Strange output about Fortran compiler

[dongli]

I found the following strange output about Fortran compiler:

==> Installing armadillo dependency: arpack
==> Using Homebrew-provided fortran compiler.
This may be changed by setting the FC environment variable.
==> Building with an alternative Fortran compiler
This is unsupported.
Warning: No Fortran optimization information was provided.  You may want to consider
setting FCFLAGS and FFLAGS or pass the `--default-fortran-flags` option to
`brew install` if your compiler is compatible with GCC.

If you like the default optimization level of your compiler, ignore this
warning.

As you can see, homebrew first told me that I am using the 'Homebrew-provided fortran compiler', then it told me that it will build with an alternative Fortran compiler. What is going on? I didn't do anything special.

EDIT:

I have added a print statement in /usr/local/Library/Homebrew/extend/ENV/shared.rb as:

  def fortran
    flags = []

    print "---> CHECK fc = #{fc}\n"
    if fc

and the output of brew install arpack is:

$ brew install arpack
---> CHECK fc =
==> Using Homebrew-provided fortran compiler.
This may be changed by setting the FC environment variable.
---> CHECK fc = /usr/local/bin/gfortran
==> Building with an alternative Fortran compiler
This is unsupported.
Warning: No Fortran optimization information was provided.  You may want to consider
setting FCFLAGS and FFLAGS or pass the `--default-fortran-flags` option to
`brew install` if your compiler is compatible with GCC.

If you like the default optimization level of your compiler, ignore this
warning.
==> Downloading http://forge.scilab.org/index.php/p/arpack-ng/downloads/get/arpack-ng_3.1.4.tar.gz
Already downloaded: /Library/Caches/Homebrew/arpack-3.1.4.tar.gz
==> ./configure --prefix=/usr/local/Cellar/arpack/3.1.4/libexec --with-blas=-L/usr/local/Cellar/veclibfort/0.4.0/lib -lvecLibFort
==> make
==> make install
🍺  /usr/local/Cellar/arpack/3.1.4: 12 files, 1.7M, built in 15 seconds

It seems that method fortran has been called twice, and for the second time, fc is not empty or nil, so the warning is printed without looking at if the fortran compiler is installed by homebrew or not.

[jacknagel]

I see the bug (it's in the dependency expansion). I'll try to get to it today or tomorrow.

[dongli]

@jacknagel This bug is still out there.

$ brew install arpack
==> Using Homebrew-provided fortran compiler.
This may be changed by setting the FC environment variable.
==> Building with an alternative Fortran compiler
This is unsupported.
Warning: No Fortran optimization information was provided.  You may want to consider
setting FCFLAGS and FFLAGS or pass the `--default-fortran-flags` option to
`brew install` if your compiler is compatible with GCC.

If you like the default optimization level of your compiler, ignore this
warning.

[AlJohri]

Does anyone know why this occurs?

[cabe56]

Maybe related? Tried installing veclibfort. Here's the gist with the ouput

[EconGeo]

bug is still there. I get the same error when installing R

[UniqMartin]

This should be fixed by #47246.