Simplify relationship check for conditional type on target side #46429

ahejlsberg · 2021-10-19T16:44:13Z

This PR simplifies our relationship checking logic for conditional types on the target side. With this PR, a source type S is assignable to a target type A extends B ? C : D when

The conditional type is not distributive, or is distributive but A is never referenced in C or D, and
B has no infer positions, and
S is assignable to C (except if A never assignable to B for any instantiation), and
S is assignable to D (except if A is always assignable to B for any instantiation).

The PR revises some of the logic that was added in #30639, specifically the logic that determines if A is referenced in C or D in a distributive conditional type. There are no baseline changes as a result of this PR, but it fixes the performance degradation reported in #44851.

Fixes #44851.

ahejlsberg · 2021-10-19T16:47:41Z

I should mention that with this PR, the check time for this repro drops from ~10s to about 0.4s.

andrewbranch · 2021-10-19T16:57:45Z

@typescript-bot test this
@typescript-bot user test this inline
@typescript-bot run DT
@typescript-bot perf test this
@typescript-bot pack this
@typescript-bot all the things please

typescript-bot · 2021-10-19T16:57:49Z

Heya @andrewbranch, I've started to run the inline community code test suite on this PR at 75ab347. You can monitor the build here.

Update: The results are in!

typescript-bot · 2021-10-19T16:57:49Z

Heya @andrewbranch, I've started to run the extended test suite on this PR at 75ab347. You can monitor the build here.

typescript-bot · 2021-10-19T16:57:49Z

Heya @andrewbranch, I've started to run the parallelized Definitely Typed test suite on this PR at 75ab347. You can monitor the build here.

typescript-bot · 2021-10-19T16:57:49Z

Heya @andrewbranch, I've started to run the tarball bundle task on this PR at 75ab347. You can monitor the build here.

typescript-bot · 2021-10-19T16:57:49Z

Heya @andrewbranch, I've started to run the perf test suite on this PR at 75ab347. You can monitor the build here.

Update: The results are in!

DanielRosenwasser · 2021-10-19T17:11:04Z

Hurray, I helped find something maybe useful!

typescript-bot · 2021-10-19T17:12:46Z

@andrewbranch
Great news! no new errors were found between main..refs/pull/46429/merge

DanielRosenwasser · 2021-10-19T17:21:15Z

tests/baselines/reference/conditionalTypeAssignabilityWhenDeferred.errors.txt

@@ -48,7 +55,13 @@ tests/cases/compiler/conditionalTypeAssignabilityWhenDeferred.ts(116,3): error T
    function f<T>(t: T) {
      var x: T | null = Math.random() > 0.5 ? null : t;
      onlyNullablePlease(x); // should work
+                         ~
+!!! error TS2345: Argument of type 'T | null' is not assignable to parameter of type 'null extends T | null ? any : never'.


This one is interesting - is this actually a distributive conditional type? Why is it deferred?

We always defer if either of the check and extends types contains generics. This is somewhat of a blunt instrument, and we could possibly do better in cases like this.

And by "contains generics" I mean we defer when isGenericType returns true for either of the check and extends types.

weswigham · 2021-10-19T17:32:16Z

If we're going to attempt to fix those, the fix really should be to have the conditional type construction logic decide to resolve the types instead of deferring them--but I think that has lower priority.

This is impossible in the general case - any condition with an infer has to be deferred so the infer can be instantiated with every possible input (since an infer result can't stand on its own) - if we don't reason about branch reachability in relationship checking, we can never handle conditional types that both filter and transform simultaneously like T extends () => infer I ? I : never. We knew that adding constraint checks on branch reachability would be expensive - but it's the typespace equivalent of doing control flow on genetics, which we also do wherever we can now.

typescript-bot · 2021-10-19T17:33:32Z

@andrewbranch
The results of the perf run you requested are in!

Here they are:

Comparison Report - main..46429

_Metric	_main	₄₆₄₂₉	_Delta	_Best	_Worst
_{Angular - node (v10.16.3, x64)}
_{Memory used}	_{354,063k (± 0.01%)}	_{354,012k (± 0.02%)}	_{-51k (- 0.01%)}	_353,868k	_354,166k
_{Parse Time}	_{1.96s (± 0.58%)}	_{1.95s (± 0.50%)}	_{-0.01s (- 0.46%)}	_1.93s	_1.97s
_{Bind Time}	_{0.84s (± 0.66%)}	_{0.84s (± 0.81%)}	_{+0.00s (+ 0.36%)}	_0.83s	_0.86s
_{Check Time}	_{5.47s (± 0.36%)}	_{5.48s (± 0.81%)}	_{+0.01s (+ 0.22%)}	_5.42s	_5.61s
_{Emit Time}	_{5.86s (± 0.67%)}	_{5.88s (± 0.70%)}	_{+0.01s (+ 0.20%)}	_5.78s	_5.98s
_{Total Time}	_{14.13s (± 0.34%)}	_{14.15s (± 0.46%)}	_{+0.02s (+ 0.12%)}	_14.04s	_14.31s
_{Compiler-Unions - node (v10.16.3, x64)}
_{Memory used}	_{203,871k (± 0.03%)}	_{203,893k (± 0.03%)}	_{+22k (+ 0.01%)}	_203,721k	_203,980k
_{Parse Time}	_{0.78s (± 0.67%)}	_{0.78s (± 0.63%)}	_{+0.00s (+ 0.38%)}	_0.78s	_0.80s
_{Bind Time}	_{0.53s (± 1.13%)}	_{0.52s (± 1.28%)}	_{-0.01s (- 1.14%)}	_0.50s	_0.53s
_{Check Time}	_{7.95s (± 0.67%)}	_{7.90s (± 0.45%)}	_{-0.05s (- 0.62%)}	_7.83s	_7.97s
_{Emit Time}	_{2.45s (± 0.80%)}	_{2.44s (± 0.65%)}	_{-0.01s (- 0.45%)}	_2.40s	_2.48s
_{Total Time}	_{11.71s (± 0.46%)}	_{11.65s (± 0.29%)}	_{-0.06s (- 0.51%)}	_11.56s	_11.72s
_{Monaco - node (v10.16.3, x64)}
_{Memory used}	_{342,091k (± 0.01%)}	_{342,060k (± 0.03%)}	_{-32k (- 0.01%)}	_341,822k	_342,213k
_{Parse Time}	_{1.48s (± 0.78%)}	_{1.49s (± 0.46%)}	_{+0.00s (+ 0.13%)}	_1.47s	_1.50s
_{Bind Time}	_{0.75s (± 0.82%)}	_{0.75s (± 0.67%)}	_{-0.00s (- 0.53%)}	_0.74s	_0.76s
_{Check Time}	_{5.46s (± 0.55%)}	_{5.42s (± 0.83%)}	_{-0.03s (- 0.59%)}	_5.33s	_5.51s
_{Emit Time}	_{3.17s (± 0.70%)}	_{3.17s (± 0.83%)}	_{+0.00s (+ 0.00%)}	_3.12s	_3.25s
_{Total Time}	_{10.86s (± 0.31%)}	_{10.82s (± 0.31%)}	_{-0.04s (- 0.33%)}	_10.74s	_10.88s
_{TFS - node (v10.16.3, x64)}
_{Memory used}	_{304,751k (± 0.01%)}	_{304,803k (± 0.02%)}	_{+52k (+ 0.02%)}	_304,682k	_304,886k
_{Parse Time}	_{1.20s (± 0.68%)}	_{1.19s (± 0.25%)}	_{-0.01s (- 0.42%)}	_1.19s	_1.20s
_{Bind Time}	_{0.71s (± 0.70%)}	_{0.71s (± 0.56%)}	_{+0.00s (+ 0.71%)}	_0.70s	_0.72s
_{Check Time}	_{4.97s (± 0.51%)}	_{4.95s (± 0.67%)}	_{-0.02s (- 0.38%)}	_4.88s	_5.03s
_{Emit Time}	_{3.30s (± 1.07%)}	_{3.32s (± 1.02%)}	_{+0.02s (+ 0.45%)}	_3.26s	_3.40s
_{Total Time}	_{10.17s (± 0.45%)}	_{10.17s (± 0.44%)}	_{-0.01s (- 0.06%)}	_10.10s	_10.28s
_{material-ui - node (v10.16.3, x64)}
_{Memory used}	_{471,094k (± 0.02%)}	_{469,960k (± 0.01%)}	_{-1,134k (- 0.24%)}	_469,861k	_470,042k
_{Parse Time}	_{1.77s (± 0.56%)}	_{1.77s (± 0.42%)}	_{-0.00s (- 0.17%)}	_1.76s	_1.79s
_{Bind Time}	_{0.66s (± 1.23%)}	_{0.66s (± 1.22%)}	_{-0.00s (- 0.30%)}	_0.64s	_0.68s
_{Check Time}	_{14.38s (± 0.41%)}	_{14.34s (± 0.56%)}	_{-0.04s (- 0.31%)}	_14.18s	_14.58s
_{Emit Time}	_{0.00s (± 0.00%)}	_{0.00s (± 0.00%)}	_{0.00s ( NaN%)}	_0.00s	_0.00s
_{Total Time}	_{16.82s (± 0.39%)}	_{16.77s (± 0.52%)}	_{-0.05s (- 0.32%)}	_16.59s	_17.02s
_{Angular - node (v12.1.0, x64)}
_{Memory used}	_{331,719k (± 0.08%)}	_{331,897k (± 0.02%)}	_{+178k (+ 0.05%)}	_331,749k	_332,046k
_{Parse Time}	_{1.96s (± 0.67%)}	_{1.94s (± 0.51%)}	_{-0.02s (- 1.02%)}	_1.92s	_1.97s
_{Bind Time}	_{0.82s (± 1.34%)}	_{0.82s (± 1.15%)}	_{0.00s ( 0.00%)}	_0.80s	_0.84s
_{Check Time}	_{5.33s (± 0.81%)}	_{5.31s (± 0.38%)}	_{-0.02s (- 0.41%)}	_5.27s	_5.36s
_{Emit Time}	_{6.15s (± 0.82%)}	_{6.09s (± 0.44%)}	_{-0.06s (- 0.99%)}	_6.05s	_6.18s
_{Total Time}	_{14.26s (± 0.59%)}	_{14.16s (± 0.28%)}	_{-0.10s (- 0.72%)}	_14.08s	_14.26s
_{Compiler-Unions - node (v12.1.0, x64)}
_{Memory used}	_{191,425k (± 0.04%)}	_{191,331k (± 0.07%)}	_{-94k (- 0.05%)}	_190,906k	_191,583k
_{Parse Time}	_{0.78s (± 0.67%)}	_{0.78s (± 0.93%)}	_{+0.00s (+ 0.13%)}	_0.77s	_0.80s
_{Bind Time}	_{0.53s (± 0.89%)}	_{0.53s (± 0.71%)}	_{-0.01s (- 0.94%)}	_0.52s	_0.53s
_{Check Time}	_{7.40s (± 0.55%)}	_{7.41s (± 0.71%)}	_{+0.00s (+ 0.07%)}	_7.32s	_7.56s
_{Emit Time}	_{2.46s (± 0.85%)}	_{2.46s (± 1.46%)}	_{+0.00s (+ 0.12%)}	_2.39s	_2.55s
_{Total Time}	_{11.17s (± 0.48%)}	_{11.17s (± 0.72%)}	_{+0.00s (+ 0.01%)}	_11.02s	_11.36s
_{Monaco - node (v12.1.0, x64)}
_{Memory used}	_{325,197k (± 0.02%)}	_{325,207k (± 0.02%)}	_{+11k (+ 0.00%)}	_325,051k	_325,336k
_{Parse Time}	_{1.48s (± 0.91%)}	_{1.46s (± 0.55%)}	_{-0.02s (- 1.15%)}	_1.45s	_1.49s
_{Bind Time}	_{0.73s (± 0.85%)}	_{0.73s (± 1.23%)}	_{-0.00s (- 0.41%)}	_0.72s	_0.76s
_{Check Time}	_{5.32s (± 0.81%)}	_{5.33s (± 0.38%)}	_{+0.01s (+ 0.23%)}	_5.28s	_5.39s
_{Emit Time}	_{3.20s (± 0.72%)}	_{3.18s (± 0.71%)}	_{-0.02s (- 0.69%)}	_3.14s	_3.23s
_{Total Time}	_{10.73s (± 0.57%)}	_{10.70s (± 0.34%)}	_{-0.03s (- 0.25%)}	_10.63s	_10.78s
_{TFS - node (v12.1.0, x64)}
_{Memory used}	_{289,506k (± 0.02%)}	_{289,475k (± 0.02%)}	_{-31k (- 0.01%)}	_289,342k	_289,574k
_{Parse Time}	_{1.22s (± 0.82%)}	_{1.21s (± 0.87%)}	_{-0.01s (- 0.90%)}	_1.20s	_1.24s
_{Bind Time}	_{0.70s (± 0.86%)}	_{0.69s (± 1.06%)}	_{-0.01s (- 1.01%)}	_0.68s	_0.71s
_{Check Time}	_{4.92s (± 0.26%)}	_{4.90s (± 0.56%)}	_{-0.02s (- 0.39%)}	_4.84s	_4.96s
_{Emit Time}	_{3.39s (± 0.99%)}	_{3.37s (± 0.65%)}	_{-0.02s (- 0.53%)}	_3.33s	_3.42s
_{Total Time}	_{10.23s (± 0.41%)}	_{10.17s (± 0.47%)}	_{-0.06s (- 0.57%)}	_10.08s	_10.30s
_{material-ui - node (v12.1.0, x64)}
_{Memory used}	_{449,723k (± 0.06%)}	_{448,617k (± 0.06%)}	_{-1,106k (- 0.25%)}	_447,464k	_448,866k
_{Parse Time}	_{1.79s (± 0.91%)}	_{1.78s (± 0.72%)}	_{-0.01s (- 0.45%)}	_1.76s	_1.82s
_{Bind Time}	_{0.65s (± 1.03%)}	_{0.64s (± 0.76%)}	_{-0.00s (- 0.46%)}	_0.63s	_0.65s
_{Check Time}	_{13.01s (± 0.85%)}	_{12.97s (± 0.73%)}	_{-0.04s (- 0.28%)}	_12.83s	_13.15s
_{Emit Time}	_{0.00s (± 0.00%)}	_{0.00s (± 0.00%)}	_{0.00s ( NaN%)}	_0.00s	_0.00s
_{Total Time}	_{15.45s (± 0.73%)}	_{15.40s (± 0.64%)}	_{-0.05s (- 0.30%)}	_15.23s	_15.58s
_{Angular - node (v14.15.1, x64)}
_{Memory used}	_{330,294k (± 0.01%)}	_{330,303k (± 0.01%)}	_{+9k (+ 0.00%)}	_330,268k	_330,340k
_{Parse Time}	_{1.96s (± 0.48%)}	_{1.94s (± 0.48%)}	_{-0.02s (- 1.27%)}	_1.91s	_1.95s
_{Bind Time}	_{0.87s (± 0.54%)}	_{0.86s (± 0.39%)}	_{-0.01s (- 0.80%)}	_0.86s	_0.87s
_{Check Time}	_{5.37s (± 0.44%)}	_{5.37s (± 0.37%)}	_{-0.00s (- 0.07%)}	_5.32s	_5.40s
_{Emit Time}	_{6.19s (± 0.98%)}	_{6.19s (± 0.63%)}	_{-0.01s (- 0.10%)}	_6.08s	_6.26s
_{Total Time}	_{14.39s (± 0.54%)}	_{14.35s (± 0.37%)}	_{-0.04s (- 0.29%)}	_14.18s	_14.43s
_{Compiler-Unions - node (v14.15.1, x64)}
_{Memory used}	_{192,554k (± 0.49%)}	_{192,879k (± 0.37%)}	_{+325k (+ 0.17%)}	_189,971k	_193,279k
_{Parse Time}	_{0.81s (± 0.72%)}	_{0.81s (± 1.17%)}	_{+0.01s (+ 0.87%)}	_0.80s	_0.84s
_{Bind Time}	_{0.56s (± 0.53%)}	_{0.55s (± 0.62%)}	_{-0.01s (- 0.90%)}	_0.55s	_0.56s
_{Check Time}	_{7.60s (± 0.38%)}	_{7.56s (± 0.47%)}	_{-0.05s (- 0.63%)}	_7.48s	_7.65s
_{Emit Time}	_{2.45s (± 0.92%)}	_{2.44s (± 0.82%)}	_{-0.01s (- 0.57%)}	_2.41s	_2.50s
_{Total Time}	_{11.42s (± 0.33%)}	_{11.36s (± 0.35%)}	_{-0.06s (- 0.49%)}	_11.29s	_11.46s
_{Monaco - node (v14.15.1, x64)}
_{Memory used}	_{323,999k (± 0.01%)}	_{323,990k (± 0.01%)}	_{-9k (- 0.00%)}	_323,951k	_324,030k
_{Parse Time}	_{1.51s (± 0.88%)}	_{1.51s (± 0.72%)}	_{-0.01s (- 0.46%)}	_1.49s	_1.53s
_{Bind Time}	_{0.76s (± 0.48%)}	_{0.76s (± 0.48%)}	_{0.00s ( 0.00%)}	_0.75s	_0.76s
_{Check Time}	_{5.33s (± 0.50%)}	_{5.30s (± 0.42%)}	_{-0.03s (- 0.53%)}	_5.27s	_5.38s
_{Emit Time}	_{3.23s (± 0.47%)}	_{3.23s (± 0.68%)}	_{-0.00s (- 0.03%)}	_3.18s	_3.27s
_{Total Time}	_{10.83s (± 0.36%)}	_{10.79s (± 0.24%)}	_{-0.04s (- 0.37%)}	_10.73s	_10.87s
_{TFS - node (v14.15.1, x64)}
_{Memory used}	_{288,354k (± 0.01%)}	_{288,339k (± 0.01%)}	_{-15k (- 0.01%)}	_288,308k	_288,377k
_{Parse Time}	_{1.24s (± 0.63%)}	_{1.23s (± 0.53%)}	_{-0.01s (- 0.89%)}	_1.21s	_1.24s
_{Bind Time}	_{0.74s (± 0.46%)}	_{0.73s (± 0.71%)}	_{-0.01s (- 1.09%)}	_0.72s	_0.74s
_{Check Time}	_{4.94s (± 0.31%)}	_{4.91s (± 0.48%)}	_{-0.03s (- 0.57%)}	_4.87s	_4.97s
_{Emit Time}	_{3.49s (± 0.35%)}	_{3.49s (± 0.82%)}	_{+0.01s (+ 0.17%)}	_3.43s	_3.55s
_{Total Time}	_{10.40s (± 0.24%)}	_{10.36s (± 0.31%)}	_{-0.04s (- 0.38%)}	_10.28s	_10.45s
_{material-ui - node (v14.15.1, x64)}
_{Memory used}	_{447,964k (± 0.06%)}	_{446,820k (± 0.08%)}	_{-1,143k (- 0.26%)}	_445,818k	_447,128k
_{Parse Time}	_{1.83s (± 0.42%)}	_{1.82s (± 0.49%)}	_{-0.01s (- 0.33%)}	_1.80s	_1.85s
_{Bind Time}	_{0.68s (± 0.70%)}	_{0.68s (± 0.44%)}	_{+0.00s (+ 0.15%)}	_0.67s	_0.68s
_{Check Time}	_{13.19s (± 0.94%)}	_{13.10s (± 0.46%)}	_{-0.09s (- 0.68%)}	_12.97s	_13.25s
_{Emit Time}	_{0.00s (± 0.00%)}	_{0.00s (± 0.00%)}	_{0.00s ( NaN%)}	_0.00s	_0.00s
_{Total Time}	_{15.70s (± 0.82%)}	_{15.61s (± 0.38%)}	_{-0.09s (- 0.59%)}	_15.48s	_15.75s

System

_{Machine Name}	_ts-ci-ubuntu
_Platform	_{linux 4.4.0-210-generic}
_Architecture	_x64
_{Available Memory}	_{16 GB}
_{Available Memory}	_{6 GB}
_CPUs	_{4 × Intel(R) Core(TM) i7-4770 CPU @ 3.40GHz}

Hosts

node (v10.16.3, x64)
node (v12.1.0, x64)
node (v14.15.1, x64)

Scenarios

Angular - node (v10.16.3, x64)
Angular - node (v12.1.0, x64)
Angular - node (v14.15.1, x64)
Compiler-Unions - node (v10.16.3, x64)
Compiler-Unions - node (v12.1.0, x64)
Compiler-Unions - node (v14.15.1, x64)
Monaco - node (v10.16.3, x64)
Monaco - node (v12.1.0, x64)
Monaco - node (v14.15.1, x64)
TFS - node (v10.16.3, x64)
TFS - node (v12.1.0, x64)
TFS - node (v14.15.1, x64)
material-ui - node (v10.16.3, x64)
material-ui - node (v12.1.0, x64)
material-ui - node (v14.15.1, x64)

_Benchmark	_Name	_Iterations
_Current	₄₆₄₂₉	₁₀
_Baseline	_main	₁₀

Developer Information:

Download Benchmark

ahejlsberg · 2021-10-19T17:48:00Z

@typescript-bot test this
@typescript-bot user test this
@typescript-bot run dt
@typescript-bot pack this

typescript-bot · 2021-10-19T17:48:04Z

Heya @ahejlsberg, I've started to run the extended test suite on this PR at 75ab347. You can monitor the build here.

typescript-bot · 2021-10-19T17:48:04Z

Heya @ahejlsberg, I've started to run the parallelized community code test suite on this PR at 75ab347. You can monitor the build here.

typescript-bot · 2021-10-19T17:48:04Z

Heya @ahejlsberg, I've started to run the tarball bundle task on this PR at 75ab347. You can monitor the build here.

typescript-bot · 2021-10-19T17:48:04Z

Heya @ahejlsberg, I've started to run the parallelized Definitely Typed test suite on this PR at 75ab347. You can monitor the build here.

ahejlsberg · 2021-10-19T17:56:07Z

This is impossible in the general case

Agreed, and so be it. But it does seem like there are classes of cases where we ought to do better in conditional type construction. Both of the test cases that revert back to failing with this PR seem quite trivial--for example, checking if the check and extends types are identical, or if the extends type is a union that contains the check type, would cause us to resolve the conditional type to the true case.

typescript-bot · 2021-10-19T18:45:22Z

Hey @ahejlsberg, 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/113306/artifacts?artifactName=tgz&fileId=A263304AC84860808E706B7F5590B0AA3616661B50F7CE35CED050B21FF1B0C802&fileName=/typescript-4.5.0-insiders.20211019.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/pr-build@4.5.0-pr-46429-17".;

andrewbranch · 2021-10-21T23:13:33Z

@ahejlsberg did you check the latest commits against ajv again? @amcasey’s Frankenstein repro is back up to a very long check time before the instantiation depth error.

ahejlsberg · 2021-10-21T23:23:11Z

@andrewbranch I've checked against my reduced repro from this comment as well as https://github.com/jonohill/tsc-bug-44851 and https://github.com/aarbmx6s/vscode-ajv-issue. Performance issues are gone in all three.

Not sure what's up with @amcasey's repro.

amcasey · 2021-10-21T23:29:47Z

I'll reiterate that I'm with ignoring my repro since I probably made nonsense out of the logic while tinkering with it. Obviously, never being slow is the ideal, but it's more important to focus on code people might actually write. Alternatively, we could call this good and file a separate bug to go investigate that repro.

ahejlsberg · 2021-10-21T23:43:11Z

I think I can say with a high degree of certainty that whatever is going on in @amcasey's example is unrelated. I removed all of the logic having to do with assignability to conditional types (i.e. both #30639 and this PR), and the example still blows up with an instantiation depth error.

DanielRosenwasser · 2021-10-21T23:46:29Z

Please, no more plot twists, my heart can't handle it anymore.

andrewbranch · 2021-10-21T23:47:02Z

Yeah, if the real world code is fast then I’m happy. Just wanted to make sure it was checked against the latest changes.

DetachHead · 2021-11-19T05:41:17Z

is there an example of a type that is no longer allowed as of this PR? the typescript 4.5 blog post mentions this PR

TypeScript no longer allows types to be assignable to conditional types that use infer, or that are distributive. Doing so previously often ended up causing major performance issues. For more information, see the specific change on GitHub.

but i can't seem to find a minimal example of what this means exactly

RyanCavanaugh · 2021-12-13T21:05:33Z

@DetachHead good news (??), we found one: #47127 (comment)

iahu · 2021-12-14T05:18:09Z

@DetachHead good news (??), we found one: #47127 (comment)

This is a BAD news for me. I deeply dependency this feature. Because of this breaking change, I cant update TypeScript, it's so bad for me, could you add a compiler option to support it as a migrate plan?

…osoft#46429) * Simplify relationship check for conditional type on target side * Accept new baselines * Better support for non-distribution-dependent types * Accept new API baselines * Accept new baselines

ahejlsberg added 2 commits October 19, 2021 09:21

Simplify relationship check for conditional type on target side

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Accept new baselines

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typescript-bot assigned ahejlsberg Oct 19, 2021

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typescript-bot added the For Milestone Bug PRs that fix a bug with a specific milestone label Oct 19, 2021

ahejlsberg requested review from weswigham, andrewbranch, armanio123 and DanielRosenwasser October 19, 2021 16:48

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andrewbranch approved these changes Oct 21, 2021

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ahejlsberg merged commit f2f35ae into main Oct 22, 2021

ahejlsberg deleted the fix44851 branch October 22, 2021 00:35

ahejlsberg mentioned this pull request Oct 22, 2021

Defer computation of isDistributionDependent to avoid circularities #46474

Merged

sandersn mentioned this pull request Oct 22, 2021

[NewErrors] 4.5.0-dev.20211017 vs 4.4.4 #46404

Closed

mmvsk mentioned this pull request Oct 24, 2021

TS 4.5 type instantiation is excessively deep and possibly infinite, with seemingly legal type #46500

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JSin mentioned this pull request Nov 8, 2021

Slow IntelliSense with react-hook-form resolvers on commands completionInfo, completionEntryDetails, and, encodedSemanticClassifications-full #46726

Open

sinclairzx81 mentioned this pull request Nov 18, 2021

TS 4.5: Type instantiation is excessively deep and possibly infinite. sinclairzx81/typebox#120

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andreialecu mentioned this pull request Nov 18, 2021

Mongoose slows down performance of VSCode (TSServer) by a lot Automattic/mongoose#10349

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RyanCavanaugh mentioned this pull request Dec 13, 2021

conditional generic Type assignable Error #47127

Closed

DanielRosenwasser mentioned this pull request Jan 20, 2022

Experiment short-circuiting of union distribution #47511

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5 tasks

Andarist mentioned this pull request Mar 12, 2022

Explicit type annotation required in TS 4.5 #47384

Open

This was referenced Apr 18, 2022

Generic Extended Types not inferring Correctly #48741

Closed

Type 'T' is not assignable to type 'T extends Sub ? Sub : T'. #48746

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whzx5byb mentioned this pull request Sep 30, 2022

InstanceType<(typeof this)["somefield"]> type issue #51013

Closed

wbt mentioned this pull request Nov 11, 2022

Can't assign type though it is on both branches of conditional type #51488

Closed

benrbray mentioned this pull request Feb 28, 2023

[chore] address breaking changes to conditional types in typescript@4.5 benrbray/noteworthy#30

Open

Andarist mentioned this pull request Apr 26, 2023

Add extra tests for recursive conditional types #54030

Merged

KaelWD mentioned this pull request May 16, 2023

[Bug Report][3.2.4] Cryptic TS error when passing generic values to v-autocomplete/v-select vuetifyjs/vuetify#17383

Closed

RyanCavanaugh mentioned this pull request Jan 23, 2024

Function fields in class with conditional optionality of parameters #57139

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Simplify relationship check for conditional type on target side #46429

Simplify relationship check for conditional type on target side #46429

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Simplify relationship check for conditional type on target side #46429

Simplify relationship check for conditional type on target side #46429

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