Problem with gfortran linking on macOS 10.15.7

[kpj]

Description
I am using this setup:

Current runner version: '2.276.0'
Operating System
  Mac OS X
  10.15.7
  19H15
Virtual Environment
  Environment: macos-10.15
  Version: 20201212.1

My goal is to compile software which relies on gfortran.
Following #1280, I added this step to my workflow:

- name: Provide gfortran
  if: runner.os == 'macOS'
  run: |
    sudo ln -s /usr/local/bin/gfortran-9 /usr/local/bin/gfortran
    gfortran --version

However, compilation of other software now fails with ld: library not found for -lgfortran (affected run).

Area for Triage:
Apple

Question, Bug, or Feature?:
Bug

Virtual environments affected

• macOS 10.15

Expected behavior
Installation of software which requires fortran should be possible.

Actual behavior
Installation of software which requires fortran crashes with

ld: warning: directory not found for option '-L/usr/local/gfortran/lib/gcc/x86_64-apple-darwin18/8.2.0'
ld: warning: directory not found for option '-L/usr/local/gfortran/lib'
ld: warning: directory not found for option '-L/usr/local/gfortran/lib/gcc/x86_64-apple-darwin18/8.2.0'
ld: warning: directory not found for option '-L/usr/local/gfortran/lib'
ld: library not found for -lgfortran
clang: error: linker command failed with exit code 1 (use -v to see invocation)

Repro steps
Affected run: https://github.com/kpj/dce/runs/1748442835

[dsame]

The quick workaround:

@kpj In order your build to success you have to create one more link

sudo ln -s /usr/local/Cellar/gcc@9/9.3.0_1/lib/gcc/9 /usr/local/gfortran/lib

@al-cheb @AlenaSviridenko @maxim-lobanov - it is not clear that caused the problem - either the build system used by the workflow picked up the incorrect path to fortran libraries (most probably) or there's something wrong with the gcc installation (almost no chance)

In order to fix the issue i suggest to improve the documentation mentioning the one more link has to be created. The other solutions require the additional triage

[kpj]

@dsame Thanks a lot! Why did you use _1 in 9.3.0_1? The readme only shows 9.3.0.

Unfortunately, your suggestion crashes with ln: /usr/local/gfortran/lib: No such file or directory (link).

If I wanted to use fortran-10, would the correct setup be something like this?

- name: Provide gfortran
  if: runner.os == 'macOS'
  run: |
    sudo ln -s /usr/local/bin/gfortran-10 /usr/local/bin/gfortran
    sudo ln -s /usr/local/Cellar/gcc@10/10.2.0/lib/gcc/10 /usr/local/gfortran/lib
    gfortran --version

[dsame]

@kpj

We use brew to install gcc and its components on macos images, so the exact paths are managed by the brew team

README shows the installed version of gfortran, but the exact directory where it is installed is 9.3.0_1
In order to get the paths you need to link please add ls /usr/local/Cellar/gcc@[version] to your pipeline

Before the creating of the link /usr/local/gfortran/lib you have to create the directory /usr/local/gfortran

For full working pipeline i created this build https://github.com/dsame/actions-demo/runs/1774695708?check_suite_focus=true , please use it as a reference

@al-cheb @AlenaSviridenko @maxim-lobanov the build https://github.com/dsame/actions-demo/runs/1774695708?check_suite_focus=true shows there's no need any extra links to build both fortran77 and fortran99 and therefore the original issue is caused by the 3rd party build system and we do not need to update the docs

@kpj please confirm the original issue is solved with

    - name: Provide gfortran9 
      run: |
        sudo ln -s /usr/local/bin/gfortran-9 /usr/local/bin/gfortran 
        sudo mkdir /usr/local/gfortran
        sudo ln -s /usr/local/Cellar/gcc@9/9.3.0_1/lib/gcc/9 /usr/local/gfortran/lib
        gfortran --version

[dsame]

Hi! I am closing this issue due to no response in a week. Please, feel free to contact us in case of any questions

[kpj]

@dsame Sorry for not responding earlier. The issue is that the (binary) dependencies of my project were updated and the fortran compiler is not required until another dependency changes. So unfortunately, I cannot confirm whether the fix works or not.

I added it successfully to my workflow nonetheless, so it will probably work out. Should other issues arise later, I'll create another issue.