fix(eslint-plugin): [no-unnecessary-type-assertion] handle assignment

[Zzzen]

should fix #2953

This is an aggressive move, but I don't why we don't use getContextualType directly. All current tests have passed. If this is feasible, I can add more test cases.

[typescript-eslint]

Thanks for the PR, @Zzzen!

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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.

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[Zzzen]

It is weird CI is failing to install dependencies.

[armano2]

this error is unrelated to your change

[bradzacher]

The getContextualType function was first added in #478 (and was moved to a shared util in #1644).

I'll be honest when I say that I don't remember why I added it - I vaguely remember that there were a number of issues with getContextualType.
The fact that there's a lint error now that you've removed this logic says that it's still the case that checker.getContextualType is not infallible.

Please augment the logic instead of removing it.

[Zzzen]

👌 👌 got it

[codecov]

Codecov Report

Merging #3133 (de87f17) into master (9323eae) will decrease coverage by 0.01%.
The diff coverage is 77.77%.

@@            Coverage Diff             @@
##           master    #3133      +/-   ##
==========================================
- Coverage   92.88%   92.86%   -0.02%     
==========================================
  Files         315      315              
  Lines       10706    10715       +9     
  Branches     3025     3030       +5     
==========================================
+ Hits         9944     9951       +7     
  Misses        342      342              
- Partials      420      422       +2     

Flag	Coverage Δ
unittest	92.86% <77.77%> (-0.02%)	⬇️

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

Impacted Files	Coverage Δ
...-plugin/src/rules/no-unnecessary-type-assertion.ts	94.66% <66.66%> (-2.44%)	⬇️
packages/eslint-plugin/src/util/types.ts	83.51% <100.00%> (+0.27%)	⬆️

[bradzacher]

LGTM - thanks for your contribution!

[bradzacher]

@danielrentz please file a new issue instead of commenting on old PRs.