Use click API for output file handling in pip-compile

[atugushev]

• Use click's file option with atomic mode instead of ExitStack+AtomicSaver.
• Less code, DRY.
• Less untested code.

Changelog-friendly one-liner: Use click API for output file handling in pip-compile

Contributor checklist

• Provided the tests for the changes.
• Requested a review from another contributor.
• Gave a clear one-line description in the PR (that the maintainers can add to CHANGELOG.md on release).
• Assign the PR to an existing or new milestone for the target version (following Semantic Versioning).

[codecov]

Codecov Report

Merging #727 into master will increase coverage by 5.55%.
The diff coverage is 100%.

@@            Coverage Diff            @@
##           master    #727      +/-   ##
=========================================
+ Coverage   92.34%   97.9%   +5.55%     
=========================================
  Files          35      34       -1     
  Lines        2285    1953     -332     
  Branches      308     254      -54     
=========================================
- Hits         2110    1912     -198     
+ Misses        147      29     -118     
+ Partials       28      12      -16

Impacted Files	Coverage Δ
piptools/utils.py	100% <ø> (ø)	⬆️
piptools/scripts/compile.py	100% <100%> (ø)	⬆️
piptools/writer.py	100% <100%> (ø)	⬆️
tests/test_writer.py	100% <100%> (ø)	⬆️
tests/conftest.py	95.18% <100%> (+0.3%)	⬆️

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[atugushev]

Hello @vphilippon. I'm just wondering whether it is worth efforts, or "don't touch if it works".

[vphilippon]

@atugushev Thanks for that PR, I'm always interested in some cleanup/maintanabillity improvements.

• Use click's file option with atomic mode instead of ExitStack+AtomicSaver.

Cool, let's get that in!

• New feature: add support for stdout as output file, for example pip-compile -o- [...]

I'd suggest to take this one out of the current MR for now. The feature is pretty much unusable with the issue you've raised, so I wouldn't merge/release that yet.
I'm super happy about seeing work done to get this feature though, so you're more than welcome to open a second MR once this is merged to get the discussion going.

I'll get on the review proper soon:tm: too.

[atugushev]

@vphilippon Thank you for the feedback! Yes, that'd be better to split up the changes.

[atugushev]

Hello @vphilippon,

The PR is ready to review. If you have a time take a look please.

[atugushev]

Conflicts are resolved.

[atugushev]

@blueyed need your feedback :)

[blueyed]

Sweet!

[atugushev]

@blueyed thanks! I'll resolve the conflicts shortly.