khepri_fun: Work around Rebar's use of cth_readable parse_transform

[dumbbell]

To improve the output of common_test in the terminal, Rebar uses cth_readable. This library comes with a parse_transform module to convert all calls to ct:pal().

The application modules are thus recompiled on-the-fly (i.e. the result is not written to disk) with this parse_transform. The result is that the module loaded in memory doesn't match the one on disk (different checksums).

This causes the following exception while trying to extract a transaction function. Here is an example:

{khepri_ex, failed_to_prepare_tx_fun,
 #{error =>
   {mismatching_module_checksum,
    #{checksum_from_fun =>
      <<194,208,71,94,61,101,247,31,220,109,126,242,101,120,40,129>>,
      checksum_on_disk =>
      <<152,39,250,105,94,89,145,46,251,4,237,114,45,132,63,33>>,
      compile_info_from_fun =>
      [{version, "8.2.1"},
       {options,
        [{d, 'COMMON_TEST'},
         {d, 'TEST'},
         {i, ".../_build/test/lib/khepri_mnesia_migration/src"},
         {i, ".../_build/test/lib/khepri_mnesia_migration/test"},
         {i, ".../_build/test/lib/khepri_mnesia_migration/include"},
         {i, ".../_build/test/lib/khepri_mnesia_migration"}]},
       {source, ".../src/m2k_table_copy.erl"}],
      compile_info_on_disk =>
      [{version, "8.2.1"},
       {options,
        [debug_info,no_spawn_compiler_process,
         {d, 'COMMON_TEST'},
         warn_export_vars,
         {d, 'TEST'},
         {parse_transform,cth_readable_transform},
         {i, ".../_build/test/lib/khepri_mnesia_migration/src"},
         {i, ".../_build/test/lib/khepri_mnesia_migration/test"},
         {i, ".../_build/test/lib/khepri_mnesia_migration/include"},
         {i, ".../_build/test/lib/khepri_mnesia_migration"}]},
       {source, ".../src/m2k_table_copy.erl"}],
      module => m2k_table_copy}}}}

The solutions consists in comparing the source filename and compiler options. If both copies are compiled for tests and one of them uses cth_readable_transform, we accept the inconsistency and continue.

While here, the error returned when modules mismatch was updated to include more details.

[codecov]

Codecov Report

Base: 90.73% // Head: 90.74% // Increases project coverage by +0.01% 🎉

Coverage data is based on head (e0af4b3) compared to base (f1c5730).
Patch coverage: 92.68% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #176      +/-   ##
==========================================
+ Coverage   90.73%   90.74%   +0.01%     
==========================================
  Files          19       19              
  Lines        3388     3427      +39     
==========================================
+ Hits         3074     3110      +36     
- Misses        314      317       +3     

Flag	Coverage Δ
erlang-24	89.58% <92.68%> (+0.14%)	⬆️
erlang-25	89.67% <92.68%> (+0.05%)	⬆️
os-ubuntu-latest	90.74% <92.68%> (+0.01%)	⬆️
os-windows-latest	89.61% <92.68%> (+0.06%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
src/khepri_fun.erl	93.62% <92.68%> (+0.20%)	⬆️
src/khepri_machine.erl	94.14% <0.00%> (-0.27%)	⬇️

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[dumbbell]

Thank you @the-mikedavis for the quick review!

I can't reproduce the problem outside of khepri_mnesia_migration. I would prefer to come up with a testcase for this patch. That's why I'm not ready to commit it yet.