fix: Support reading empty parquet files

[corwinjoy]

Fix #13457

Add support for reading empty parquet files.
I'm new to this project so I could use help with the unit tests that I added to verify correct behavior. I'm not sure if they are in the correct place/am having trouble getting make test to pick up the new tests.

[adamreeve]

I'm not sure if they are in the correct place/am having trouble getting make test to pick up the new tests.

make test will skip tests that are marked with write_disk by default due to the pytest config:

polars/py-polars/pyproject.toml

Line 231 in 6f5851d

"-m not slow and not write_disk and not release and not docs and not hypothesis and not benchmark and not ci_only",

You can run all tests from the py-polars directory with make test-all, or run pytest directly and only include the write_disk tests with something like:

make build
../.venv/bin/pytest -m 'write_disk'

To run the Rust tests you can run make test from the crates directory.

[adamreeve]

I don't know if this is still the case but I've previously had feedback that Python tests are preferred over Rust tests due to the impact of building Rust tests on CI times (#13139 (comment)). So possibly only having the Python tests is enough.

[codecov]

Codecov Report

Attention: Patch coverage is 75.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 79.80%. Comparing base (d6703c4) to head (9642aec).
Report is 25 commits behind head on main.

Files	Patch %	Lines
...arquet/src/parquet/schema/io_thrift/from_thrift.rs	75.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #18392      +/-   ##
==========================================
- Coverage   79.87%   79.80%   -0.07%     
==========================================
  Files        1496     1497       +1     
  Lines      200281   200428     +147     
  Branches     2841     2844       +3     
==========================================
- Hits       159966   159956      -10     
- Misses      39790    39947     +157     
  Partials      525      525              

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[coastalwhite]

Some minor nits, nothing stopping it from getting merged and me fixing those immediately afterward. @ritchie46

[ritchie46]

@coastalwhite, it is fine to take the PR from here and apply those nits.

[corwinjoy]

Thanks everyone for being so helpful to a newbie to this project! Much appreciated, @coastalwhite for the fixup and the prompt review by everyone, you are awesome!