Don't compare "missing" to `undefined` in `compareProperties` under `exactOptionalPropertyTypes` #61683

HansBrende · 2025-05-09T21:11:45Z

I'm aware that the underlying issue is (currently) labeled "not a defect", however, the behavior is undeniably strange, most likely simply overlooked when exactOptionalPropertyTypes was implemented, in my view. Therefore I am opening this PR to demonstrate what an easy fix it is (and that no other tests are broken as a result).

jakebailey · 2025-05-09T21:13:59Z

@typescript-bot test it

typescript-bot · 2025-05-09T21:14:04Z

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 · 2025-05-09T21:35:48Z

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

Everything looks the same!

You can check the log here.

typescript-bot · 2025-05-09T21:37:51Z

@jakebailey Here are the results of running the user tests with tsc comparing main and refs/pull/61683/merge:

Everything looks good!

typescript-bot · 2025-05-09T22:09:20Z

@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	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}	_{194,755k (± 1.00%)}	_{193,619k (± 0.74%)}	_~	_192,937k	_196,535k	_{p=0.230 n=6}
_{Parse Time}	_{1.31s (± 0.39%)}	_{1.30s (± 0.94%)}	_~	_1.29s	_1.32s	_{p=0.241 n=6}
_{Bind Time}	_0.73s	_0.73s	_~	_~	_~	_{p=1.000 n=6}
_{Check Time}	_{9.73s (± 0.39%)}	_{9.76s (± 0.54%)}	_~	_9.68s	_9.82s	_{p=0.221 n=6}
_{Emit Time}	_{2.73s (± 0.50%)}	_{2.73s (± 0.67%)}	_~	_2.71s	_2.76s	_{p=0.591 n=6}
_{Total Time}	_{14.51s (± 0.21%)}	_{14.53s (± 0.30%)}	_~	_14.48s	_14.59s	_{p=0.376 n=6}
_{angular-1 - node (v18.15.0, x64)}
_Errors	₅₆	₅₆	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_949,240	_949,240	_~	_~	_~	_{p=1.000 n=6}
_Types	_411,065	_411,065	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{1,225,103k (± 0.00%)}	_{1,225,092k (± 0.00%)}	_~	_1,225,021k	_1,225,126k	_{p=0.378 n=6}
_{Parse Time}	_{6.63s (± 0.95%)}	_{6.67s (± 0.84%)}	_~	_6.56s	_6.71s	_{p=0.289 n=6}
_{Bind Time}	_{1.88s (± 0.43%)}	_{1.88s (± 0.40%)}	_~	_1.87s	_1.89s	_{p=0.729 n=6}
_{Check Time}	_{31.92s (± 0.27%)}	_{31.93s (± 0.22%)}	_~	_31.83s	_32.00s	_{p=0.936 n=6}
_{Emit Time}	_{15.22s (± 0.25%)}	_{15.20s (± 0.74%)}	_~	_15.11s	_15.42s	_{p=0.127 n=6}
_{Total Time}	_{55.66s (± 0.22%)}	_{55.68s (± 0.19%)}	_~	_55.53s	_55.82s	_{p=0.872 n=6}
_{mui-docs - node (v18.15.0, x64)}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_2,439,920	_2,439,920	_~	_~	_~	_{p=1.000 n=6}
_Types	_872,553	_872,553	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{2,448,534k (± 0.00%)}	_{2,448,463k (± 0.00%)}	_~	_2,448,390k	_2,448,583k	_{p=0.066 n=6}
_{Parse Time}	_{10.54s (± 0.65%)}	_{10.58s (± 0.62%)}	_~	_10.47s	_10.66s	_{p=0.377 n=6}
_{Bind Time}	_{2.72s (± 0.45%)}	_{2.71s (± 1.01%)}	_~	_2.67s	_2.75s	_{p=0.462 n=6}
_{Check Time}	_{88.08s (± 1.75%)}	_{87.44s (± 2.62%)}	_~	_86.06s	_92.06s	_{p=0.298 n=6}
_{Emit Time}	_{0.37s (± 2.67%)}	_{0.37s (± 2.41%)}	_~	_0.36s	_0.38s	_{p=0.931 n=6}
_{Total Time}	_{101.70s (± 1.54%)}	_{101.10s (± 2.27%)}	_~	_99.84s	_105.74s	_{p=0.378 n=6}
_{self-build-src - node (v18.15.0, x64)}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_1,228,241	_1,228,241	_~	_~	_~	_{p=1.000 n=6}
_Types	_267,270	_267,270	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{3,094,833k (± 0.02%)}	_{3,095,338k (± 0.02%)}	_~	_3,094,660k	_3,096,308k	_{p=0.093 n=6}
_{Parse Time}	_{6.72s (± 0.34%)}	_{6.70s (± 0.32%)}	_~	_6.67s	_6.72s	_{p=0.128 n=6}
_{Bind Time}	_{2.13s (± 0.78%)}	_{2.16s (± 0.86%)}	_{+0.03s (+ 1.56%)}	_2.14s	_2.18s	_{p=0.030 n=6}
_{Check Time}	_{42.79s (± 0.49%)}	_{42.88s (± 0.22%)}	_~	_42.79s	_43.05s	_{p=0.575 n=6}
_{Emit Time}	_{3.50s (± 1.57%)}	_{3.42s (± 2.81%)}	_~	_3.33s	_3.57s	_{p=0.128 n=6}
_{Total Time}	_{55.13s (± 0.43%)}	_{55.16s (± 0.16%)}	_~	_55.01s	_55.24s	_{p=0.575 n=6}
_{self-build-src-public-api - node (v18.15.0, x64)}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_1,228,241	_1,228,241	_~	_~	_~	_{p=1.000 n=6}
_Types	_267,270	_267,270	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{2,674,444k (±14.04%)}	_{3,038,397k (± 9.78%)}	_~	_2,431,009k	_3,161,183k	_{p=0.173 n=6}
_{Parse Time}	_{6.87s (± 1.84%)}	_{6.95s (± 2.40%)}	_~	_6.65s	_7.16s	_{p=0.575 n=6}
_{Bind Time}	_{2.21s (± 1.55%)}	_{2.15s (± 2.59%)}	_~	_2.10s	_2.26s	_{p=0.077 n=6}
_{Check Time}	_{42.75s (± 0.50%)}	_{42.98s (± 0.34%)}	_~	_42.79s	_43.13s	_{p=0.066 n=6}
_{Emit Time}	_{3.56s (± 2.74%)}	_{3.48s (± 2.92%)}	_~	_3.37s	_3.63s	_{p=0.378 n=6}
_{Total Time}	_{55.39s (± 0.72%)}	_{55.54s (± 0.60%)}	_~	_55.13s	_56.02s	_{p=0.471 n=6}
_{self-compiler - node (v18.15.0, x64)}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_263,442	_263,442	_~	_~	_~	_{p=1.000 n=6}
_Types	_107,097	_107,097	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{441,827k (± 0.01%)}	_{441,786k (± 0.02%)}	_~	_441,682k	_441,930k	_{p=0.298 n=6}
_{Parse Time}	_{3.56s (± 1.22%)}	_{3.56s (± 0.73%)}	_~	_3.54s	_3.61s	_{p=0.871 n=6}
_{Bind Time}	_{1.33s (± 0.95%)}	_{1.33s (± 1.00%)}	_~	_1.31s	_1.35s	_{p=0.788 n=6}
_{Check Time}	_{19.04s (± 0.33%)}	_{19.06s (± 0.17%)}	_~	_19.02s	_19.12s	_{p=0.124 n=6}
_{Emit Time}	_{1.54s (± 0.79%)}	_{1.52s (± 0.59%)}	_{-0.02s (- 1.08%)}	_1.51s	_1.53s	_{p=0.039 n=6}
_{Total Time}	_{25.46s (± 0.30%)}	_{25.47s (± 0.14%)}	_~	_25.44s	_25.53s	_{p=0.936 n=6}
_{ts-pre-modules - node (v18.15.0, x64)}
_Errors	₇₁	₇₁	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_225,981	_225,981	_~	_~	_~	_{p=1.000 n=6}
_Types	_94,356	_94,356	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{371,270k (± 0.01%)}	_{371,373k (± 0.05%)}	_~	_371,210k	_371,633k	_{p=0.689 n=6}
_{Parse Time}	_{3.58s (± 0.86%)}	_{3.59s (± 0.95%)}	_~	_3.55s	_3.63s	_{p=0.629 n=6}
_{Bind Time}	_{1.96s (± 1.04%)}	_{1.97s (± 0.75%)}	_~	_1.95s	_1.99s	_{p=0.370 n=6}
_{Check Time}	_{20.50s (± 0.40%)}	_{20.46s (± 0.11%)}	_~	_20.43s	_20.49s	_{p=0.261 n=6}
_{Emit Time}	_0.00s	_0.00s	_~	_~	_~	_{p=1.000 n=6}
_{Total Time}	_{26.04s (± 0.31%)}	_{26.01s (± 0.23%)}	_~	_25.94s	_26.08s	_{p=0.629 n=6}
_{vscode - node (v18.15.0, x64)}
_Errors	₅₁	₅₁	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_3,427,972	_3,427,972	_~	_~	_~	_{p=1.000 n=6}
_Types	_1,156,170	_1,156,170	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{3,477,054k (± 0.01%)}	_{3,477,182k (± 0.00%)}	_~	_3,477,048k	_3,477,353k	_{p=0.230 n=6}
_{Parse Time}	_{18.03s (± 0.35%)}	_{18.02s (± 0.34%)}	_~	_17.92s	_18.09s	_{p=0.688 n=6}
_{Bind Time}	_{5.78s (± 0.37%)}	_{5.77s (± 0.40%)}	_~	_5.74s	_5.80s	_{p=0.413 n=6}
_{Check Time}	_{116.14s (± 2.64%)}	_{114.09s (± 2.69%)}	_~	_112.29s	_120.32s	_{p=0.066 n=6}
_{Emit Time}	_{37.01s (± 2.21%)}	_{36.28s (± 0.37%)}	_~	_36.07s	_36.46s	_{p=0.261 n=6}
_{Total Time}	_{176.97s (± 2.15%)}	_{174.17s (± 1.75%)}	_~	_172.47s	_180.36s	_{p=0.066 n=6}
_{webpack - node (v18.15.0, x64)}
_Errors	₂	₂	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_317,848	_317,848	_~	_~	_~	_{p=1.000 n=6}
_Types	_140,485	_140,485	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{473,085k (± 0.01%)}	_{473,071k (± 0.02%)}	_~	_472,881k	_473,168k	_{p=0.936 n=6}
_{Parse Time}	_{4.12s (± 1.05%)}	_{4.14s (± 0.91%)}	_~	_4.08s	_4.19s	_{p=0.336 n=6}
_{Bind Time}	_{1.82s (± 1.30%)}	_{1.83s (± 1.58%)}	_~	_1.79s	_1.86s	_{p=0.936 n=6}
_{Check Time}	_{21.00s (± 0.39%)}	_{20.89s (± 0.33%)}	_~	_20.81s	_20.98s	_{p=0.065 n=6}
_{Emit Time}	_0.00s	_0.00s	_~	_~	_~	_{p=1.000 n=6}
_{Total Time}	_{26.95s (± 0.38%)}	_{26.86s (± 0.48%)}	_~	_26.71s	_26.98s	_{p=0.199 n=6}
_{xstate-main - node (v18.15.0, x64)}
_Errors	₅	₅	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_570,733	_570,733	_~	_~	_~	_{p=1.000 n=6}
_Types	_191,446	_191,446	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{501,130k (± 0.04%)}	_{501,354k (± 0.02%)}	_~	_501,253k	_501,465k	_{p=0.066 n=6}
_{Parse Time}	_{4.33s (± 0.68%)}	_{4.32s (± 0.54%)}	_~	_4.28s	_4.35s	_{p=0.372 n=6}
_{Bind Time}	_{1.53s (± 1.91%)}	_{1.54s (± 1.06%)}	_~	_1.53s	_1.57s	_{p=0.805 n=6}
_{Check Time}	_{25.97s (± 3.61%)}	_{25.01s (± 0.47%)}	_~	_24.80s	_25.13s	_{p=0.230 n=6}
_{Emit Time}	_0.00s	_{0.00s (±244.70%)}	_~	_0.00s	_0.01s	_{p=0.405 n=6}
_{Total Time}	_{31.83s (± 2.82%)}	_{30.87s (± 0.36%)}	_~	_30.66s	_30.96s	_{p=0.229 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 · 2025-05-09T22:55:53Z

@jakebailey Here are the results of running the top 400 repos with tsc comparing main and refs/pull/61683/merge:

Everything looks good!

HansBrende · 2025-05-20T18:33:50Z

@jakebailey given the likelihood of this being an oversight when exactOptionalPropertyTypes was implemented and the simplicity of the fix, do you see it likely we'd be able to remove the "not a defect" label from the original issue (and hopefully add it to the backlog so that this PR can be reviewed)?

As you saw, I was hoping to get confirmation from the original author @ahejlsberg that it was simply a case of "missed a spot" when changing getTypeOfSymbol to getNonMissingTypeOfSymbol, but I haven't heard anything back as of yet.

jakebailey · 2025-06-09T23:23:52Z

@typescript-bot pack this

typescript-bot · 2025-06-09T23:23:56Z

Starting jobs; this comment will be updated as builds start and complete.

Command	Status	Results
`pack this`	✅ Started	✅ Results

typescript-bot · 2025-06-09T23:28:17Z

Hey @jakebailey, I've packed this into an installable tgz. You can install it for testing by referencing it in your package.json like so:

{
    "devDependencies": {
        "typescript": "https://typescript.visualstudio.com/cf7ac146-d525-443c-b23c-0d58337efebc/_apis/build/builds/165319/artifacts?artifactName=tgz&fileId=4F665885689AA916692B97D478FF2A8630D9C111C45A58BF75E4C117B832487302&fileName=/typescript-5.9.0-insiders.20250609.tgz"
    }
}

and then running npm install.

There is also a playground for this build and an npm module you can use via "typescript": "npm:@typescript-deploys/[email protected]".;

jakebailey · 2025-06-09T23:37:44Z

Testing #61547 with Playground Link, are these errors right? The first one is the reported one, sure, but it's seemingly missing two errors.

I think this PR should be encoding all of the test provided in the issue in any case. But, it's not clear if the new behavior is correct either.

HansBrende · 2025-06-09T23:45:32Z

@jakebailey hi! Can you explain what you mean by "missing two errors"? Not sure I follow. The issue is complaining that the Assert<Equal<T1, T2>> is not considered an error in v5.8.3, but it should be considered an error. (While all of the assertions that follow this are correct and their behavior should not be changed--these code paths are already heavily tested, hence why I did not include additional tests for them.)

jakebailey · 2025-06-09T23:50:25Z

The example seemingly implies that under exactOptionalPropertyTypes that all of those assertions should pass, except that the first one doesn't. But with this PR, the first is eliminated but the next two now fail.

jakebailey · 2025-06-09T23:52:18Z

Hm, I might have some wires crossed in my explanation given there are 2 playgrounds, 2 settings, and 4 assertions (sorry, I need to explain it better), but the gist is that it seems like this PR introduces errors into one of the variants that weren't there previously in 5.8.

HansBrende · 2025-06-10T01:17:13Z

The example seemingly implies that under exactOptionalPropertyTypes that all of those assertions should pass, except that the first one doesn't.

@jakebailey I can see how the issue could be misconstrued, however, simply changing the environment to 5.8.3 shows that the first assertion does pass currently.

The issue was raised to highlight that the first assertion should fail but currently passes. This is the reason for the "❌" in the comment above just that one assertion: identifying that this current behavior is incorrect.

The subsequent assertions are only provided to show that under exactOptionalPropertyTypes, T2 is not assignable to T1: evidence that T2 & T1 should not be considered identical types, and therefore that the first assertion is incorrectly passing.

with this PR, the first is eliminated but the next two now fail

I'm still not seeing these 2 failures you're mentioning... opening your playground link gives me what I would expect:

it seems like this PR introduces errors into one of the variants that weren't there previously in 5.8.

Yes, this is absolutely correct and very much intended! The whole point of the issue is to do exactly that, to introduce one error into the first assertion. (If there were any other assertions besides the first that became an error, that would definitely be a bug in my implementation, but I don't see how that could be possible because I haven't touched those code paths.)

jakebailey · 2025-06-10T01:31:48Z

Let me go through the matrix:

Version	`exactOptionalPropertyTypes=false`	`exactOptionalPropertyTypes=true`
5.8.3
This PR

I think I was just mistaken. exactOptionalPropertyTypes=false is unaffected.

HansBrende · 2025-06-10T02:39:20Z

@jakebailey correct, because getNonMissingTypeOfSymbol is semantically identical to getTypeOfSymbol under exactOptionalPropertyTypes=false, so this PR is a no-op in that case.

Let me know if you need anything else from me! 😃

fix 61547

307b09b

github-project-automation bot added this to PR Backlog May 9, 2025

github-project-automation bot moved this to Not started in PR Backlog May 9, 2025

typescript-bot added the For Uncommitted Bug PR for untriaged, rejected, closed or missing bug label May 9, 2025

HansBrende changed the title ~~fix 61547~~ Don't compare "missing" to undefined in compareProperties under exactOptionalPropertyTypes May 9, 2025

Don't compare "missing" to undefined in compareProperties under exactOptionalPropertyTypes #61683

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Don't compare "missing" to undefined in compareProperties under exactOptionalPropertyTypes #61683

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Don't compare "missing" to `undefined` in `compareProperties` under `exactOptionalPropertyTypes` #61683

Don't compare "missing" to `undefined` in `compareProperties` under `exactOptionalPropertyTypes` #61683

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