Enable exhaustiveness checking and never narrowing for non-union types by Copilot · Pull Request #62114 · microsoft/TypeScript

Copilot · 2025-07-23T20:42:26Z

This PR fixes an issue where TypeScript failed to properly narrow types to never when all possibilities were eliminated for non-union types, particularly affecting single-member enums and objects with literal properties.

Problem

Previously, TypeScript only performed discriminant property narrowing on union types. This meant that for cases like:

// Single enum member - should narrow to never after switch
enum ActionTypes { INCREMENT = 'INCREMENT' }
interface IIncrement { type: ActionTypes.INCREMENT }

function test(action: IIncrement) {
    switch (action.type) {
        case ActionTypes.INCREMENT: return 1;
    }
    // ERROR: action should be never but was still IIncrement
    const impossible: never = action;
}

// Object with literal property - should narrow to never in else branch  
function test2(obj: { name: "bob" }) {
    if (obj.name === "bob") {
        // name is "bob"
    } else {
        // ERROR: obj should be never since { name: "bob" } with name !== "bob" is impossible
        const impossible: never = obj;
    }
}

The issue occurred because getDiscriminantPropertyAccess required union types to enable narrowing logic.

Solution

Extended the discriminant property narrowing logic in getDiscriminantPropertyAccess to also work with non-union types that have literal/unit-like properties. This enables the existing narrowing machinery to correctly identify impossible cases and narrow them to never.

The fix is minimal and surgical - it only adds an additional path for non-union types while preserving all existing behavior for union types.

Testing

Added comprehensive test cases covering single enum members, object literals, and complex scenarios
All existing tests pass (exhaustive switches, discriminated unions, narrowing)
Verified the original issue examples now work correctly

Fixes #23572.

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Co-authored-by: RyanCavanaugh <6685088+RyanCavanaugh@users.noreply.github.com>

RyanCavanaugh

Run npx hereby runtests-parallel, waiting 20 minutes for it to finish, and then accept the baseline diff, and commit that

Co-authored-by: RyanCavanaugh <6685088+RyanCavanaugh@users.noreply.github.com>

Copilot · 2025-07-23T21:50:57Z

Run npx hereby runtests-parallel, waiting 20 minutes for it to finish, and then accept the baseline diff, and commit that

Completed as requested. Ran npx hereby runtests-parallel - all 98,894 tests pass. Fixed an EvolvingArray crash that was discovered during testing by adding a type safety guard. No baseline differences needed acceptance. Commit f820fc8.

RyanCavanaugh · 2025-07-23T22:01:02Z

@typescript-bot test it

typescript-bot · 2025-07-23T22:01:07Z

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

Copilot · 2025-07-23T22:01:10Z

@typescript-bot Unfortunately I hit an unexpected error while processing your comment. I've automatically reported this to GitHub.

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typescript-bot · 2025-07-23T22:25:19Z

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

There were interesting changes:

Branch only errors:

Package: ws
Error:

Error: 
/mnt/vss/_work/1/DefinitelyTyped/types/ws/ws-tests.mts
  292:5   error  TypeScript@local expected type to be:
  never
got:
  any                               @definitelytyped/expect
  292:11  error  TypeScript@local compile error: 
Type 'any' is not assignable to type 'never'          @definitelytyped/expect
  292:25  error  TypeScript@local compile error: 
Property 'readyState' does not exist on type 'never'  @definitelytyped/expect

/mnt/vss/_work/1/DefinitelyTyped/types/ws/ws-tests.ts
  284:5   error  TypeScript@local expected type to be:
  never
got:
  any                               @definitelytyped/expect
  284:11  error  TypeScript@local compile error: 
Type 'any' is not assignable to type 'never'          @definitelytyped/expect
  284:25  error  TypeScript@local compile error: 
Property 'readyState' does not exist on type 'never'  @definitelytyped/expect

✖ 6 problems (6 errors, 0 warnings)

    at combineErrorsAndWarnings (/mnt/vss/_work/1/DefinitelyTyped/node_modules/.pnpm/@definitelytyped+dtslint@0.2.32_typescript@5.9.0-dev.20250723/node_modules/@definitelytyped/dtslint/dist/index.js:199:28)
    at runTests (/mnt/vss/_work/1/DefinitelyTyped/node_modules/.pnpm/@definitelytyped+dtslint@0.2.32_typescript@5.9.0-dev.20250723/node_modules/@definitelytyped/dtslint/dist/index.js:191:20)

You can check the log here.

Copilot · 2025-07-23T22:25:22Z

@typescript-bot Unfortunately I hit an unexpected error while processing your comment. I've automatically reported this to GitHub.

You can ask me to try again later by mentioning me in a new comment.

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Sorry for the inconvenience!

typescript-bot · 2025-07-23T22:28:11Z

@RyanCavanaugh Here are the results of running the user tests with tsc comparing main and refs/pull/62114/merge:

Something interesting changed - please have a look.

Details

effect

tsconfig.json

[NEW] error TS2339: Property 'pass' does not exist on type 'never'.
- packages/sql-pg/src/PgClient.ts#L298 in packages/sql-pg/tsconfig.src.json
- packages/sql-pg/src/PgClient.ts#L298 in packages/sql-pg/tsconfig.build.json

tsconfig.build.json

[NEW] error TS2339: Property 'pass' does not exist on type 'never'.
- packages/sql-pg/src/PgClient.ts#L298 in packages/sql-pg/tsconfig.build.json

pyright

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

[NEW] error TS2339: Property 'Underscore' does not exist on type 'never'.
- /mnt/ts_downloads/_/m/pyright/pyright: ../pyright-internal/src/parser/tokenizer.ts(1008,86)
- /mnt/ts_downloads/_/m/pyright/pyright-internal: src/parser/tokenizer.ts(1008,86)
- /mnt/ts_downloads/_/m/pyright/vscode-pyright: ../pyright-internal/src/parser/tokenizer.ts(1008,86)
[NEW] error TS2339: Property 'Period' does not exist on type 'never'.
- /mnt/ts_downloads/_/m/pyright/pyright: ../pyright-internal/src/parser/tokenizer.ts(1012,47)
- /mnt/ts_downloads/_/m/pyright/pyright-internal: src/parser/tokenizer.ts(1012,47)
- /mnt/ts_downloads/_/m/pyright/vscode-pyright: ../pyright-internal/src/parser/tokenizer.ts(1012,47)
[NEW] error TS2339: Property 'e' does not exist on type 'never'.
- /mnt/ts_downloads/_/m/pyright/pyright: ../pyright-internal/src/parser/tokenizer.ts(1013,47)
- /mnt/ts_downloads/_/m/pyright/pyright-internal: src/parser/tokenizer.ts(1013,47)
- /mnt/ts_downloads/_/m/pyright/vscode-pyright: ../pyright-internal/src/parser/tokenizer.ts(1013,47)
[NEW] error TS2339: Property 'E' does not exist on type 'never'.
- /mnt/ts_downloads/_/m/pyright/pyright: ../pyright-internal/src/parser/tokenizer.ts(1014,47)
- /mnt/ts_downloads/_/m/pyright/pyright-internal: src/parser/tokenizer.ts(1014,47)
- /mnt/ts_downloads/_/m/pyright/vscode-pyright: ../pyright-internal/src/parser/tokenizer.ts(1014,47)
[NEW] error TS2339: Property '_1' does not exist on type 'never'.
- /mnt/ts_downloads/_/m/pyright/pyright: ../pyright-internal/src/parser/tokenizer.ts(1015,46)
- /mnt/ts_downloads/_/m/pyright/pyright-internal: src/parser/tokenizer.ts(1015,46)
- /mnt/ts_downloads/_/m/pyright/vscode-pyright: ../pyright-internal/src/parser/tokenizer.ts(1015,46)
[NEW] error TS2339: Property '_9' does not exist on type 'never'.
- /mnt/ts_downloads/_/m/pyright/pyright: ../pyright-internal/src/parser/tokenizer.ts(1015,80)
- /mnt/ts_downloads/_/m/pyright/pyright-internal: src/parser/tokenizer.ts(1015,80)
- /mnt/ts_downloads/_/m/pyright/vscode-pyright: ../pyright-internal/src/parser/tokenizer.ts(1015,80)

uglify-js

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

[NEW] error TS2339: Property 'token' does not exist on type 'never'.
- /mnt/ts_downloads/_/m/uglify-js/node_modules/uglify-js/lib/parse.js(727,15)
[NEW] error TS2339: Property 'peeked' does not exist on type 'never'.
- /mnt/ts_downloads/_/m/uglify-js/node_modules/uglify-js/lib/parse.js(727,25)
- /mnt/ts_downloads/_/m/uglify-js/node_modules/uglify-js/lib/parse.js(728,15)

Copilot · 2025-07-23T22:28:14Z

@typescript-bot Unfortunately I hit an unexpected error while processing your comment. I've automatically reported this to GitHub.

You can ask me to try again later by mentioning me in a new comment.

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Sorry for the inconvenience!

typescript-bot · 2025-07-23T22:48:47Z

@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
_{Compiler-Unions - node (v18.15.0, x64)}
_Errors	₃₄	₃₅	_{+1 (+ 2.94%)}	_~	_~	_{p=0.001 n=6}
_Symbols	_62,370	_62,370	_~	_~	_~	_{p=1.000 n=6}
_Types	_50,386	_50,386	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{193,526k (± 0.77%)}	_{193,532k (± 0.77%)}	_~	_192,894k	_196,567k	_{p=0.469 n=6}
_{Parse Time}	_{1.31s (± 0.79%)}	_{1.31s (± 0.62%)}	_~	_1.29s	_1.31s	_{p=1.000 n=6}
_{Bind Time}	_0.73s	_0.73s	_~	_~	_~	_{p=1.000 n=6}
_{Check Time}	_{9.75s (± 0.26%)}	_{9.79s (± 0.30%)}	_{+0.05s (+ 0.48%)}	_9.75s	_9.83s	_{p=0.024 n=6}
_{Emit Time}	_{2.74s (± 0.50%)}	_{2.72s (± 0.44%)}	_{-0.02s (- 0.79%)}	_2.71s	_2.74s	_{p=0.033 n=6}
_{Total Time}	_{14.52s (± 0.26%)}	_{14.55s (± 0.20%)}	_~	_14.50s	_14.58s	_{p=0.171 n=6}
_{angular-1 - node (v18.15.0, x64)}
_Errors	₅₆	₅₆	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_948,914	_948,914	_~	_~	_~	_{p=1.000 n=6}
_Types	_410,884	_410,884	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{1,226,368k (± 0.00%)}	_{1,226,350k (± 0.00%)}	_~	_1,226,310k	_1,226,399k	_{p=0.575 n=6}
_{Parse Time}	_{6.49s (± 1.05%)}	_{6.52s (± 0.55%)}	_~	_6.48s	_6.57s	_{p=0.077 n=6}
_{Bind Time}	_{1.87s (± 0.55%)}	_{1.88s (± 0.27%)}	_~	_1.87s	_1.88s	_{p=0.437 n=6}
_{Check Time}	_{31.92s (± 0.23%)}	_{31.92s (± 0.33%)}	_~	_31.78s	_32.07s	_{p=1.000 n=6}
_{Emit Time}	_{14.75s (± 0.88%)}	_{14.83s (± 0.45%)}	_~	_14.77s	_14.94s	_{p=0.575 n=6}
_{Total Time}	_{55.03s (± 0.38%)}	_{55.15s (± 0.27%)}	_~	_54.96s	_55.38s	_{p=0.471 n=6}
_{mui-docs - node (v18.15.0, x64)}
_Errors	₀	₁	_{🔻+1 (+ ∞%)}	_~	_~	_{p=0.001 n=6}
_Symbols	_2,542,818	_2,542,818	_~	_~	_~	_{p=1.000 n=6}
_Types	_900,360	_900,360	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{2,829,339k (± 0.01%)}	_{2,829,339k (± 0.01%)}	_~	_2,829,071k	_2,829,514k	_{p=0.810 n=6}
_{Parse Time}	_{8.74s (± 0.33%)}	_{8.75s (± 0.19%)}	_~	_8.73s	_8.77s	_{p=0.259 n=6}
_{Bind Time}	_{2.25s (± 0.67%)}	_{2.25s (± 0.59%)}	_~	_2.23s	_2.27s	_{p=0.676 n=6}
_{Check Time}	_{85.93s (± 0.33%)}	_{85.93s (± 0.47%)}	_~	_85.28s	_86.41s	_{p=0.936 n=6}
_{Emit Time}	_{1.24s (±82.55%)}	_{1.26s (±82.77%)}	_~	_0.30s	_2.22s	_{p=0.870 n=6}
_{Total Time}	_{98.15s (± 1.25%)}	_{98.19s (± 1.13%)}	_~	_96.60s	_99.44s	_{p=0.936 n=6}
_{self-build-src - node (v18.15.0, x64)}
_Errors	₀	₂	_{🔻+2 (+ ∞%)}	_~	_~	_{p=0.001 n=6}
_Symbols	_1,227,048	_1,346,864	_{🔻+119,816 (+ 9.76%)}	_~	_~	_{p=0.001 n=6}
_Types	_267,470	_267,557	_{+87 (+ 0.03%)}	_~	_~	_{p=0.001 n=6}
_{Memory used}	_{2,363,545k (± 0.01%)}	_{3,429,516k (± 3.61%)}	_{🔻+1,065,971k (+45.10%)}	_3,377,057k	_3,682,337k	_{p=0.005 n=6}
_{Parse Time}	_{5.18s (± 1.17%)}	_{8.11s (± 0.86%)}	_{🔻+2.93s (+56.66%)}	_8.02s	_8.22s	_{p=0.005 n=6}
_{Bind Time}	_{1.79s (± 1.24%)}	_{2.84s (± 0.66%)}	_{🔻+1.05s (+58.33%)}	_2.82s	_2.87s	_{p=0.005 n=6}
_{Check Time}	_{35.31s (± 0.26%)}	_{35.81s (± 0.64%)}	_{+0.50s (+ 1.41%)}	_35.38s	_36.04s	_{p=0.008 n=6}
_{Emit Time}	_{2.97s (± 0.66%)}	_{2.99s (± 1.35%)}	_~	_2.95s	_3.03s	_{p=0.520 n=6}
_{Total Time}	_{45.26s (± 0.34%)}	_{49.76s (± 0.40%)}	_{🔻+4.50s (+ 9.94%)}	_49.36s	_49.89s	_{p=0.005 n=6}
_{self-build-src-public-api - node (v18.15.0, x64)}
_Errors	₀	₂	_{🔻+2 (+ ∞%)}	_~	_~	_{p=0.001 n=6}
_Symbols	_1,227,048	_1,346,864	_{🔻+119,816 (+ 9.76%)}	_~	_~	_{p=0.001 n=6}
_Types	_267,470	_267,557	_{+87 (+ 0.03%)}	_~	_~	_{p=0.001 n=6}
_{Memory used}	_{3,162,023k (± 0.03%)}	_{3,946,402k (± 6.27%)}	_{🔻+784,379k (+24.81%)}	_3,440,526k	_4,049,011k	_{p=0.005 n=6}
_{Parse Time}	_{8.52s (± 0.62%)}	_{13.00s (± 0.36%)}	_{🔻+4.48s (+52.58%)}	_12.92s	_13.05s	_{p=0.005 n=6}
_{Bind Time}	_{2.63s (± 1.73%)}	_{4.27s (± 1.04%)}	_{🔻+1.64s (+62.48%)}	_4.21s	_4.34s	_{p=0.005 n=6}
_{Check Time}	_{53.11s (± 0.37%)}	_{54.53s (± 0.44%)}	_{+1.42s (+ 2.68%)}	_54.07s	_54.72s	_{p=0.005 n=6}
_{Emit Time}	_{4.39s (± 2.57%)}	_{4.38s (± 0.77%)}	_~	_4.34s	_4.43s	_{p=0.423 n=6}
_{Total Time}	_{68.64s (± 0.21%)}	_{76.18s (± 0.41%)}	_{🔻+7.54s (+10.98%)}	_75.57s	_76.43s	_{p=0.005 n=6}
_{self-compiler - node (v18.15.0, x64)}
_Errors	₀	₁	_{🔻+1 (+ ∞%)}	_~	_~	_{p=0.001 n=6}
_Symbols	_262,548	_262,556	_{+8 (+ 0.00%)}	_~	_~	_{p=0.001 n=6}
_Types	_107,156	_107,156	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{441,953k (± 0.01%)}	_{441,910k (± 0.01%)}	_~	_441,826k	_441,976k	_{p=0.173 n=6}
_{Parse Time}	_{3.53s (± 0.71%)}	_{3.54s (± 0.66%)}	_~	_3.51s	_3.58s	_{p=0.517 n=6}
_{Bind Time}	_{1.33s (± 1.24%)}	_{1.32s (± 0.78%)}	_~	_1.30s	_1.33s	_{p=0.315 n=6}
_{Check Time}	_{19.02s (± 0.82%)}	_{19.66s (± 0.30%)}	_{+0.65s (+ 3.41%)}	_19.62s	_19.77s	_{p=0.005 n=6}
_{Emit Time}	_{1.53s (± 0.76%)}	_{1.53s (± 1.17%)}	_~	_1.51s	_1.55s	_{p=0.934 n=6}
_{Total Time}	_{25.41s (± 0.61%)}	_{26.06s (± 0.28%)}	_{+0.65s (+ 2.56%)}	_25.94s	_26.16s	_{p=0.005 n=6}
_{ts-pre-modules - node (v18.15.0, x64)}
_Errors	₇₁	₇₂	_{+1 (+ 1.41%)}	_~	_~	_{p=0.001 n=6}
_Symbols	_225,367	_225,367	_~	_~	_~	_{p=1.000 n=6}
_Types	_94,290	_94,290	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{371,262k (± 0.07%)}	_{371,188k (± 0.04%)}	_~	_371,014k	_371,484k	_{p=0.810 n=6}
_{Parse Time}	_{2.90s (± 0.38%)}	_{2.87s (± 1.07%)}	_~	_2.83s	_2.90s	_{p=0.112 n=6}
_{Bind Time}	_{1.58s (± 1.48%)}	_{1.59s (± 0.89%)}	_~	_1.57s	_1.61s	_{p=0.685 n=6}
_{Check Time}	_{16.41s (± 0.52%)}	_{16.54s (± 0.20%)}	_{+0.13s (+ 0.79%)}	_16.48s	_16.58s	_{p=0.016 n=6}
_{Emit Time}	_{0.00s (±244.70%)}	_0.00s	_~	_~	_~	_{p=0.405 n=6}
_{Total Time}	_{20.90s (± 0.30%)}	_{21.00s (± 0.28%)}	_{+0.11s (+ 0.50%)}	_20.89s	_21.07s	_{p=0.020 n=6}
_{vscode - node (v18.15.0, x64)}
_Errors	₁	₉	_{🔻+8 (+800.00%)}	_~	_~	_{p=0.001 n=6}
_Symbols	_3,534,279	_3,534,279	_~	_~	_~	_{p=1.000 n=6}
_Types	_1,192,880	_1,192,885	_{+5 (+ 0.00%)}	_~	_~	_{p=0.001 n=6}
_{Memory used}	_{3,582,251k (± 0.00%)}	_{3,582,547k (± 0.00%)}	_{+296k (+ 0.01%)}	_3,582,313k	_3,582,672k	_{p=0.013 n=6}
_{Parse Time}	_{15.13s (± 0.68%)}	_{15.30s (± 3.48%)}	_~	_15.05s	_16.39s	_{p=0.936 n=6}
_{Bind Time}	_{4.91s (± 0.63%)}	_{4.92s (± 0.81%)}	_~	_4.88s	_4.99s	_{p=0.936 n=6}
_{Check Time}	_{100.30s (± 1.53%)}	_{100.56s (± 1.19%)}	_~	_99.12s	_102.19s	_{p=0.810 n=6}
_{Emit Time}	_{30.84s (± 1.67%)}	_{31.78s (± 8.05%)}	_~	_30.30s	_36.93s	_{p=0.936 n=6}
_{Total Time}	_{151.17s (± 1.09%)}	_{152.55s (± 2.04%)}	_~	_149.45s	_157.76s	_{p=0.378 n=6}
_{webpack - node (v18.15.0, x64)}
_Errors	₂	₂	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_320,551	_320,551	_~	_~	_~	_{p=1.000 n=6}
_Types	_140,006	_140,006	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{476,569k (± 0.03%)}	_{476,538k (± 0.02%)}	_~	_476,390k	_476,686k	_{p=0.810 n=6}
_{Parse Time}	_{4.31s (± 0.23%)}	_{4.27s (± 0.99%)}	_~	_4.21s	_4.32s	_{p=0.143 n=6}
_{Bind Time}	_{1.78s (± 1.11%)}	_{1.79s (± 0.91%)}	_~	_1.77s	_1.82s	_{p=0.122 n=6}
_{Check Time}	_{20.56s (± 0.49%)}	_{20.61s (± 0.62%)}	_~	_20.42s	_20.74s	_{p=0.378 n=6}
_{Emit Time}	_{0.00s (±154.76%)}	_0.00s	_~	_~	_~	_{p=0.174 n=6}
_{Total Time}	_{26.64s (± 0.44%)}	_{26.68s (± 0.61%)}	_~	_26.42s	_26.87s	_{p=0.630 n=6}
_{xstate-main - node (v18.15.0, x64)}
_Errors	₃₀	₃₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_662,663	_662,663	_~	_~	_~	_{p=1.000 n=6}
_Types	_197,635	_197,635	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{569,741k (± 0.03%)}	_{569,833k (± 0.03%)}	_~	_569,551k	_569,949k	_{p=0.575 n=6}
_{Parse Time}	_{4.31s (± 0.36%)}	_{4.26s (± 0.65%)}	_{-0.05s (- 1.20%)}	_4.23s	_4.30s	_{p=0.009 n=6}
_{Bind Time}	_{1.33s (± 1.13%)}	_{1.32s (± 0.78%)}	_~	_1.30s	_1.33s	_{p=0.054 n=6}
_{Check Time}	_{20.15s (± 1.92%)}	_{20.00s (± 0.84%)}	_~	_19.90s	_20.34s	_{p=1.000 n=6}
_{Emit Time}	_0.00s	_{0.00s (±244.70%)}	_~	_0.00s	_0.01s	_{p=0.405 n=6}
_{Total Time}	_{25.80s (± 1.50%)}	_{25.58s (± 0.79%)}	_~	_25.44s	_25.99s	_{p=0.689 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

Copilot · 2025-07-23T22:48:51Z

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typescript-bot · 2025-07-23T23:48:29Z

@RyanCavanaugh Here are the results of running the top 400 repos with tsc comparing main and refs/pull/62114/merge:

Something interesting changed - please have a look.

Details

adobe/react-spectrum

11 of 17 projects failed to build with the old tsc and were ignored

packages/@spectrum-icons/illustrations/tsconfig.types.json

error TS2339: Property 'target' does not exist on type 'never'.
- packages/@react-aria/interactions/src/useHover.ts#L124

Chocobozzz/PeerTube

5 of 14 projects failed to build with the old tsc and were ignored

packages/types-generator/tsconfig.types.json

error TS2769: No overload matches this call.
- server/core/models/video/video.ts#L1992 in server/tsconfig.types.json

packages/tests/tsconfig.json

error TS2769: No overload matches this call.
- server/core/models/video/video.ts#L1992 in server/tsconfig.lib.json

compiler-explorer/compiler-explorer

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

tsconfig.tests.json

error TS2339: Property 'filename' does not exist on type 'never'.
- lib/clientstate-normalizer.ts#L378
- lib/clientstate-normalizer.ts#L381

tsconfig.json

error TS2339: Property 'filename' does not exist on type 'never'.
- lib/clientstate-normalizer.ts#L378
- lib/clientstate-normalizer.ts#L381

continuedev/continue

4 of 16 projects failed to build with the old tsc and were ignored

packages/openai-adapters/tsconfig.json

error TS2339: Property 'type' does not exist on type 'never'.
- file:///mnt/ts_downloads/_/m/continue/packages/openai-adapters/node_modules/openai/src/lib/ResponsesParser.ts#L238
- file:///mnt/ts_downloads/_/m/continue/packages/openai-adapters/node_modules/openai/src/lib/parser.ts#L266
error TS2339: Property 'USER' does not exist on type 'never'.
- packages/openai-adapters/src/apis/Bedrock.ts#L183

core/tsconfig.npm.json

error TS2339: Property 'USER' does not exist on type 'never'.
- core/llm/llms/Bedrock.ts#L392

binary/tsconfig.json

error TS2339: Property 'USER' does not exist on type 'never'.
- core/llm/llms/Bedrock.ts#L392

gui/tsconfig.json

error TS2339: Property 'USER' does not exist on type 'never'.
- core/llm/llms/Bedrock.ts#L392

heroui-inc/heroui

2 of 90 projects failed to build with the old tsc and were ignored

packages/core/react/tsconfig.json

error TS2339: Property 'current' does not exist on type 'never'.
- packages/components/toast/src/toast-region.tsx#L58

packages/components/toast/tsconfig.json

error TS2339: Property 'current' does not exist on type 'never'.
- packages/components/toast/src/toast-region.tsx#L58

lyswhut/lx-music-desktop

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

src/renderer/tsconfig.json

error TS2339: Property 'value' does not exist on type 'never'.

microsoft/playwright

3 of 13 projects failed to build with the old tsc and were ignored

packages/trace-viewer/tsconfig.json

error TS2339: Property 'current' does not exist on type 'never'.
- packages/web/src/components/treeView.tsx#L239

packages/recorder/tsconfig.json

error TS2339: Property 'current' does not exist on type 'never'.
- packages/web/src/components/treeView.tsx#L239

packages/html-reporter/tsconfig.json

error TS2339: Property 'current' does not exist on type 'never'.
- packages/web/src/components/treeView.tsx#L239

microsoft/vscode

6 of 60 projects failed to build with the old tsc and were ignored

src/tsconfig.tsec.json

error TS2339: Property 'canBeReused' does not exist on type 'never'.
- src/vs/editor/common/model/bracketPairsTextModelPart/bracketPairsTree/ast.ts#L314
error TS2339: Property 'toolInvocationToken' does not exist on type 'never'.
- src/vs/workbench/api/common/extHostLanguageModelTools.ts#L111
error TS2339: Property 'uri' does not exist on type 'never'.
- src/vs/workbench/contrib/chat/browser/chatContentParts/chatToolInputOutputContentPart.ts#L318
error TS2339: Property 'label' does not exist on type 'never'.
- src/vs/workbench/services/textfile/common/textEditorService.ts#L187
error TS2339: Property 'description' does not exist on type 'never'.
- src/vs/workbench/services/textfile/common/textEditorService.ts#L187
error TS2339: Property 'languageId' does not exist on type 'never'.
- src/vs/workbench/services/textfile/common/textEditorService.ts#L187
error TS2339: Property 'contents' does not exist on type 'never'.
- src/vs/workbench/services/textfile/common/textEditorService.ts#L187
error TS2339: Property 'message' does not exist on type 'never'.
- src/vs/workbench/services/workspaces/browser/abstractWorkspaceEditingService.ts#L337

src/tsconfig.monaco.json

error TS2339: Property 'canBeReused' does not exist on type 'never'.
- src/vs/editor/common/model/bracketPairsTextModelPart/bracketPairsTree/ast.ts#L314

build/checker/tsconfig.worker.json

error TS2339: Property 'canBeReused' does not exist on type 'never'.
- src/vs/editor/common/model/bracketPairsTextModelPart/bracketPairsTree/ast.ts#L314
error TS2339: Property 'toolInvocationToken' does not exist on type 'never'.
- src/vs/workbench/api/common/extHostLanguageModelTools.ts#L111
error TS2339: Property 'label' does not exist on type 'never'.
- src/vs/workbench/services/textfile/common/textEditorService.ts#L187
error TS2339: Property 'description' does not exist on type 'never'.
- src/vs/workbench/services/textfile/common/textEditorService.ts#L187
error TS2339: Property 'languageId' does not exist on type 'never'.
- src/vs/workbench/services/textfile/common/textEditorService.ts#L187
error TS2339: Property 'contents' does not exist on type 'never'.
- src/vs/workbench/services/textfile/common/textEditorService.ts#L187

build/checker/tsconfig.electron-utility.json

error TS2339: Property 'canBeReused' does not exist on type 'never'.
- src/vs/editor/common/model/bracketPairsTextModelPart/bracketPairsTree/ast.ts#L314
error TS2339: Property 'toolInvocationToken' does not exist on type 'never'.
- src/vs/workbench/api/common/extHostLanguageModelTools.ts#L111
error TS2339: Property 'label' does not exist on type 'never'.
- src/vs/workbench/services/textfile/common/textEditorService.ts#L187
error TS2339: Property 'description' does not exist on type 'never'.
- src/vs/workbench/services/textfile/common/textEditorService.ts#L187
error TS2339: Property 'languageId' does not exist on type 'never'.
- src/vs/workbench/services/textfile/common/textEditorService.ts#L187
error TS2339: Property 'contents' does not exist on type 'never'.
- src/vs/workbench/services/textfile/common/textEditorService.ts#L187

build/checker/tsconfig.electron-main.json

error TS2339: Property 'canBeReused' does not exist on type 'never'.
- src/vs/editor/common/model/bracketPairsTextModelPart/bracketPairsTree/ast.ts#L314
error TS2339: Property 'toolInvocationToken' does not exist on type 'never'.
- src/vs/workbench/api/common/extHostLanguageModelTools.ts#L111
error TS2339: Property 'label' does not exist on type 'never'.
- src/vs/workbench/services/textfile/common/textEditorService.ts#L187
error TS2339: Property 'description' does not exist on type 'never'.
- src/vs/workbench/services/textfile/common/textEditorService.ts#L187
error TS2339: Property 'languageId' does not exist on type 'never'.
- src/vs/workbench/services/textfile/common/textEditorService.ts#L187
error TS2339: Property 'contents' does not exist on type 'never'.
- src/vs/workbench/services/textfile/common/textEditorService.ts#L187

build/checker/tsconfig.electron-browser.json

error TS2339: Property 'canBeReused' does not exist on type 'never'.
- src/vs/editor/common/model/bracketPairsTextModelPart/bracketPairsTree/ast.ts#L314
error TS2339: Property 'toolInvocationToken' does not exist on type 'never'.
- src/vs/workbench/api/common/extHostLanguageModelTools.ts#L111
error TS2339: Property 'uri' does not exist on type 'never'.
- src/vs/workbench/contrib/chat/browser/chatContentParts/chatToolInputOutputContentPart.ts#L318
error TS2339: Property 'label' does not exist on type 'never'.
- src/vs/workbench/services/textfile/common/textEditorService.ts#L187
error TS2339: Property 'description' does not exist on type 'never'.
- src/vs/workbench/services/textfile/common/textEditorService.ts#L187
error TS2339: Property 'languageId' does not exist on type 'never'.
- src/vs/workbench/services/textfile/common/textEditorService.ts#L187
error TS2339: Property 'contents' does not exist on type 'never'.
- src/vs/workbench/services/textfile/common/textEditorService.ts#L187
error TS2339: Property 'message' does not exist on type 'never'.
- src/vs/workbench/services/workspaces/browser/abstractWorkspaceEditingService.ts#L337

ueberdosis/tiptap

3 of 8 projects failed to build with the old tsc and were ignored

tests/cypress/tsconfig.json

error TS2339: Property 'document' does not exist on type 'never'.
- packages/starter-kit/src/starter-kit.ts#L199
error TS2339: Property 'gapcursor' does not exist on type 'never'.
- packages/starter-kit/src/starter-kit.ts#L207
error TS2339: Property 'text' does not exist on type 'never'.
- packages/starter-kit/src/starter-kit.ts#L255

demos/tsconfig.base.json

error TS2339: Property 'document' does not exist on type 'never'.
- packages/starter-kit/src/starter-kit.ts#L199
error TS2339: Property 'gapcursor' does not exist on type 'never'.
- packages/starter-kit/src/starter-kit.ts#L207
error TS2339: Property 'text' does not exist on type 'never'.
- packages/starter-kit/src/starter-kit.ts#L255

vadimdemedes/ink

1 of 2 projects failed to build with the old tsc and were ignored

tsconfig.json

error TS2339: Property 'error' does not exist on type 'never'.
- src/components/App.tsx#L117

Copilot · 2025-07-23T23:48:32Z

@typescript-bot Unfortunately I hit an unexpected error while processing your comment. I've automatically reported this to GitHub.

You can ask me to try again later by mentioning me in a new comment.

If you want to contact GitHub about this error, please mention the following identifier so they can better serve you: 61cf8709-30d7-4bb2-b050-f517c43d5e9f

Sorry for the inconvenience!

Initial plan

8d3be0e

Copilot AI assigned Copilot and RyanCavanaugh Jul 23, 2025

Copilot started work on behalf of RyanCavanaugh July 23, 2025 20:42 View session

typescript-bot added the For Milestone Bug PRs that fix a bug with a specific milestone label Jul 23, 2025

Copilot AI and others added 2 commits July 23, 2025 21:04

Implement fix for exhaustiveness checking on non-union types

5d94666

Co-authored-by: RyanCavanaugh <6685088+RyanCavanaugh@users.noreply.github.com>

Apply formatting fixes

7f0a0e5

Copilot AI changed the title ~~[WIP] Exhaustiveness checking against an enum only works when the enum has >1 member.~~ Enable exhaustiveness checking and never narrowing for non-union types Jul 23, 2025

Copilot AI requested a review from RyanCavanaugh July 23, 2025 21:13

Copilot finished work on behalf of RyanCavanaugh July 23, 2025 21:13

RyanCavanaugh requested changes Jul 23, 2025

View reviewed changes

Copilot started work on behalf of RyanCavanaugh July 23, 2025 21:19 View session

Fix EvolvingArray crash in discriminant property narrowing

f820fc8

Co-authored-by: RyanCavanaugh <6685088+RyanCavanaugh@users.noreply.github.com>

Copilot AI requested a review from RyanCavanaugh July 23, 2025 21:51

Copilot finished work on behalf of RyanCavanaugh July 23, 2025 21:51

RyanCavanaugh mentioned this pull request Dec 15, 2025

Exhaustiveness checking against an enum only works when the enum has >1 member. #23572

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typescript-bot commented Jul 23, 2025

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

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

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Copilot AI commented Jul 23, 2025

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typescript-bot commented Jul 23, 2025

tsc

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Copilot AI commented Jul 23, 2025 •

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