Flang-compiled MOPAC problems
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Describe the bug
Flang-compiled MOPAC on Linux fails to read input files with DOS-style carriage returns.
To Reproduce
This problem occurs with the version of flang classic available on conda-forge, and is likely to occur with other, similar versions.
Expected behavior
DOS-style carriage returns should be ignored by Fortran read commands, and their appearance is probably a compiler bug.
Operating system
I encountered this problem on Linux/x86.
Additional context
Flang is under active development, so this bug will probably be resolved in a timely manner. It's also easy to avoid this bug if you aren't regularly transferring input files between Linux and Windows.
Actually, on closer inspection, this isn't strictly a bug. Flang is based on the legacy PGI Fortran compiler, and its default behavior is NOT to ignore the carriage return (CR) character in Windows-style CRLF line breaks. This compiler behavior can be adjusted, but it requires the setting of a specific environment variable at build time rather than being accessible via a compiler flag. CMake does not presently have convenient support for setting build-time environment variables, so I've added a message in the CMake script instructing users to set it for themselves when a legacy PGI compiler is detected.