Implement standard assert subroutine and associated macros

[rweed]

Per @certiks request, I propose we extend his stdlib_experimental_error.f90 code to a standard assert subroutine and supplement it with some pre-processor macros. As an example here is my implementation of an assert routine and the associated macros

assertions.f90

assert.txt

The associated preprocessor macros are
assert_macros.txt

Note, these are my implementation of similar routine and macros found in the FTL project

[milancurcic]

I think this is a good step forward. I planned to propose adding optional message to assert so that it can be used more universally for tests and validating user inputs, and this takes it even further with file, line, and optional abort on failure.

I suggest everything but the first argument to be optional so it can be used in its minimal capacity.

Minor nit-pick: assertion .NEQV. .TRUE. can be just .not. assertion.

[rweed]

My primary use for assert was in testing which is why I have the two global variables (num_failed_asserts, and num_asserts). Usually you have several tests you want to perform at one time and want some record of the number of failed tests versus the number of tests and additional information as to when/where the failed test occured. However, I tried to also allow for the case where you want to use assert for error_handling in a given subroutine etc and do a hard abort/stop when an appropriate stop condition was met. A couple of things with my code.

1. IK=>INT32 should be appended to the end of the USE ISO_FORTRAN_ENV. I normally have a module that defines IK but I removed it for simplicity.

2. There probably needs to be some kind of RESET_ASSERT subroutine to reset the num_failed_assert and num_assert values. Another option would be to make them PRIVATE and provide getter and setter functions but I considered that overkill for just two variables.

[certik]

I think for testing, it's better to use or develop a more specific framework just for testing.

I think the main advantage of the assert macro is to test things like sizes of arrays when entering a subroutine, and other conditions that the code depends on. And in Release mode the macro is not executed, so there is no overhead.

[ivan-pi]

Have we considered using fypp for assert macros? We already have it as a dependency.

[certik]

To clarify: this issue is for Debug time assert statements, that get skipped in Release mode. Testing framework is a different use case, to be discussed in #162. Note however, that a project like stdlib will have a test suite, executed by the testing framework (#162), and this will call functions from stdlib such as save_txt() to ensure they work, and those functions internally would have ASSERT macros that would ensure that things are internally consistent (in Debug mode).

@milancurcic, @everythingfunctional I think stdlib should have such a macro.

However, the issue is that then by default the files ending with .f90 are not pre-processed by default, so the macro would not work. I can see two approaches:

1. rename all files to .F90
2. pass the proper compiler flag to the Fortran compiler in CMake (later on, once we switch to fpm, it would do the same)

A third approach is to only do this for files that would use ASSERT. I don't like this third option, as we should be free to use ASSERT in any file, without having to fiddle with the build system or with a file extension.

Which approach do you prefer, 1) or 2)?

I think I prefer 2), simply because using upper case extension feels old fashioned, I am not aware of any modern language that would require that. See also j3-fortran/fortran_proposals#56.

[everythingfunctional]

I think I would lean towards 2. A standard preprocessor is something Fortran probably should have settled on a long time ago. There are simply too many use cases for macros and preprocessor directives not too. I would be fine if fpm picked a preprocessor and just always used it, whether that file needed it or not.

[certik]

@everythingfunctional exactly. See also j3-fortran/fortran_proposals#65 for a related discussion about standardizing a pre-processor.

The only issue that I can see is that the typical CPP preprocessor is pretty limited in what it can do, and it does not understand Fortran's syntax. fypp is an improvement. Even better would be to design intelligent macros for Fortran. That is all long term, a short term solution is to use CPP. However, I wouldn't like our choice to prevent us to implement intelligent macros in the future. However, for this we could use the edition keyword (j3-fortran/fortran_proposals#83) that we can specify in fpm.toml, just like Rust does it. So from some future moment, we could switch the pre-processor to something more intelligent and for legacy codes we would provide an option to explicitly keep using CPP for a particular file (one would have to specify that explicitly in fpm.toml if a newer edition was required).

[certik]

Also note that the NAG compilers do not pre-process .F90 automatically, instead one has to use the -fpp option, per open-mpi/ompi#7584. So that leaves us with option 2, as option 1 would not work anyway in all compilers.