Properly account for intersections in `getKeyPropertyName` by Andarist · Pull Request #63117 · microsoft/TypeScript

Andarist · 2026-02-08T17:41:55Z

In the code below, getMatchingUnionConstituentForType (and thus typeRelatedToSomeType) can't benefit from the key property optimization. So in certain situations (like this one) the source has to be related to each constituent of the target union (until it finds a match) - but it should be able to find the matching constituent using a fast path.

This issue affects test1. I've included test2 for comparison purposes - the optimization kicks in there.

TS playground:

type Identity<T> = { [K in keyof T]: T[K] } & unknown;

type A = { kind: "a" } & { a: string };
type B = { kind: "b" } & { b: string };
type C = { kind: "c" } & { c: string };
type D = { kind: "d" } & { d: string };
type E = { kind: "e" } & { e: string };
type F = { kind: "f" } & { f: string };
type G = { kind: "g" } & { g: string };
type H = { kind: "h" } & { h: string };
type I = { kind: "i" } & { i: string };
type J = { kind: "j" } & { j: string };
type K = { kind: "k" } & { k: string };
type L = { kind: "l" } & { l: string };
type M = { kind: "m" } & { m: string };
type N = { kind: "n" } & { n: string };
type O = { kind: "o" } & { o: string };
type P = { kind: "p" } & { p: string };
type Q = { kind: "q" } & { q: string };
type R = { kind: "r" } & { r: string };
type S = { kind: "s" } & { s: string };
type T = { kind: "t" } & { t: string };
type U = { kind: "u" } & { u: string };
type V = { kind: "v" } & { v: string };
type W = { kind: "w" } & { w: string };
type X = { kind: "x" } & { x: string };
type Y = { kind: "y" } & { y: string };
type Z = { kind: "z" } & { z: string };

type MyUnion = A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z;

type SomeType = { kind: "z"; z: string; other: number };

function test1(u1: MyUnion, obj: SomeType) {
  u1 = obj;
}

// using Identity here just to "flatten" the contained intersections
function test2(u1: Identity<MyUnion>, obj: SomeType) {
  u1 = obj;
}

typescript-bot · 2026-02-08T17:41:59Z

This PR doesn't have any linked issues. Please open an issue that references this PR. From there we can discuss and prioritise.

Andarist · 2026-02-08T17:43:07Z

src/compiler/checker.ts

        if (
            types.length < 10 || getObjectFlags(unionType) & ObjectFlags.PrimitiveUnion ||
-            countWhere(types, t => !!(t.flags & (TypeFlags.Object | TypeFlags.InstantiableNonPrimitive))) < 10
+            countWhere(types, t => !!(t.flags & (TypeFlags.Object | TypeFlags.Intersection | TypeFlags.InstantiableNonPrimitive))) < 10


This condition matches now the existing flags check in mapTypesByKeyProperty (that function is already called only from within the containing function here - getKeyPropertyName)

jakebailey · 2026-02-08T17:45:56Z

@typescript-bot test it

typescript-bot · 2026-02-08T17:46:00Z

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 · 2026-02-08T18:07:21Z

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

Everything looks the same!

You can check the log here.

typescript-bot · 2026-02-08T18:16:05Z

@jakebailey Here are the results of running the user tests with tsc comparing main and refs/pull/63117/merge:

There were infrastructure failures potentially unrelated to your change:

1 instance of "Git clone failed"

Otherwise...

Everything looks good!

typescript-bot · 2026-02-08T18:45:04Z

@jakebailey
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	₃	₃	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_82,521	_82,521	_~	_~	_~	_{p=1.000 n=6}
_Types	_125,280	_125,280	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{276,131k (± 0.68%)}	_{274,975k (± 0.50%)}	_~	_274,399k	_277,803k	_{p=0.575 n=6}
_{Parse Time}	_{1.30s (± 0.40%)}	_{1.31s (± 0.31%)}	_~	_1.30s	_1.31s	_{p=0.112 n=6}
_{Bind Time}	_{0.75s (± 0.68%)}	_{0.75s (± 0.72%)}	_~	_0.75s	_0.76s	_{p=0.640 n=6}
_{Check Time}	_{14.16s (± 0.60%)}	_{14.14s (± 0.06%)}	_~	_14.13s	_14.15s	_{p=0.373 n=6}
_{Emit Time}	_{2.66s (± 0.84%)}	_{2.66s (± 0.58%)}	_~	_2.65s	_2.69s	_{p=0.604 n=6}
_{Total Time}	_{18.88s (± 0.46%)}	_{18.86s (± 0.09%)}	_~	_18.84s	_18.89s	_{p=0.743 n=6}
_{angular-1 - node (v18.15.0, x64)}
_Errors	₃	₃	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_957,952	_957,952	_~	_~	_~	_{p=1.000 n=6}
_Types	_416,021	_416,019	_{-2 (- 0.00%)}	_~	_~	_{p=0.001 n=6}
_{Memory used}	_{1,259,098k (± 0.00%)}	_{1,259,061k (± 0.01%)}	_~	_1,258,963k	_1,259,164k	_{p=0.575 n=6}
_{Parse Time}	_{6.52s (± 0.64%)}	_{6.52s (± 0.66%)}	_~	_6.47s	_6.57s	_{p=0.936 n=6}
_{Bind Time}	_{1.98s (± 0.38%)}	_{1.98s (± 0.41%)}	_~	_1.97s	_1.99s	_{p=0.729 n=6}
_{Check Time}	_{32.41s (± 0.30%)}	_{32.38s (± 0.47%)}	_~	_32.21s	_32.63s	_{p=0.689 n=6}
_{Emit Time}	_{14.99s (± 0.65%)}	_{14.96s (± 0.53%)}	_~	_14.85s	_15.07s	_{p=0.688 n=6}
_{Total Time}	_{55.89s (± 0.32%)}	_{55.84s (± 0.42%)}	_~	_55.59s	_56.26s	_{p=0.630 n=6}
_{mui-docs - node (v18.15.0, x64)}
_Errors	_11,439	_11,439	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_2,702,777	_2,710,413	_{+7,636 (+ 0.28%)}	_~	_~	_{p=0.001 n=6}
_Types	_930,725	_947,613	_{+16,888 (+ 1.81%)}	_~	_~	_{p=0.001 n=6}
_{Memory used}	_{3,043,677k (± 0.00%)}	_{3,057,722k (± 0.00%)}	_{+14,045k (+ 0.46%)}	_3,057,577k	_3,057,871k	_{p=0.005 n=6}
_{Parse Time}	_{10.38s (± 0.45%)}	_{10.31s (± 0.33%)}	_{-0.06s (- 0.61%)}	_10.27s	_10.37s	_{p=0.030 n=6}
_{Bind Time}	_{2.78s (± 0.53%)}	_{2.78s (± 0.48%)}	_~	_2.76s	_2.80s	_{p=1.000 n=6}
_{Check Time}	_{114.25s (± 1.38%)}	_{115.26s (± 1.29%)}	_~	_114.06s	_117.31s	_{p=0.378 n=6}
_{Emit Time}	_{0.41s (± 2.59%)}	_{0.40s (± 1.39%)}	_~	_0.39s	_0.40s	_{p=0.090 n=6}
_{Total Time}	_{127.81s (± 1.25%)}	_{128.75s (± 1.15%)}	_~	_127.54s	_130.79s	_{p=0.378 n=6}
_{self-build-src - node (v18.15.0, x64)}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_1,253,407	_1,253,407	_~	_~	_~	_{p=1.000 n=6}
_Types	_260,208	_260,207	_{-1 (- 0.00%)}	_~	_~	_{p=0.001 n=6}
_{Memory used}	_{2,396,836k (± 0.04%)}	_{2,457,458k (± 6.06%)}	_~	_2,396,224k	_2,761,611k	_{p=0.575 n=6}
_{Parse Time}	_{5.14s (± 0.70%)}	_{5.18s (± 0.77%)}	_~	_5.13s	_5.23s	_{p=0.199 n=6}
_{Bind Time}	_{1.84s (± 1.52%)}	_{1.84s (± 1.53%)}	_~	_1.81s	_1.87s	_{p=0.677 n=6}
_{Check Time}	_{35.72s (± 0.45%)}	_{35.60s (± 0.85%)}	_~	_34.99s	_35.76s	_{p=0.226 n=6}
_{Emit Time}	_{2.99s (± 1.80%)}	_{3.07s (± 2.16%)}	_{+0.08s (+ 2.67%)}	_3.00s	_3.19s	_{p=0.037 n=6}
_{Total Time}	_{45.73s (± 0.37%)}	_{45.71s (± 0.67%)}	_~	_45.10s	_45.97s	_{p=0.810 n=6}
_{self-build-src-public-api - node (v18.15.0, x64)}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_1,253,407	_1,253,407	_~	_~	_~	_{p=1.000 n=6}
_Types	_260,208	_260,207	_{-1 (- 0.00%)}	_~	_~	_{p=0.001 n=6}
_{Memory used}	_{2,523,836k (± 5.88%)}	_{2,584,227k (±11.49%)}	_~	_2,462,601k	_3,191,074k	_{p=0.230 n=6}
_{Parse Time}	_{5.34s (± 0.42%)}	_{5.37s (± 1.42%)}	_~	_5.28s	_5.47s	_{p=0.630 n=6}
_{Bind Time}	_{1.88s (± 0.62%)}	_{1.88s (± 0.92%)}	_~	_1.86s	_1.90s	_{p=0.935 n=6}
_{Check Time}	_{35.62s (± 0.58%)}	_{35.77s (± 0.47%)}	_~	_35.48s	_35.99s	_{p=0.149 n=6}
_{Emit Time}	_{3.07s (± 1.57%)}	_{3.06s (± 1.44%)}	_~	_3.01s	_3.13s	_{p=0.469 n=6}
_{Total Time}	_{45.93s (± 0.54%)}	_{46.09s (± 0.42%)}	_~	_45.81s	_46.38s	_{p=0.230 n=6}
_{self-compiler - node (v18.15.0, x64)}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_265,173	_265,173	_~	_~	_~	_{p=1.000 n=6}
_Types	_104,282	_104,282	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{444,503k (± 0.02%)}	_{444,541k (± 0.01%)}	_~	_444,482k	_444,574k	_{p=0.471 n=6}
_{Parse Time}	_{4.35s (± 0.67%)}	_{4.37s (± 0.72%)}	_~	_4.31s	_4.40s	_{p=0.421 n=6}
_{Bind Time}	_{1.70s (± 0.87%)}	_{1.69s (± 1.02%)}	_~	_1.66s	_1.71s	_{p=0.742 n=6}
_{Check Time}	_{23.94s (± 0.19%)}	_{23.86s (± 0.46%)}	_~	_23.74s	_24.02s	_{p=0.128 n=6}
_{Emit Time}	_{1.93s (± 0.76%)}	_{1.93s (± 1.02%)}	_~	_1.91s	_1.96s	_{p=1.000 n=6}
_{Total Time}	_{31.92s (± 0.16%)}	_{31.85s (± 0.32%)}	_~	_31.73s	_31.99s	_{p=0.261 n=6}
_{ts-pre-modules - node (v18.15.0, x64)}
_Errors	₂₇₁	₂₇₁	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_225,885	_225,885	_~	_~	_~	_{p=1.000 n=6}
_Types	_93,564	_93,564	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{371,621k (± 0.03%)}	_{371,664k (± 0.02%)}	_~	_371,579k	_371,787k	_{p=0.128 n=6}
_{Parse Time}	_{2.84s (± 1.20%)}	_{2.84s (± 1.11%)}	_~	_2.80s	_2.88s	_{p=0.936 n=6}
_{Bind Time}	_{1.62s (± 0.94%)}	_{1.64s (± 0.64%)}	_{+0.02s (+ 1.24%)}	_1.62s	_1.65s	_{p=0.042 n=6}
_{Check Time}	_{17.45s (± 0.29%)}	_{17.43s (± 0.28%)}	_~	_17.36s	_17.50s	_{p=0.520 n=6}
_{Emit Time}	_0.00s	_0.00s	_~	_~	_~	_{p=1.000 n=6}
_{Total Time}	_{21.91s (± 0.19%)}	_{21.90s (± 0.36%)}	_~	_21.81s	_22.03s	_{p=0.688 n=6}
_{vscode - node (v18.15.0, x64)}
_Errors	₄₀	₄₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_4,235,336	_4,235,310	_{-26 (- 0.00%)}	_~	_~	_{p=0.001 n=6}
_Types	_1,345,132	_1,345,130	_{-2 (- 0.00%)}	_~	_~	_{p=0.001 n=6}
_{Memory used}	_{4,027,988k (± 0.00%)}	_{4,028,001k (± 0.00%)}	_~	_4,027,825k	_4,028,117k	_{p=0.689 n=6}
_{Parse Time}	_{16.30s (± 0.63%)}	_{16.28s (± 0.26%)}	_~	_16.23s	_16.34s	_{p=0.574 n=6}
_{Bind Time}	_{5.55s (± 2.25%)}	_{5.53s (± 1.79%)}	_~	_5.47s	_5.73s	_{p=0.293 n=6}
_{Check Time}	_{127.18s (± 7.30%)}	_{126.35s (± 5.70%)}	_~	_121.60s	_140.42s	_{p=0.689 n=6}
_{Emit Time}	_{51.69s (±14.03%)}	_{52.56s (±15.87%)}	_~	_45.54s	_65.49s	_{p=0.810 n=6}
_{Total Time}	_{200.72s (± 7.98%)}	_{200.72s (± 7.46%)}	_~	_190.10s	_227.76s	_{p=0.689 n=6}
_{webpack - node (v18.15.0, x64)}
_Errors	₄₁	₄₁	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_403,253	_403,369	_{+116 (+ 0.03%)}	_~	_~	_{p=0.001 n=6}
_Types	_178,748	_178,764	_{+16 (+ 0.01%)}	_~	_~	_{p=0.001 n=6}
_{Memory used}	_{561,100k (± 0.02%)}	_{561,255k (± 0.05%)}	_~	_561,039k	_561,822k	_{p=0.298 n=6}
_{Parse Time}	_{4.77s (± 0.68%)}	_{4.75s (± 0.38%)}	_~	_4.72s	_4.77s	_{p=0.124 n=6}
_{Bind Time}	_{2.03s (± 1.22%)}	_{2.02s (± 0.85%)}	_~	_2.00s	_2.04s	_{p=0.459 n=6}
_{Check Time}	_{24.51s (± 0.30%)}	_{24.44s (± 0.75%)}	_~	_24.10s	_24.65s	_{p=0.630 n=6}
_{Emit Time}	_{0.01s (±109.43%)}	_{0.01s (±48.94%)}	_~	_0.00s	_0.01s	_{p=0.282 n=6}
_{Total Time}	_{31.32s (± 0.17%)}	_{31.22s (± 0.57%)}	_~	_30.88s	_31.41s	_{p=0.170 n=6}
_{xstate-main - node (v18.15.0, x64)}
_Errors	₃₀	₃₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_753,485	_753,622	_{+137 (+ 0.02%)}	_~	_~	_{p=0.001 n=6}
_Types	_215,172	_215,193	_{+21 (+ 0.01%)}	_~	_~	_{p=0.001 n=6}
_{Memory used}	_{678,560k (± 0.01%)}	_{678,634k (± 0.01%)}	_{+74k (+ 0.01%)}	_678,555k	_678,679k	_{p=0.045 n=6}
_{Parse Time}	_{4.91s (± 0.66%)}	_{4.91s (± 0.60%)}	_~	_4.86s	_4.94s	_{p=1.000 n=6}
_{Bind Time}	_{1.58s (± 0.98%)}	_{1.56s (± 0.75%)}	_~	_1.55s	_1.58s	_{p=0.061 n=6}
_{Check Time}	_{22.21s (± 0.44%)}	_{22.35s (± 0.58%)}	_~	_22.23s	_22.58s	_{p=0.054 n=6}
_{Emit Time}	_0.00s	_0.00s	_~	_~	_~	_{p=1.000 n=6}
_{Total Time}	_{28.70s (± 0.33%)}	_{28.81s (± 0.39%)}	_~	_28.71s	_29.02s	_{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 · 2026-02-08T19:03:35Z

@jakebailey Here are the results of running the top 400 repos with tsc comparing main and refs/pull/63117/merge:

Everything looks good!

Andarist · 2026-02-09T07:01:32Z

It's kinda a bummer the benchmark numbers don't conclusively show this is an improvement. I'd argue this is like it should have always been unless there is some specific undocumented reason why it shouldn't be. To my best understanding though { kind: 'a' } & { prop: string } should really behave in the same way as { kind: 'a'; prop: string }. This is just an optimization though so the overall behavior stays the same but it's still very much surprising to me that, as a user, I'd pay a penalty like this just because my types were generated dynamically~ using intersections.

FWIW, with the test1 alone this PR leads to:

Strict subtype cache: 0
Subtype cache: 0
Identity cache: 0
-Assignability cache: 58
+Assignability cache: 8
Type Count: 227 -> 228
Instantiation count: 0
Symbol count: 32,634

Properly account for intersections in getKeyPropertyName

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github-project-automation bot added this to PR Backlog Feb 8, 2026

github-project-automation bot moved this to Not started in PR Backlog Feb 8, 2026

typescript-bot added the For Uncommitted Bug PR for untriaged, rejected, closed or missing bug label Feb 8, 2026

Andarist commented Feb 8, 2026

View reviewed changes

Andarist mentioned this pull request Feb 9, 2026

TypeScript OOM when using TLGlobalShapePropsMap with complex discriminated union prop types tldraw/tldraw#7755

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Properly account for intersections in `getKeyPropertyName`#63117

Properly account for intersections in `getKeyPropertyName`#63117
Andarist wants to merge 1 commit intomicrosoft:mainfrom
Andarist:fix/union-optimization-for-intersections

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