Treat void-typed properties as optional

[Ron Buckton (rbuckton)]

This treats void-typed properties (or properties with a void constituent) as optional for the purpose of assignability. This is similar to how we treat trailing void parameters in signatures. The primary intended use case is to address an ECMAScript spec-compliance issue with IteratorResult, though this has possibly further-reaching consequences than just that change:

// giveninterfaceIteratorYieldResult<TYield>{done?: false;value: TYield;}interfaceIteratorReturnResult<TReturn>{done: true;value: TReturn;}typeIteratorResult<T,TReturn=any>=IteratorYieldResult<T>|IteratorReturnResult<TReturn>;constmyIterator: Iterator<number,void>={next(value?: number){return{done: true};// `value` is not required because it is typed `void`.}}

Unfortunately, simply making value optional isn't an option as it would make the result of yield* essentially always optional, as well as the result from calling .next() when iteration has completed. For example:

function*g()/*: Generator<never, number, undefined> */{return1;}function*f(){constx=yield*g();// x should be `number`, but if `value` is optional it is `number | undefined`.}constresult=g().next();// IteratorResult<never, number>;if(result.done){result;// IteratorReturnResult<number>;result.value;// should be `number`, but if `value` is optional it is `number | undefined`.}

I did consider changing the type of IteratorResult:

interfaceIteratorYieldResult<TYield>{done?: false;value: TYield;}interfaceIteratorReturnResult<TReturn>{done: true;value: TReturn;}interfaceIteratorVoidReturnResult{done: true;value?: void;}typeIteratorResult<T,TReturn=any>=|IteratorYieldResult<T>|IteratorReturnResult<TReturn>|(TReturnextendsvoid ? IteratorVoidReturnResult : never);

However that would require adding additional complexity to getIterationTypesOfIteratorResult to extract iteration types, and I'm also concerned that changing IteratorResult in this way would cause issues with assignability for existing custom iterators.

Fixes#38479

[Ron Buckton (rbuckton)]

TypeScript Bot (@typescript-bot) perf test
TypeScript Bot (@typescript-bot) run dt
TypeScript Bot (@typescript-bot) test this
TypeScript Bot (@typescript-bot) user test this

[TypeScript Bot (typescript-bot)]

Heya Ron Buckton (@rbuckton), I've started to run the parallelized Definitely Typed test suite on this PR at be9b85d. You can monitor the build here.

[TypeScript Bot (typescript-bot)]

Heya Ron Buckton (@rbuckton), I've started to run the parallelized community code test suite on this PR at be9b85d. You can monitor the build here.

[TypeScript Bot (typescript-bot)]

Heya Ron Buckton (@rbuckton), I've started to run the extended test suite on this PR at be9b85d. You can monitor the build here.

[TypeScript Bot (typescript-bot)]

Heya Ron Buckton (@rbuckton), I've started to run the perf test suite on this PR at be9b85d. You can monitor the build here.

Update: The results are in!

[TypeScript Bot (typescript-bot)]

Ron Buckton (@rbuckton)
The results of the perf run you requested are in!

Here they are:

Comparison Report - master..40823

Metric	master	40823	Delta	Best	Worst
Angular - node (v10.16.3, x64)
Memory used	349,616k (± 0.01%)	349,665k (± 0.03%)	+49k (+ 0.01%)	349,497k	349,945k
Parse Time	2.00s (± 0.26%)	2.01s (± 0.42%)	+0.01s (+ 0.50%)	1.98s	2.02s
Bind Time	0.82s (± 0.81%)	0.82s (± 0.91%)	0.00s ( 0.00%)	0.81s	0.85s
Check Time	4.90s (± 0.77%)	4.89s (± 0.49%)	-0.01s (- 0.16%)	4.85s	4.96s
Emit Time	5.19s (± 0.52%)	5.17s (± 0.51%)	-0.02s (- 0.35%)	5.09s	5.22s
Total Time	12.91s (± 0.43%)	12.90s (± 0.33%)	-0.01s (- 0.11%)	12.81s	13.00s
Monaco - node (v10.16.3, x64)
Memory used	354,341k (± 0.03%)	354,311k (± 0.02%)	-30k (- 0.01%)	354,162k	354,413k
Parse Time	1.56s (± 0.52%)	1.56s (± 0.51%)	-0.00s (- 0.13%)	1.54s	1.58s
Bind Time	0.71s (± 0.52%)	0.71s (± 0.69%)	-0.00s (- 0.14%)	0.70s	0.72s
Check Time	5.07s (± 0.61%)	5.06s (± 0.50%)	-0.01s (- 0.14%)	4.99s	5.12s
Emit Time	2.76s (± 0.86%)	2.75s (± 0.59%)	-0.01s (- 0.43%)	2.72s	2.79s
Total Time	10.10s (± 0.49%)	10.08s (± 0.22%)	-0.02s (- 0.23%)	10.03s	10.13s
TFS - node (v10.16.3, x64)
Memory used	307,541k (± 0.04%)	307,560k (± 0.02%)	+19k (+ 0.01%)	307,429k	307,667k
Parse Time	1.21s (± 0.56%)	1.21s (± 0.49%)	0.00s ( 0.00%)	1.20s	1.22s
Bind Time	0.67s (± 0.99%)	0.67s (± 1.21%)	-0.00s (- 0.45%)	0.64s	0.68s
Check Time	4.54s (± 0.49%)	4.54s (± 0.46%)	-0.00s (- 0.07%)	4.48s	4.58s
Emit Time	2.90s (± 1.00%)	2.92s (± 0.81%)	+0.02s (+ 0.62%)	2.85s	2.97s
Total Time	9.33s (± 0.46%)	9.34s (± 0.47%)	+0.01s (+ 0.12%)	9.21s	9.41s
material-ui - node (v10.16.3, x64)
Memory used	489,001k (± 0.01%)	488,962k (± 0.01%)	-39k (- 0.01%)	488,898k	489,067k
Parse Time	1.98s (± 0.45%)	1.98s (± 0.69%)	-0.00s (- 0.10%)	1.96s	2.02s
Bind Time	0.65s (± 0.86%)	0.65s (± 0.53%)	-0.00s (- 0.15%)	0.64s	0.65s
Check Time	13.50s (± 0.78%)	13.59s (± 0.66%)	+0.09s (+ 0.64%)	13.32s	13.73s
Emit Time	0.00s (± 0.00%)	0.00s (± 0.00%)	0.00s ( NaN%)	0.00s	0.00s
Total Time	16.14s (± 0.64%)	16.22s (± 0.60%)	+0.08s (+ 0.50%)	15.93s	16.38s
Angular - node (v12.1.0, x64)
Memory used	326,839k (± 0.03%)	326,684k (± 0.09%)	-155k (- 0.05%)	325,639k	327,041k
Parse Time	1.99s (± 0.51%)	1.99s (± 0.61%)	+0.00s (+ 0.15%)	1.97s	2.03s
Bind Time	0.81s (± 0.64%)	0.81s (± 0.45%)	-0.00s (- 0.37%)	0.80s	0.81s
Check Time	4.80s (± 0.57%)	4.79s (± 0.40%)	-0.01s (- 0.19%)	4.75s	4.84s
Emit Time	5.36s (± 0.68%)	5.35s (± 0.82%)	-0.00s (- 0.04%)	5.29s	5.51s
Total Time	12.95s (± 0.46%)	12.94s (± 0.46%)	-0.01s (- 0.08%)	12.85s	13.15s
Monaco - node (v12.1.0, x64)
Memory used	336,492k (± 0.01%)	336,509k (± 0.03%)	+18k (+ 0.01%)	336,355k	336,697k
Parse Time	1.54s (± 0.86%)	1.54s (± 0.84%)	-0.00s (- 0.13%)	1.51s	1.57s
Bind Time	0.70s (± 1.84%)	0.69s (± 0.32%)	-0.01s (- 1.29%)	0.69s	0.70s
Check Time	4.87s (± 0.47%)	4.87s (± 0.51%)	+0.00s (+ 0.08%)	4.83s	4.92s
Emit Time	2.83s (± 0.76%)	2.81s (± 0.81%)	-0.02s (- 0.67%)	2.77s	2.88s
Total Time	9.93s (± 0.47%)	9.91s (± 0.38%)	-0.03s (- 0.26%)	9.84s	10.03s
TFS - node (v12.1.0, x64)
Memory used	291,819k (± 0.02%)	291,850k (± 0.02%)	+31k (+ 0.01%)	291,708k	291,960k
Parse Time	1.23s (± 0.66%)	1.23s (± 0.59%)	-0.00s (- 0.16%)	1.22s	1.25s
Bind Time	0.64s (± 0.90%)	0.65s (± 1.15%)	+0.00s (+ 0.62%)	0.64s	0.67s
Check Time	4.44s (± 0.36%)	4.45s (± 0.45%)	+0.01s (+ 0.16%)	4.40s	4.50s
Emit Time	2.94s (± 0.96%)	2.93s (± 0.75%)	-0.00s (- 0.07%)	2.90s	2.98s
Total Time	9.25s (± 0.42%)	9.26s (± 0.34%)	+0.01s (+ 0.12%)	9.18s	9.31s
material-ui - node (v12.1.0, x64)
Memory used	466,976k (± 0.05%)	466,897k (± 0.05%)	-78k (- 0.02%)	466,019k	467,077k
Parse Time	2.00s (± 0.38%)	2.00s (± 0.35%)	-0.00s (- 0.15%)	1.99s	2.02s
Bind Time	0.64s (± 0.58%)	0.64s (± 0.81%)	+0.00s (+ 0.63%)	0.63s	0.65s
Check Time	12.01s (± 0.69%)	12.12s (± 0.66%)	+0.11s (+ 0.93%)	12.00s	12.28s
Emit Time	0.00s (± 0.00%)	0.00s (± 0.00%)	0.00s ( NaN%)	0.00s	0.00s
Total Time	14.65s (± 0.59%)	14.76s (± 0.60%)	+0.11s (+ 0.76%)	14.62s	14.94s
Angular - node (v8.9.0, x64)
Memory used	346,316k (± 0.02%)	346,375k (± 0.03%)	+59k (+ 0.02%)	346,082k	346,566k
Parse Time	2.55s (± 0.37%)	2.55s (± 0.29%)	+0.01s (+ 0.20%)	2.54s	2.57s
Bind Time	0.86s (± 0.58%)	0.87s (± 1.17%)	+0.00s (+ 0.46%)	0.85s	0.90s
Check Time	5.54s (± 0.73%)	5.55s (± 0.46%)	+0.01s (+ 0.16%)	5.48s	5.59s
Emit Time	6.21s (± 1.36%)	6.13s (± 1.42%)	-0.09s (- 1.38%)	5.92s	6.34s
Total Time	15.17s (± 0.51%)	15.09s (± 0.55%)	-0.07s (- 0.47%)	14.86s	15.31s
Monaco - node (v8.9.0, x64)
Memory used	355,579k (± 0.02%)	355,628k (± 0.01%)	+50k (+ 0.01%)	355,564k	355,690k
Parse Time	1.90s (± 0.44%)	1.89s (± 0.47%)	-0.01s (- 0.47%)	1.87s	1.91s
Bind Time	0.89s (± 0.82%)	0.90s (± 0.67%)	+0.00s (+ 0.34%)	0.88s	0.91s
Check Time	5.62s (± 0.55%)	5.60s (± 0.57%)	-0.01s (- 0.25%)	5.50s	5.67s
Emit Time	3.31s (± 1.50%)	3.31s (± 1.15%)	+0.00s (+ 0.12%)	3.19s	3.36s
Total Time	11.71s (± 0.55%)	11.70s (± 0.58%)	-0.01s (- 0.12%)	11.50s	11.80s
TFS - node (v8.9.0, x64)
Memory used	309,276k (± 0.01%)	309,310k (± 0.01%)	+34k (+ 0.01%)	309,218k	309,401k
Parse Time	1.56s (± 0.32%)	1.55s (± 0.54%)	-0.01s (- 0.45%)	1.54s	1.58s
Bind Time	0.68s (± 0.95%)	0.68s (± 0.86%)	-0.00s (- 0.15%)	0.66s	0.69s
Check Time	5.30s (± 0.59%)	5.29s (± 0.37%)	-0.00s (- 0.08%)	5.25s	5.33s
Emit Time	2.93s (± 0.80%)	2.93s (± 0.48%)	-0.00s (- 0.14%)	2.90s	2.95s
Total Time	10.46s (± 0.28%)	10.45s (± 0.21%)	-0.02s (- 0.14%)	10.38s	10.48s
material-ui - node (v8.9.0, x64)
Memory used	493,347k (± 0.02%)	493,314k (± 0.01%)	-33k (- 0.01%)	493,128k	493,459k
Parse Time	2.40s (± 0.36%)	2.40s (± 0.44%)	+0.00s (+ 0.04%)	2.38s	2.43s
Bind Time	0.81s (± 1.17%)	0.82s (± 0.71%)	+0.00s (+ 0.37%)	0.80s	0.83s
Check Time	17.92s (± 0.84%)	18.09s (± 0.92%)	+0.17s (+ 0.97%)	17.67s	18.42s
Emit Time	0.00s (± 0.00%)	0.00s (± 0.00%)	0.00s ( NaN%)	0.00s	0.00s
Total Time	21.14s (± 0.68%)	21.32s (± 0.77%)	+0.18s (+ 0.85%)	20.89s	21.65s
Angular - node (v8.9.0, x86)
Memory used	198,593k (± 0.02%)	198,625k (± 0.02%)	+32k (+ 0.02%)	198,529k	198,736k
Parse Time	2.48s (± 0.81%)	2.47s (± 0.43%)	-0.01s (- 0.44%)	2.44s	2.49s
Bind Time	1.00s (± 0.93%)	1.00s (± 1.15%)	+0.00s (+ 0.50%)	0.97s	1.03s
Check Time	4.99s (± 0.61%)	5.00s (± 0.43%)	+0.01s (+ 0.14%)	4.95s	5.05s
Emit Time	5.92s (± 0.90%)	5.93s (± 1.24%)	+0.01s (+ 0.17%)	5.80s	6.14s
Total Time	14.39s (± 0.56%)	14.40s (± 0.47%)	+0.01s (+ 0.08%)	14.23s	14.57s
Monaco - node (v8.9.0, x86)
Memory used	201,394k (± 0.01%)	201,381k (± 0.02%)	-13k (- 0.01%)	201,277k	201,437k
Parse Time	1.93s (± 0.81%)	1.93s (± 0.69%)	-0.00s (- 0.21%)	1.90s	1.96s
Bind Time	0.71s (± 0.91%)	0.71s (± 0.78%)	0.00s ( 0.00%)	0.70s	0.72s
Check Time	5.46s (± 1.24%)	5.50s (± 1.37%)	+0.04s (+ 0.79%)	5.38s	5.68s
Emit Time	3.03s (± 3.23%)	2.97s (± 3.51%)	-0.06s (- 1.91%)	2.65s	3.08s
Total Time	11.13s (± 0.64%)	11.10s (± 0.71%)	-0.02s (- 0.22%)	10.92s	11.30s
TFS - node (v8.9.0, x86)
Memory used	176,811k (± 0.02%)	176,806k (± 0.03%)	-5k (- 0.00%)	176,732k	176,961k
Parse Time	1.58s (± 0.84%)	1.58s (± 0.53%)	-0.00s (- 0.13%)	1.57s	1.60s
Bind Time	0.65s (± 1.23%)	0.64s (± 0.90%)	-0.01s (- 0.77%)	0.63s	0.66s
Check Time	4.79s (± 0.56%)	4.78s (± 0.65%)	-0.00s (- 0.10%)	4.73s	4.85s
Emit Time	2.80s (± 1.10%)	2.79s (± 1.14%)	-0.01s (- 0.36%)	2.73s	2.90s
Total Time	9.82s (± 0.40%)	9.80s (± 0.47%)	-0.02s (- 0.17%)	9.71s	9.88s
material-ui - node (v8.9.0, x86)
Memory used	277,775k (± 0.01%)	277,740k (± 0.02%)	-35k (- 0.01%)	277,637k	277,879k
Parse Time	2.46s (± 0.82%)	2.46s (± 0.54%)	-0.00s (- 0.04%)	2.43s	2.50s
Bind Time	0.71s (± 5.86%)	0.74s (± 7.55%)	+0.02s (+ 3.51%)	0.67s	0.87s
Check Time	16.38s (± 0.69%)	16.55s (± 0.74%)	+0.17s (+ 1.01%)	16.37s	16.92s
Emit Time	0.00s (± 0.00%)	0.00s (± 0.00%)	0.00s ( NaN%)	0.00s	0.00s
Total Time	19.55s (± 0.74%)	19.74s (± 0.69%)	+0.19s (+ 0.96%)	19.48s	20.07s

System

Machine Name	ts-ci-ubuntu
Platform	linux 4.4.0-166-generic
Architecture	x64
Available Memory	16 GB
Available Memory	1 GB
CPUs	4 × Intel(R) Core(TM) i7-4770 CPU @ 3.40GHz

Hosts

• node (v10.16.3, x64)
• node (v12.1.0, x64)
• node (v8.9.0, x64)
• node (v8.9.0, x86)

Scenarios

• Angular - node (v10.16.3, x64)
• Angular - node (v12.1.0, x64)
• Angular - node (v8.9.0, x64)
• Angular - node (v8.9.0, x86)
• Monaco - node (v10.16.3, x64)
• Monaco - node (v12.1.0, x64)
• Monaco - node (v8.9.0, x64)
• Monaco - node (v8.9.0, x86)
• TFS - node (v10.16.3, x64)
• TFS - node (v12.1.0, x64)
• TFS - node (v8.9.0, x64)
• TFS - node (v8.9.0, x86)
• material-ui - node (v10.16.3, x64)
• material-ui - node (v12.1.0, x64)
• material-ui - node (v8.9.0, x64)
• material-ui - node (v8.9.0, x86)

Benchmark	Name	Iterations
Current	40823	10
Baseline	master	10

[TypeScript Bot (typescript-bot)]

The user suite test run you requested has finished and failed. I've opened a PR with the baseline diff from master.

[Nathan Shively-Sanders (sandersn)]

Ron Buckton (@rbuckton) where did we land on this? I remember discussing something like this in the design meeting, but not whether we decided to go forward with it.

[Nathan Shively-Sanders (sandersn)]

Ron Buckton (@rbuckton) do you mind if I close this until we come up with a comprehensive reform of void? At least, my memory of our last discussion of this is that we're kind of stuck on this particular change. I might be mis-remembering, though.

[Nathan Shively-Sanders (sandersn)]

Closing this for now.