: Semantic errors in test01.f90
./test01.f90:13:7: error: Module 'mod' cannot USE itself from its own submodule 'smod'
    use mod
        ^^^
$

$ gfortran test01.f90; ./a.out
           1
 pass
$

$ ifx test01.f90
test01.f90(12): error #6406: Conflicting attributes or multiple declaration of name.   [SUB]
  module subroutine sub
--------------------^
compilation aborted for test01.f90 (code 1)
$

[llvmbot]

@llvm/issue-subscribers-flang-frontend

Author: ohno-fj (ohno-fj)

``` Version of flang : 22.0.0(7761a89)/AArch64 ```

The attached program (test01.f90) contains module (mod) and submodule (smod) that extends this module (mod). Within module subroutine sub section following CONTAINS statement in submodule (smod), the ancestor module (mod) is referenced via USE statement.

According to Fortran Standard 2023 14.2.2 The USE statement and use association, it states: A module shall not reference itself, either directly or indirectly.
and according to Fortran Standard 2023 5.2.1 Program units and scoping units, it states: The module or submodule containing a module subprogram is the host scoping unit of the module subprogram.

I believe this program does not fall under the above specification.
The scope extends only to the definitions of declared procedures, which is separate from the module's program unit, and I do not believe it falls under the above.
Therefore, the compilation error of Flang appears to be incorrect.
Is my interpretation of this specification incorrect?

The following are the test program, Flang-new, Gfortran and ifx compilation/execution result.

test01.f90:

module mod
  integer:: var=1
  interface
    module subroutine sub
    end
  end interface
end

submodule (mod) smod
  integer:: var=100
  contains
  module subroutine sub
  use mod
   print *,var
  end
end

use mod
call sub
print *,'pass'
end

$ flang test01.f90
error: Semantic errors in test01.f90
./test01.f90:13:7: error: Module 'mod' cannot USE itself from its own submodule 'smod'
    use mod
        ^^^
$

$ gfortran test01.f90; ./a.out
           1
 pass
$

$ ifx test01.f90
test01.f90(12): error #<!-- -->6406: Conflicting attributes or multiple declaration of name.   [SUB]
  module subroutine sub
--------------------^
compilation aborted for test01.f90 (code 1)
$

[eugeneepshteyn]

I think 14.2.2, paragraph 1 applies to all USE statements, whether at module level or procedure level. Thus, "A module shall
23 not reference itself, either directly or indirectly" should apply anywhere the USE statement is used. I believe flang is correct here.

[ohno-fj]

I think 14.2.2, paragraph 1 applies to all USE statements, whether at module level or procedure level.
Thus, "A module shall not reference itself, either directly or indirectly" should apply anywhere the USE
statement is used.

As you pointed out, I understand that flang's behavior is correct.
I close this issue.