Bring back return type narrowing + fixes #61359

gabritto · 2025-03-05T22:04:28Z

This PR brings back conditional and indexed access return type narrowing from #56941, but with a few updates.
The main motivation behind those updates is described in https://gist.github.com/gabritto/b6ebd5f9fc2bb3cfc305027609e66bca,
but to put it shortly, type narrowing very often cannot distinguish between two non-primitive types,
and since return type narrowing depends on type narrowing to work, it often didn't.

Update 1: non-primitive restriction

To deal with those problematic type narrowing scenarios, the first update is to disallow narrowing of conditional return types that
attempt to distinguish between two non-primitive types.
So this example will not work:

type QuickPickReturn<T extends QuickPickOptions> =
    T extends { canSelectMultiple: true } ? string[] :
    T extends { canSelectMultiple: false } ? string :
    never;
    
type QuickPickOptions = {
    prompt: string;
    items: string[];
    canSelectMultiple: true;
} | {
    prompt: string;
    items: string[];
    canSelectMultiple: false;
}

function showQuickPick<T extends QuickPickOptions>(options: T): QuickPickReturn<T> {
    if (options.canSelectMultiple) {
        return options.items; // Error
    }
    return options.items[0]; // Error
}

That's because the conditional return type QuickPickReturn has one branch with type { canSelectMultiple: true }, which is non-primitive,
and another branch with type { canSelectMultiple: false }, which is also non-primitive.

However, the following will work:

type QuickPickOptions<T extends boolean> = {
    prompt: string;
    items: string[];
    canSelectMultiple: T;
};

type QuickPickReturn<T extends boolean> =
    T extends true ? string[] :
    T extends false ? string :
    never;

function showQuickPick<T extends boolean>(options: QuickPickOptions<T>): QuickPickReturn<T> {
    if (options.canSelectMultiple) {
        return options.items;
    }
    return options.items[0];
}

type QuickPickOptions = {
    prompt: string;
    items: string[];
};

type QuickPickReturn<T extends string | QuickPickOptions> =
    T extends string ? string :
    T extends QuickPickOptions ? string[] :
    never;

function showQuickPick<T extends string | QuickPickOptions>(optionsOrItem: T): QuickPickReturn<T> {
    if (typeof optionsOrItem === "string") {
        return optionsOrItem;
    }
    return optionsOrItem.items;
}

Distinguishing between two primitive types or between a primitive and non-primitive type in the conditional type's branches is allowed.

Update 2: type parameter embedding

We can now detect that a type parameter is a candidate for being used in return type narrowing (i.e. it's a narrowable type parameter) in
cases where the type parameter is indirectly used as a type of a parameter or property.
Before, only this type of usage of T in a parameter type annotation would be recognized:

type PickNumberRet<T> =
    T extends true ? 1 :
    T extends false ? 2 :
    never;

function pickNumber<T extends boolean>(b: T): PickNumberRet<T> {
    return b ? 1 : 2;
}

Now, the following also work:

type PickNumberRet<T> =
    T extends true ? 1 :
    T extends false ? 2 :
    never;

function pickNumber<T extends boolean>({ b }: { b: T }): PickNumberRet<T> {
    return b ? 1 : 2;
}

function pickNumber<T extends boolean>(opts: { b: T }): PickNumberRet<T> {
    return opts.b ? 1 : 2;
}

Combined with the non-primitive restriction mentioned above, this enables users to place narrowable type parameters inside object types
at the exact property that is used for narrowing, so instead of writing this: function fun<T extends { prop: true } | { prop: false }>(param: T): ...,
users can write this: function fun<T extends true | false>(param: { prop: T }): ....

Note that the analysis done to decide if a type parameter is used the parameter in a way that allows it to be narrowed is a syntactical one.
We want to avoid resolving and inspecting actual types during the analysis, because a lot of types are lazy in some sense, and we don't
want this analysis to cause unintended side effects, e.g. circularity errors.
But this means that any usage of a type parameter that requires semantically resolving types to validate it is not going to work.

For a more complete list of what's currently supported here in terms of usages of type parameters, see test tests\cases\compiler\dependentReturnType11.ts.

Update 3: relax extends type restriction

This is a small improvement unrelated to the previous updates.
In the original PR, this was disallowed because we required that a conditional return type's extends types be identical to the types
in the type parameter constraint:

interface Dog {
    name: string;
    bark(): string;
}

type NormalizedRet<T> =
    T extends {} ? T :
    T extends null | undefined ? undefined :
    never;

function normalizeDog<T extends Dog | undefined | null>(dog: T): NormalizedRet<T> {
    if (dog == undefined) {
        return undefined; // Originally an error
    }
    return dog; // Originally an error
}

Note that in NormalizedRet, the first branch's extends type is {}, not Dog, so this wasn't allowed because those types are not identical.
With this PR, we only require that a type in the constraint is assignable to the extends type, i.e. that Dog is assignable to {},
so the code above is now allowed for return type narrowing.

This reverts commit c3ae7c4.

…ches

gabritto · 2025-03-20T18:23:26Z

@typescript-bot pack this

typescript-bot · 2025-03-20T18:23:31Z

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

Command	Status	Results
`pack this`	✅ Started	✅ Results

gabritto · 2025-03-20T18:23:32Z

@typescript-bot test it

typescript-bot · 2025-03-20T18:23:38Z

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 · 2025-03-20T18:27:47Z

Hey @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/164947/artifacts?artifactName=tgz&fileId=D8EFF21205462B38E502A6643448F71CEACCECECE108A3D1D461EC8F7E9FF1E702&fileName=/typescript-5.9.0-insiders.20250320.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@5.9.0-pr-61359-4".;

typescript-bot · 2025-03-20T18:46:53Z

Hey @gabritto, the results of running the DT tests are ready.

Everything looks the same!

You can check the log here.

typescript-bot · 2025-03-20T18:51:59Z

@gabritto Here are the results of running the user tests with tsc comparing main and refs/pull/61359/merge:

Everything looks good!

typescript-bot · 2025-03-20T19:09:50Z

@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	_62,390	_62,390	_~	_~	_~	_{p=1.000 n=6}
_Types	_50,395	_50,395	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{194,123k (± 0.96%)}	_{193,824k (± 0.80%)}	_~	_193,125k	_196,973k	_{p=0.230 n=6}
_{Parse Time}	_{1.31s (± 0.79%)}	_{1.31s (± 0.75%)}	_~	_1.30s	_1.33s	_{p=0.591 n=6}
_{Bind Time}	_0.73s	_0.73s	_~	_~	_~	_{p=1.000 n=6}
_{Check Time}	_{9.74s (± 0.43%)}	_{9.74s (± 0.18%)}	_~	_9.72s	_9.76s	_{p=0.935 n=6}
_{Emit Time}	_{2.74s (± 1.10%)}	_{2.72s (± 0.72%)}	_~	_2.70s	_2.75s	_{p=0.258 n=6}
_{Total Time}	_{14.53s (± 0.31%)}	_{14.51s (± 0.17%)}	_~	_14.46s	_14.53s	_{p=0.259 n=6}
_{angular-1 - node (v18.15.0, x64)}
_Errors	₅₆	₅₆	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_948,670	_948,670	_~	_~	_~	_{p=1.000 n=6}
_Types	_410,947	_410,947	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{1,224,316k (± 0.00%)}	_{1,225,575k (± 0.00%)}	_{+1,259k (+ 0.10%)}	_1,225,549k	_1,225,617k	_{p=0.005 n=6}
_{Parse Time}	_{6.64s (± 0.98%)}	_{6.66s (± 0.59%)}	_~	_6.60s	_6.70s	_{p=0.810 n=6}
_{Bind Time}	_{1.88s (± 0.58%)}	_{1.88s (± 0.78%)}	_~	_1.86s	_1.90s	_{p=0.866 n=6}
_{Check Time}	_{31.88s (± 0.31%)}	_{31.99s (± 0.24%)}	_{+0.11s (+ 0.33%)}	_31.92s	_32.10s	_{p=0.037 n=6}
_{Emit Time}	_{15.23s (± 0.21%)}	_{15.25s (± 0.55%)}	_~	_15.11s	_15.33s	_{p=0.468 n=6}
_{Total Time}	_{55.63s (± 0.25%)}	_{55.77s (± 0.28%)}	_~	_55.58s	_56.01s	_{p=0.127 n=6}
_{mui-docs - node (v18.15.0, x64)}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_2,363,778	_2,363,778	_~	_~	_~	_{p=1.000 n=6}
_Types	_846,530	_846,530	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{2,133,827k (± 0.01%)}	_{2,138,080k (± 0.01%)}	_{+4,253k (+ 0.20%)}	_2,137,887k	_2,138,228k	_{p=0.005 n=6}
_{Parse Time}	_{7.22s (± 0.25%)}	_{7.24s (± 0.39%)}	_~	_7.21s	_7.29s	_{p=0.256 n=6}
_{Bind Time}	_{2.52s (± 0.39%)}	_{2.53s (± 0.41%)}	_~	_2.52s	_2.55s	_{p=0.103 n=6}
_{Check Time}	_{74.09s (± 0.26%)}	_{74.34s (± 0.45%)}	_~	_73.88s	_74.77s	_{p=0.173 n=6}
_{Emit Time}	_{0.16s (± 3.29%)}	_{0.16s (± 4.75%)}	_~	_0.15s	_0.17s	_{p=0.784 n=6}
_{Total Time}	_{83.99s (± 0.21%)}	_{84.27s (± 0.38%)}	_~	_83.82s	_84.68s	_{p=0.128 n=6}
_{self-build-src - node (v18.15.0, x64)}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_1,226,713	_1,227,156	_{+443 (+ 0.04%)}	_~	_~	_{p=0.001 n=6}
_Types	_266,991	_267,114	_{+123 (+ 0.05%)}	_~	_~	_{p=0.001 n=6}
_{Memory used}	_{2,357,851k (± 0.02%)}	_{2,360,494k (± 0.02%)}	_{+2,643k (+ 0.11%)}	_2,359,892k	_2,361,297k	_{p=0.005 n=6}
_{Parse Time}	_{5.19s (± 1.21%)}	_{5.22s (± 0.66%)}	_~	_5.19s	_5.28s	_{p=0.521 n=6}
_{Bind Time}	_{1.80s (± 1.82%)}	_{1.81s (± 0.57%)}	_~	_1.80s	_1.82s	_{p=0.806 n=6}
_{Check Time}	_{35.31s (± 0.34%)}	_{35.38s (± 0.17%)}	_~	_35.30s	_35.45s	_{p=0.297 n=6}
_{Emit Time}	_{2.99s (± 1.21%)}	_{3.00s (± 1.38%)}	_~	_2.96s	_3.06s	_{p=0.574 n=6}
_{Total Time}	_{45.29s (± 0.40%)}	_{45.41s (± 0.17%)}	_~	_45.32s	_45.54s	_{p=0.230 n=6}
_{self-build-src-public-api - node (v18.15.0, x64)}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_1,226,713	_1,227,156	_{+443 (+ 0.04%)}	_~	_~	_{p=0.001 n=6}
_Types	_266,991	_267,114	_{+123 (+ 0.05%)}	_~	_~	_{p=0.001 n=6}
_{Memory used}	_{2,910,623k (±12.87%)}	_{3,037,919k (± 9.77%)}	_{🔻+127,296k (+ 4.37%)}	_2,431,304k	_3,160,174k	_{p=0.031 n=6}
_{Parse Time}	_{6.94s (± 1.85%)}	_{7.00s (± 1.66%)}	_~	_6.78s	_7.12s	_{p=0.471 n=6}
_{Bind Time}	_{2.14s (± 0.71%)}	_{2.16s (± 1.07%)}	_~	_2.14s	_2.20s	_{p=0.126 n=6}
_{Check Time}	_{42.89s (± 0.52%)}	_{43.02s (± 0.72%)}	_~	_42.42s	_43.26s	_{p=0.230 n=6}
_{Emit Time}	_{3.57s (± 1.32%)}	_{3.53s (± 2.18%)}	_~	_3.44s	_3.65s	_{p=0.336 n=6}
_{Total Time}	_{55.54s (± 0.64%)}	_{55.70s (± 0.71%)}	_~	_54.98s	_56.18s	_{p=0.378 n=6}
_{self-compiler - node (v18.15.0, x64)}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_262,674	_263,095	_{+421 (+ 0.16%)}	_~	_~	_{p=0.001 n=6}
_Types	_106,849	_106,972	_{+123 (+ 0.12%)}	_~	_~	_{p=0.001 n=6}
_{Memory used}	_{440,508k (± 0.01%)}	_{441,629k (± 0.02%)}	_{+1,120k (+ 0.25%)}	_441,562k	_441,739k	_{p=0.005 n=6}
_{Parse Time}	_{3.55s (± 0.66%)}	_{3.56s (± 0.54%)}	_~	_3.54s	_3.59s	_{p=0.465 n=6}
_{Bind Time}	_{1.30s (± 0.64%)}	_{1.30s (± 0.42%)}	_~	_1.30s	_1.31s	_{p=0.855 n=6}
_{Check Time}	_{18.93s (± 0.57%)}	_{19.00s (± 0.44%)}	_~	_18.90s	_19.10s	_{p=0.520 n=6}
_{Emit Time}	_{1.52s (± 1.15%)}	_{1.51s (± 1.08%)}	_~	_1.49s	_1.54s	_{p=0.934 n=6}
_{Total Time}	_{25.31s (± 0.53%)}	_{25.38s (± 0.32%)}	_~	_25.29s	_25.47s	_{p=0.688 n=6}
_{ts-pre-modules - node (v18.15.0, x64)}
_Errors	₇₁	₇₁	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_225,981	_225,981	_~	_~	_~	_{p=1.000 n=6}
_Types	_94,356	_94,356	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{371,202k (± 0.02%)}	_{371,814k (± 0.04%)}	_{+612k (+ 0.16%)}	_371,656k	_372,006k	_{p=0.005 n=6}
_{Parse Time}	_{2.89s (± 0.63%)}	_{2.89s (± 0.87%)}	_~	_2.86s	_2.93s	_{p=0.807 n=6}
_{Bind Time}	_{1.61s (± 2.02%)}	_{1.61s (± 1.27%)}	_~	_1.58s	_1.64s	_{p=0.871 n=6}
_{Check Time}	_{16.49s (± 0.37%)}	_{16.50s (± 0.47%)}	_~	_16.40s	_16.60s	_{p=0.936 n=6}
_{Emit Time}	_0.00s	_0.00s	_~	_~	_~	_{p=1.000 n=6}
_{Total Time}	_{20.99s (± 0.31%)}	_{20.99s (± 0.32%)}	_~	_20.89s	_21.09s	_{p=1.000 n=6}
_{vscode - node (v18.15.0, x64)}
_Errors	₈	₈	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_3,320,535	_3,320,535	_~	_~	_~	_{p=1.000 n=6}
_Types	_1,125,763	_1,125,763	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{3,382,323k (± 0.00%)}	_{3,387,326k (± 0.01%)}	_{+5,003k (+ 0.15%)}	_3,386,997k	_3,387,570k	_{p=0.005 n=6}
_{Parse Time}	_{14.78s (± 3.65%)}	_{14.66s (± 0.63%)}	_~	_14.56s	_14.80s	_{p=0.229 n=6}
_{Bind Time}	_{4.65s (± 0.42%)}	_{4.71s (± 2.25%)}	_~	_4.65s	_4.93s	_{p=0.075 n=6}
_{Check Time}	_{91.25s (± 1.44%)}	_{92.39s (± 3.01%)}	_~	_88.97s	_96.95s	_{p=0.471 n=6}
_{Emit Time}	_{29.29s (± 0.55%)}	_{29.91s (± 2.63%)}	_~	_29.10s	_30.93s	_{p=0.128 n=6}
_{Total Time}	_{139.96s (± 0.96%)}	_{141.67s (± 1.59%)}	_~	_138.32s	_145.29s	_{p=0.173 n=6}
_{webpack - node (v18.15.0, x64)}
_Errors	₂	₂	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_308,237	_308,237	_~	_~	_~	_{p=1.000 n=6}
_Types	_134,948	_134,948	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{463,416k (± 0.03%)}	_{463,566k (± 0.02%)}	_~	_463,395k	_463,653k	_{p=0.078 n=6}
_{Parse Time}	_{4.14s (± 0.47%)}	_{4.11s (± 0.78%)}	_~	_4.06s	_4.14s	_{p=0.088 n=6}
_{Bind Time}	_{1.80s (± 1.24%)}	_{1.80s (± 1.35%)}	_~	_1.75s	_1.82s	_{p=0.622 n=6}
_{Check Time}	_{20.40s (± 0.16%)}	_{20.46s (± 0.48%)}	_~	_20.29s	_20.57s	_{p=0.127 n=6}
_{Emit Time}	_{0.00s (±244.70%)}	_0.00s	_~	_~	_~	_{p=0.405 n=6}
_{Total Time}	_{26.34s (± 0.21%)}	_{26.36s (± 0.27%)}	_~	_26.24s	_26.45s	_{p=0.226 n=6}
_{xstate-main - node (v18.15.0, x64)}
_Errors	₅	₅	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_566,532	_566,532	_~	_~	_~	_{p=1.000 n=6}
_Types	_189,740	_189,740	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{497,449k (± 0.01%)}	_{497,946k (± 0.02%)}	_{+498k (+ 0.10%)}	_497,832k	_498,093k	_{p=0.005 n=6}
_{Parse Time}	_{4.19s (± 0.49%)}	_{4.17s (± 0.70%)}	_~	_4.12s	_4.20s	_{p=0.191 n=6}
_{Bind Time}	_{1.50s (± 1.19%)}	_{1.50s (± 1.03%)}	_~	_1.48s	_1.52s	_{p=1.000 n=6}
_{Check Time}	_{24.73s (± 0.25%)}	_{24.85s (± 0.27%)}	_{+0.11s (+ 0.46%)}	_24.74s	_24.93s	_{p=0.020 n=6}
_{Emit Time}	_0.00s	_0.00s	_~	_~	_~	_{p=1.000 n=6}
_{Total Time}	_{30.43s (± 0.29%)}	_{30.52s (± 0.24%)}	_~	_30.41s	_30.62s	_{p=0.077 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 · 2025-03-20T20:01:24Z

@gabritto Here are the results of running the top 400 repos with tsc comparing main and refs/pull/61359/merge:

Everything looks good!

gabritto · 2025-03-21T17:47:06Z

@typescript-bot perf test this faster

typescript-bot · 2025-03-21T17:47:10Z

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

Command	Status	Results
`perf test this faster`	✅ Started	👀 Results

typescript-bot · 2025-03-21T18:33:30Z

@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	_62,390	_62,390	_~	_~	_~	_{p=1.000 n=6}
_Types	_50,395	_50,395	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{194,255k (± 0.92%)}	_{193,140k (± 0.01%)}	_~	_193,110k	_193,184k	_{p=0.378 n=6}
_{Parse Time}	_{1.31s (± 0.68%)}	_{1.32s (± 0.42%)}	_~	_1.31s	_1.32s	_{p=0.341 n=6}
_{Bind Time}	_0.73s	_0.73s	_~	_~	_~	_{p=1.000 n=6}
_{Check Time}	_{9.74s (± 0.28%)}	_{9.74s (± 0.47%)}	_~	_9.69s	_9.80s	_{p=1.000 n=6}
_{Emit Time}	_{2.73s (± 0.55%)}	_{2.73s (± 0.51%)}	_~	_2.71s	_2.74s	_{p=0.461 n=6}
_{Total Time}	_{14.51s (± 0.23%)}	_{14.51s (± 0.32%)}	_~	_14.46s	_14.57s	_{p=0.872 n=6}
_{angular-1 - node (v18.15.0, x64)}
_Errors	₅₆	₅₆	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_948,670	_948,670	_~	_~	_~	_{p=1.000 n=6}
_Types	_410,947	_410,947	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{1,224,347k (± 0.01%)}	_{1,225,556k (± 0.00%)}	_{+1,209k (+ 0.10%)}	_1,225,534k	_1,225,574k	_{p=0.005 n=6}
_{Parse Time}	_{6.62s (± 0.92%)}	_{6.67s (± 0.41%)}	_~	_6.63s	_6.70s	_{p=0.332 n=6}
_{Bind Time}	_{1.88s (± 0.43%)}	_{1.87s (± 0.28%)}	_{-0.01s (- 0.53%)}	_1.87s	_1.88s	_{p=0.050 n=6}
_{Check Time}	_{31.88s (± 0.45%)}	_{31.98s (± 0.62%)}	_~	_31.73s	_32.27s	_{p=0.575 n=6}
_{Emit Time}	_{15.31s (± 0.48%)}	_{15.19s (± 0.68%)}	_~	_15.08s	_15.35s	_{p=0.066 n=6}
_{Total Time}	_{55.69s (± 0.37%)}	_{55.71s (± 0.53%)}	_~	_55.39s	_56.07s	_{p=1.000 n=6}
_{mui-docs - node (v18.15.0, x64)}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_2,338,004	_2,338,004	_~	_~	_~	_{p=1.000 n=6}
_Types	_832,025	_832,025	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{2,105,904k (± 0.00%)}	_{2,109,988k (± 0.00%)}	_{+4,084k (+ 0.19%)}	_2,109,951k	_2,110,056k	_{p=0.005 n=6}
_{Parse Time}	_{7.21s (± 0.08%)}	_{7.21s (± 0.30%)}	_~	_7.20s	_7.25s	_{p=0.363 n=6}
_{Bind Time}	_{2.50s (± 0.30%)}	_{2.51s (± 0.48%)}	_~	_2.50s	_2.53s	_{p=0.652 n=6}
_{Check Time}	_{73.38s (± 0.38%)}	_{73.76s (± 0.53%)}	_~	_73.26s	_74.22s	_{p=0.173 n=6}
_{Emit Time}	_0.16s	_{0.16s (± 3.95%)}	_~	_0.15s	_0.17s	_{p=1.000 n=6}
_{Total Time}	_{83.26s (± 0.34%)}	_{83.64s (± 0.47%)}	_~	_83.13s	_84.11s	_{p=0.173 n=6}
_{self-build-src - node (v18.15.0, x64)}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_1,226,713	_1,227,156	_{+443 (+ 0.04%)}	_~	_~	_{p=0.001 n=6}
_Types	_266,991	_267,114	_{+123 (+ 0.05%)}	_~	_~	_{p=0.001 n=6}
_{Memory used}	_{2,357,352k (± 0.03%)}	_{2,360,552k (± 0.02%)}	_{+3,200k (+ 0.14%)}	_2,359,990k	_2,361,021k	_{p=0.005 n=6}
_{Parse Time}	_{5.20s (± 0.47%)}	_{5.19s (± 1.09%)}	_~	_5.12s	_5.29s	_{p=0.688 n=6}
_{Bind Time}	_{1.80s (± 0.93%)}	_{1.80s (± 0.96%)}	_~	_1.78s	_1.83s	_{p=0.932 n=6}
_{Check Time}	_{35.32s (± 0.23%)}	_{35.35s (± 0.28%)}	_~	_35.20s	_35.44s	_{p=0.378 n=6}
_{Emit Time}	_{3.02s (± 0.99%)}	_{3.00s (± 0.81%)}	_~	_2.95s	_3.01s	_{p=0.166 n=6}
_{Total Time}	_{45.35s (± 0.21%)}	_{45.34s (± 0.26%)}	_~	_45.22s	_45.53s	_{p=0.873 n=6}
_{self-build-src-public-api - node (v18.15.0, x64)}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_1,226,713	_1,227,156	_{+443 (+ 0.04%)}	_~	_~	_{p=0.001 n=6}
_Types	_266,991	_267,114	_{+123 (+ 0.05%)}	_~	_~	_{p=0.001 n=6}
_{Memory used}	_{2,911,756k (±12.87%)}	_{2,916,546k (±12.87%)}	_~	_2,431,200k	_3,159,843k	_{p=0.128 n=6}
_{Parse Time}	_{6.91s (± 1.62%)}	_{6.92s (± 1.86%)}	_~	_6.78s	_7.07s	_{p=1.000 n=6}
_{Bind Time}	_{2.12s (± 2.05%)}	_{2.17s (± 1.28%)}	_~	_2.15s	_2.22s	_{p=0.170 n=6}
_{Check Time}	_{42.78s (± 0.51%)}	_{42.89s (± 0.68%)}	_~	_42.53s	_43.26s	_{p=0.471 n=6}
_{Emit Time}	_{3.46s (± 2.23%)}	_{3.42s (± 2.45%)}	_~	_3.35s	_3.58s	_{p=0.471 n=6}
_{Total Time}	_{55.29s (± 0.49%)}	_{55.39s (± 0.73%)}	_~	_54.90s	_55.84s	_{p=0.810 n=6}
_{self-compiler - node (v18.15.0, x64)}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_262,674	_263,095	_{+421 (+ 0.16%)}	_~	_~	_{p=0.001 n=6}
_Types	_106,849	_106,972	_{+123 (+ 0.12%)}	_~	_~	_{p=0.001 n=6}
_{Memory used}	_{440,467k (± 0.01%)}	_{441,611k (± 0.02%)}	_{+1,145k (+ 0.26%)}	_441,501k	_441,749k	_{p=0.005 n=6}
_{Parse Time}	_{3.53s (± 1.72%)}	_{3.57s (± 0.89%)}	_~	_3.54s	_3.61s	_{p=0.169 n=6}
_{Bind Time}	_{1.32s (± 0.57%)}	_{1.32s (± 0.88%)}	_~	_1.30s	_1.33s	_{p=0.396 n=6}
_{Check Time}	_{18.98s (± 0.22%)}	_{19.02s (± 0.47%)}	_~	_18.93s	_19.13s	_{p=0.809 n=6}
_{Emit Time}	_{1.53s (± 0.99%)}	_{1.52s (± 1.29%)}	_~	_1.50s	_1.55s	_{p=0.935 n=6}
_{Total Time}	_{25.36s (± 0.35%)}	_{25.43s (± 0.36%)}	_~	_25.31s	_25.57s	_{p=0.229 n=6}
_{ts-pre-modules - node (v18.15.0, x64)}
_Errors	₇₁	₇₁	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_225,981	_225,981	_~	_~	_~	_{p=1.000 n=6}
_Types	_94,356	_94,356	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{371,187k (± 0.02%)}	_{371,720k (± 0.03%)}	_{+532k (+ 0.14%)}	_371,589k	_371,828k	_{p=0.005 n=6}
_{Parse Time}	_{2.89s (± 0.55%)}	_{2.88s (± 1.01%)}	_~	_2.83s	_2.90s	_{p=0.684 n=6}
_{Bind Time}	_{1.59s (± 1.30%)}	_{1.58s (± 1.10%)}	_~	_1.57s	_1.61s	_{p=0.416 n=6}
_{Check Time}	_{16.52s (± 0.35%)}	_{16.47s (± 0.28%)}	_~	_16.41s	_16.52s	_{p=0.199 n=6}
_{Emit Time}	_0.00s	_0.00s	_~	_~	_~	_{p=1.000 n=6}
_{Total Time}	_{21.00s (± 0.27%)}	_{20.93s (± 0.22%)}	_~	_20.88s	_21.00s	_{p=0.064 n=6}
_{vscode - node (v18.15.0, x64)}
_Errors	₈	₈	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_3,323,316	_3,323,316	_~	_~	_~	_{p=1.000 n=6}
_Types	_1,126,439	_1,126,439	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{3,383,716k (± 0.01%)}	_{3,389,145k (± 0.01%)}	_{+5,430k (+ 0.16%)}	_3,388,828k	_3,389,364k	_{p=0.005 n=6}
_{Parse Time}	_{14.60s (± 0.59%)}	_{14.64s (± 0.49%)}	_~	_14.55s	_14.75s	_{p=0.376 n=6}
_{Bind Time}	_{4.66s (± 0.55%)}	_{4.65s (± 0.78%)}	_~	_4.61s	_4.70s	_{p=0.630 n=6}
_{Check Time}	_{91.25s (± 1.89%)}	_{90.75s (± 1.77%)}	_~	_89.52s	_93.90s	_{p=0.470 n=6}
_{Emit Time}	_{29.84s (± 2.63%)}	_{28.86s (± 6.33%)}	_~	_25.31s	_30.62s	_{p=0.199 n=6}
_{Total Time}	_{140.36s (± 1.79%)}	_{138.91s (± 0.57%)}	_~	_138.09s	_139.93s	_{p=0.298 n=6}
_{webpack - node (v18.15.0, x64)}
_Errors	₂	₂	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_308,237	_308,237	_~	_~	_~	_{p=1.000 n=6}
_Types	_134,948	_134,948	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{463,361k (± 0.03%)}	_{463,558k (± 0.02%)}	_{+198k (+ 0.04%)}	_463,429k	_463,661k	_{p=0.031 n=6}
_{Parse Time}	_{4.11s (± 0.50%)}	_{4.10s (± 0.82%)}	_~	_4.06s	_4.16s	_{p=0.572 n=6}
_{Bind Time}	_{1.80s (± 0.55%)}	_{1.80s (± 1.15%)}	_~	_1.76s	_1.82s	_{p=0.869 n=6}
_{Check Time}	_{20.46s (± 0.38%)}	_{20.43s (± 0.26%)}	_~	_20.37s	_20.52s	_{p=0.747 n=6}
_{Emit Time}	_0.00s	_{0.00s (±244.70%)}	_~	_0.00s	_0.01s	_{p=0.405 n=6}
_{Total Time}	_{26.36s (± 0.33%)}	_{26.33s (± 0.14%)}	_~	_26.28s	_26.38s	_{p=0.687 n=6}
_{xstate-main - node (v18.15.0, x64)}
_Errors	₅	₅	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_566,532	_566,532	_~	_~	_~	_{p=1.000 n=6}
_Types	_189,740	_189,740	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{497,380k (± 0.04%)}	_{497,910k (± 0.02%)}	_{+530k (+ 0.11%)}	_497,738k	_498,004k	_{p=0.005 n=6}
_{Parse Time}	_{4.18s (± 0.49%)}	_{4.17s (± 0.91%)}	_~	_4.12s	_4.20s	_{p=0.685 n=6}
_{Bind Time}	_{1.51s (± 0.68%)}	_{1.50s (± 0.91%)}	_~	_1.48s	_1.52s	_{p=0.190 n=6}
_{Check Time}	_{24.95s (± 1.24%)}	_{24.77s (± 0.48%)}	_~	_24.58s	_24.88s	_{p=0.261 n=6}
_{Emit Time}	_{0.00s (±244.70%)}	_0.00s	_~	_~	_~	_{p=0.405 n=6}
_{Total Time}	_{30.64s (± 0.96%)}	_{30.43s (± 0.45%)}	_~	_30.25s	_30.60s	_{p=0.128 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:

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gabritto · 2025-03-21T20:00:26Z

Note to self:

Add tests with typeof param as a way of accessing the narrowable type parameter
Support parameter properties

gabritto added 10 commits March 5, 2025 10:59

Revert "Revert return type narrowing (#61136)"

aa38e34

This reverts commit c3ae7c4.

add restriction on narrowable type constraint

073d868

relax restriction on extends type of narrowable conditional type

17ed356

WIP: detect embedded references to a narrowable type parameter

fdb6bea

Detect and construct narrowable references for embedded type parameters

1849292

validate optional param/property

009d152

format

5cb7e90

rework non-primitive restriction to be based on conditional type bran…

3c5327e

…ches

update tests

7464af0

bring back conditional expression test

c96e01e

typescript-bot assigned gabritto Mar 5, 2025

typescript-bot added Author: Team For Uncommitted Bug labels Mar 5, 2025

gabritto requested review from sandersn, DanielRosenwasser, weswigham and andrewbranch March 5, 2025 22:07

controversial mentioned this pull request Mar 6, 2025

feat: implement typed Input/Output interface for resolvers react-hook-form/resolvers#753

Draft

This was referenced Mar 7, 2025

Allow extends type to be supertype of constraint types when narrowing conditional return type #61117

Closed

Fix detection of single usage of type parameter for return type narrowing #61115

Closed

Also support classes. TODO: support parameter properties

c872eb8

fix baselines

2084fa0

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Bring back return type narrowing + fixes #61359

Bring back return type narrowing + fixes #61359

gabritto commented Mar 5, 2025

gabritto commented Mar 20, 2025

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gabritto commented Mar 21, 2025

Bring back return type narrowing + fixes #61359

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Bring back return type narrowing + fixes #61359

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gabritto commented Mar 5, 2025

Update 1: non-primitive restriction

Update 2: type parameter embedding

Update 3: relax extends type restriction

gabritto commented Mar 20, 2025

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