Use comparability for discriminant properties when narrowing types for a default switch clause by Andarist · Pull Request #61211 · microsoft/TypeScript

Andarist · 2025-02-18T08:34:45Z

…r a default switch clause

Andarist · 2025-02-18T08:40:46Z

src/compiler/checker.ts

                return caseType;
            }
-            const defaultType = filterType(type, t => !(isUnitLikeType(t) && contains(switchTypes, t.flags & TypeFlags.Undefined ? undefinedType : getRegularTypeOfLiteralType(extractUnitType(t)))));
+            const defaultType = filterType(type, t => !(isUnitLikeType(t) && contains(switchTypes, t.flags & TypeFlags.Undefined ? undefinedType : getRegularTypeOfLiteralType(extractUnitType(t)), (t1, t2) => isUnitType(t1) && areTypesComparable(t1, t2))));


This essentially matches the logic used by narrowTypeByEquality here

if (isUnitType(valueType)) { return filterType(type, t => !(isUnitLikeType(t) && areTypesComparable(t, valueType))); }

As we can see, the valueType has to pass isUnitType there and the equivalent of the valueType here are all the types in switchTypes. Note that in the case of switch/case here that check mainly ensures we ignore neverType as that's comparable to everything. neverType is specifically used within switchTypes to indicate that this switch statement has a default case (see getTypeOfSwitchClause here and hasDefaultClause here)

DanielRosenwasser · 2025-02-18T18:46:11Z

@typescript-bot test it

typescript-bot · 2025-02-18T18:46:16Z

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 · 2025-02-18T19:09:25Z

@DanielRosenwasser Here are the results of running the user tests with tsc comparing main and refs/pull/61211/merge:

Everything looks good!

typescript-bot · 2025-02-18T19:09:44Z

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

Everything looks the same!

You can check the log here.

typescript-bot · 2025-02-18T19:30:52Z

@DanielRosenwasser
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}	_{193,006k (± 0.07%)}	_{194,721k (± 1.01%)}	_~	_192,917k	_196,553k	_{p=0.936 n=6}
_{Parse Time}	_{1.31s (± 0.84%)}	_{1.31s (± 1.04%)}	_~	_1.28s	_1.32s	_{p=0.929 n=6}
_{Bind Time}	_0.73s	_0.73s	_~	_~	_~	_{p=1.000 n=6}
_{Check Time}	_{9.72s (± 0.33%)}	_{9.85s (± 0.25%)}	_{+0.13s (+ 1.29%)}	_9.81s	_9.87s	_{p=0.005 n=6}
_{Emit Time}	_{2.72s (± 0.72%)}	_{2.73s (± 0.71%)}	_~	_2.71s	_2.76s	_{p=0.167 n=6}
_{Total Time}	_{14.48s (± 0.39%)}	_{14.61s (± 0.13%)}	_{+0.14s (+ 0.94%)}	_14.59s	_14.64s	_{p=0.005 n=6}
_{angular-1 - node (v18.15.0, x64)}
_Errors	₃₇	₃₇	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_948,488	_948,488	_~	_~	_~	_{p=1.000 n=6}
_Types	_411,006	_411,006	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{1,224,196k (± 0.00%)}	_{1,224,238k (± 0.01%)}	_~	_1,224,172k	_1,224,335k	_{p=0.336 n=6}
_{Parse Time}	_{6.66s (± 0.63%)}	_{6.62s (± 0.78%)}	_~	_6.57s	_6.68s	_{p=0.220 n=6}
_{Bind Time}	_{1.89s (± 0.27%)}	_{1.88s (± 0.64%)}	_~	_1.87s	_1.90s	_{p=0.142 n=6}
_{Check Time}	_{31.89s (± 0.26%)}	_{31.73s (± 0.15%)}	_{-0.16s (- 0.50%)}	_31.66s	_31.79s	_{p=0.005 n=6}
_{Emit Time}	_{15.22s (± 0.27%)}	_{15.24s (± 0.56%)}	_~	_15.14s	_15.35s	_{p=1.000 n=6}
_{Total Time}	_{55.67s (± 0.12%)}	_{55.48s (± 0.23%)}	_{-0.19s (- 0.34%)}	_55.25s	_55.61s	_{p=0.010 n=6}
_{mui-docs - node (v18.15.0, x64)}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_2,347,799	_2,347,799	_~	_~	_~	_{p=1.000 n=6}
_Types	_845,614	_845,614	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{2,120,232k (± 0.01%)}	_{2,120,126k (± 0.01%)}	_~	_2,119,964k	_2,120,268k	_{p=0.173 n=6}
_{Parse Time}	_{8.79s (± 0.53%)}	_{8.75s (± 0.37%)}	_~	_8.72s	_8.81s	_{p=0.170 n=6}
_{Bind Time}	_{2.91s (± 0.73%)}	_{2.93s (± 0.50%)}	_~	_2.91s	_2.95s	_{p=0.075 n=6}
_{Check Time}	_{86.46s (± 0.39%)}	_{86.37s (± 0.37%)}	_~	_85.95s	_86.73s	_{p=0.936 n=6}
_{Emit Time}	_{0.20s (± 5.11%)}	_{0.19s (± 3.92%)}	_{🟩-0.01s (- 6.50%)}	_0.18s	_0.20s	_{p=0.046 n=6}
_{Total Time}	_{98.36s (± 0.36%)}	_{98.25s (± 0.32%)}	_~	_97.84s	_98.55s	_{p=0.936 n=6}
_{self-build-src - node (v18.15.0, x64)}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_1,228,510	_1,228,515	_{+5 (+ 0.00%)}	_~	_~	_{p=0.001 n=6}
_Types	_266,960	_266,961	_{+1 (+ 0.00%)}	_~	_~	_{p=0.001 n=6}
_{Memory used}	_{2,358,701k (± 0.02%)}	_{2,358,352k (± 0.03%)}	_~	_2,357,678k	_2,359,123k	_{p=0.378 n=6}
_{Parse Time}	_{5.20s (± 1.18%)}	_{5.19s (± 1.20%)}	_~	_5.14s	_5.28s	_{p=0.810 n=6}
_{Bind Time}	_{1.78s (± 0.90%)}	_{1.79s (± 1.79%)}	_~	_1.76s	_1.84s	_{p=0.935 n=6}
_{Check Time}	_{35.26s (± 0.21%)}	_{35.33s (± 0.34%)}	_~	_35.16s	_35.51s	_{p=0.261 n=6}
_{Emit Time}	_{2.96s (± 2.04%)}	_{3.06s (± 4.91%)}	_~	_2.94s	_3.36s	_{p=0.149 n=6}
_{Total Time}	_{45.19s (± 0.17%)}	_{45.36s (± 0.43%)}	_~	_45.16s	_45.65s	_{p=0.173 n=6}
_{self-build-src-public-api - node (v18.15.0, x64)}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_1,228,510	_1,228,515	_{+5 (+ 0.00%)}	_~	_~	_{p=0.001 n=6}
_Types	_266,960	_266,961	_{+1 (+ 0.00%)}	_~	_~	_{p=0.001 n=6}
_{Memory used}	_{2,912,881k (±12.88%)}	_{2,575,965k (±11.24%)}	_~	_2,426,612k	_3,153,816k	_{p=0.230 n=6}
_{Parse Time}	_{6.91s (± 1.65%)}	_{6.83s (± 1.15%)}	_~	_6.75s	_6.96s	_{p=0.230 n=6}
_{Bind Time}	_{2.16s (± 1.87%)}	_{2.15s (± 0.81%)}	_~	_2.12s	_2.17s	_{p=0.936 n=6}
_{Check Time}	_{42.76s (± 0.55%)}	_{42.76s (± 0.27%)}	_~	_42.62s	_42.90s	_{p=0.936 n=6}
_{Emit Time}	_{3.52s (± 1.82%)}	_{3.49s (± 2.44%)}	_~	_3.36s	_3.61s	_{p=0.687 n=6}
_{Total Time}	_{55.33s (± 0.54%)}	_{55.23s (± 0.23%)}	_~	_55.02s	_55.41s	_{p=0.128 n=6}
_{self-compiler - node (v18.15.0, x64)}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_262,816	_262,821	_{+5 (+ 0.00%)}	_~	_~	_{p=0.001 n=6}
_Types	_106,833	_106,834	_{+1 (+ 0.00%)}	_~	_~	_{p=0.001 n=6}
_{Memory used}	_{440,544k (± 0.01%)}	_{440,495k (± 0.02%)}	_~	_440,341k	_440,570k	_{p=0.471 n=6}
_{Parse Time}	_{3.56s (± 0.60%)}	_{3.54s (± 0.86%)}	_~	_3.49s	_3.57s	_{p=0.375 n=6}
_{Bind Time}	_{1.33s (± 1.30%)}	_{1.32s (± 0.64%)}	_~	_1.30s	_1.32s	_{p=0.122 n=6}
_{Check Time}	_{18.94s (± 0.11%)}	_{19.01s (± 0.31%)}	_{+0.07s (+ 0.40%)}	_18.95s	_19.12s	_{p=0.016 n=6}
_{Emit Time}	_{1.52s (± 1.13%)}	_{1.53s (± 0.99%)}	_~	_1.51s	_1.55s	_{p=0.677 n=6}
_{Total Time}	_{25.34s (± 0.14%)}	_{25.40s (± 0.16%)}	_~	_25.35s	_25.45s	_{p=0.089 n=6}
_{ts-pre-modules - node (v18.15.0, x64)}
_Errors	₇₀	₇₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_226,113	_226,113	_~	_~	_~	_{p=1.000 n=6}
_Types	_94,488	_94,488	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{371,289k (± 0.01%)}	_{371,293k (± 0.01%)}	_~	_371,230k	_371,317k	_{p=0.936 n=6}
_{Parse Time}	_{2.32s (± 0.74%)}	_{2.33s (± 0.79%)}	_~	_2.30s	_2.35s	_{p=0.366 n=6}
_{Bind Time}	_{1.34s (± 1.68%)}	_{1.34s (± 1.68%)}	_~	_1.32s	_1.37s	_{p=1.000 n=6}
_{Check Time}	_{13.70s (± 0.20%)}	_{13.71s (± 0.25%)}	_~	_13.69s	_13.78s	_{p=0.871 n=6}
_{Emit Time}	_0.00s	_0.00s	_~	_~	_~	_{p=1.000 n=6}
_{Total Time}	_{17.36s (± 0.32%)}	_{17.38s (± 0.12%)}	_~	_17.36s	_17.42s	_{p=0.574 n=6}
_{vscode - node (v18.15.0, x64)}
_Errors	₃	₃	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_3,221,220	_3,221,220	_~	_~	_~	_{p=1.000 n=6}
_Types	_1,092,664	_1,092,666	_{+2 (+ 0.00%)}	_~	_~	_{p=0.001 n=6}
_{Memory used}	_{3,293,569k (± 0.00%)}	_{3,293,391k (± 0.01%)}	_{-178k (- 0.01%)}	_3,293,070k	_3,293,553k	_{p=0.031 n=6}
_{Parse Time}	_{14.29s (± 0.48%)}	_{14.24s (± 0.55%)}	_~	_14.17s	_14.35s	_{p=0.229 n=6}
_{Bind Time}	_{4.62s (± 0.61%)}	_{4.64s (± 1.82%)}	_~	_4.56s	_4.79s	_{p=1.000 n=6}
_{Check Time}	_{90.11s (± 2.70%)}	_{88.67s (± 1.28%)}	_~	_87.79s	_90.90s	_{p=0.471 n=6}
_{Emit Time}	_{25.97s (± 9.18%)}	_{25.72s (± 8.49%)}	_~	_22.88s	_27.65s	_{p=0.688 n=6}
_{Total Time}	_{135.00s (± 3.18%)}	_{133.27s (± 2.15%)}	_~	_129.52s	_137.15s	_{p=0.471 n=6}
_{webpack - node (v18.15.0, x64)}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_293,866	_293,866	_~	_~	_~	_{p=1.000 n=6}
_Types	_119,617	_119,617	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{447,165k (± 0.02%)}	_{447,200k (± 0.03%)}	_~	_447,058k	_447,424k	_{p=0.936 n=6}
_{Parse Time}	_{4.11s (± 1.35%)}	_{4.09s (± 1.03%)}	_~	_4.05s	_4.15s	_{p=0.520 n=6}
_{Bind Time}	_{1.77s (± 0.94%)}	_{1.76s (± 0.66%)}	_~	_1.75s	_1.78s	_{p=0.287 n=6}
_{Check Time}	_{18.74s (± 0.83%)}	_{18.75s (± 0.51%)}	_~	_18.63s	_18.89s	_{p=0.872 n=6}
_{Emit Time}	_0.00s	_0.00s	_~	_~	_~	_{p=1.000 n=6}
_{Total Time}	_{24.62s (± 0.75%)}	_{24.60s (± 0.53%)}	_~	_24.46s	_24.81s	_{p=0.575 n=6}
_{xstate-main - node (v18.15.0, x64)}
_Errors	₅	₅	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_558,084	_558,084	_~	_~	_~	_{p=1.000 n=6}
_Types	_186,415	_186,415	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{495,046k (± 0.01%)}	_{494,961k (± 0.03%)}	_~	_494,721k	_495,062k	_{p=0.378 n=6}
_{Parse Time}	_{3.40s (± 0.70%)}	_{3.40s (± 0.85%)}	_~	_3.37s	_3.45s	_{p=0.872 n=6}
_{Bind Time}	_{1.18s (± 1.46%)}	_{1.19s (± 0.92%)}	_~	_1.18s	_1.21s	_{p=0.731 n=6}
_{Check Time}	_{19.57s (± 0.43%)}	_{19.82s (± 2.42%)}	_~	_19.49s	_20.63s	_{p=1.000 n=6}
_{Emit Time}	_0.00s	_0.00s	_~	_~	_~	_{p=1.000 n=6}
_{Total Time}	_{24.16s (± 0.34%)}	_{24.41s (± 1.96%)}	_~	_24.06s	_25.22s	_{p=0.936 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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typescript-bot · 2025-02-18T20:24:45Z

@DanielRosenwasser Here are the results of running the top 400 repos with tsc comparing main and refs/pull/61211/merge:

Everything looks good!

yavanosta · 2025-03-12T23:53:32Z

Hi @Andarist

Is there anything blocking this pull request?

Use comparability for discriminant properties when narrowing types fo…

0baf4d5

…r a default switch clause

Andarist commented Feb 18, 2025

View reviewed changes

jakebailey approved these changes Feb 22, 2025

View reviewed changes

Merge branch 'main' into fix/narrow-type-by-switch-on-discriminant

69aeca4

RyanCavanaugh enabled auto-merge (squash) October 29, 2025 17:04

Merge branch 'main' into fix/narrow-type-by-switch-on-discriminant

7a7fad2

typescript-bot added the For Backlog Bug PRs that fix a backlog bug label Oct 30, 2025

RyanCavanaugh merged commit 6fd2874 into microsoft:main Oct 30, 2025
33 checks passed

github-project-automation bot moved this from Needs merge to Done in PR Backlog Oct 30, 2025

Andarist deleted the fix/narrow-type-by-switch-on-discriminant branch October 30, 2025 14:26

Copilot AI mentioned this pull request Feb 10, 2026

Use comparability for discriminant properties when narrowing types for a default switch clause microsoft/typescript-go#2734

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Use comparability for discriminant properties when narrowing types for a default switch clause#61211

Use comparability for discriminant properties when narrowing types for a default switch clause#61211
RyanCavanaugh merged 3 commits intomicrosoft:mainfrom
Andarist:fix/narrow-type-by-switch-on-discriminant

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