Add support for short-circuit || in non-conditional flows

[sonalmahajan15]

This PR adds support for short-circuit || in non-conditional flows, thereby reducing false positives. For example,

return x == nil || *x == 1

was reported as a false positive, since NilAway only analyzed &&.

We apply logic similar to the handling of &&. Because this analysis resides in the recursion of the short-circuit expression, where we have limited context visibility, it makes it difficult to accurately analyze complex expressions. Therefore, with extending support for ||, we had to trade-off some of the precision we previously had with only the && support. However, we made this tough choice since empirically we observed that complex cases that we had to trade-off did not occur frequently enough, while simple || patterns were more prevalent. I have created issue #226 to keep a track of the comprehensive support that we plan to add in the future.

[closes #92 ]

[github-actions]

Golden Test

Note

✅ NilAway errors reported on standard libraries are identical.

3261 errors on base branch (main, 29def5e)
3261 errors on test branch (1312f57)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 87.25%. Comparing base (29def5e) to head (bc65217).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #227   +/-   ##
=======================================
  Coverage   87.25%   87.25%           
=======================================
  Files          60       60           
  Lines        7727     7731    +4     
=======================================
+ Hits         6742     6746    +4     
  Misses        807      807           
  Partials      178      178           

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[yuxincs]

Thanks for the comprehensive test suite!

Let's keep this in mind for the potential false negatives and think of more general ways to handle this in the future :)