Fix suppressed default visible

[michele-riva]

For some parser arguments (e.g., action='version'), the "==SUPPRESSED==" default would be unexpectedly shown.

Added also regression test.

[michele-riva]

Failure in py3.7 is out of my control. Seems to be due to an argument-less @functools.lru_cache decoration, which is only supported starting from Python 3.8. A search for lru_cache brought up the following potentially problematic modules, involved during testing:

• PIL.ImageMode.py L42
• packaging._manylinux.py L172 (this is the one that causes the build error)
• packaging._musllinux.py L33

[michele-riva]

I guess the 3.7 build requires some more specification in poetry.lock, as it seems that poetry is installing a version of packaging that is incompatible with Python 3.7. I'm not familiar enough with poetry to do anything about this myself, though.

[ashb]

I should remove 3.7 from the supported versions now I think as it's end-of-lifed.

[michele-riva]

I should remove 3.7 from the supported versions now I think as it's end-of-lifed.

Works for me. Would you like to do it in a separate PR?

[michele-riva]

@ashb, let me know if I should do anything about the py3.7 support, either here or in a separate PR. It would be nice if I could tick this PR off my TODO list.