fix(eslint-plugin): [no-misused-promises] avoid unnecessary calls to getContextualType

[scottarver]

PR Checklist

• Addresses an existing open issue: fixes Enhancement: no-misused-promises small performance improvement, avoiding unnecessary call to getContextualType #6186
• That issue was marked as accepting prs
• Steps in CONTRIBUTING.md were taken

Overview

It appears that returnsThenable is faster than getContextualType in almost all cases.
This PR only calls getContextualType when needed, after returnsThenable returns true.

I ran numbers on how often this is the case: Out of 19,425 total checks, only 96 (33+63) needed a call to getContextualType, this saved 19329 (17289 + 2040 ) calls to getContextualType by short circuiting with returnsThenable
Also of note on average, returnsThenable took 0.12891074558698418ms to run vs getContextualType taking 0.5058407855855643ms, saving 9.8 seconds.

total time saved:  9817.560766001232
{
  thenableAndContextual: 33,
  NotThenableAndContextual: 17289,
  thenableAndNotContextual: 63,
  NotThenableAndNotContextual: 2040
}
thenable count:  19425
thenable average: 0.12891074558698418
contextualType count:  19425
contextualType average: 0.5058407855855643

Using the chrome profiler to compare: ran with node --inspect-brk ./node_modules/.bin/eslint src
Each check* fn has to be looked at together as a whole, in the table below on a single run it saved 1.2 seconds

Before	After

	before	after
checkTestConditional	73.6	77
checkConditional	2.4	3.6
checkAssignment	1.7	2.9
checkVariableDeclaration	1160.5	1207.4
checkProperty	74.4	40.2
checkReturnStatement	9.2	56.1
checkJSXAttribute	2076.9	754.7
checkArguments	121.6	125.6
checkSpread	5.5	4.4		ms diff	seconds
	3525.8	2271.9		1253.9	1.2539

[typescript-eslint]

Thanks for the PR, @scottarver!

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 #6193 (b039619) into main (2b2a075) will increase coverage by 6.06%.
The diff coverage is 63.63%.

❗ Current head b039619 differs from pull request most recent head 8797d46. Consider uploading reports for the commit 8797d46 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6193      +/-   ##
==========================================
+ Coverage   85.16%   91.23%   +6.06%     
==========================================
  Files         383      366      -17     
  Lines       13025    12442     -583     
  Branches     3839     3645     -194     
==========================================
+ Hits        11093    11351     +258     
+ Misses       1570      780     -790     
+ Partials      362      311      -51     

Flag	Coverage Δ
unittest	91.23% <63.63%> (+6.06%)	⬆️

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	95.63% <63.63%> (-2.85%)	⬇️

... and 65 files with indirect coverage changes

[JoshuaKGoldberg]

This started out as a nice performance improvement - and now is also an unnecessary code removal and/or test expansion opportunity! Great either way 😄

[JoshuaKGoldberg]

👋 ping @scottarver - is this still something you have time for? No worries if not, just checking in.

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✅ Successfully ran 25 targets

• Node 14 - nx test eslint-plugin --coverage=false
• Node 18 - nx test eslint-plugin
• Node 18 - nx test visitor-keys
• Node 18 - nx run-many --target=build --parallel --exclude website
• Node 18 - nx test utils
• Node 18 - nx test typescript-estree
• nx run-many --target=lint --parallel
• nx run-many --target=typecheck --parallel
• Node 14 - nx test eslint-plugin-internal --coverage=false
• Node 14 - nx run-many --target=build --parallel --exclude website
• Node 14 - nx test parser --coverage=false
• Node 14 - nx test ast-spec --coverage=false
• Node 18 - nx test eslint-plugin-internal
• Node 14 - nx test typescript-estree --coverage=false
• Node 14 - nx test scope-manager --coverage=false
• Node 14 - nx test eslint-plugin-tslint --coverage=false
• Node 18 - nx test scope-manager
• Node 14 - nx test utils --coverage=false
• Node 18 - nx test type-utils
• Node 14 - nx test visitor-keys --coverage=false
• Node 18 - nx test parser
• nx run-many --target=build --parallel --exclude website
• Node 14 - nx test type-utils --coverage=false
• Node 18 - nx test ast-spec
• Node 18 - nx test eslint-plugin-tslint

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[JoshuaKGoldberg]

Ooh, I removed some more calls and all of the unit tests are failing... but now we've got lint failures in the project itself. So we've got to add unit tests! 🙌

https://cloud.nx.app/runs/NHi3D9Xh0H

/home/runner/work/typescript-eslint/typescript-eslint/packages/eslint-plugin/src/rules/adjacent-overload-signatures.ts
  172:18  error  Promise-returning function provided to property where a void return was expected  @typescript-eslint/no-misused-promises
  173:16  error  Promise-returning function provided to property where a void return was expected  @typescript-eslint/no-misused-promises
  174:22  error  Promise-returning function provided to property where a void return was expected  @typescript-eslint/no-misused-promises
  175:22  error  Promise-returning function provided to property where a void return was expected  @typescript-eslint/no-misused-promises
  176:24  error  Promise-returning function provided to property where a void return was expected  @typescript-eslint/no-misused-promises
  177:23  error  Promise-returning function provided to property where a void return was expected  @typescript-eslint/no-misused-promises

/home/runner/work/typescript-eslint/typescript-eslint/packages/eslint-plugin/src/rules/ban-types.ts
  203:41  error  Promise-returning function provided to variable where a void return was expected  @typescript-eslint/no-misused-promises

/home/runner/work/typescript-eslint/typescript-eslint/packages/eslint-plugin/src/rules/block-spacing.ts
...

Edit: 8797d46 ✅

[bradzacher]

It's worth noting that the two functions in question have different usecases. returnsThenable uses the "apparent type" which is sometimes different to the contextual type (I believe??)

Cc @jakebailey this is an example of a piece of the TS API that isn't very clear - type vs apparent type vs instantiated type vs contextual type. I couldn't find any documentation about what to use and when.

[jakebailey]

Truthfully I didn't even realize these APIs were available, let alone useful externally. Clearly, I'm wrong.

I think someone more experienced than me will have to write out explanations of those. I'll file an issue to track this request; meant to do that post-meeting but forgot.