feat(eslint-plugin): Check 'rest' parameters in no-misused-promises

[Aaron1011]

Fixes #4015

This extends 'no-misued-promises' with support for checking variadic arguments passed to a 'rest' parameter. If a function is declared with an argument like '...handlers: Array<() => void>', we now check if the type argument to Array is a void-returning function, and if so, check if any of the variadic arguments return a Promise.

PR Checklist

• Addresses an existing open issue: fixes [no-misused-promises] checksVoidReturn=true doesn't catch the error when variadic arguments are used (like ...handlers: Array<() => void>) #4015
• That issue was marked as accepting prs
• Steps in CONTRIBUTING.md were taken

Overview

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• Node 14 - nx test @typescript-eslint/ast-spec --coverage=false
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• Node 14 - nx test @typescript-eslint/eslint-plugin-tslint --coverage=false
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• Node 18 - nx test @typescript-eslint/parser
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[typescript-eslint]

Thanks for the PR, @Aaron1011!

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

Merging #5731 (3a3bb21) into main (7a377e4) will increase coverage by 0.13%.
The diff coverage is 100.00%.

❗ Current head 3a3bb21 differs from pull request most recent head 1342a7e. Consider uploading reports for the commit 1342a7e to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5731      +/-   ##
==========================================
+ Coverage   93.82%   93.96%   +0.13%     
==========================================
  Files         134      288     +154     
  Lines        1506     9592    +8086     
  Branches      226     2889    +2663     
==========================================
+ Hits         1413     9013    +7600     
- Misses         60      333     +273     
- Partials       33      246     +213     

Flag	Coverage Δ
unittest	93.96% <100.00%> (+0.13%)	⬆️

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

Impacted Files	Coverage Δ
...ges/eslint-plugin/src/rules/no-misused-promises.ts	98.46% <100.00%> (ø)
...nt-plugin/src/rules/consistent-type-definitions.ts	97.29% <0.00%> (ø)
...s/eslint-plugin/src/rules/no-unused-expressions.ts	89.47% <0.00%> (ø)
packages/eslint-plugin/src/util/objectIterators.ts	66.66% <0.00%> (ø)
packages/eslint-plugin/src/rules/ban-ts-comment.ts	96.96% <0.00%> (ø)
...ackages/eslint-plugin/src/rules/member-ordering.ts	95.62% <0.00%> (ø)
...plugin/src/rules/explicit-module-boundary-types.ts	91.04% <0.00%> (ø)
...lugin/src/rules/prefer-readonly-parameter-types.ts	100.00% <0.00%> (ø)
packages/eslint-plugin/src/util/isNullLiteral.ts	100.00% <0.00%> (ø)
...ackages/eslint-plugin/src/rules/prefer-as-const.ts	100.00% <0.00%> (ø)
... and 145 more

[JoshuaKGoldberg]

Looks like a great start, thanks for sending this in! Mostly requesting changes around adding unit test coverage for more edge cases, in particular tuples. Cheers!

[Aaron1011]

@JoshuaKGoldberg Thanks for the fast review! I've pushed a new commit that should address all of your comments.

[JoshuaKGoldberg]

This is looking good! Just a couple non-nits blocking. I'm feeling good about this one!

[Aaron1011]

@JoshuaKGoldberg I've addressed your latest comments

[JoshuaKGoldberg]

Fantastic, thanks! 👏

[jlowcs]

Following this change, my project's linting broke. I'm seeing the following:

TypeError: Cannot read properties of undefined (reading 'flags')
Occurred while linting /tmp/workspace/x/y/z/index.ts:19
Rule: "@typescript-eslint/no-misused-promises"
    at Object.isUnionType (/tmp/workspace/node_modules/tsutils/typeguard/2.8/type.ts:68:18)
    at Object.unionTypeParts (/tmp/workspace/node_modules/tsutils/util/type.ts:145:12)
    at isThenableReturningFunctionType (/tmp/workspace/node_modules/@typescript-eslint/eslint-plugin/src/rules/no-misused-promises.ts:625:33)
    at checkThenableOrVoidArgument (/tmp/workspace/node_modules/@typescript-eslint/eslint-plugin/src/rules/no-misused-promises.ts:497:7)
    at voidFunctionArguments (/tmp/workspace/node_modules/@typescript-eslint/eslint-plugin/src/rules/no-misused-promises.ts:568:15)
    at checkArguments (/tmp/workspace/node_modules/@typescript-eslint/eslint-plugin/src/rules/no-misused-promises.ts:216:24)
    at ruleErrorHandler (/tmp/workspace/node_modules/eslint/lib/linter/linter.js:1114:28)
    at /tmp/workspace/node_modules/eslint/lib/linter/safe-emitter.js:45:58
    at Array.forEach (<anonymous>)
    at Object.emit (/tmp/workspace/node_modules/eslint/lib/linter/safe-emitter.js:45:38)

The issue seems to be coming from a function being called in that file. That function is defined in a polymorphism manner with rest args.

For instance, this produces the error:

function getInnerValue(...args: readonly []): undefined;
function getInnerValue(...args: readonly [string]): undefined;
function getInnerValue(..._args: readonly string[]): undefined {
	return undefined;
}

export function getValue(): undefined {
	return getInnerValue('a');
}

But this does not:

function getInnerValue(args: readonly []): undefined;
function getInnerValue(args: readonly [string]): undefined;
function getInnerValue(_args: readonly string[]): undefined {
	return undefined;
}

export function getValue(): undefined {
	return getInnerValue(['a']);
}

And neither does this:

function getInnerValue(...args: readonly string[]): undefined {
	return undefined;
}

export function getValue(): undefined {
	return getInnerValue('a');
}

[jlowcs]

submitted an issue: #5807