Improve logic that chooses co- vs. contra-variant inferences

[Mateusz Burzyński (Andarist)]

To review this it might be helpful to see how this evolved over time:
#27028
#46392
#52123
#52180
#54072

The reason why this inference fails today is that isTypeSubtypeOf leads to requireOptionalProperties === true. This has such inferences:

inferredCovariantType// { query: string }inferredContravariantType// { query?: unknown; body?: unknown; }

So the covariant inference lacks body property and thus it fails the check and the contravariant inference gets chosen at the end.

fixes#57908
fixes#58468

[TypeScript Bot (typescript-bot)]

This PR doesn't have any linked issues. Please open an issue that references this PR. From there we can discuss and prioritise.

[Jake Bailey (jakebailey)]

TypeScript Bot (@typescript-bot) test top800
TypeScript Bot (@typescript-bot) user test this
TypeScript Bot (@typescript-bot) run dt

TypeScript Bot (@typescript-bot) perf test this faster

[TypeScript Bot (typescript-bot)]

Starting jobs; this comment will be updated as builds start and complete.

Command	Status	Results
test top800	✅ Started
user test this	✅ Started	👀 Results
run dt	✅ Started	👀 Results
perf test this faster	✅ Started	👀 Results

[Mateusz Burzyński (Andarist)]

If this is not the correct change then at the very least a test case should be proposed that shows how the isTypeSubtypeOf is better.

When this check was originally introduced by Anders Hejlsberg (@ahejlsberg)here it was states that:

Furthermore, knowing that an error will result when the co-variant inference is not a subtype of the contra-variant inference, we now prefer the contra-variant inference because it is likely to have come from an explicit type annotation on a function. This improves our error reporting.

An alternative idea to fix this example would be to keep coAndContraRelationCheck on inferenceContext. From what I understand, the subtypeRelation in this context is mainly used when dealing with multiple overloads - a single signature case uses assignableRelation with chooseOverload. So perhaps the used relation should determine what is being used here.

[TypeScript Bot (typescript-bot)]

Hey Jake Bailey (@jakebailey), the results of running the DT tests are ready.

There were interesting changes:

Branch only errors:

Package: react
Error:

Error: /mnt/vss/_work/1/DefinitelyTyped/types/react/test/index.ts
794:5 error TypeScript@local compile error: Unused '@ts-expect-error' directive @definitelytyped/expect
✖ 1 problem (1 error, 0 warnings)
at combineErrorsAndWarnings (/mnt/vss/_work/1/DefinitelyTyped/node_modules/.pnpm/@definitelytyped+dtslint@0.2.18_typescript@5.5.0-dev.20240322/node_modules/@definitelytyped/dtslint/dist/index.js:194:28)
at runTests (/mnt/vss/_work/1/DefinitelyTyped/node_modules/.pnpm/@definitelytyped+dtslint@0.2.18_typescript@5.5.0-dev.20240322/node_modules/@definitelytyped/dtslint/dist/index.js:186:20)

Package: styled-theming
Error:

Error: /mnt/vss/_work/1/DefinitelyTyped/types/styled-theming/styled-theming-tests.tsx
72:47 error TypeScript@local compile error: No overload matches this call.
The last overload gave the following error.
Type '"wrong variant"' is not assignable to type '"primary" | "secondary" | undefined' @definitelytyped/expect
✖ 1 problem (1 error, 0 warnings)
at combineErrorsAndWarnings (/mnt/vss/_work/1/DefinitelyTyped/node_modules/.pnpm/@definitelytyped+dtslint@0.2.18_typescript@5.5.0-dev.20240322/node_modules/@definitelytyped/dtslint/dist/index.js:194:28)
at runTests (/mnt/vss/_work/1/DefinitelyTyped/node_modules/.pnpm/@definitelytyped+dtslint@0.2.18_typescript@5.5.0-dev.20240322/node_modules/@definitelytyped/dtslint/dist/index.js:186:20)

You can check the log here.

[TypeScript Bot (typescript-bot)]

Jake Bailey (@jakebailey) Here are the results of running the user tests comparing main and refs/pull/57909/merge:

Something interesting changed - please have a look.

Details

uglify-js

/mnt/ts_downloads/_/m/uglify-js/tsconfig.json

• [NEW] error TS2684: The 'this' context of type '(...items: never[]) => number' is not assignable to method's 'this' of type '(this: any[], ...args: any) => number'.
  • /mnt/ts_downloads/_/m/uglify-js/node_modules/uglify-js/lib/compress.js(293,17)
  • /mnt/ts_downloads/_/m/uglify-js/node_modules/uglify-js/lib/compress.js(2472,29)
  • /mnt/ts_downloads/_/m/uglify-js/node_modules/uglify-js/lib/compress.js(7469,47)
  • /mnt/ts_downloads/_/m/uglify-js/node_modules/uglify-js/lib/compress.js(14005,13)
• [NEW] error TS2684: The 'this' context of type '(...items: never[]) => number' is not assignable to method's 'this' of type '(this: any, ...args: any) => number'.
  • /mnt/ts_downloads/_/m/uglify-js/node_modules/uglify-js/lib/compress.js(1867,13)
  • /mnt/ts_downloads/_/m/uglify-js/node_modules/uglify-js/lib/compress.js(7298,64)
  • /mnt/ts_downloads/_/m/uglify-js/node_modules/uglify-js/lib/compress.js(7981,33)
  • /mnt/ts_downloads/_/m/uglify-js/node_modules/uglify-js/lib/compress.js(8012,29)
  • /mnt/ts_downloads/_/m/uglify-js/node_modules/uglify-js/lib/compress.js(14002,17)
  • /mnt/ts_downloads/_/m/uglify-js/node_modules/uglify-js/lib/parse.js(1863,17)

[TypeScript Bot (typescript-bot)]

Jake Bailey (@jakebailey)
The results of the perf run you requested are in!

Here they are:

tsc

Comparison Report - baseline..pr

Metric	baseline	pr	Delta	Best	Worst	p-value
Angular - node (v18.15.0, x64)
Memory used	295,529k (± 0.00%)	295,524k (± 0.00%)	~	295,506k	295,544k	p=0.423 n=6
Parse Time	2.66s (± 0.31%)	2.66s (± 0.28%)	~	2.65s	2.67s	p=0.209 n=6
Bind Time	0.83s (± 0.66%)	0.82s (± 0.99%)	~	0.81s	0.83s	p=0.859 n=6
Check Time	8.20s (± 0.37%)	8.20s (± 0.15%)	~	8.18s	8.21s	p=0.809 n=6
Emit Time	7.04s (± 0.20%)	7.09s (± 0.88%)	~	7.00s	7.18s	p=0.107 n=6
Total Time	18.72s (± 0.16%)	18.76s (± 0.32%)	~	18.69s	18.86s	p=0.225 n=6
Compiler-Unions - node (v18.15.0, x64)
Memory used	191,964k (± 0.06%)	193,733k (± 0.95%)	~	191,878k	195,497k	p=0.128 n=6
Parse Time	1.36s (± 0.89%)	1.36s (± 1.21%)	~	1.33s	1.38s	p=1.000 n=6
Bind Time	0.72s (± 0.00%)	0.72s (± 0.00%)	~	0.72s	0.72s	p=1.000 n=6
Check Time	9.56s (± 0.60%)	9.49s (± 0.37%)	-0.08s (- 0.80%)	9.44s	9.54s	p=0.045 n=6
Emit Time	2.62s (± 0.51%)	2.63s (± 0.64%)	~	2.61s	2.65s	p=0.227 n=6
Total Time	14.26s (± 0.40%)	14.19s (± 0.39%)	~	14.11s	14.28s	p=0.090 n=6
Monaco - node (v18.15.0, x64)
Memory used	347,372k (± 0.01%)	347,374k (± 0.01%)	~	347,324k	347,407k	p=0.873 n=6
Parse Time	2.47s (± 0.33%)	2.48s (± 0.40%)	~	2.47s	2.49s	p=0.498 n=6
Bind Time	0.93s (± 0.44%)	0.92s (± 0.59%)	~	0.92s	0.93s	p=0.282 n=6
Check Time	7.00s (± 0.41%)	7.02s (± 0.49%)	~	6.97s	7.07s	p=0.465 n=6
Emit Time	4.08s (± 0.37%)	4.07s (± 0.40%)	~	4.04s	4.08s	p=0.157 n=6
Total Time	14.49s (± 0.26%)	14.49s (± 0.23%)	~	14.45s	14.55s	p=0.872 n=6
TFS - node (v18.15.0, x64)
Memory used	302,726k (± 0.02%)	302,708k (± 0.01%)	~	302,678k	302,760k	p=0.575 n=6
Parse Time	2.41s (± 0.68%)	2.39s (± 1.72%)	~	2.34s	2.44s	p=0.571 n=6
Bind Time	1.19s (± 0.53%)	1.19s (± 1.02%)	~	1.17s	1.20s	p=0.673 n=6
Check Time	7.44s (± 0.56%)	7.45s (± 0.46%)	~	7.41s	7.50s	p=0.376 n=6
Emit Time	4.28s (± 0.41%)	4.29s (± 0.58%)	~	4.26s	4.33s	p=1.000 n=6
Total Time	15.33s (± 0.34%)	15.32s (± 0.48%)	~	15.24s	15.42s	p=0.688 n=6
material-ui - node (v18.15.0, x64)
Memory used	509,876k (± 0.01%)	509,895k (± 0.00%)	~	509,875k	509,907k	p=0.125 n=6
Parse Time	2.64s (± 0.37%)	2.65s (± 0.65%)	~	2.63s	2.67s	p=0.215 n=6
Bind Time	0.99s (± 0.99%)	0.98s (± 0.56%)	~	0.98s	0.99s	p=0.322 n=6
Check Time	17.23s (± 0.22%)	17.23s (± 0.37%)	~	17.15s	17.32s	p=1.000 n=6
Emit Time	0.00s (± 0.00%)	0.00s (± 0.00%)	~	0.00s	0.00s	p=1.000 n=6
Total Time	20.86s (± 0.19%)	20.87s (± 0.29%)	~	20.81s	20.98s	p=0.746 n=6
mui-docs - node (v18.15.0, x64)
Memory used	1,737,544k (± 0.00%)	1,737,524k (± 0.00%)	~	1,737,491k	1,737,554k	p=0.230 n=6
Parse Time	7.78s (± 0.38%)	7.80s (± 0.61%)	~	7.74s	7.88s	p=0.373 n=6
Bind Time	2.80s (± 0.32%)	2.81s (± 0.83%)	~	2.78s	2.84s	p=0.806 n=6
Check Time	66.38s (± 0.34%)	66.49s (± 0.45%)	~	66.11s	66.91s	p=0.521 n=6
Emit Time	0.15s (± 3.53%)	0.16s (± 3.29%)	~	0.15s	0.16s	p=0.640 n=6
Total Time	77.12s (± 0.32%)	77.25s (± 0.34%)	~	76.98s	77.63s	p=0.471 n=6
self-build-src - node (v18.15.0, x64)
Memory used	2,394,217k (± 0.02%)	2,393,952k (± 0.04%)	~	2,392,566k	2,394,786k	p=0.471 n=6
Parse Time	6.07s (± 0.90%)	6.07s (± 0.68%)	~	6.02s	6.11s	p=0.688 n=6
Bind Time	2.26s (± 0.52%)	2.24s (± 1.68%)	~	2.17s	2.28s	p=0.415 n=6
Check Time	39.48s (± 0.29%)	39.61s (± 0.22%)	+0.14s (+ 0.34%)	39.48s	39.73s	p=0.045 n=6
Emit Time	3.12s (± 0.48%)	3.15s (± 1.61%)	~	3.08s	3.21s	p=0.520 n=6
Total Time	50.94s (± 0.22%)	51.08s (± 0.20%)	+0.14s (+ 0.27%)	50.89s	51.20s	p=0.045 n=6
self-compiler - node (v18.15.0, x64)
Memory used	415,185k (± 0.01%)	415,193k (± 0.01%)	~	415,144k	415,226k	p=0.936 n=6
Parse Time	3.43s (± 0.96%)	3.42s (± 0.75%)	~	3.39s	3.45s	p=0.807 n=6
Bind Time	1.29s (± 0.76%)	1.29s (± 0.82%)	~	1.27s	1.30s	p=0.547 n=6
Check Time	18.02s (± 0.35%)	18.01s (± 0.43%)	~	17.89s	18.11s	p=0.872 n=6
Emit Time	1.31s (± 1.12%)	1.32s (± 0.88%)	~	1.31s	1.34s	p=0.324 n=6
Total Time	24.06s (± 0.35%)	24.04s (± 0.30%)	~	23.94s	24.16s	p=0.806 n=6
vscode - node (v18.15.0, x64)
Memory used	2,889,942k (± 0.00%)	2,889,412k (± 0.00%)	-531k (- 0.02%)	2,889,325k	2,889,479k	p=0.005 n=6
Parse Time	12.95s (± 0.27%)	12.94s (± 0.27%)	~	12.91s	13.00s	p=0.683 n=6
Bind Time	4.13s (± 0.82%)	4.14s (± 0.64%)	~	4.10s	4.17s	p=0.746 n=6
Check Time	71.13s (± 0.24%)	71.45s (± 0.31%)	+0.32s (+ 0.45%)	71.14s	71.74s	p=0.045 n=6
Emit Time	19.50s (± 0.88%)	19.40s (± 0.79%)	~	19.18s	19.60s	p=0.336 n=6
Total Time	107.71s (± 0.35%)	107.93s (± 0.32%)	~	107.57s	108.40s	p=0.378 n=6
webpack - node (v18.15.0, x64)
Memory used	408,193k (± 0.03%)	408,153k (± 0.01%)	~	408,080k	408,221k	p=0.810 n=6
Parse Time	3.89s (± 0.72%)	3.90s (± 0.67%)	~	3.86s	3.94s	p=0.623 n=6
Bind Time	1.67s (± 0.49%)	1.69s (± 0.89%)	+0.02s (+ 1.20%)	1.67s	1.70s	p=0.031 n=6
Check Time	16.80s (± 0.32%)	16.72s (± 0.20%)	-0.08s (- 0.46%)	16.67s	16.77s	p=0.037 n=6
Emit Time	0.00s (± 0.00%)	0.00s (± 0.00%)	~	0.00s	0.00s	p=1.000 n=6
Total Time	22.36s (± 0.18%)	22.31s (± 0.20%)	~	22.25s	22.36s	p=0.077 n=6
xstate - node (v18.15.0, x64)
Memory used	512,982k (± 0.01%)	513,035k (± 0.02%)	~	512,919k	513,174k	p=0.471 n=6
Parse Time	3.96s (± 0.43%)	3.94s (± 0.42%)	~	3.92s	3.97s	p=0.052 n=6
Bind Time	1.85s (± 0.90%)	1.85s (± 1.15%)	~	1.82s	1.87s	p=1.000 n=6
Check Time	3.37s (± 0.55%)	3.37s (± 0.24%)	~	3.36s	3.38s	p=0.870 n=6
Emit Time	0.08s (± 6.19%)	0.09s (± 6.44%)	~	0.08s	0.09s	p=0.640 n=6
Total Time	9.28s (± 0.19%)	9.25s (± 0.33%)	~	9.22s	9.30s	p=0.090 n=6

System info unknown

Hosts

• node (v18.15.0, x64)

Scenarios

• Angular - node (v18.15.0, x64)
• Compiler-Unions - node (v18.15.0, x64)
• Monaco - node (v18.15.0, x64)
• TFS - node (v18.15.0, x64)
• material-ui - node (v18.15.0, x64)
• mui-docs - node (v18.15.0, x64)
• self-build-src - node (v18.15.0, x64)
• self-compiler - node (v18.15.0, x64)
• vscode - node (v18.15.0, x64)
• webpack - node (v18.15.0, x64)
• xstate - node (v18.15.0, x64)

Benchmark	Name	Iterations
Current	pr	6
Baseline	baseline	6

Developer Information:

Download Benchmarks

[Jake Bailey (jakebailey)]

TypeScript Bot (@typescript-bot) pack this

[TypeScript Bot (typescript-bot)]

Starting jobs; this comment will be updated as builds start and complete.

Command	Status	Results
pack this	✅ Started	✅ Results

[TypeScript Bot (typescript-bot)]

Hey Jake Bailey (@jakebailey), I've packed this into an installable tgz. You can install it for testing by referencing it in your package.json like so:

{
"devDependencies": {
"typescript": "https://typescript.visualstudio.com/cf7ac146-d525-443c-b23c-0d58337efebc/_apis/build/builds/160700/artifacts?artifactName=tgz&fileId=09532E0BDDB3EF1D0C0185CBFA531EE829D75833400D06C510FCB93118E30D0C02&fileName=/typescript-5.5.0-insiders.20240322.tgz"
}
}

and then running npm install.

---

There is also a playground for this build and an npm module you can use via "typescript": "npm:@typescript-deploys/pr-build@5.5.0-pr-57909-8".;

[Mateusz Burzyński (Andarist)]

Jake Bailey (@jakebailey) could you rerun top800, dt and perf suites? a new playground would also be appreciated :)

[Jake Bailey (jakebailey)]

TypeScript Bot (@typescript-bot) test top800
TypeScript Bot (@typescript-bot) user test this
TypeScript Bot (@typescript-bot) run dt

TypeScript Bot (@typescript-bot) perf test this faster
TypeScript Bot (@typescript-bot) pack this

[TypeScript Bot (typescript-bot)]

Starting jobs; this comment will be updated as builds start and complete.

Command	Status	Results
test top800	✅ Started	✅ Results
user test this	✅ Started	✅ Results
run dt	✅ Started	👀 Results
perf test this faster	✅ Started	👀 Results
pack this	✅ Started	✅ Results

[TypeScript Bot (typescript-bot)]

Hey Jake Bailey (@jakebailey), I've packed this into an installable tgz. You can install it for testing by referencing it in your package.json like so:

{
"devDependencies": {
"typescript": "https://typescript.visualstudio.com/cf7ac146-d525-443c-b23c-0d58337efebc/_apis/build/builds/160702/artifacts?artifactName=tgz&fileId=C476EBF980531EB5F87264AF4D7EFD709FC10481D708D1A72266850B714544B902&fileName=/typescript-5.5.0-insiders.20240323.tgz"
}
}

and then running npm install.

---

There is also a playground for this build and an npm module you can use via "typescript": "npm:@typescript-deploys/pr-build@5.5.0-pr-57909-12".;

[TypeScript Bot (typescript-bot)]

Hey Jake Bailey (@jakebailey), the results of running the DT tests are ready.

There were interesting changes:

Branch only errors:

Package: styled-theming
Error:

Error: /mnt/vss/_work/1/DefinitelyTyped/types/styled-theming/styled-theming-tests.tsx
72:47 error TypeScript@local compile error: No overload matches this call.
The last overload gave the following error.
Type '"wrong variant"' is not assignable to type '"primary" | "secondary" | undefined' @definitelytyped/expect
✖ 1 problem (1 error, 0 warnings)
at combineErrorsAndWarnings (/mnt/vss/_work/1/DefinitelyTyped/node_modules/.pnpm/@definitelytyped+dtslint@0.2.18_typescript@5.5.0-dev.20240323/node_modules/@definitelytyped/dtslint/dist/index.js:194:28)
at runTests (/mnt/vss/_work/1/DefinitelyTyped/node_modules/.pnpm/@definitelytyped+dtslint@0.2.18_typescript@5.5.0-dev.20240323/node_modules/@definitelytyped/dtslint/dist/index.js:186:20)

You can check the log here.

[TypeScript Bot (typescript-bot)]

Jake Bailey (@jakebailey) Here are the results of running the user tests comparing main and refs/pull/57909/merge:

Everything looks good!

[TypeScript Bot (typescript-bot)]

Jake Bailey (@jakebailey)
The results of the perf run you requested are in!

Here they are:

tsc

Comparison Report - baseline..pr

Metric	baseline	pr	Delta	Best	Worst	p-value
Angular - node (v18.15.0, x64)
Memory used	295,530k (± 0.01%)	295,537k (± 0.01%)	~	295,512k	295,555k	p=1.000 n=6
Parse Time	2.66s (± 0.37%)	2.66s (± 0.28%)	~	2.65s	2.67s	p=0.652 n=6
Bind Time	0.82s (± 0.66%)	0.83s (± 0.49%)	~	0.83s	0.84s	p=0.054 n=6
Check Time	8.20s (± 0.32%)	8.22s (± 0.60%)	~	8.17s	8.29s	p=0.872 n=6
Emit Time	7.07s (± 0.35%)	7.05s (± 0.64%)	~	7.02s	7.14s	p=0.222 n=6
Total Time	18.76s (± 0.19%)	18.76s (± 0.33%)	~	18.68s	18.84s	p=1.000 n=6
Compiler-Unions - node (v18.15.0, x64)
Memory used	192,468k (± 0.73%)	194,259k (± 0.94%)	~	191,886k	195,602k	p=0.093 n=6
Parse Time	1.37s (± 0.97%)	1.36s (± 1.52%)	~	1.33s	1.39s	p=0.250 n=6
Bind Time	0.72s (± 0.00%)	0.72s (± 0.00%)	~	0.72s	0.72s	p=1.000 n=6
Check Time	9.51s (± 0.66%)	9.52s (± 0.57%)	~	9.43s	9.59s	p=1.000 n=6
Emit Time	2.63s (± 0.95%)	2.62s (± 0.96%)	~	2.58s	2.64s	p=0.461 n=6
Total Time	14.23s (± 0.53%)	14.21s (± 0.41%)	~	14.11s	14.26s	p=0.573 n=6
Monaco - node (v18.15.0, x64)
Memory used	347,373k (± 0.01%)	347,383k (± 0.00%)	~	347,358k	347,402k	p=0.575 n=6
Parse Time	2.48s (± 0.33%)	2.48s (± 0.30%)	~	2.47s	2.49s	p=0.729 n=6
Bind Time	0.93s (± 0.88%)	0.93s (± 0.56%)	~	0.92s	0.93s	p=0.929 n=6
Check Time	7.00s (± 0.49%)	7.00s (± 0.38%)	~	6.97s	7.04s	p=0.686 n=6
Emit Time	4.07s (± 0.34%)	4.07s (± 0.26%)	~	4.05s	4.08s	p=1.000 n=6
Total Time	14.48s (± 0.28%)	14.48s (± 0.18%)	~	14.45s	14.52s	p=0.808 n=6
TFS - node (v18.15.0, x64)
Memory used	302,725k (± 0.01%)	302,715k (± 0.02%)	~	302,659k	302,798k	p=0.575 n=6
Parse Time	2.40s (± 1.41%)	2.51s (± 8.80%)	~	2.39s	2.96s	p=0.260 n=6
Bind Time	1.21s (± 0.68%)	1.24s (±10.13%)	~	1.18s	1.50s	p=0.230 n=6
Check Time	7.46s (± 0.50%)	7.75s (± 9.17%)	~	7.43s	9.20s	p=0.574 n=6
Emit Time	4.29s (± 0.54%)	4.45s (± 9.53%)	~	4.25s	5.31s	p=0.571 n=6
Total Time	15.35s (± 0.38%)	15.95s (± 9.29%)	~	15.32s	18.97s	p=0.748 n=6
material-ui - node (v18.15.0, x64)
Memory used	509,900k (± 0.00%)	509,884k (± 0.00%)	~	509,859k	509,917k	p=0.128 n=6
Parse Time	2.66s (± 0.63%)	2.65s (± 0.70%)	~	2.62s	2.67s	p=0.325 n=6
Bind Time	0.99s (± 1.05%)	0.99s (± 0.82%)	~	0.98s	1.00s	p=0.270 n=6
Check Time	17.22s (± 0.44%)	17.23s (± 0.53%)	~	17.17s	17.41s	p=0.936 n=6
Emit Time	0.00s (± 0.00%)	0.00s (± 0.00%)	~	0.00s	0.00s	p=1.000 n=6
Total Time	20.86s (± 0.41%)	20.87s (± 0.48%)	~	20.81s	21.07s	p=0.936 n=6
mui-docs - node (v18.15.0, x64)
Memory used	1,737,562k (± 0.00%)	1,737,442k (± 0.00%)	-120k (- 0.01%)	1,737,418k	1,737,479k	p=0.005 n=6
Parse Time	7.77s (± 0.27%)	7.79s (± 0.86%)	~	7.73s	7.92s	p=0.746 n=6
Bind Time	2.80s (± 0.27%)	2.80s (± 0.42%)	~	2.79s	2.82s	p=0.933 n=6
Check Time	66.67s (± 0.41%)	66.46s (± 0.27%)	~	66.19s	66.65s	p=0.229 n=6
Emit Time	0.15s (± 2.69%)	0.15s (± 3.36%)	~	0.15s	0.16s	p=0.595 n=6
Total Time	77.40s (± 0.34%)	77.21s (± 0.22%)	~	76.94s	77.36s	p=0.173 n=6
self-build-src - node (v18.15.0, x64)
Memory used	2,393,895k (± 0.05%)	2,393,977k (± 0.02%)	~	2,393,272k	2,394,910k	p=0.471 n=6
Parse Time	6.10s (± 0.95%)	6.05s (± 1.13%)	~	5.96s	6.14s	p=0.261 n=6
Bind Time	2.26s (± 0.78%)	2.25s (± 1.21%)	~	2.20s	2.27s	p=1.000 n=6
Check Time	39.45s (± 0.41%)	39.49s (± 0.41%)	~	39.38s	39.81s	p=0.810 n=6
Emit Time	3.10s (± 2.12%)	3.11s (± 1.39%)	~	3.04s	3.17s	p=0.936 n=6
Total Time	50.90s (± 0.36%)	50.93s (± 0.40%)	~	50.74s	51.30s	p=0.936 n=6
self-compiler - node (v18.15.0, x64)
Memory used	415,116k (± 0.01%)	415,122k (± 0.01%)	~	415,083k	415,153k	p=0.936 n=6
Parse Time	4.19s (± 0.63%)	4.20s (± 0.53%)	~	4.17s	4.23s	p=0.864 n=6
Bind Time	1.58s (± 1.36%)	1.60s (± 1.62%)	~	1.56s	1.63s	p=0.421 n=6
Check Time	22.33s (± 0.38%)	22.27s (± 0.47%)	~	22.16s	22.46s	p=0.228 n=6
Emit Time	1.65s (± 0.99%)	1.66s (± 0.62%)	~	1.65s	1.67s	p=0.242 n=6
Total Time	29.76s (± 0.35%)	29.72s (± 0.32%)	~	29.62s	29.88s	p=0.575 n=6
vscode - node (v18.15.0, x64)
Memory used	2,891,049k (± 0.00%)	2,891,279k (± 0.00%)	+230k (+ 0.01%)	2,891,226k	2,891,343k	p=0.005 n=6
Parse Time	12.93s (± 0.35%)	12.92s (± 0.26%)	~	12.88s	12.98s	p=1.000 n=6
Bind Time	4.13s (± 0.54%)	4.13s (± 0.32%)	~	4.12s	4.15s	p=0.807 n=6
Check Time	71.47s (± 0.29%)	71.67s (± 0.34%)	~	71.32s	71.99s	p=0.230 n=6
Emit Time	19.43s (± 0.95%)	19.41s (± 0.84%)	~	19.25s	19.64s	p=0.872 n=6
Total Time	107.96s (± 0.27%)	108.12s (± 0.24%)	~	107.85s	108.59s	p=0.575 n=6
webpack - node (v18.15.0, x64)
Memory used	408,129k (± 0.01%)	408,163k (± 0.01%)	~	408,104k	408,215k	p=0.173 n=6
Parse Time	3.90s (± 0.70%)	3.89s (± 0.23%)	~	3.88s	3.90s	p=0.934 n=6
Bind Time	1.68s (± 0.58%)	1.67s (± 0.76%)	~	1.65s	1.69s	p=0.116 n=6
Check Time	16.78s (± 0.24%)	16.74s (± 0.20%)	~	16.69s	16.77s	p=0.086 n=6
Emit Time	0.00s (± 0.00%)	0.00s (± 0.00%)	~	0.00s	0.00s	p=1.000 n=6
Total Time	22.36s (± 0.24%)	22.31s (± 0.19%)	~	22.25s	22.36s	p=0.064 n=6
xstate - node (v18.15.0, x64)
Memory used	513,044k (± 0.02%)	513,043k (± 0.02%)	~	512,923k	513,149k	p=0.936 n=6
Parse Time	3.95s (± 0.55%)	3.94s (± 0.30%)	~	3.92s	3.95s	p=0.747 n=6
Bind Time	1.84s (± 0.95%)	1.85s (± 0.99%)	~	1.83s	1.87s	p=0.508 n=6
Check Time	3.37s (± 0.99%)	3.37s (± 0.55%)	~	3.35s	3.40s	p=0.515 n=6
Emit Time	0.09s (± 6.44%)	0.08s (± 4.99%)	~	0.08s	0.09s	p=0.282 n=6
Total Time	9.24s (± 0.61%)	9.25s (± 0.38%)	~	9.19s	9.29s	p=0.688 n=6

System info unknown

Hosts

• node (v18.15.0, x64)

Scenarios

• Angular - node (v18.15.0, x64)
• Compiler-Unions - node (v18.15.0, x64)
• Monaco - node (v18.15.0, x64)
• TFS - node (v18.15.0, x64)
• material-ui - node (v18.15.0, x64)
• mui-docs - node (v18.15.0, x64)
• self-build-src - node (v18.15.0, x64)
• self-compiler - node (v18.15.0, x64)
• vscode - node (v18.15.0, x64)
• webpack - node (v18.15.0, x64)
• xstate - node (v18.15.0, x64)

Benchmark	Name	Iterations
Current	pr	6
Baseline	baseline	6

Developer Information:

Download Benchmarks

[TypeScript Bot (typescript-bot)]

Jake Bailey (@jakebailey) Here are the results of running the top 800 repos comparing main and refs/pull/57909/merge:

Everything looks good!

[Mateusz Burzyński (Andarist)]

The only reported error here is actually desired! See the comment here. I didn't look into this one before because of that and because it just involves multiple libraries with complicated type. I plan to reduce it to a test case now and add it here.

EDIT:// From this initial repro: TS playground to this TS playground. It's pretty lengthy but I already have problems with removing from it just about anything.

[Mateusz Burzyński (Andarist)]

Still just one error :p and I have commented on it already here

[TypeScript Bot (typescript-bot)]

Jake Bailey (@jakebailey)
The results of the perf run you requested are in!

Here they are:

tsc

Comparison Report - baseline..pr

Metric	baseline	pr	Delta	Best	Worst	p-value
Compiler-Unions - node (v18.15.0, x64)
Errors	30	30	~	~	~	p=1.000 n=6
Symbols	62,154	62,154	~	~	~	p=1.000 n=6
Types	50,248	50,248	~	~	~	p=1.000 n=6
Memory used	192,795k (± 0.76%)	192,759k (± 0.78%)	~	192,109k	195,825k	p=0.378 n=6
Parse Time	1.29s (± 1.74%)	1.30s (± 1.16%)	~	1.28s	1.31s	p=0.864 n=6
Bind Time	0.72s	0.72s	~	~	~	p=1.000 n=6
Check Time	9.52s (± 0.32%)	9.51s (± 0.19%)	~	9.49s	9.54s	p=0.419 n=6
Emit Time	2.65s (± 0.19%)	2.64s (± 0.31%)	-0.01s (- 0.38%)	2.63s	2.65s	p=0.050 n=6
Total Time	14.19s (± 0.36%)	14.16s (± 0.13%)	~	14.13s	14.18s	p=0.294 n=6
angular-1 - node (v18.15.0, x64)
Errors	5	5	~	~	~	p=1.000 n=6
Symbols	944,110	944,120	+10 (+ 0.00%)	~	~	p=0.001 n=6
Types	407,141	407,148	+7 (+ 0.00%)	~	~	p=0.001 n=6
Memory used	1,221,999k (± 0.00%)	1,222,003k (± 0.00%)	~	1,221,955k	1,222,042k	p=1.000 n=6
Parse Time	6.80s (± 0.71%)	6.81s (± 0.66%)	~	6.75s	6.87s	p=0.810 n=6
Bind Time	1.88s (± 0.48%)	1.88s (± 0.88%)	~	1.85s	1.89s	p=0.803 n=6
Check Time	31.09s (± 0.34%)	31.15s (± 0.53%)	~	31.03s	31.47s	p=0.630 n=6
Emit Time	14.72s (± 0.66%)	14.78s (± 0.29%)	~	14.72s	14.84s	p=0.377 n=6
Total Time	54.49s (± 0.17%)	54.61s (± 0.34%)	~	54.42s	54.93s	p=0.173 n=6
mui-docs - node (v18.15.0, x64)
Errors	5	5	~	~	~	p=1.000 n=6
Symbols	1,961,290	1,961,274	-16 (- 0.00%)	~	~	p=0.001 n=6
Types	696,905	696,860	-45 (- 0.01%)	~	~	p=0.001 n=6
Memory used	1,778,074k (± 0.00%)	1,778,019k (± 0.00%)	-56k (- 0.00%)	1,778,006k	1,778,038k	p=0.005 n=6
Parse Time	6.77s (± 0.38%)	6.78s (± 0.24%)	~	6.76s	6.81s	p=0.332 n=6
Bind Time	2.31s (± 1.11%)	2.31s (± 0.22%)	~	2.31s	2.32s	p=0.928 n=6
Check Time	57.01s (± 0.32%)	56.97s (± 0.34%)	~	56.74s	57.28s	p=0.575 n=6
Emit Time	0.14s	0.14s	~	~	~	p=1.000 n=6
Total Time	66.23s (± 0.29%)	66.20s (± 0.28%)	~	65.97s	66.49s	p=0.575 n=6
self-build-src - node (v18.15.0, x64)
Errors	0	0	~	~	~	p=1.000 n=6
Symbols	1,220,247	1,220,280	+33 (+ 0.00%)	~	~	p=0.001 n=6
Types	258,932	258,941	+9 (+ 0.00%)	~	~	p=0.001 n=6
Memory used	2,334,478k (± 0.04%)	2,334,608k (± 0.03%)	~	2,333,545k	2,335,230k	p=0.936 n=6
Parse Time	4.99s (± 1.79%)	4.96s (± 1.57%)	~	4.85s	5.07s	p=0.810 n=6
Bind Time	1.86s (± 0.63%)	1.88s (± 1.00%)	~	1.86s	1.91s	p=0.187 n=6
Check Time	33.48s (± 0.32%)	33.37s (± 0.32%)	~	33.26s	33.54s	p=0.109 n=6
Emit Time	2.61s (± 2.40%)	2.64s (± 1.82%)	~	2.55s	2.68s	p=0.228 n=6
Total Time	42.94s (± 0.46%)	42.86s (± 0.41%)	~	42.72s	43.20s	p=0.630 n=6
self-build-src-public-api - node (v18.15.0, x64)
Errors	0	0	~	~	~	p=1.000 n=6
Symbols	1,220,247	1,220,280	+33 (+ 0.00%)	~	~	p=0.001 n=6
Types	258,932	258,941	+9 (+ 0.00%)	~	~	p=0.001 n=6
Memory used	2,410,887k (± 0.02%)	2,411,704k (± 0.03%)	+817k (+ 0.03%)	2,410,948k	2,412,348k	p=0.045 n=6
Parse Time	7.68s (± 0.84%)	7.73s (± 1.46%)	~	7.58s	7.91s	p=0.378 n=6
Bind Time	2.50s (± 1.87%)	2.50s (± 0.93%)	~	2.46s	2.53s	p=0.575 n=6
Check Time	49.26s (± 0.48%)	49.38s (± 0.34%)	~	49.07s	49.57s	p=0.336 n=6
Emit Time	3.85s (± 3.34%)	3.81s (± 1.33%)	~	3.74s	3.86s	p=0.810 n=6
Total Time	63.28s (± 0.39%)	63.42s (± 0.43%)	~	62.89s	63.64s	p=0.173 n=6
self-compiler - node (v18.15.0, x64)
Errors	0	0	~	~	~	p=1.000 n=6
Symbols	256,476	256,479	+3 (+ 0.00%)	~	~	p=0.001 n=6
Types	104,239	104,238	-1 (- 0.00%)	~	~	p=0.001 n=6
Memory used	425,330k (± 0.00%)	425,345k (± 0.01%)	~	425,313k	425,384k	p=0.471 n=6
Parse Time	3.38s (± 0.16%)	3.35s (± 0.82%)	~	3.32s	3.39s	p=0.250 n=6
Bind Time	1.30s (± 0.90%)	1.31s (± 0.89%)	~	1.29s	1.32s	p=0.185 n=6
Check Time	17.79s (± 0.23%)	17.75s (± 0.58%)	~	17.56s	17.86s	p=0.630 n=6
Emit Time	1.35s (± 0.89%)	1.36s (± 2.18%)	~	1.33s	1.41s	p=1.000 n=6
Total Time	23.82s (± 0.21%)	23.78s (± 0.48%)	~	23.58s	23.91s	p=0.521 n=6
ts-pre-modules - node (v18.15.0, x64)
Errors	35	35	~	~	~	p=1.000 n=6
Symbols	224,575	224,575	~	~	~	p=1.000 n=6
Types	93,785	93,785	~	~	~	p=1.000 n=6
Memory used	369,747k (± 0.02%)	369,852k (± 0.03%)	~	369,702k	370,016k	p=0.093 n=6
Parse Time	2.83s (± 0.86%)	2.82s (± 1.47%)	~	2.77s	2.88s	p=0.686 n=6
Bind Time	1.58s (± 0.66%)	1.60s (± 0.94%)	~	1.57s	1.61s	p=0.142 n=6
Check Time	15.57s (± 0.36%)	15.57s (± 0.42%)	~	15.47s	15.67s	p=0.571 n=6
Emit Time	0.00s	0.00s	~	~	~	p=1.000 n=6
Total Time	19.98s (± 0.41%)	19.99s (± 0.41%)	~	19.88s	20.13s	p=0.687 n=6
vscode - node (v18.15.0, x64)
Errors	0	0	~	~	~	p=1.000 n=6
Symbols	2,809,653	2,809,890	+237 (+ 0.01%)	~	~	p=0.001 n=6
Types	953,438	953,461	+23 (+ 0.00%)	~	~	p=0.001 n=6
Memory used	2,981,399k (± 0.00%)	2,981,559k (± 0.00%)	~	2,981,474k	2,981,687k	p=0.054 n=6
Parse Time	13.69s (± 0.41%)	13.72s (± 0.61%)	~	13.60s	13.83s	p=0.575 n=6
Bind Time	4.10s (± 2.02%)	4.14s (± 2.62%)	~	4.06s	4.28s	p=0.570 n=6
Check Time	72.99s (± 2.66%)	72.30s (± 0.56%)	~	71.85s	73.03s	p=0.575 n=6
Emit Time	22.97s (± 7.08%)	23.57s (± 0.88%)	~	23.37s	23.84s	p=0.936 n=6
Total Time	113.75s (± 0.44%)	113.72s (± 0.49%)	~	113.04s	114.32s	p=1.000 n=6
webpack - node (v18.15.0, x64)
Errors	0	0	~	~	~	p=1.000 n=6
Symbols	265,866	265,866	~	~	~	p=1.000 n=6
Types	108,424	108,424	~	~	~	p=1.000 n=6
Memory used	410,525k (± 0.02%)	410,556k (± 0.01%)	~	410,483k	410,640k	p=0.575 n=6
Parse Time	4.75s (± 0.74%)	4.73s (± 0.80%)	~	4.68s	4.79s	p=0.198 n=6
Bind Time	2.07s (± 0.61%)	2.05s (± 1.33%)	~	2.01s	2.08s	p=0.285 n=6
Check Time	20.89s (± 0.18%)	20.91s (± 0.51%)	~	20.73s	21.03s	p=0.471 n=6
Emit Time	0.00s (±244.70%)	0.00s	~	~	~	p=0.405 n=6
Total Time	27.72s (± 0.16%)	27.69s (± 0.50%)	~	27.49s	27.85s	p=0.872 n=6
xstate-main - node (v18.15.0, x64)
Errors	0	0	~	~	~	p=1.000 n=6
Symbols	524,576	524,841	+265 (+ 0.05%)	~	~	p=0.001 n=6
Types	178,847	178,899	+52 (+ 0.03%)	~	~	p=0.001 n=6
Memory used	462,531k (± 0.01%)	462,674k (± 0.02%)	+144k (+ 0.03%)	462,549k	462,824k	p=0.031 n=6
Parse Time	3.89s (± 0.41%)	3.89s (± 0.25%)	~	3.88s	3.90s	p=1.000 n=6
Bind Time	1.45s (± 1.40%)	1.44s (± 1.16%)	~	1.42s	1.46s	p=0.367 n=6
Check Time	22.46s (± 0.63%)	22.41s (± 0.56%)	~	22.27s	22.57s	p=0.521 n=6
Emit Time	0.00s	0.00s	~	~	~	p=1.000 n=6
Total Time	27.80s (± 0.49%)	27.74s (± 0.42%)	~	27.62s	27.89s	p=0.423 n=6

System info unknown

Hosts

• node (v18.15.0, x64)

Scenarios

• Compiler-Unions - node (v18.15.0, x64)
• angular-1 - node (v18.15.0, x64)
• mui-docs - node (v18.15.0, x64)
• self-build-src - node (v18.15.0, x64)
• self-build-src-public-api - node (v18.15.0, x64)
• self-compiler - node (v18.15.0, x64)
• ts-pre-modules - node (v18.15.0, x64)
• vscode - node (v18.15.0, x64)
• webpack - node (v18.15.0, x64)
• xstate-main - node (v18.15.0, x64)

Benchmark	Name	Iterations
Current	pr	6
Baseline	baseline	6

Developer Information:

Download Benchmarks

[TypeScript Bot (typescript-bot)]

Jake Bailey (@jakebailey) Here are the results of running the top 400 repos comparing main and refs/pull/57909/merge:

Everything looks good!

[Jake Bailey (jakebailey)]

Indeed, just rechecking since this is old and also we have new perf benchmarks / stats.

[Wesley Wigham (weswigham)]

Since the tests are good, I'm fine with this (nice cheeky PR title that copies the title given to two other PRs that have edited this), but I do want to take a moment to write about this function at a conceptual level. The comment in the code does a poor job of this - it's literally restating what the code below does, rather than really expounding on the why it's doing what it does.

We're trying to pick between the covariant position inference result and the contravariant position inference result. Strictly speaking, when the results differ, you can easily be in a situation where there simply is no correct inference. For example, if we're inferring from (x: number) => string to (x: T) => T. Picking either number or string instead is basically just a choice of which error to produce at the argument site - there is no single T that the input type will be assignable to (except any). However, if you're a bit lucky, one of the two results will work in both positions and produce a type for which the overall argument is assignable. For example, if you have (x: number) => 0, 0 will work for T in both positions. So will number. Ideally, we'd just note all the possible inferences and try them all to see if any choice results in a valid assignment of the argument, then pick that one. Instead we hem and haw a bit because we don't really want to do all that backtracking (it's costly), and try to find a local heuristic to pick one or the other for each type argument. And, moreover, when multiple results are valid, determining a useful "ranking" of them for the "best" match is helpful, since users typically have an intent or expectation for how we bias our choices in situations like these.

As of this PR, that ranking is:

1. Covariant result if not never or any, assignable to all contravariant candidates, and the variable being inferred isn't referred to by another variable's constraint directly and every covariant inference candidate is assignable to the chosen covariant inference result
2. Contravariant result, if present
3. Covariant result

Why is this the ranking? Uh... I dunno. Mostly just empirical testing of "this gives good results". I really wish I could point to more rigor here. Certainly, I cannot point to an algebra from which this algorithm arises. Heck, I'd argue it's kinda wrong and bad - in the (x: number) => 0 example above, it picks 0, but number would be a more reasonable pick. By what metric? Feels. Literals are constraining, and I'd feel you should only pick them as a last resort.

But at least over our current implementation, assignability over subtyping makes sense, since arguments are ultimately compared via assignability and not subtyping (though using the compareTypes on the inference context may be better still, since that would allow the subtype overload pass to use subtypes for its heuristic as those arguments are compared via subtype, while the second pass can use assignment), and excepting Any in the same way as Never from the ranking also tracks (since they're basically the same on the source side of a relationship, as is compared in the first step here).

[Jake Bailey (jakebailey)]

Hm, baselines don't seem to be fully up to date.

[Mateusz Burzyński (Andarist)]

Jake Bailey (@jakebailey) fixed that :)

[Mateusz Burzyński (Andarist)]

though using the compareTypes on the inference context may be better still, since that would allow the subtype overload pass to use subtypes for its heuristic as those arguments are compared via subtype, while the second pass can use assignment

I see why you mention this but I failed to create a reasonable test case showing this is better in practice. I could apply this change blindly as it doesn't make a difference for the existing test suite. I also don't think it would surface anything in the extended test suite since that would essentially move the needle closer to the state before this PR for some cases. So I'm hesitant to make this change as I'd prefer to do it with a test case at hand.

At the same time, I see a risk in introducing this change (and funny enough I failed to create a test case showing this too, even a contrived one) since contextual parameter types (cached!) would be assigned based on the proposed subtyped check from the first overload pass. This could potentially yield worse results for them when the secondary pass (using assignableRelation) could still succeed.

[Trevor Florence (trevorade)]

Should this PR be mentioned in the 5.6 Announcements under Notable Behavioral Changes?

I realize the Beta and RC announcements have already gone out.