Experiment: report functions with multiple returns that could be type predicates #58173

danvk · 2024-04-12T21:33:52Z

This is a side experiment for #58154. That PR extends type predicate inference to functions with multiple returns. It seems to have minimal perf impact and also minimal breakages. This makes you wonder… are there any such functions?

This fork of the PR should answer that question by reporting errors on all functions with 2+ return statements where it can infer a type predicate. To be clear, these aren't real errors! They're just identifying multi-return predicates in the wild.

There are three such function in TypeScript itself:

tryAddPropertyAssignment in nodeFactory.ts:

function tryAddPropertyAssignment(properties: PropertyAssignment[], propertyName: string, expression: Expression | undefined) {
    if (expression) {
        properties.push(createPropertyAssignment(propertyName, expression));
        return true;
    }
    return false;
}

This gets an inferred return type of expression is Expression. This is accurate, though not consequential for any of the code that calls this function.

charIsPunctuation in patternMatcher.ts:

function charIsPunctuation(ch: number) {
    switch (ch) {
        case CharacterCodes.exclamation:
        case CharacterCodes.doubleQuote:
        // ...
        case CharacterCodes._:
        case CharacterCodes.openBrace:
        case CharacterCodes.closeBrace:
            return true;
    }

    return false;
}

This gets an inferred return type of ch is CharacterCodes._ | CharacterCodes.ampersand | CharacterCodes.asterisk | ... | CharacterCodes.slash. Again, this is accurate but not consequential for any of the calling code.

An anonymous function in getLinkedEditingRangeAtPosition in services.ts:

const tag = findAncestor(token.parent, n => {
    if (isJsxOpeningElement(n) || isJsxClosingElement(n)) {
        return true;
    }
    return false;
});
if (!tag) return undefined;
Debug.assert(isJsxOpeningElement(tag) || isJsxClosingElement(tag), "tag should be opening or closing element");

The arrow function becomes a type predicate with #58154 which changes the type of tag. This is a positive change that eliminates the need for the Debug.assert statement.

Of course, the function could have been written more succinctly as n => isJsxOpeningElement(n) || isJsxClosingElement(n) and the existing code would infer a type predicate.

I'm curious what other errors this reports on the user/top/etc suites. This will characterize whether this is a common pattern in the wild.

RyanCavanaugh · 2024-04-12T21:43:23Z

@typescript-bot test it

typescript-bot · 2024-04-12T21:43:26Z

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 · 2024-04-12T22:02:38Z

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

Everything looks the same!

You can check the log here.

typescript-bot · 2024-04-12T22:11:22Z

@RyanCavanaugh Here are the results of running the user tests comparing main and refs/pull/58173/merge:

Something interesting changed - please have a look.

Details

pyright

/mnt/ts_downloads/_/m/pyright/build.sh

[NEW] error TS1499: Function with multiple returns is implicitly a type predicate.
- /mnt/ts_downloads/_/m/pyright/pyright: ../pyright-internal/src/analyzer/parseTreeUtils.ts(2588,17)
- /mnt/ts_downloads/_/m/pyright/pyright-internal: src/analyzer/parseTreeUtils.ts(2588,17)
- /mnt/ts_downloads/_/m/pyright/vscode-pyright: ../pyright-internal/src/analyzer/parseTreeUtils.ts(2588,17)

typescript-bot · 2024-04-12T22:17:59Z

@RyanCavanaugh
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}	_{296,989k (± 0.00%)}	_{297,001k (± 0.01%)}	_~	_296,971k	_297,013k	_{p=0.298 n=6}
_{Parse Time}	_{2.69s (± 0.45%)}	_{2.69s (± 0.38%)}	_~	_2.67s	_2.70s	_{p=0.408 n=6}
_{Bind Time}	_{0.82s (± 0.50%)}	_{0.82s (± 0.00%)}	_~	_0.82s	_0.82s	_{p=0.405 n=6}
_{Check Time}	_{8.33s (± 0.42%)}	_{8.35s (± 0.37%)}	_~	_8.32s	_8.40s	_{p=0.469 n=6}
_{Emit Time}	_{7.05s (± 0.31%)}	_{7.05s (± 0.32%)}	_~	_7.01s	_7.07s	_{p=1.000 n=6}
_{Total Time}	_{18.89s (± 0.20%)}	_{18.90s (± 0.26%)}	_~	_18.83s	_18.95s	_{p=0.629 n=6}
_{Compiler-Unions - node (v18.15.0, x64)}
_{Memory used}	_{192,371k (± 0.74%)}	_{194,332k (± 0.94%)}	_{+1,961k (+ 1.02%)}	_191,962k	_195,646k	_{p=0.013 n=6}
_{Parse Time}	_{2.01s (± 1.53%)}	_{2.02s (± 0.60%)}	_~	_2.01s	_2.04s	_{p=0.416 n=6}
_{Bind Time}	_{1.07s (± 0.92%)}	_{1.07s (± 0.97%)}	_~	_1.05s	_1.08s	_{p=0.788 n=6}
_{Check Time}	_{14.04s (± 0.18%)}	_{14.06s (± 0.50%)}	_~	_13.96s	_14.13s	_{p=0.574 n=6}
_{Emit Time}	_{3.89s (± 2.32%)}	_{3.87s (± 1.04%)}	_~	_3.79s	_3.90s	_{p=0.292 n=6}
_{Total Time}	_{21.01s (± 0.49%)}	_{21.02s (± 0.42%)}	_~	_20.88s	_21.09s	_{p=0.747 n=6}
_{Monaco - node (v18.15.0, x64)}
_{Memory used}	_{348,863k (± 0.01%)}	_{348,866k (± 0.00%)}	_~	_348,847k	_348,882k	_{p=0.688 n=6}
_{Parse Time}	_{3.85s (± 0.86%)}	_{3.85s (± 1.12%)}	_~	_3.79s	_3.90s	_{p=0.936 n=6}
_{Bind Time}	_{1.32s (± 0.62%)}	_{1.32s (± 0.80%)}	_~	_1.30s	_1.33s	_{p=0.865 n=6}
_{Check Time}	_{10.26s (± 0.42%)}	_{10.27s (± 0.49%)}	_~	_10.18s	_10.31s	_{p=0.872 n=6}
_{Emit Time}	_{5.99s (± 0.52%)}	_{6.00s (± 0.61%)}	_~	_5.94s	_6.03s	_{p=0.809 n=6}
_{Total Time}	_{21.42s (± 0.32%)}	_{21.42s (± 0.23%)}	_~	_21.35s	_21.50s	_{p=1.000 n=6}
_{TFS - node (v18.15.0, x64)}
_{Memory used}	_{302,975k (± 0.01%)}	_{302,982k (± 0.00%)}	_~	_302,964k	_303,001k	_{p=0.471 n=6}
_{Parse Time}	_{2.04s (± 0.51%)}	_{2.02s (± 0.67%)}	_~	_2.01s	_2.04s	_{p=0.161 n=6}
_{Bind Time}	_{0.98s (± 0.77%)}	_{0.98s (± 0.77%)}	_~	_0.97s	_0.99s	_{p=1.000 n=6}
_{Check Time}	_{6.47s (± 0.49%)}	_{6.45s (± 0.51%)}	_~	_6.41s	_6.51s	_{p=0.519 n=6}
_{Emit Time}	_{3.58s (± 0.23%)}	_{3.58s (± 0.51%)}	_~	_3.56s	_3.60s	_{p=1.000 n=6}
_{Total Time}	_{13.07s (± 0.27%)}	_{13.04s (± 0.31%)}	_~	_12.97s	_13.08s	_{p=0.170 n=6}
_{material-ui - node (v18.15.0, x64)}
_{Memory used}	_{511,624k (± 0.01%)}	_{511,617k (± 0.00%)}	_~	_511,579k	_511,646k	_{p=0.575 n=6}
_{Parse Time}	_{4.01s (± 0.66%)}	_{4.02s (± 1.04%)}	_~	_3.99s	_4.09s	_{p=0.681 n=6}
_{Bind Time}	_{1.46s (± 1.42%)}	_{1.45s (± 2.02%)}	_~	_1.42s	_1.50s	_{p=0.872 n=6}
_{Check Time}	_{25.32s (± 0.24%)}	_{25.27s (± 0.18%)}	_~	_25.22s	_25.35s	_{p=0.148 n=6}
_{Emit Time}	_{0.00s (± 0.00%)}	_{0.00s (± 0.00%)}	_~	_0.00s	_0.00s	_{p=1.000 n=6}
_{Total Time}	_{30.79s (± 0.23%)}	_{30.75s (± 0.22%)}	_~	_30.69s	_30.88s	_{p=0.335 n=6}
_{mui-docs - node (v18.15.0, x64)}
_{Memory used}	_{1,748,693k (± 0.00%)}	_{1,748,679k (± 0.00%)}	_~	_1,748,618k	_1,748,755k	_{p=0.471 n=6}
_{Parse Time}	_{9.96s (± 0.38%)}	_{10.03s (± 0.88%)}	_~	_9.93s	_10.12s	_{p=0.261 n=6}
_{Bind Time}	_{3.35s (± 0.27%)}	_{3.36s (± 0.87%)}	_~	_3.32s	_3.40s	_{p=0.370 n=6}
_{Check Time}	_{81.76s (± 0.27%)}	_{82.04s (± 0.60%)}	_~	_81.29s	_82.68s	_{p=0.230 n=6}
_{Emit Time}	_{0.19s (± 2.81%)}	_{0.20s (± 5.07%)}	_~	_0.19s	_0.22s	_{p=0.138 n=6}
_{Total Time}	_{95.26s (± 0.21%)}	_{95.63s (± 0.47%)}	_~	_95.00s	_96.17s	_{p=0.229 n=6}
_{self-build-src - node (v18.15.0, x64)}
_{Memory used}	_{2,306,333k (± 0.06%)}	_{2,307,414k (± 0.03%)}	_~	_2,306,245k	_2,308,046k	_{p=0.093 n=6}
_{Parse Time}	_{6.04s (± 0.68%)}	_{6.03s (± 0.69%)}	_~	_5.97s	_6.08s	_{p=0.872 n=6}
_{Bind Time}	_{2.23s (± 1.05%)}	_{2.24s (± 1.28%)}	_~	_2.20s	_2.29s	_{p=0.520 n=6}
_{Check Time}	_{39.84s (± 0.28%)}	_{39.90s (± 0.39%)}	_~	_39.72s	_40.17s	_{p=0.423 n=6}
_{Emit Time}	_{3.17s (± 3.58%)}	_{3.19s (± 3.58%)}	_~	_3.04s	_3.35s	_{p=1.000 n=6}
_{Total Time}	_{51.30s (± 0.43%)}	_{51.38s (± 0.38%)}	_~	_51.15s	_51.67s	_{p=0.688 n=6}
_{self-build-src-public-api - node (v18.15.0, x64)}
_{Memory used}	_{2,380,781k (± 0.04%)}	_{2,381,898k (± 0.03%)}	_~	_2,381,032k	_2,382,892k	_{p=0.066 n=6}
_{Parse Time}	_{7.63s (± 0.36%)}	_{7.66s (± 0.82%)}	_~	_7.56s	_7.74s	_{p=0.230 n=6}
_{Bind Time}	_{2.52s (± 1.24%)}	_{2.51s (± 1.12%)}	_~	_2.48s	_2.56s	_{p=0.368 n=6}
_{Check Time}	_{49.80s (± 0.92%)}	_{49.52s (± 0.53%)}	_~	_49.22s	_49.97s	_{p=0.298 n=6}
_{Emit Time}	_{3.92s (± 1.70%)}	_{3.96s (± 1.99%)}	_~	_3.83s	_4.03s	_{p=0.261 n=6}
_{Total Time}	_{63.87s (± 0.70%)}	_{63.65s (± 0.40%)}	_~	_63.29s	_64.03s	_{p=0.575 n=6}
_{self-compiler - node (v18.15.0, x64)}
_{Memory used}	_{419,069k (± 0.01%)}	_{419,192k (± 0.01%)}	_{+123k (+ 0.03%)}	_419,131k	_419,245k	_{p=0.005 n=6}
_{Parse Time}	_{3.40s (± 0.76%)}	_{3.37s (± 2.43%)}	_~	_3.21s	_3.44s	_{p=0.808 n=6}
_{Bind Time}	_{1.31s (± 1.01%)}	_{1.33s (± 4.80%)}	_~	_1.26s	_1.45s	_{p=0.466 n=6}
_{Check Time}	_{18.04s (± 0.30%)}	_{18.02s (± 0.41%)}	_~	_17.94s	_18.14s	_{p=0.686 n=6}
_{Emit Time}	_{1.37s (± 1.36%)}	_{1.37s (± 2.62%)}	_~	_1.33s	_1.41s	_{p=0.872 n=6}
_{Total Time}	_{24.11s (± 0.20%)}	_{24.10s (± 0.32%)}	_~	_24.01s	_24.22s	_{p=0.748 n=6}
_{vscode - node (v18.15.0, x64)}
_{Memory used}	_{2,912,926k (± 0.00%)}	_{2,912,839k (± 0.00%)}	_~	_2,912,683k	_2,912,925k	_{p=0.066 n=6}
_{Parse Time}	_{13.39s (± 0.21%)}	_{13.42s (± 0.34%)}	_~	_13.35s	_13.49s	_{p=0.255 n=6}
_{Bind Time}	_{4.06s (± 0.40%)}	_{4.10s (± 2.29%)}	_~	_4.05s	_4.29s	_{p=0.807 n=6}
_{Check Time}	_{72.46s (± 0.41%)}	_{72.48s (± 0.27%)}	_~	_72.33s	_72.80s	_{p=0.689 n=6}
_{Emit Time}	_{19.48s (± 0.82%)}	_{20.14s (± 7.49%)}	_~	_19.37s	_23.22s	_{p=0.172 n=6}
_{Total Time}	_{109.39s (± 0.39%)}	_{110.15s (± 1.31%)}	_~	_109.31s	_113.06s	_{p=0.199 n=6}
_{webpack - node (v18.15.0, x64)}
_{Memory used}	_{409,375k (± 0.01%)}	_{409,385k (± 0.01%)}	_~	_409,324k	_409,429k	_{p=0.689 n=6}
_{Parse Time}	_{3.26s (± 0.82%)}	_{3.27s (± 1.19%)}	_~	_3.24s	_3.32s	_{p=0.466 n=6}
_{Bind Time}	_{1.37s (± 0.75%)}	_{1.38s (± 0.76%)}	_~	_1.37s	_1.40s	_{p=0.098 n=6}
_{Check Time}	_{14.38s (± 0.15%)}	_{14.39s (± 0.29%)}	_~	_14.35s	_14.45s	_{p=0.872 n=6}
_{Emit Time}	_{0.00s (± 0.00%)}	_{0.00s (± 0.00%)}	_~	_0.00s	_0.00s	_{p=1.000 n=6}
_{Total Time}	_{19.01s (± 0.23%)}	_{19.04s (± 0.21%)}	_~	_18.99s	_19.08s	_{p=0.191 n=6}
_{xstate - node (v18.15.0, x64)}
_{Memory used}	_{671,977k (± 0.01%)}	_{672,047k (± 0.02%)}	_~	_671,934k	_672,265k	_{p=0.689 n=6}
_{Parse Time}	_{4.12s (± 0.84%)}	_{4.12s (± 0.74%)}	_~	_4.08s	_4.17s	_{p=1.000 n=6}
_{Bind Time}	_{1.87s (± 0.83%)}	_{1.88s (± 0.87%)}	_~	_1.86s	_1.90s	_{p=0.511 n=6}
_{Check Time}	_{3.43s (± 0.24%)}	_{3.45s (± 0.57%)}	_~	_3.42s	_3.47s	_{p=0.081 n=6}
_{Emit Time}	_{0.03s (±19.35%)}	_{0.03s (±14.39%)}	_~	_0.02s	_0.03s	_{p=0.595 n=6}
_{Total Time}	_{9.46s (± 0.48%)}	_{9.47s (± 0.58%)}	_~	_9.40s	_9.56s	_{p=0.746 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-build-src-public-api - 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

jakebailey · 2024-04-12T22:38:34Z

The pyright one is: /~https://github.com/microsoft/pyright/blob/92f2284d2459fed8a9fdaab023527d8598749fcc/packages/pyright-internal/src/analyzer/parseTreeUtils.ts#L2588

Basically the same as charIsPunctuation.

typescript-bot · 2024-04-12T23:28:14Z

@RyanCavanaugh Here are the results of running the top 400 repos comparing main and refs/pull/58173/merge:

Something interesting changed - please have a look.

Details

facebook/lexical

3 of 7 projects failed to build with the old tsc and were ignored

tsconfig.json

error TS1499: Function with multiple returns is implicitly a type predicate.
- packages/lexical-playground/src/plugins/TableCellResizer/index.tsx#L147

Tencent/omi

6 of 19 projects failed to build with the old tsc and were ignored

packages/reactive-signal/tsconfig.json

error TS1499: Function with multiple returns is implicitly a type predicate.
- packages/reactive-signal/src/reactivity.ts#L76

packages/reactive-signal/examples/tsconfig.json

error TS1499: Function with multiple returns is implicitly a type predicate.
- packages/reactive-signal/src/reactivity.ts#L76

jakebailey · 2024-04-12T23:35:16Z

I feel like it's telling that we're seeing so few of these, and that when we do, the code still compiles as it did before. That makes it seem like this isn't very valuable, and that the initial design was good enough.

danvk · 2024-04-12T23:46:17Z

Closing this out since we've learned what we're going to from it.

jakebailey · 2024-04-12T23:48:18Z

BTW thank you for sending these PRs in exactly the format we need to let the infra report something, super helpful.

danvk added 5 commits April 11, 2024 17:18

Infer type predicates with multiple returns

30aef71

make multi-return predicate an error

4bfb712

accept baselines

d79581e

add explicit return type annotation to inferred predicate

2bfca2a

add explicit return types to two more inferred predicates

3352863

typescript-bot added the For Uncommitted Bug PR for untriaged, rejected, closed or missing bug label Apr 12, 2024

danvk mentioned this pull request Apr 12, 2024

Infer type predicates for functions with multiple returns #58154

Open

danvk closed this Apr 12, 2024

danvk mentioned this pull request May 10, 2024

Infer AssertsIdentifier type predicates #58495

Open

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Experiment: report functions with multiple returns that could be type predicates #58173

Experiment: report functions with multiple returns that could be type predicates #58173

danvk commented Apr 12, 2024

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pyright

/mnt/ts_downloads/_/m/pyright/build.sh

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tsc

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facebook/lexical

tsconfig.json

Tencent/omi

packages/reactive-signal/tsconfig.json

packages/reactive-signal/examples/tsconfig.json

jakebailey commented Apr 12, 2024

danvk commented Apr 12, 2024

jakebailey commented Apr 12, 2024

Experiment: report functions with multiple returns that could be type predicates #58173

Experiment: report functions with multiple returns that could be type predicates #58173

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typescript-bot commented Apr 12, 2024 • edited Loading

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typescript-bot commented Apr 12, 2024

pyright

/mnt/ts_downloads/_/m/pyright/build.sh

typescript-bot commented Apr 12, 2024

tsc

jakebailey commented Apr 12, 2024 • edited Loading

typescript-bot commented Apr 12, 2024

facebook/lexical

tsconfig.json

Tencent/omi

packages/reactive-signal/tsconfig.json

packages/reactive-signal/examples/tsconfig.json

jakebailey commented Apr 12, 2024

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