Caching properties to deduplicate sources

[kalebmckale]

Without caching, the Resolver duplicates the sources listed in the Pipfile multiple times (since the property re-adds them every time they're called) in the arguments sent to the pip parser.

Removing unused command-line option --debug

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The issue

While diagnosing another issue, I found through print debugging that the multiple calls to these properties, pip_args and pip_options, ended up duplicating the sources listed in the Pipfile multiple times for the pip parser.

Related to the resolver, the --debug command-line option for pipenv-resolver is unused.

The fix

To fix this, I replaced property decorator with cached_property, which was already imported in the module. As best as I can tell, these properties (and a number of other ones) only need to be evaluated once instead of every single time they are called. Caching not only fixes this duplication but will also lead to faster, more efficient code.

If a debug option is later implemented, the command-line option can be added at that time.

The checklist

• Associated issue
• A news fragment in the news/ directory to describe this fix with the extension .bugfix.rst, .feature.rst, .behavior.rst, .doc.rst. .vendor.rst. or .trivial.rst (this will appear in the release changelog). Use semantic line breaks and name the file after the issue number or the PR #.

[kalebmckale]

@matteius What type of change would this be considered for my news file?

[matteius]

@kalebmckale I'd be fine with bugfix.

[matteius]

I am going to include a news fragment on your behalf so we can include this fix in the release.

[kalebmckale]

Thanks!