Request: llvm: add flang Fortran compiler

[scivision]

Output of brew config

N/A

Output of brew doctor

N/A

Description of issue

Flang the LLVM Fortran compiler has matured in LLVM 19 to where Flang can now compile most Fortran code, even for major projects. I would like to have "flang" be installed as part of "llvm" or at least make "flang" its own formula.

What I've been doing is to build Flang with a script, in case this is helpful to see what options are used.

reference, flang has progressed beyond thisN

[alebcay]

Some related work is currently happening in Homebrew/homebrew-core#191829.

[mathomp4]

So, I saw today that flang is now in Brew and decided to try it out. Unfortunately, I think I'm missing something:

❯ which flang-newv
/Users/mathomp4/.homebrew/brew/bin/flang-new
❯ cat test.F90
program main

end
❯ flang-new test.F90
Undefined symbols for architecture arm64:
  "std::exception::~exception()", referenced from:
      std::bad_variant_access::~bad_variant_access() in libFortranRuntime.a[19](edit-output.cpp.o)
  "std::terminate()", referenced from:
      ___clang_call_terminate in libFortranRuntime.a[5](assign.cpp.o)
  "typeinfo for std::bad_variant_access", referenced from:
      std::__1::__throw_bad_variant_access[abi:ue170006]() in libFortranRuntime.a[19](edit-output.cpp.o)
  "vtable for std::bad_variant_access", referenced from:
      std::__1::__throw_bad_variant_access[abi:ue170006]() in libFortranRuntime.a[19](edit-output.cpp.o)
   NOTE: a missing vtable usually means the first non-inline virtual member function has no definition.
  "___cxa_allocate_exception", referenced from:
      std::__1::__throw_bad_variant_access[abi:ue170006]() in libFortranRuntime.a[19](edit-output.cpp.o)
  "___cxa_begin_catch", referenced from:
      ___clang_call_terminate in libFortranRuntime.a[5](assign.cpp.o)
  "___cxa_throw", referenced from:
      std::__1::__throw_bad_variant_access[abi:ue170006]() in libFortranRuntime.a[19](edit-output.cpp.o)
  "___gxx_personality_v0", referenced from:
      /Users/mathomp4/.homebrew/brew/Cellar/flang/19.1.0/libexec/lib/libFortranRuntime.a[52](stop.cpp.o)
ld: symbol(s) not found for architecture arm64
flang-new: error: linker command failed with exit code 1 (use -v to see invocation)

I've tried this with both CC as Apple clang and with CC as brew llvm clang. Staring at the brew info llvm output I also tried:

flang-new -L/Users/mathomp4/.homebrew/brew/opt/llvm/lib -I/Users/mathomp4/.homebrew/brew/opt/llvm/include test.F90

flang-new -L/Users/mathomp4/.homebrew/brew/opt/llvm/lib/c++ -L/Users/mathomp4/.homebrew/brew/opt/llvm/lib/unwind -lunwind test.F90

flang-new -L/Users/mathomp4/.homebrew/brew/opt/llvm/lib/unwind -lunwind test.F90

But they all fail. So I'm obviously missing something.

NOTE: One issue could be that on this machine I'm not allowed to install to /opt. But that doesn't stop brew llvm clang from working:

❯ /Users/mathomp4/.homebrew/brew/opt/llvm/bin/clang test.c
❯ ./a.out
Hello, World!%

[scivision]

Is this -lc++ something that the Flang Homebrew package should automatically do as part of its self-defined toolchain?

I.e. like GCC automatically adds -lgfortran when linking a C or C++ main program with a Fortran library.

I experience the same symptoms as @mathomp4

For now what I do is add to my source file ~/flang.sh (say)

export FC=flang-new 

export LDFLAGS=-lc++

The LDFLAGS is consumed by build systems such as CMake--be sure to make a fresh project build directory as prior attempts to use the compiler will mess up the detection of the compiler by CMake.

[mathomp4]

Interesting. That does not work for me:

❯ export LDFLAGS='-lc++'
❯ flang-new test.F90
Undefined symbols for architecture arm64:
  "std::exception::~exception()", referenced from:
      std::bad_variant_access::~bad_variant_access() in libFortranRuntime.a[19](edit-output.cpp.o)
...

[scivision]

Right, you would need the LDFLAGS to be specified on the command line if manually compiling a single file.

LDFLAGS is intended to be consumed by build systems like Meson or CMake on their first configure step--make a fresh build directory to clear out prior unsuccessful compiler detection attempts.

I have to do things like this for other compilers too--but not for GCC. It would be nice if Flang Homebrew package would "know" it needs "-lc++" implicit in every link command by flang-new.

[mathomp4]

Ahh. Feelin' dumb now. I guess I thought you were applying that to all.

[mathomp4]

Meanwhile, my home laptop (which can use the bottle) seems to have a different error:

❯ which flang-new
/opt/homebrew/bin/flang-new
❯ flang-new test.F90
ld: library 'System' not found
flang-new: error: linker command failed with exit code 1 (use -v to see invocation)
❯ flang-new test.F90 -lc++
ld: library 'c++' not found
flang-new: error: linker command failed with exit code 1 (use -v to see invocation)

Huh.