Fixed an issue with apparent mapped type keys by Andarist · Pull Request #57838 · microsoft/TypeScript

Mateusz Burzyński (Andarist) · 2024-03-18T23:19:59Z

Mateusz Burzyński (Andarist) · 2024-03-18T23:30:09Z

 t => void mappedKeys.push(instantiateType(nameType, appendTypeMapping(targetType.mapper, getTypeParameterFromMappedType(targetType), t))),
 );
- return getUnionType(mappedKeys);
+ return mappedKeys.length ? getUnionType(mappedKeys) : stringNumberSymbolType;


The problem here is that when modifiersType is unknown (or {}) then keyof modifiersType is never. Since never is assignable to everything, the checker assumed that keyof { [P in keyof T as T[P] extends string ? P: never]: any } is assignable to string.
Then based on that information it managed to simplify the instantiated substitution type of Extract to just keyof { [P in keyof T as T[P] extends string ? P: never]: any } (its newBaseType). Then in turn getNarrowableTypeForReference concluded that it should substitute constraints. Those were substituted with stringNumberSymbolType (for the keyof ...) and that's not assignable to string.
Before #56742 , it didn't mistakenly assume that keyof { [P in keyof T as T[P] extends string ? P: never]: any } is assignable to string so the substitution type was instantiated as (keyof { [P in keyof T as T[P] extends string ? P: never]: any }) & string and that is assignable to a string.

…ype-keys-with-unknown-modifier

LukeAbby · 2024-11-24T22:09:12Z

Hi! I appreciate that reviewers can be very busy but I discovered this PR when bisecting my own issue with a bit of an absurd reproduction that was erroring with a much more opaque error "Type instantiation is excessively deep and possibly infinite." so I was unable to find any workarounds before the process of bisecting.

I'd really like to see this PR merged because when I built it locally it makes my code work! I wouldn't want to ask this of anyone else without being willing to do it myself so I did also review it and I can't find anything objectionable, though of course my opinion doesn't weigh as much given I'm not a maintainer.

…ype-keys-with-unknown-modifier

Gabriela Araujo Britto (gabritto) · 2024-11-30T00:06:02Z

TypeScript Bot (@typescript-bot) pack this

TypeScript Bot (typescript-bot) · 2024-11-30T00:06:06Z

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

Command	Status	Results
`pack this`	✅ Started	✅ Results

TypeScript Bot (typescript-bot) · 2024-11-30T00:08:16Z

Hey Gabriela Araujo Britto (@gabritto), 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/164242/artifacts?artifactName=tgz&fileId=63DB465238EF48184C9FE24AA2B166C04B5AAA3CA7F9AFB4F3F63BF467E24E8402&fileName=/typescript-5.8.0-insiders.20241130.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@5.8.0-pr-57838-3".;

Gabriela Araujo Britto (gabritto) · 2024-11-30T00:27:44Z

TypeScript Bot (@typescript-bot) test it

TypeScript Bot (typescript-bot) · 2024-11-30T00:27:48Z

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

Command	Status	Results
`test top400`	✅ Started	✅ Results
`user test this`	✅ Started	✅ Results
`run dt`	✅ Started	✅ Results
`perf test this faster`	✅ Started	👀 Results

TypeScript Bot (typescript-bot) · 2024-11-30T00:46:46Z

Gabriela Araujo Britto (@gabritto) Here are the results of running the user tests with tsc comparing main and refs/pull/57838/merge:

Everything looks good!

TypeScript Bot (typescript-bot) · 2024-11-30T00:49:42Z

Hey Gabriela Araujo Britto (@gabritto), the results of running the DT tests are ready.

Everything looks the same!

You can check the log here.

TypeScript Bot (typescript-bot) · 2024-11-30T01:09:20Z

Gabriela Araujo Britto (@gabritto)
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	₃₄	₃₄	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_62,363	_62,363	_~	_~	_~	_{p=1.000 n=6}
_Types	_50,395	_50,395	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{194,857k (± 1.02%)}	_{194,229k (± 0.95%)}	_~	_193,006k	_196,645k	_{p=0.173 n=6}
_{Parse Time}	_{1.30s (± 0.75%)}	_{1.31s (± 0.89%)}	_~	_1.29s	_1.32s	_{p=0.109 n=6}
_{Bind Time}	_0.72s	_0.72s	_~	_~	_~	_{p=1.000 n=6}
_{Check Time}	_{9.81s (± 0.28%)}	_{9.81s (± 0.51%)}	_~	_9.71s	_9.85s	_{p=0.809 n=6}
_{Emit Time}	_{2.74s (± 0.64%)}	_{2.72s (± 0.23%)}	_~	_2.71s	_2.73s	_{p=0.070 n=6}
_{Total Time}	_{14.57s (± 0.11%)}	_{14.56s (± 0.38%)}	_~	_14.45s	_14.60s	_{p=1.000 n=6}
_{angular-1 - node (v18.15.0, x64)}
_Errors	₃₇	₃₇	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_947,936	_947,936	_~	_~	_~	_{p=1.000 n=6}
_Types	_410,955	_410,955	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{1,226,005k (± 0.00%)}	_{1,226,007k (± 0.00%)}	_~	_1,225,969k	_1,226,073k	_{p=0.936 n=6}
_{Parse Time}	_{6.65s (± 0.64%)}	_{6.65s (± 0.46%)}	_~	_6.61s	_6.70s	_{p=1.000 n=6}
_{Bind Time}	_{1.89s (± 0.33%)}	_{1.89s (± 0.27%)}	_~	_1.88s	_1.89s	_{p=0.386 n=6}
_{Check Time}	_{31.96s (± 0.24%)}	_{31.95s (± 0.39%)}	_~	_31.73s	_32.06s	_{p=0.810 n=6}
_{Emit Time}	_{15.22s (± 0.51%)}	_{15.20s (± 0.51%)}	_~	_15.11s	_15.33s	_{p=0.688 n=6}
_{Total Time}	_{55.72s (± 0.14%)}	_{55.69s (± 0.22%)}	_~	_55.55s	_55.84s	_{p=0.688 n=6}
_{mui-docs - node (v18.15.0, x64)}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_2,501,464	_2,501,464	_~	_~	_~	_{p=1.000 n=6}
_Types	_909,569	_909,569	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{2,318,592k (± 0.00%)}	_{2,318,551k (± 0.00%)}	_~	_2,318,489k	_2,318,648k	_{p=0.230 n=6}
_{Parse Time}	_{9.29s (± 0.32%)}	_{9.28s (± 0.24%)}	_~	_9.25s	_9.32s	_{p=0.681 n=6}
_{Bind Time}	_{2.18s (± 0.69%)}	_{2.16s (± 0.63%)}	_{-0.02s (- 0.92%)}	_2.14s	_2.18s	_{p=0.040 n=6}
_{Check Time}	_{74.81s (± 0.54%)}	_{75.28s (± 0.61%)}	_~	_74.90s	_76.10s	_{p=0.173 n=6}
_{Emit Time}	_{0.29s (± 3.60%)}	_{0.29s (± 2.61%)}	_~	_0.28s	_0.30s	_{p=0.931 n=6}
_{Total Time}	_{86.56s (± 0.46%)}	_{87.01s (± 0.53%)}	_~	_86.63s	_87.84s	_{p=0.229 n=6}
_{self-build-src - node (v18.15.0, x64)}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_1,225,251	_1,225,251	_~	_~	_~	_{p=1.000 n=6}
_Types	_266,546	_266,546	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{2,354,384k (± 0.01%)}	_{2,414,937k (± 6.12%)}	_~	_2,353,863k	_2,717,160k	_{p=1.000 n=6}
_{Parse Time}	_{5.26s (± 0.79%)}	_{5.21s (± 1.14%)}	_~	_5.16s	_5.33s	_{p=0.066 n=6}
_{Bind Time}	_{1.80s (± 0.58%)}	_{1.78s (± 1.23%)}	_~	_1.74s	_1.80s	_{p=0.210 n=6}
_{Check Time}	_{35.20s (± 0.20%)}	_{35.16s (± 0.41%)}	_~	_34.96s	_35.36s	_{p=0.575 n=6}
_{Emit Time}	_{2.98s (± 1.57%)}	_{2.97s (± 2.65%)}	_~	_2.82s	_3.04s	_{p=1.000 n=6}
_{Total Time}	_{45.25s (± 0.24%)}	_{45.14s (± 0.38%)}	_~	_44.87s	_45.31s	_{p=0.296 n=6}
_{self-build-src-public-api - node (v18.15.0, x64)}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_1,225,251	_1,225,251	_~	_~	_~	_{p=1.000 n=6}
_Types	_266,546	_266,546	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{2,786,942k (±14.25%)}	_{2,907,388k (±12.89%)}	_~	_2,422,757k	_3,149,947k	_{p=0.936 n=6}
_{Parse Time}	_{6.91s (± 2.11%)}	_{6.99s (± 1.69%)}	_~	_6.82s	_7.11s	_{p=0.261 n=6}
_{Bind Time}	_{2.18s (± 1.12%)}	_{2.15s (± 2.23%)}	_~	_2.10s	_2.22s	_{p=0.470 n=6}
_{Check Time}	_{42.86s (± 0.64%)}	_{42.81s (± 0.45%)}	_~	_42.46s	_43.03s	_{p=0.378 n=6}
_{Emit Time}	_{3.51s (± 4.08%)}	_{3.54s (± 2.34%)}	_~	_3.45s	_3.66s	_{p=0.810 n=6}
_{Total Time}	_{55.46s (± 0.67%)}	_{55.50s (± 0.29%)}	_~	_55.18s	_55.61s	_{p=0.810 n=6}
_{self-compiler - node (v18.15.0, x64)}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_262,223	_262,223	_~	_~	_~	_{p=1.000 n=6}
_Types	_106,607	_106,607	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{439,759k (± 0.01%)}	_{439,832k (± 0.02%)}	_~	_439,755k	_439,988k	_{p=0.092 n=6}
_{Parse Time}	_{3.56s (± 0.92%)}	_{3.57s (± 0.62%)}	_~	_3.54s	_3.60s	_{p=0.418 n=6}
_{Bind Time}	_{1.32s (± 1.27%)}	_{1.32s (± 1.24%)}	_~	_1.30s	_1.34s	_{p=0.742 n=6}
_{Check Time}	_{18.96s (± 0.42%)}	_{18.98s (± 0.35%)}	_~	_18.88s	_19.07s	_{p=0.810 n=6}
_{Emit Time}	_{1.53s (± 0.99%)}	_{1.54s (± 0.76%)}	_~	_1.53s	_1.56s	_{p=0.071 n=6}
_{Total Time}	_{25.36s (± 0.32%)}	_{25.42s (± 0.34%)}	_~	_25.32s	_25.54s	_{p=0.260 n=6}
_{ts-pre-modules - node (v18.15.0, x64)}
_Errors	₇₀	₇₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_226,062	_226,062	_~	_~	_~	_{p=1.000 n=6}
_Types	_94,488	_94,488	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{371,703k (± 0.07%)}	_{371,545k (± 0.01%)}	_{-158k (- 0.04%)}	_371,497k	_371,567k	_{p=0.005 n=6}
_{Parse Time}	_{2.90s (± 1.38%)}	_{2.87s (± 1.48%)}	_~	_2.81s	_2.93s	_{p=0.258 n=6}
_{Bind Time}	_{1.58s (± 1.31%)}	_{1.59s (± 1.08%)}	_~	_1.57s	_1.62s	_{p=0.288 n=6}
_{Check Time}	_{16.46s (± 0.46%)}	_{16.46s (± 0.24%)}	_~	_16.41s	_16.50s	_{p=0.936 n=6}
_{Emit Time}	_0.00s	_{0.00s (±244.70%)}	_~	_0.00s	_0.01s	_{p=0.405 n=6}
_{Total Time}	_{20.93s (± 0.52%)}	_{20.92s (± 0.30%)}	_~	_20.82s	_20.97s	_{p=0.936 n=6}
_{vscode - node (v18.15.0, x64)}
_Errors	₄	₄	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_3,188,226	_3,188,226	_~	_~	_~	_{p=1.000 n=6}
_Types	_1,096,566	_1,096,566	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{3,262,606k (± 0.02%)}	_{3,262,564k (± 0.01%)}	_~	_3,262,003k	_3,263,113k	_{p=0.936 n=6}
_{Parse Time}	_{14.12s (± 0.49%)}	_{14.16s (± 0.58%)}	_~	_14.08s	_14.30s	_{p=0.226 n=6}
_{Bind Time}	_{4.56s (± 2.12%)}	_{4.57s (± 1.87%)}	_~	_4.52s	_4.74s	_{p=0.462 n=6}
_{Check Time}	_{87.52s (± 1.53%)}	_{87.41s (± 2.21%)}	_~	_85.83s	_89.91s	_{p=0.575 n=6}
_{Emit Time}	_{28.05s (± 3.03%)}	_{27.31s (± 7.94%)}	_~	_23.07s	_28.89s	_{p=0.936 n=6}
_{Total Time}	_{134.24s (± 0.83%)}	_{133.44s (± 1.09%)}	_~	_131.81s	_135.89s	_{p=0.230 n=6}
_{webpack - node (v18.15.0, x64)}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_288,733	_288,733	_~	_~	_~	_{p=1.000 n=6}
_Types	_117,152	_117,152	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{441,046k (± 0.03%)}	_{440,980k (± 0.03%)}	_~	_440,825k	_441,235k	_{p=0.471 n=6}
_{Parse Time}	_{4.08s (± 0.59%)}	_{4.09s (± 0.51%)}	_~	_4.06s	_4.12s	_{p=0.375 n=6}
_{Bind Time}	_{1.73s (± 0.87%)}	_{1.75s (± 1.02%)}	_~	_1.73s	_1.78s	_{p=0.164 n=6}
_{Check Time}	_{18.86s (± 0.33%)}	_{18.88s (± 0.58%)}	_~	_18.75s	_19.01s	_{p=0.936 n=6}
_{Emit Time}	_{0.00s (±244.70%)}	_0.00s	_~	_~	_~	_{p=0.405 n=6}
_{Total Time}	_{24.68s (± 0.34%)}	_{24.73s (± 0.39%)}	_~	_24.60s	_24.84s	_{p=0.261 n=6}
_{xstate-main - node (v18.15.0, x64)}
_Errors	₅	₅	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_552,390	_552,390	_~	_~	_~	_{p=1.000 n=6}
_Types	_185,096	_185,096	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{492,477k (± 0.02%)}	_{492,467k (± 0.01%)}	_~	_492,390k	_492,517k	_{p=0.575 n=6}
_{Parse Time}	_{3.41s (± 1.28%)}	_{3.41s (± 0.79%)}	_~	_3.37s	_3.45s	_{p=0.746 n=6}
_{Bind Time}	_{1.17s (± 1.00%)}	_{1.18s (± 0.93%)}	_~	_1.17s	_1.20s	_{p=0.383 n=6}
_{Check Time}	_{19.59s (± 1.48%)}	_{19.43s (± 0.40%)}	_~	_19.33s	_19.56s	_{p=0.296 n=6}
_{Emit Time}	_0.00s	_0.00s	_~	_~	_~	_{p=1.000 n=6}
_{Total Time}	_{24.18s (± 1.32%)}	_{24.03s (± 0.36%)}	_~	_23.93s	_24.16s	_{p=0.376 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) · 2024-11-30T01:53:38Z

Gabriela Araujo Britto (@gabritto) Here are the results of running the top 400 repos with tsc comparing main and refs/pull/57838/merge:

Everything looks good!

…ype-keys-with-unknown-modifier

Gabriela Araujo Britto (gabritto) · 2026-01-20T19:41:30Z

TypeScript Bot (@typescript-bot) test it

TypeScript Bot (typescript-bot) · 2026-01-20T19:41:34Z

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

Command	Status	Results
`test top400`	✅ Started	✅ Results
`user test this`	✅ Started	✅ Results
`run dt`	✅ Started	✅ Results
`perf test this faster`	✅ Started	👀 Results

TypeScript Bot (typescript-bot) · 2026-01-20T20:04:36Z

Hey Gabriela Araujo Britto (@gabritto), the results of running the DT tests are ready.

Everything looks the same!

You can check the log here.

TypeScript Bot (typescript-bot) · 2026-01-20T20:10:53Z

Gabriela Araujo Britto (@gabritto) Here are the results of running the user tests with tsc comparing main and refs/pull/57838/merge:

There were infrastructure failures potentially unrelated to your change:

1 instance of "Package install failed"
1 instance of "Git clone failed"

Otherwise...

Everything looks good!

TypeScript Bot (typescript-bot) · 2026-01-20T20:36:10Z

Gabriela Araujo Britto (@gabritto)
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	₂	₂	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_62,370	_62,370	_~	_~	_~	_{p=1.000 n=6}
_Types	_50,387	_50,387	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{194,389k (± 1.03%)}	_{193,173k (± 0.80%)}	_~	_192,520k	_196,349k	_{p=0.173 n=6}
_{Parse Time}	_{1.30s (± 0.76%)}	_{1.30s (± 0.75%)}	_~	_1.29s	_1.32s	_{p=0.924 n=6}
_{Bind Time}	_0.76s	_0.76s	_~	_~	_~	_{p=1.000 n=6}
_{Check Time}	_{9.90s (± 0.40%)}	_{9.85s (± 0.17%)}	_{-0.05s (- 0.54%)}	_9.82s	_9.87s	_{p=0.043 n=6}
_{Emit Time}	_{2.73s (± 0.40%)}	_{2.73s (± 0.44%)}	_~	_2.72s	_2.75s	_{p=0.666 n=6}
_{Total Time}	_{14.69s (± 0.31%)}	_{14.65s (± 0.20%)}	_~	_14.61s	_14.69s	_{p=0.077 n=6}
_{angular-1 - node (v18.15.0, x64)}
_Errors	₂	₂	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_955,823	_955,823	_~	_~	_~	_{p=1.000 n=6}
_Types	_415,853	_415,853	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{1,253,913k (± 0.01%)}	_{1,253,962k (± 0.00%)}	_~	_1,253,896k	_1,254,007k	_{p=0.173 n=6}
_{Parse Time}	_{6.55s (± 0.59%)}	_{6.51s (± 0.60%)}	_~	_6.47s	_6.58s	_{p=0.147 n=6}
_{Bind Time}	_{1.96s (± 0.26%)}	_{1.95s (± 0.28%)}	_~	_1.95s	_1.96s	_{p=0.640 n=6}
_{Check Time}	_{32.38s (± 0.36%)}	_{32.40s (± 0.34%)}	_~	_32.28s	_32.56s	_{p=1.000 n=6}
_{Emit Time}	_{15.03s (± 0.28%)}	_{15.01s (± 0.27%)}	_~	_14.94s	_15.05s	_{p=0.377 n=6}
_{Total Time}	_{55.92s (± 0.25%)}	_{55.88s (± 0.24%)}	_~	_55.73s	_56.09s	_{p=0.378 n=6}
_{mui-docs - node (v18.15.0, x64)}
_Errors	_11,439	_11,439	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_2,700,237	_2,700,237	_~	_~	_~	_{p=1.000 n=6}
_Types	_930,441	_930,441	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{3,036,188k (± 0.00%)}	_{3,036,138k (± 0.00%)}	_~	_3,036,042k	_3,036,274k	_{p=0.423 n=6}
_{Parse Time}	_{8.58s (± 0.14%)}	_{8.58s (± 0.32%)}	_~	_8.55s	_8.63s	_{p=0.742 n=6}
_{Bind Time}	_2.30s	_{2.30s (± 0.35%)}	_~	_2.29s	_2.31s	_{p=0.290 n=6}
_{Check Time}	_{92.83s (± 0.33%)}	_{92.79s (± 0.91%)}	_~	_91.08s	_93.28s	_{p=0.298 n=6}
_{Emit Time}	_{0.31s (± 2.60%)}	_{0.32s (± 1.63%)}	_~	_0.31s	_0.32s	_{p=0.523 n=6}
_{Total Time}	_{104.02s (± 0.29%)}	_{103.99s (± 0.82%)}	_~	_102.26s	_104.44s	_{p=0.297 n=6}
_{self-build-src - node (v18.15.0, x64)}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_1,252,444	_1,252,446	_{+2 (+ 0.00%)}	_~	_~	_{p=0.001 n=6}
_Types	_259,946	_259,946	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{2,448,166k (± 6.06%)}	_{2,448,668k (± 6.06%)}	_~	_2,387,309k	_2,751,714k	_{p=0.378 n=6}
_{Parse Time}	_{5.18s (± 0.57%)}	_{5.14s (± 0.95%)}	_~	_5.07s	_5.22s	_{p=0.077 n=6}
_{Bind Time}	_{1.86s (± 0.81%)}	_{1.86s (± 0.63%)}	_~	_1.85s	_1.88s	_{p=0.621 n=6}
_{Check Time}	_{35.38s (± 0.55%)}	_{35.38s (± 0.41%)}	_~	_35.12s	_35.52s	_{p=0.936 n=6}
_{Emit Time}	_{3.04s (± 1.52%)}	_{2.97s (± 1.36%)}	_{-0.07s (- 2.30%)}	_2.92s	_3.03s	_{p=0.030 n=6}
_{Total Time}	_{45.46s (± 0.30%)}	_{45.38s (± 0.26%)}	_~	_45.23s	_45.52s	_{p=0.298 n=6}
_{self-build-src-public-api - node (v18.15.0, x64)}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_1,252,444	_1,252,446	_{+2 (+ 0.00%)}	_~	_~	_{p=0.001 n=6}
_Types	_259,946	_259,946	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{3,183,385k (± 0.03%)}	_{3,062,085k (± 9.66%)}	_~	_2,457,737k	_3,183,539k	_{p=0.230 n=6}
_{Parse Time}	_{6.79s (± 0.58%)}	_{6.77s (± 1.33%)}	_~	_6.61s	_6.88s	_{p=0.810 n=6}
_{Bind Time}	_{2.27s (± 1.45%)}	_{2.26s (± 1.62%)}	_~	_2.21s	_2.31s	_{p=0.872 n=6}
_{Check Time}	_{43.22s (± 0.26%)}	_{43.06s (± 0.63%)}	_~	_42.57s	_43.31s	_{p=0.471 n=6}
_{Emit Time}	_{3.49s (± 1.81%)}	_{3.47s (± 2.15%)}	_~	_3.34s	_3.55s	_{p=0.810 n=6}
_{Total Time}	_{55.77s (± 0.31%)}	_{55.56s (± 0.65%)}	_~	_54.92s	_55.93s	_{p=0.298 n=6}
_{self-compiler - node (v18.15.0, x64)}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_264,690	_264,692	_{+2 (+ 0.00%)}	_~	_~	_{p=0.001 n=6}
_Types	_104,079	_104,079	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{443,095k (± 0.01%)}	_{443,077k (± 0.03%)}	_~	_442,845k	_443,232k	_{p=0.936 n=6}
_{Parse Time}	_{3.52s (± 1.41%)}	_{3.53s (± 0.94%)}	_~	_3.49s	_3.58s	_{p=0.747 n=6}
_{Bind Time}	_{1.38s (± 1.33%)}	_{1.38s (± 0.92%)}	_~	_1.37s	_1.40s	_{p=1.000 n=6}
_{Check Time}	_{19.08s (± 0.37%)}	_{19.22s (± 0.37%)}	_{+0.14s (+ 0.71%)}	_19.09s	_19.29s	_{p=0.013 n=6}
_{Emit Time}	_{1.53s (± 1.73%)}	_{1.54s (± 1.57%)}	_~	_1.51s	_1.57s	_{p=0.625 n=6}
_{Total Time}	_{25.52s (± 0.30%)}	_{25.67s (± 0.41%)}	_{+0.15s (+ 0.60%)}	_25.48s	_25.78s	_{p=0.045 n=6}
_{ts-pre-modules - node (v18.15.0, x64)}
_Errors	₇₃	₇₃	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_225,493	_225,493	_~	_~	_~	_{p=1.000 n=6}
_Types	_94,373	_94,373	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{369,855k (± 0.02%)}	_{369,872k (± 0.04%)}	_~	_369,732k	_370,161k	_{p=0.936 n=6}
_{Parse Time}	_{2.81s (± 1.04%)}	_{2.80s (± 0.63%)}	_~	_2.78s	_2.83s	_{p=0.371 n=6}
_{Bind Time}	_{1.64s (± 0.81%)}	_{1.64s (± 1.18%)}	_~	_1.62s	_1.67s	_{p=0.934 n=6}
_{Check Time}	_{16.59s (± 0.20%)}	_{16.60s (± 0.53%)}	_~	_16.51s	_16.73s	_{p=1.000 n=6}
_{Emit Time}	_0.00s	_0.00s	_~	_~	_~	_{p=1.000 n=6}
_{Total Time}	_{21.05s (± 0.22%)}	_{21.05s (± 0.41%)}	_~	_20.95s	_21.18s	_{p=0.872 n=6}
_{vscode - node (v18.15.0, x64)}
_Errors	₁₁	₁₁	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_4,136,531	_4,136,531	_~	_~	_~	_{p=1.000 n=6}
_Types	_1,309,957	_1,309,957	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{3,932,744k (± 0.00%)}	_{3,932,730k (± 0.00%)}	_~	_3,932,553k	_3,932,940k	_{p=0.810 n=6}
_{Parse Time}	_{16.02s (± 1.00%)}	_{16.05s (± 0.67%)}	_~	_15.92s	_16.19s	_{p=0.689 n=6}
_{Bind Time}	_{5.54s (± 2.69%)}	_{5.67s (± 0.38%)}	_~	_5.64s	_5.69s	_{p=0.223 n=6}
_{Check Time}	_{115.50s (± 2.45%)}	_{114.17s (± 2.01%)}	_~	_112.14s	_118.32s	_{p=0.378 n=6}
_{Emit Time}	_{47.17s (±17.07%)}	_{47.36s (±18.97%)}	_~	_39.33s	_57.85s	_{p=0.810 n=6}
_{Total Time}	_{184.24s (± 5.35%)}	_{183.25s (± 5.75%)}	_~	_173.13s	_193.96s	_{p=0.689 n=6}
_{webpack - node (v18.15.0, x64)}
_Errors	₄₁	₄₁	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_383,981	_383,981	_~	_~	_~	_{p=1.000 n=6}
_Types	_167,978	_167,978	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{543,784k (± 0.02%)}	_{543,718k (± 0.03%)}	_~	_543,545k	_544,045k	_{p=0.471 n=6}
_{Parse Time}	_{4.63s (± 0.26%)}	_{4.63s (± 0.59%)}	_~	_4.60s	_4.68s	_{p=0.684 n=6}
_{Bind Time}	_{2.02s (± 1.14%)}	_{2.04s (± 1.02%)}	_~	_2.00s	_2.06s	_{p=0.331 n=6}
_{Check Time}	_{23.66s (± 1.45%)}	_{23.67s (± 1.64%)}	_~	_23.13s	_23.97s	_{p=1.000 n=6}
_{Emit Time}	_{0.00s (±244.70%)}	_0.00s	_~	_~	_~	_{p=0.405 n=6}
_{Total Time}	_{30.31s (± 1.14%)}	_{30.34s (± 1.31%)}	_~	_29.80s	_30.64s	_{p=0.688 n=6}
_{xstate-main - node (v18.15.0, x64)}
_Errors	₃₀	₃₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_729,756	_729,721	_{-35 (- 0.00%)}	_~	_~	_{p=0.001 n=6}
_Types	_218,510	_218,479	_{-31 (- 0.01%)}	_~	_~	_{p=0.001 n=6}
_{Memory used}	_{633,780k (± 0.01%)}	_{633,742k (± 0.01%)}	_~	_633,662k	_633,834k	_{p=0.575 n=6}
_{Parse Time}	_{4.56s (± 0.43%)}	_{4.57s (± 0.55%)}	_~	_4.53s	_4.60s	_{p=0.622 n=6}
_{Bind Time}	_{1.47s (± 0.90%)}	_{1.48s (± 0.92%)}	_~	_1.47s	_1.51s	_{p=0.068 n=6}
_{Check Time}	_{22.01s (± 0.52%)}	_{22.05s (± 0.34%)}	_~	_21.98s	_22.17s	_{p=0.518 n=6}
_{Emit Time}	_0.00s	_0.00s	_~	_~	_~	_{p=1.000 n=6}
_{Total Time}	_{28.05s (± 0.46%)}	_{28.10s (± 0.32%)}	_~	_27.98s	_28.23s	_{p=0.422 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) · 2026-01-20T21:04:11Z

Gabriela Araujo Britto (@gabritto) Here are the results of running the top 400 repos with tsc comparing main and refs/pull/57838/merge:

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Gabriela Araujo Britto (gabritto) · 2026-01-20T22:57:18Z

 );
- return getUnionType(mappedKeys);
+ const apparentKeys = getUnionType(mappedKeys);
+ if (forSource && apparentKeys.flags & TypeFlags.Never) {


Sorry if I wasn't completely clear, I think moving this check to this function allows us to simply check if modifiersType is unknown, and then we return string | number | symbol instead of never. To me this would make more clear where the special case is coming from and when it should be applied. But maybe this should actually be applied whenever never is there result, regardless of what the modifiers type was? That's what I'm confused about still.
What I also find confusing about the existing use of getApparentMappedTypeKeys is that, if we're using it to compare a source type with a target type, I would imagine we want to be conservative and obtain the largest possible type the source type could be. But the logic of getApparentMappedTypeKeys seems to compute the smallest possible type the source type could be: if we have some generic mapped type M, its apparent type will be, say, M1, and M <: M1 (M``` is a subtype of M1). We then compute the keyof M1, but I think keyofis contravariant, and sokeyof M :> keyof M1, so we're effectively approximating keyof M by a subtype of it, whereas to be conservative on the side of a source type, we'd need to approximate keyof M by a supertype. Wesley Wigham (@weswigham) is my thinking wrong here?
If that all made sense, then this PR fixes the keyof approximation by inverting never (smallest type for a key) and string | number | symbol (largest type for a key), but then I still worry the cases in between could be wrong.

You raise a good point here, I'll research this further and come back with some thoughts

I think it's wrong:
typeAcceptString<Textendsstring>=T;typeFilterByLiteralValue<T,V>={[PinkeyofTasT[P]extendsV ? P : never]: any};functiontest<Textends{a: 1;b: 2}>(k: keyofFilterByLiteralValue<T,1>){consts: string=k;// errors correctlytypeResult=AcceptString<typeofk>// doesn't error but it should}
So yes, you are right - obtaining apparent keys on the source side isn't the right approach at all.

…ype-keys-with-unknown-modifier

TypeScript Bot (typescript-bot) · 2026-03-24T21:18:55Z

With 6.0 out as the final release vehicle for this codebase, we're closing all PRs that don't fit the merge criteria for post-6.0 patches. If you think this was a mistake and this PR fits the post-6.0 patch criteria, please post to the 6.0 iteration issue with details (specifically, which PR and which patch criteria it satisfies).

Next steps for PRs:

For crash bugfixes or language service improvements, PRs are currently accepted at the typescript-go repo
Changes to type system behavior should wait until after 7.0, at which point mainline TypeScript development will resume in this repository with the Go codebase
Library file updates (lib.d.ts etc) continue to live in this repo or the DOM Generator repo as appropriate

Fixed an issue with apparent mapped type keys
1a27fd9

TypeScript Bot (typescript-bot) assigned Wesley Wigham (weswigham)Mar 18, 2024

TypeScript Bot (typescript-bot) added the For Uncommitted Bug PR for untriaged, rejected, closed or missing bug label Mar 18, 2024

Mateusz Burzyński (Andarist) commented Mar 18, 2024
View reviewed changes

Nathan Shively-Sanders (sandersn) requested review from Gabriela Araujo Britto (gabritto) and Wesley Wigham (weswigham)March 27, 2024 21:04

Merge remote-tracking branch 'origin/main' into fix/apparent-mapped-t…
8d18d2d
…ype-keys-with-unknown-modifier

Mateusz Burzyński (Andarist) added 2 commits November 24, 2024 23:36

Merge remote-tracking branch 'origin/main' into fix/apparent-mapped-t…
8c95b0e
…ype-keys-with-unknown-modifier

improve the fix
04976bf

Gabriela Araujo Britto (gabritto) reviewed Nov 30, 2024
View reviewed changes

Comment threadtests/cases/compiler/keyRemappingKeyofResult.ts
Comment threadsrc/compiler/checker.ts Outdated

Mateusz Burzyński (Andarist) requested a review from Gabriela Araujo Britto (gabritto)November 30, 2024 15:22

add extra test case
cad532a

Mateusz Burzyński (Andarist)force-pushed the fix/apparent-mapped-type-keys-with-unknown-modifier branch from 2f2b500 to cad532aCompare November 30, 2024 15:45

Gabriela Araujo Britto (gabritto) reviewed Jan 20, 2026
View reviewed changes

Comment threadsrc/compiler/checker.ts Outdated

Mateusz Burzyński (Andarist) added 2 commits January 20, 2026 20:33

Merge remote-tracking branch 'origin/main' into fix/apparent-mapped-t…
05cc6dd
…ype-keys-with-unknown-modifier

move the fix to getApparentMappedTypeKeys
21f4f7c

Mateusz Burzyński (Andarist)force-pushed the fix/apparent-mapped-type-keys-with-unknown-modifier branch from cf0355f to 21f4f7cCompare January 20, 2026 19:40

Gabriela Araujo Britto (gabritto) reviewed Jan 20, 2026
View reviewed changes

Mateusz Burzyński (Andarist) added 2 commits January 26, 2026 15:58

remove getApparentMappedTypeKeys on the source side
fcdaa91

Merge remote-tracking branch 'origin/main' into fix/apparent-mapped-t…
81185ac
…ype-keys-with-unknown-modifier

Mateusz Burzyński (Andarist) marked this pull request as draft February 9, 2026 10:32

fix index type constraints on mapped types with name types
73d96e1

Mateusz Burzyński (Andarist)force-pushed the fix/apparent-mapped-type-keys-with-unknown-modifier branch from 7c57147 to 73d96e1Compare February 9, 2026 13:10

TypeScript Bot (typescript-bot) closed this Mar 24, 2026

github-project-automationBot moved this from Waiting on reviewers to Done in PR Backlog Mar 24, 2026

Mateusz Burzyński (Andarist) mentioned this pull request Mar 30, 2026
Omit causes function to lose contextual typing #63225
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