fix(eslint-plugin): [prefer-optional-chain] properly disambiguate between boolean and false

[abrahamguo]

PR Checklist

• Addresses an existing open issue: fixes Docs: [prefer-optional-chain] improve the playground and examples for allowPotentiallyUnsafeFixesThatModifyTheReturnTypeIKnowWhatImDoing #8659
• That issue was marked as accepting prs
• Steps in Contributing were taken

Overview

In #8659, we see that the example in the docs for prefer-optional-chain: allowPotentiallyUnsafeFixesThatModifyTheReturnTypeIKnowWhatImDoing is not reporting an error.

The root cause is actually unrelated to allowPotentiallyUnsafeFixesThatModifyTheReturnTypeIKnowWhatImDoing — it is because foo.bar is of type boolean.

In the rule, there is a bypass to avoid flagging unions with falsy members, such as

declare const foo: { bar: boolean } | boolean | null | undefined;
foo && foo.bar;

since changing that to an optional chain would cause a TS error.

However, if the falsy literal is the last operand, then we should report it. This is the change made by this PR.

declare const foo: { bar: boolean } | null | undefined;
foo && foo.bar;

[typescript-eslint]

Thanks for the PR, @abrahamguo!

typescript-eslint is a 100% community driven project, and we are incredibly grateful that you are contributing to that community.

The core maintainers work on this in their personal time, so please understand that it may not be possible for them to review your work immediately.

Thanks again!

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 87.23%. Comparing base (609a000) to head (43a2514).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #8685   +/-   ##
=======================================
  Coverage   87.23%   87.23%           
=======================================
  Files         251      251           
  Lines       12319    12321    +2     
  Branches     3884     3885    +1     
=======================================
+ Hits        10746    10748    +2     
  Misses       1303     1303           
  Partials      270      270           

Flag	Coverage Δ
unittest	87.23% <100.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
...efer-optional-chain-utils/gatherLogicalOperands.ts	100.00% <100.00%> (ø)

[JoshuaKGoldberg]

Clever - I like the changes. Very minimal and clean. Nicely done! 🙌