Build errors with flang

[ivan-pi]

Description

When building with a recent version of flang (installed using brew), I get the following error:

$ cmake .. -G Ninja -DCMAKE_Fortran_COMPILER=flang -DCMAKE_Fortran_FLAGS="-O3 -march=native" -DCMAKE_C_COMPILER=clang
...
$ ninja -j 8
...

error: Semantic errors in src/CMakeFiles/fortran_stdlib.dir/stdlib_error.f90-pp.f90
/code/rbfx-new/standalone/batched-assembly/stdlib/build/src/stdlib_error.f90:245:14: error: Left-hand side of assignment is not definable
               ierr_out = ierr
               ^^^^^^^^
/code/rbfx-new/standalone/batched-assembly/stdlib/build/src/stdlib_error.f90:245:14: because: 'ierr_out' is polymorphic in a pure subprogram
               ierr_out = ierr
               ^^^^^^^^
/code/rbfx-new/standalone/batched-assembly/stdlib/build/src/stdlib_error.f90:239:56: Declaration of 'ierr_out'
           class(state_type), optional, intent(inout) :: ierr_out
                                                         ^^^^^^^^

Expected Behaviour

Build should succeed.

Version of stdlib

c14d599

Platform and Architecture

MacOS (Aarch64)

Additional Information

No response

[ivan-pi]

The flang version is the following

$ flang --version
Homebrew flang version 20.1.2
Target: arm64-apple-darwin24.4.0
Thread model: posix
InstalledDir: /opt/homebrew/Cellar/flang/20.1.2/libexec
Configuration file: /opt/homebrew/Cellar/flang/20.1.2/libexec/flang.cfg
Configuration file: /opt/homebrew/etc/clang/arm64-apple-darwin24.cfg

[jalvesz]

Similar issue found here #978

[R-Goc]

Flang might be right?

C1597 An INTENT(OUT) dummy argument of a pure procedure shall not be polymorphic or have a polymorphic allocatable ultimate component.

class(state_type) means that it can accept a type that extends from state_type?

[Romendakil]

Flang might be right?

C1597 An INTENT(OUT) dummy argument of a pure procedure shall not be polymorphic or have a polymorphic allocatable ultimate component.

class(state_type) means that it can accept a type that extends from state_type?

No, this part of the standard doesn't apply here, as ierr_out is intent(inout).

[R-Goc]

PR in llvm: llvm/llvm-project#139186

[perazz]

I will close this one as it occurs to me that flang is still changing fast under active development, so it may still be a bit rough aroung the edges. I secong @Romendakil that the code is fully standard compliant. Closing for now.