Port https://github.com/microsoft/typescript-go/pull/1759 by ahejlsberg · Pull Request #62502 · microsoft/TypeScript

ahejlsberg · 2025-09-28T15:24:45Z

Copilot

Pull Request Overview

This PR ports changes from typescript-go repository pull request #1759, focusing on improving type checking behavior for object literal types and updating test baselines accordingly.

Updates type checking logic for fresh literal types to use object flags instead of type checking
Removes redundant undefined type checking for source properties
Updates test baseline to reflect more precise type information

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/compiler/checker.ts	Refactors object literal type checking to use ObjectFlags.FreshLiteral and removes unnecessary undefined checking
tests/baselines/reference/jsDeclarationsFunctionClassesCjsExportAssignment.js	Updates baseline to show State type instead of any for the state property

Comments suppressed due to low confidence (1)

src/compiler/checker.ts:1

The removal of the undefined type check may cause incorrect behavior. Previously, properties with undefined types were allowed to not exist on the target type, but now all source properties must exist on the target regardless of their type. This could break valid TypeScript code where optional properties are involved.

import {

ahejlsberg · 2025-09-28T15:25:57Z

Not sure why the .d.ts emit changed, though looks it actually improved.

ahejlsberg · 2025-09-28T15:26:19Z

@typescript-bot test it

typescript-bot · 2025-09-28T15:26:24Z

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 · 2025-09-28T15:50:17Z

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

Everything looks the same!

You can check the log here.

typescript-bot · 2025-09-28T15:52:21Z

@ahejlsberg Here are the results of running the user tests with tsc comparing main and refs/pull/62502/merge:

There were infrastructure failures potentially unrelated to your change:

1 instance of "Git clone failed"

Otherwise...

Everything looks good!

typescript-bot · 2025-09-28T16:14:44Z

@ahejlsberg
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	_62,370	_62,370	_~	_~	_~	_{p=1.000 n=6}
_Types	_50,386	_50,386	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{193,972k (± 0.95%)}	_{193,385k (± 0.77%)}	_~	_192,750k	_196,432k	_{p=0.873 n=6}
_{Parse Time}	_{1.30s (± 0.76%)}	_{1.30s (± 0.49%)}	_~	_1.29s	_1.31s	_{p=0.733 n=6}
_{Bind Time}	_{0.72s (± 0.57%)}	_0.72s	_~	_~	_~	_{p=0.405 n=6}
_{Check Time}	_{9.73s (± 0.30%)}	_{9.72s (± 0.26%)}	_~	_9.69s	_9.75s	_{p=0.809 n=6}
_{Emit Time}	_{2.76s (± 0.55%)}	_{2.74s (± 0.46%)}	_~	_2.73s	_2.76s	_{p=0.101 n=6}
_{Total Time}	_{14.50s (± 0.21%)}	_{14.49s (± 0.24%)}	_~	_14.43s	_14.53s	_{p=0.421 n=6}
_{angular-1 - node (v18.15.0, x64)}
_Errors	₁	₁	_~	_~	_~	_{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}	_{1,245,586k (± 0.00%)}	_{1,245,619k (± 0.00%)}	_~	_1,245,569k	_1,245,682k	_{p=0.173 n=6}
_{Parse Time}	_{6.53s (± 0.69%)}	_{6.48s (± 0.43%)}	_~	_6.45s	_6.53s	_{p=0.065 n=6}
_{Bind Time}	_{1.88s (± 0.27%)}	_{1.87s (± 0.44%)}	_~	_1.86s	_1.88s	_{p=0.523 n=6}
_{Check Time}	_{32.23s (± 0.24%)}	_{32.16s (± 0.33%)}	_~	_32.03s	_32.30s	_{p=0.258 n=6}
_{Emit Time}	_{14.79s (± 0.22%)}	_{14.82s (± 0.32%)}	_~	_14.74s	_14.86s	_{p=0.198 n=6}
_{Total Time}	_{55.42s (± 0.14%)}	_{55.34s (± 0.25%)}	_~	_55.15s	_55.49s	_{p=0.261 n=6}
_{mui-docs - node (v18.15.0, x64)}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_2,544,632	_2,544,632	_~	_~	_~	_{p=1.000 n=6}
_Types	_903,208	_903,208	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{2,829,801k (± 0.00%)}	_{2,829,938k (± 0.00%)}	_~	_2,829,698k	_2,830,075k	_{p=0.066 n=6}
_{Parse Time}	_{8.71s (± 0.35%)}	_{8.74s (± 0.63%)}	_~	_8.67s	_8.82s	_{p=0.260 n=6}
_{Bind Time}	_{2.19s (± 0.25%)}	_{2.20s (± 0.48%)}	_~	_2.18s	_2.21s	_{p=1.000 n=6}
_{Check Time}	_{86.94s (± 1.21%)}	_{86.69s (± 1.33%)}	_~	_85.90s	_88.57s	_{p=0.936 n=6}
_{Emit Time}	_{0.63s (±125.53%)}	_{0.31s (± 1.68%)}	_~	_0.30s	_0.31s	_{p=0.784 n=6}
_{Total Time}	_{98.46s (± 1.21%)}	_{97.93s (± 1.19%)}	_~	_97.13s	_99.88s	_{p=0.936 n=6}
_{self-build-src - node (v18.15.0, x64)}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_1,237,064	_1,237,063	_{-1 (- 0.00%)}	_~	_~	_{p=0.001 n=6}
_Types	_259,743	_259,743	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{2,364,574k (± 0.02%)}	_{2,424,816k (± 6.11%)}	_~	_2,363,837k	_2,727,636k	_{p=0.810 n=6}
_{Parse Time}	_{5.14s (± 1.32%)}	_{5.16s (± 1.22%)}	_~	_5.05s	_5.22s	_{p=0.689 n=6}
_{Bind Time}	_{1.77s (± 0.87%)}	_{1.80s (± 1.72%)}	_{+0.03s (+ 1.69%)}	_1.77s	_1.85s	_{p=0.040 n=6}
_{Check Time}	_{35.15s (± 0.12%)}	_{34.91s (± 0.63%)}	_{-0.24s (- 0.68%)}	_34.48s	_35.07s	_{p=0.005 n=6}
_{Emit Time}	_{2.99s (± 1.32%)}	_{3.01s (± 0.30%)}	_~	_3.00s	_3.02s	_{p=0.078 n=6}
_{Total Time}	_{45.07s (± 0.23%)}	_{44.89s (± 0.46%)}	_~	_44.51s	_45.05s	_{p=0.066 n=6}
_{self-build-src-public-api - node (v18.15.0, x64)}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_1,237,064	_1,237,063	_{-1 (- 0.00%)}	_~	_~	_{p=0.001 n=6}
_Types	_259,743	_259,743	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{3,158,503k (± 0.01%)}	_{3,157,640k (± 0.02%)}	_{-863k (- 0.03%)}	_3,156,827k	_3,158,454k	_{p=0.045 n=6}
_{Parse Time}	_{6.89s (± 0.57%)}	_{6.87s (± 0.77%)}	_~	_6.82s	_6.94s	_{p=0.378 n=6}
_{Bind Time}	_{2.16s (± 0.91%)}	_{2.15s (± 0.93%)}	_~	_2.12s	_2.18s	_{p=0.225 n=6}
_{Check Time}	_{42.56s (± 0.06%)}	_{42.56s (± 0.25%)}	_~	_42.44s	_42.71s	_{p=1.000 n=6}
_{Emit Time}	_{3.50s (± 3.38%)}	_{3.59s (± 1.55%)}	_~	_3.52s	_3.69s	_{p=0.226 n=6}
_{Total Time}	_{55.11s (± 0.27%)}	_{55.17s (± 0.26%)}	_~	_55.01s	_55.38s	_{p=0.810 n=6}
_{self-compiler - node (v18.15.0, x64)}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_262,412	_262,411	_{-1 (- 0.00%)}	_~	_~	_{p=0.001 n=6}
_Types	_103,924	_103,924	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{440,422k (± 0.01%)}	_{440,471k (± 0.01%)}	_~	_440,393k	_440,563k	_{p=0.230 n=6}
_{Parse Time}	_{3.46s (± 0.96%)}	_{3.51s (± 1.14%)}	_~	_3.46s	_3.58s	_{p=0.077 n=6}
_{Bind Time}	_{1.31s (± 1.12%)}	_{1.32s (± 0.78%)}	_~	_1.31s	_1.34s	_{p=0.211 n=6}
_{Check Time}	_{18.99s (± 0.27%)}	_{18.93s (± 0.51%)}	_~	_18.85s	_19.10s	_{p=0.172 n=6}
_{Emit Time}	_{1.53s (± 0.76%)}	_{1.52s (± 1.07%)}	_~	_1.50s	_1.54s	_{p=0.462 n=6}
_{Total Time}	_{25.30s (± 0.31%)}	_{25.29s (± 0.38%)}	_~	_25.21s	_25.47s	_{p=0.575 n=6}
_{ts-pre-modules - node (v18.15.0, x64)}
_Errors	₇₂	₇₂	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_225,367	_225,367	_~	_~	_~	_{p=1.000 n=6}
_Types	_94,290	_94,290	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{370,111k (± 0.06%)}	_{370,069k (± 0.06%)}	_~	_369,867k	_370,393k	_{p=0.810 n=6}
_{Parse Time}	_{2.83s (± 1.17%)}	_{2.82s (± 1.26%)}	_~	_2.78s	_2.87s	_{p=0.573 n=6}
_{Bind Time}	_{1.60s (± 1.46%)}	_{1.60s (± 1.55%)}	_~	_1.57s	_1.64s	_{p=0.808 n=6}
_{Check Time}	_{16.44s (± 0.51%)}	_{16.49s (± 0.39%)}	_~	_16.40s	_16.54s	_{p=0.261 n=6}
_{Emit Time}	_0.00s	_0.00s	_~	_~	_~	_{p=1.000 n=6}
_{Total Time}	_{20.88s (± 0.47%)}	_{20.91s (± 0.25%)}	_~	_20.81s	_20.95s	_{p=0.261 n=6}
_{vscode - node (v18.15.0, x64)}
_Errors	₁	₁	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_3,890,940	_3,890,942	_{+2 (+ 0.00%)}	_~	_~	_{p=0.001 n=6}
_Types	_1,224,250	_1,224,251	_{+1 (+ 0.00%)}	_~	_~	_{p=0.001 n=6}
_{Memory used}	_{3,704,567k (± 0.01%)}	_{3,704,494k (± 0.00%)}	_~	_3,704,345k	_3,704,657k	_{p=0.471 n=6}
_{Parse Time}	_{15.44s (± 3.27%)}	_{15.24s (± 0.60%)}	_~	_15.13s	_15.36s	_{p=0.689 n=6}
_{Bind Time}	_{4.94s (± 0.56%)}	_{4.95s (± 0.56%)}	_~	_4.91s	_4.99s	_{p=0.683 n=6}
_{Check Time}	_{102.07s (± 1.15%)}	_{101.51s (± 1.30%)}	_~	_100.50s	_103.25s	_{p=0.298 n=6}
_{Emit Time}	_{34.07s (±14.93%)}	_{36.00s (±16.98%)}	_~	_30.83s	_46.36s	_{p=0.298 n=6}
_{Total Time}	_{156.51s (± 3.52%)}	_{157.69s (± 4.15%)}	_~	_151.62s	_167.21s	_{p=1.000 n=6}
_{webpack - node (v18.15.0, x64)}
_Errors	₃₈	₃₈	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_361,753	_361,753	_~	_~	_~	_{p=1.000 n=6}
_Types	_158,862	_158,862	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{516,484k (± 0.02%)}	_{516,495k (± 0.02%)}	_~	_516,397k	_516,644k	_{p=0.936 n=6}
_{Parse Time}	_{4.47s (± 0.72%)}	_{4.44s (± 0.60%)}	_~	_4.40s	_4.47s	_{p=0.466 n=6}
_{Bind Time}	_{1.91s (± 1.13%)}	_{1.91s (± 0.72%)}	_~	_1.89s	_1.92s	_{p=0.514 n=6}
_{Check Time}	_{21.87s (± 0.26%)}	_{21.82s (± 0.29%)}	_~	_21.71s	_21.88s	_{p=0.377 n=6}
_{Emit Time}	_0.00s	_{0.00s (±154.76%)}	_~	_0.00s	_0.01s	_{p=0.174 n=6}
_{Total Time}	_{28.25s (± 0.19%)}	_{28.18s (± 0.32%)}	_~	_28.01s	_28.27s	_{p=0.076 n=6}
_{xstate-main - node (v18.15.0, x64)}
_Errors	₃₀	₃₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_672,790	_672,790	_~	_~	_~	_{p=1.000 n=6}
_Types	_201,962	_201,962	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{574,862k (± 0.02%)}	_{574,960k (± 0.03%)}	_~	_574,701k	_575,140k	_{p=0.230 n=6}
_{Parse Time}	_{4.17s (± 0.86%)}	_{4.17s (± 1.29%)}	_~	_4.13s	_4.27s	_{p=0.872 n=6}
_{Bind Time}	_{1.33s (± 0.61%)}	_{1.33s (± 0.63%)}	_~	_1.31s	_1.33s	_{p=0.120 n=6}
_{Check Time}	_{20.57s (± 1.88%)}	_{20.46s (± 1.71%)}	_~	_20.12s	_20.95s	_{p=0.688 n=6}
_{Emit Time}	_0.00s	_0.00s	_~	_~	_~	_{p=1.000 n=6}
_{Total Time}	_{26.07s (± 1.44%)}	_{25.96s (± 1.38%)}	_~	_25.60s	_26.46s	_{p=0.630 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 · 2025-09-28T16:41:45Z

@ahejlsberg Here are the results of running the top 400 repos with tsc comparing main and refs/pull/62502/merge:

Everything looks good!

imbant · 2025-09-29T02:15:46Z

Looks like Strada’s code is already being back-ported to Corsa. Interesting.

ahejlsberg added 2 commits September 28, 2025 11:21

Port microsoft/typescript-go#1759

f914cb0

Accept new baselines

b9edcc1

Copilot AI review requested due to automatic review settings September 28, 2025 15:24

github-project-automation bot added this to PR Backlog Sep 28, 2025

github-project-automation bot moved this to Not started in PR Backlog Sep 28, 2025

typescript-bot assigned ahejlsberg Sep 28, 2025

typescript-bot added Author: Team For Uncommitted Bug PR for untriaged, rejected, closed or missing bug labels Sep 28, 2025

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github-project-automation bot moved this from Not started to Needs merge in PR Backlog Sep 28, 2025

ahejlsberg enabled auto-merge (squash) September 28, 2025 20:55

ahejlsberg merged commit 1cd5309 into main Sep 28, 2025
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ahejlsberg deleted the port-tsgo-1759 branch September 28, 2025 20:55

github-project-automation bot moved this from Needs merge to Done in PR Backlog Sep 28, 2025

jakebailey mentioned this pull request Sep 29, 2025

Revert back to isObjectLiteralType check microsoft/typescript-go#1764

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Andarist mentioned this pull request Dec 11, 2025

Inference from variable reference produces different type argument microsoft/typescript-go#2321

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Andarist mentioned this pull request Mar 10, 2026

Inference from result of generic function no longer produces a union #63227

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Port https://github.com/microsoft/typescript-go/pull/1759#62502

Port https://github.com/microsoft/typescript-go/pull/1759#62502
ahejlsberg merged 2 commits intomainfrom
port-tsgo-1759

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