feat(eslint-plugin): [no-unsafe-assignment/return] allow assigning any => unknown

[yasarsid]

Fixes #2325

Overview

This PR looks to relax restrictions to allow any => unknown assignment for no-unsafe-assignment and no-unsafe-return.

Approach

Initially we are checking for Any or AnyArray as senderType, if found we used to stop processing with the relevant message.
Now we additionally check if the recieverType is Unknown or Unknown array. If yes - then we do not treat this as an error case.

Special Focus

I would like you to specifically look at the coding style, so that we don't adversely affect future contributors. I have tried to align with the existing style. Feel free to point out where we could align more.

Checklist

• Have updated the documentation for these rule and called these relaxation separately.
• Have added UTs for the cases added.

[typescript-eslint]

Thanks for the PR, @yasarsid!

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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.

Thanks again!

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[codecov]

Codecov Report

Merging #2371 into master will increase coverage by 0.05%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #2371      +/-   ##
==========================================
+ Coverage   93.10%   93.15%   +0.05%     
==========================================
  Files         285      285              
  Lines        9125     9150      +25     
  Branches     2504     2513       +9     
==========================================
+ Hits         8496     8524      +28     
+ Misses        302      301       -1     
+ Partials      327      325       -2     

Flag	Coverage Δ
#unittest	93.15% <100.00%> (+0.05%)	⬆️

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

Impacted Files	Coverage Δ
...es/eslint-plugin/src/rules/no-unsafe-assignment.ts	80.50% <100.00%> (+0.33%)	⬆️
...ckages/eslint-plugin/src/rules/no-unsafe-return.ts	100.00% <100.00%> (+5.00%)	⬆️
packages/eslint-plugin/src/util/types.ts	83.24% <100.00%> (+1.15%)	⬆️
packages/visitor-keys/src/visitor-keys.ts	100.00% <0.00%> (ø)
...nt-plugin/src/rules/no-unused-vars-experimental.ts	91.48% <0.00%> (ø)
packages/typescript-estree/src/convert.ts	98.36% <0.00%> (+0.01%)	⬆️
...ckages/scope-manager/src/referencer/TypeVisitor.ts	89.55% <0.00%> (+0.15%)	⬆️

[bradzacher]

Thanks for doing this! The changes LGTM.

One request:
could you please add some tests for isUnsafeAssignment into
https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/tests/util/isUnsafeAssignment.test.ts

Great work!

[yasarsid]

@bradzacher - Good catch for missing UTs. 👍

As suggested - have added tests in isUnsafeAssignment.test.ts

[bradzacher]

ezpz - thanks for your work!