feat(eslint-plugin): [unbound-method] Support Array methods with 'this' argument

[jacekjagiello]

#743

Hey, this is my first PR. I don't have much experience with AST, so it feels for me like walking in the fog 😄 I assume there is a better solution for this bug. Any help appreciated. I'll leave some questions in PR

[typescript-eslint]

Thanks for the PR, @jacekjagiello!

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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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[jacekjagiello]

What I really would like to do, is to check if callee for ex. nodes is an Array. Is this possible?

[bradzacher]

you should be able to get the type of the node, and ensure its type is an array.
I can't remember the flags exactly, so you might want to spend some time with the debugger in vscode.

[jacekjagiello]

I've spent some time trying to play with the debugger to find any flags that might indicate Array type, but with no success for now. If you think we can't leave it like this, I'll spend more time and maybe find the better way.

[bradzacher]

Digging back into this, sorry a lot going on. Finally taken time to tackle the PR queue.

Feel free to add this file into your PR, and use that API.
https://github.com/typescript-eslint/typescript-eslint/blob/naming-conventions/packages/eslint-plugin/typings/typescript.d.ts

The API is "internal", but it's stable - they just haven't gotten around to exposing their type relationship API yet (there's a whole discussion around why they haven't yet...)

You can then pass the typechecker into this function and call checker.isArrayType(type) (you'll also have to pass the type map in).

Also just as an FYI - this site is amazing for playing with TS's type API: https://ts-ast-viewer.com/
You can open the chrome dev tools, and interrogate the selected type via the global variables it maintains: type, program and typeChecker.

Also as an example, here is another PR doing a similar thing in looking for array functions: #1206

[codecov]

Codecov Report

Merging #797 into master will increase coverage by 0.03%.
The diff coverage is 85%.

@@            Coverage Diff             @@
##           master     #797      +/-   ##
==========================================
+ Coverage   94.13%   94.17%   +0.03%     
==========================================
  Files         115      112       -3     
  Lines        5016     4841     -175     
  Branches     1403     1341      -62     
==========================================
- Hits         4722     4559     -163     
+ Misses        166      160       -6     
+ Partials      128      122       -6

Impacted Files	Coverage Δ
packages/eslint-plugin/src/rules/unbound-method.ts	92.3% <85%> (-4.76%)	⬇️
...-plugin/src/rules/explicit-member-accessibility.ts	89.58% <0%> (-1.33%)	⬇️
...kages/eslint-plugin/src/rules/class-name-casing.ts	85.71% <0%> (-1.25%)	⬇️
...ckages/eslint-plugin/src/rules/no-magic-numbers.ts	91.42% <0%> (-1.08%)	⬇️
packages/eslint-plugin/src/rules/require-await.ts	92.1% <0%> (-0.58%)	⬇️
...ackages/eslint-plugin/src/rules/prefer-readonly.ts	99% <0%> (-0.1%)	⬇️
...nt-plugin/src/rules/indent-new-do-not-use/index.ts	98.4% <0%> (ø)	⬆️
packages/eslint-plugin/src/rules/index.ts	100% <0%> (ø)	⬆️
packages/parser/src/parser.ts	100% <0%> (ø)	⬆️
packages/eslint-plugin/src/rules/ban-types.ts	100% <0%> (ø)	⬆️
... and 50 more

[bradzacher]

you should be able to get the type of the node, and ensure its type is an array.
I can't remember the flags exactly, so you might want to spend some time with the debugger in vscode.