[Wesley Wigham (weswigham)]

…inference where all the signature type parameters have defaults

Fixes #38969

So, when I was looking into #38969 I was tempted to call it working as intended, as it's a logical fallout of current rules for inference and contextual typing; but that felt really unsatisfying, as we know that binding pattern shapes are rather poor inference targets. I went through a few iterations, but here have settled on the simple addition of a new heuristic for inference: If all type parameters the signature we're inferring to have defaults, then we disable the usage of binding patterns in contextual type lookup, which, in turn, allows us to fallback to using those defaults, over those binding pattern types.

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

Heya Wesley Wigham (@weswigham), I've started to run the parallelized Definitely Typed test suite on this PR at a42e1ae. You can monitor the build here.

Heya Wesley Wigham (@weswigham), I've started to run the perf test suite on this PR at a42e1ae. You can monitor the build here.

Update: The results are in!

Heya Wesley Wigham (@weswigham), I've started to run the parallelized community code test suite on this PR at a42e1ae. You can monitor the build here.

Heya Wesley Wigham (@weswigham), I've started to run the extended test suite on this PR at a42e1ae. You can monitor the build here.

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

User baselines are fine, as are rwc baselines. DT has one new failure, in react-router, which has a single test doing

const { id } = useParams();

useParams has a default on it's return type type parameter of {} (yes, we have a lint rule forbidding this, yes, they suppress that rule), so this new error seems reasonable to me (it's the expected fallout, at least). Simply removing the default can restore the old behavior, if it's desirable (which, to me, seems questionable, as it leaks anys into the program and the intent of the type would seem to be only allowing indexes to strings, but what do I know). You can actually get a type for the signature which works better (ie, doesn't produce anys), and is forward compatible with this change (albeit in a more complex way) using

export function useParams<Params extends { [K in keyof Params]?: string }>(): {[K in keyof Params]: Params[K] extends never ? string : Params[K]};

Wesley Wigham (@weswigham)
The results of the perf run you requested are in!

Here they are:

Comparison Report - master..39081

Metric	master	39081	Delta	Best	Worst
Angular - node (v10.16.3, x64)
Memory used	328,370k (± 0.02%)	328,057k (± 0.01%)	-313k (- 0.10%)	327,945k	328,161k
Parse Time	1.65s (± 0.45%)	1.65s (± 0.71%)	-0.00s (- 0.12%)	1.62s	1.67s
Bind Time	0.92s (± 1.10%)	0.91s (± 0.66%)	-0.01s (- 0.98%)	0.89s	0.92s
Check Time	4.87s (± 0.50%)	4.87s (± 0.48%)	+0.00s (+ 0.06%)	4.83s	4.93s
Emit Time	5.42s (± 0.31%)	5.42s (± 0.82%)	-0.00s (- 0.02%)	5.34s	5.53s
Total Time	12.85s (± 0.28%)	12.84s (± 0.40%)	-0.01s (- 0.08%)	12.75s	12.97s
Monaco - node (v10.16.3, x64)
Memory used	327,439k (± 0.02%)	327,431k (± 0.02%)	-9k (- 0.00%)	327,356k	327,560k
Parse Time	1.27s (± 0.91%)	1.27s (± 1.03%)	+0.00s (+ 0.08%)	1.25s	1.31s
Bind Time	0.80s (± 0.86%)	0.79s (± 0.60%)	-0.00s (- 0.38%)	0.78s	0.80s
Check Time	4.90s (± 0.61%)	4.91s (± 0.40%)	+0.01s (+ 0.29%)	4.86s	4.95s
Emit Time	2.96s (± 0.68%)	2.95s (± 0.81%)	-0.01s (- 0.20%)	2.91s	3.01s
Total Time	9.92s (± 0.52%)	9.93s (± 0.46%)	+0.01s (+ 0.09%)	9.84s	10.05s
TFS - node (v10.16.3, x64)
Memory used	292,600k (± 0.02%)	292,569k (± 0.02%)	-31k (- 0.01%)	292,408k	292,737k
Parse Time	0.96s (± 0.73%)	0.95s (± 0.38%)	-0.01s (- 0.52%)	0.95s	0.96s
Bind Time	0.77s (± 0.68%)	0.76s (± 0.48%)	-0.00s (- 0.65%)	0.76s	0.77s
Check Time	4.40s (± 0.28%)	4.40s (± 0.36%)	-0.00s (- 0.11%)	4.36s	4.44s
Emit Time	3.08s (± 0.78%)	3.09s (± 0.51%)	+0.01s (+ 0.16%)	3.06s	3.13s
Total Time	9.21s (± 0.36%)	9.20s (± 0.31%)	-0.01s (- 0.10%)	9.14s	9.27s
material-ui - node (v10.16.3, x64)
Memory used	450,097k (± 0.02%)	449,429k (± 0.01%)	-668k (- 0.15%)	449,370k	449,511k
Parse Time	1.79s (± 0.41%)	1.79s (± 0.46%)	-0.00s (- 0.22%)	1.77s	1.81s
Bind Time	0.71s (± 1.07%)	0.70s (± 0.47%)	-0.01s (- 0.85%)	0.69s	0.71s
Check Time	12.82s (± 0.77%)	12.86s (± 0.83%)	+0.04s (+ 0.30%)	12.69s	13.20s
Emit Time	0.00s (± 0.00%)	0.00s (± 0.00%)	0.00s ( NaN%)	0.00s	0.00s
Total Time	15.32s (± 0.65%)	15.35s (± 0.69%)	+0.03s (+ 0.18%)	15.17s	15.68s
Angular - node (v12.1.0, x64)
Memory used	303,940k (± 0.04%)	303,658k (± 0.03%)	-282k (- 0.09%)	303,424k	303,914k
Parse Time	1.61s (± 0.92%)	1.60s (± 0.50%)	-0.01s (- 0.62%)	1.58s	1.62s
Bind Time	0.89s (± 0.75%)	0.89s (± 0.69%)	-0.00s (- 0.11%)	0.88s	0.90s
Check Time	4.74s (± 0.44%)	4.74s (± 0.45%)	-0.00s (- 0.04%)	4.67s	4.78s
Emit Time	5.59s (± 1.26%)	5.57s (± 0.75%)	-0.02s (- 0.27%)	5.49s	5.67s
Total Time	12.83s (± 0.64%)	12.79s (± 0.39%)	-0.03s (- 0.27%)	12.70s	12.91s
Monaco - node (v12.1.0, x64)
Memory used	307,358k (± 0.02%)	307,352k (± 0.01%)	-6k (- 0.00%)	307,261k	307,430k
Parse Time	1.23s (± 0.49%)	1.22s (± 0.51%)	-0.01s (- 0.49%)	1.20s	1.23s
Bind Time	0.77s (± 0.61%)	0.77s (± 0.90%)	-0.00s (- 0.65%)	0.75s	0.78s
Check Time	4.70s (± 0.53%)	4.70s (± 0.53%)	-0.00s (- 0.02%)	4.65s	4.77s
Emit Time	2.99s (± 0.74%)	3.00s (± 0.84%)	+0.01s (+ 0.37%)	2.94s	3.05s
Total Time	9.68s (± 0.34%)	9.69s (± 0.49%)	+0.01s (+ 0.06%)	9.59s	9.83s
TFS - node (v12.1.0, x64)
Memory used	274,825k (± 0.02%)	274,895k (± 0.02%)	+70k (+ 0.03%)	274,819k	275,042k
Parse Time	0.93s (± 0.53%)	0.93s (± 0.39%)	-0.01s (- 0.86%)	0.92s	0.93s
Bind Time	0.75s (± 1.27%)	0.74s (± 1.00%)	-0.00s (- 0.40%)	0.73s	0.76s
Check Time	4.31s (± 0.33%)	4.30s (± 0.28%)	-0.01s (- 0.21%)	4.26s	4.32s
Emit Time	3.11s (± 0.58%)	3.13s (± 0.64%)	+0.01s (+ 0.42%)	3.10s	3.19s
Total Time	9.10s (± 0.22%)	9.10s (± 0.28%)	-0.01s (- 0.07%)	9.05s	9.16s
material-ui - node (v12.1.0, x64)
Memory used	427,408k (± 0.05%)	426,730k (± 0.05%)	-678k (- 0.16%)	425,822k	426,927k
Parse Time	1.77s (± 0.53%)	1.76s (± 0.42%)	-0.01s (- 0.56%)	1.75s	1.79s
Bind Time	0.65s (± 1.26%)	0.65s (± 0.51%)	+0.00s (+ 0.46%)	0.64s	0.66s
Check Time	11.48s (± 0.77%)	11.46s (± 0.66%)	-0.02s (- 0.21%)	11.36s	11.68s
Emit Time	0.00s (± 0.00%)	0.00s (± 0.00%)	0.00s ( NaN%)	0.00s	0.00s
Total Time	13.90s (± 0.68%)	13.87s (± 0.55%)	-0.03s (- 0.23%)	13.75s	14.10s
Angular - node (v8.9.0, x64)
Memory used	323,361k (± 0.02%)	323,016k (± 0.02%)	-346k (- 0.11%)	322,869k	323,205k
Parse Time	2.12s (± 0.29%)	2.12s (± 0.52%)	+0.00s (+ 0.14%)	2.10s	2.15s
Bind Time	0.94s (± 0.88%)	0.94s (± 0.90%)	-0.00s (- 0.42%)	0.93s	0.97s
Check Time	5.53s (± 1.78%)	5.55s (± 1.12%)	+0.03s (+ 0.52%)	5.31s	5.61s
Emit Time	6.37s (± 2.48%)	6.31s (± 0.88%)	-0.06s (- 0.88%)	6.16s	6.43s
Total Time	14.96s (± 0.59%)	14.93s (± 0.43%)	-0.03s (- 0.20%)	14.78s	15.09s
Monaco - node (v8.9.0, x64)
Memory used	326,072k (± 0.01%)	326,091k (± 0.02%)	+19k (+ 0.01%)	325,973k	326,167k
Parse Time	1.55s (± 0.30%)	1.54s (± 0.32%)	-0.01s (- 0.32%)	1.54s	1.56s
Bind Time	0.92s (± 1.11%)	0.92s (± 1.27%)	0.00s ( 0.00%)	0.91s	0.96s
Check Time	5.47s (± 0.52%)	5.48s (± 0.59%)	+0.01s (+ 0.18%)	5.41s	5.56s
Emit Time	3.48s (± 0.80%)	3.50s (± 0.74%)	+0.01s (+ 0.43%)	3.45s	3.55s
Total Time	11.42s (± 0.34%)	11.44s (± 0.44%)	+0.02s (+ 0.18%)	11.34s	11.55s
TFS - node (v8.9.0, x64)
Memory used	292,236k (± 0.01%)	292,214k (± 0.02%)	-22k (- 0.01%)	292,099k	292,390k
Parse Time	1.26s (± 0.47%)	1.25s (± 0.39%)	-0.00s (- 0.16%)	1.25s	1.27s
Bind Time	0.76s (± 0.99%)	0.76s (± 0.96%)	-0.01s (- 0.79%)	0.74s	0.77s
Check Time	5.03s (± 2.18%)	5.04s (± 1.75%)	+0.01s (+ 0.22%)	4.89s	5.21s
Emit Time	3.26s (± 2.69%)	3.28s (± 3.14%)	+0.02s (+ 0.71%)	3.10s	3.49s
Total Time	10.31s (± 0.42%)	10.34s (± 0.38%)	+0.02s (+ 0.24%)	10.29s	10.46s
material-ui - node (v8.9.0, x64)
Memory used	453,098k (± 0.01%)	452,492k (± 0.01%)	-606k (- 0.13%)	452,350k	452,587k
Parse Time	2.13s (± 0.58%)	2.12s (± 0.47%)	-0.01s (- 0.42%)	2.10s	2.15s
Bind Time	0.82s (± 0.85%)	0.82s (± 1.15%)	+0.00s (+ 0.24%)	0.81s	0.85s
Check Time	16.89s (± 0.68%)	16.87s (± 0.57%)	-0.01s (- 0.09%)	16.64s	17.03s
Emit Time	0.00s (± 0.00%)	0.00s (± 0.00%)	0.00s ( NaN%)	0.00s	0.00s
Total Time	19.84s (± 0.62%)	19.82s (± 0.52%)	-0.02s (- 0.13%)	19.58s	20.03s
Angular - node (v8.9.0, x86)
Memory used	186,352k (± 0.03%)	186,186k (± 0.03%)	-166k (- 0.09%)	186,055k	186,289k
Parse Time	2.07s (± 0.76%)	2.05s (± 0.70%)	-0.02s (- 0.92%)	2.03s	2.10s
Bind Time	1.09s (± 0.62%)	1.08s (± 0.45%)	-0.01s (- 0.91%)	1.07s	1.09s
Check Time	5.11s (± 0.54%)	5.09s (± 0.48%)	-0.02s (- 0.45%)	5.03s	5.14s
Emit Time	6.15s (± 0.84%)	6.13s (± 0.86%)	-0.01s (- 0.23%)	6.04s	6.26s
Total Time	14.42s (± 0.45%)	14.36s (± 0.44%)	-0.06s (- 0.43%)	14.17s	14.45s
Monaco - node (v8.9.0, x86)
Memory used	185,907k (± 0.02%)	185,884k (± 0.02%)	-24k (- 0.01%)	185,823k	185,954k
Parse Time	1.61s (± 0.85%)	1.60s (± 0.58%)	-0.01s (- 0.50%)	1.59s	1.63s
Bind Time	0.78s (± 0.87%)	0.78s (± 0.93%)	-0.00s (- 0.26%)	0.77s	0.80s
Check Time	5.53s (± 0.47%)	5.50s (± 0.46%)	-0.03s (- 0.51%)	5.45s	5.57s
Emit Time	2.90s (± 0.73%)	2.88s (± 0.55%)	-0.02s (- 0.69%)	2.84s	2.91s
Total Time	10.82s (± 0.44%)	10.76s (± 0.28%)	-0.06s (- 0.51%)	10.70s	10.84s
TFS - node (v8.9.0, x86)
Memory used	167,519k (± 0.03%)	167,551k (± 0.02%)	+32k (+ 0.02%)	167,487k	167,630k
Parse Time	1.30s (± 0.54%)	1.30s (± 0.57%)	+0.00s (+ 0.08%)	1.29s	1.32s
Bind Time	0.73s (± 0.82%)	0.73s (± 1.21%)	+0.00s (+ 0.14%)	0.71s	0.75s
Check Time	4.72s (± 0.64%)	4.70s (± 0.72%)	-0.02s (- 0.42%)	4.64s	4.78s
Emit Time	2.98s (± 0.89%)	3.03s (± 2.23%)	+0.05s (+ 1.68%)	2.96s	3.25s
Total Time	9.73s (± 0.41%)	9.76s (± 0.82%)	+0.03s (+ 0.32%)	9.64s	9.97s
material-ui - node (v8.9.0, x86)
Memory used	256,773k (± 0.01%)	256,437k (± 0.01%)	-336k (- 0.13%)	256,372k	256,500k
Parse Time	2.19s (± 0.43%)	2.19s (± 0.51%)	+0.00s (+ 0.05%)	2.17s	2.22s
Bind Time	0.70s (± 1.00%)	0.70s (± 1.32%)	+0.00s (+ 0.43%)	0.68s	0.73s
Check Time	15.56s (± 0.88%)	15.57s (± 0.61%)	+0.01s (+ 0.04%)	15.37s	15.90s
Emit Time	0.00s (± 0.00%)	0.00s (± 0.00%)	0.00s ( NaN%)	0.00s	0.00s
Total Time	18.45s (± 0.74%)	18.46s (± 0.55%)	+0.01s (+ 0.05%)	18.22s	18.79s

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	39081	10
Baseline	master	10

And perf is fine, not that I expected a diff.

This seems totally reasonable to me. I’m a bit surprised we ever inferred from binding patterns in the first place.

Anders Hejlsberg (@ahejlsberg) wanna take a look at this? I know we've discussed how we handle binding pattern contextual types (and how odd they are) before.

BTW, looks like this would fix #32003, yes?

easy way to find out: TypeScript Bot (@typescript-bot) pack this

Heya Wesley Wigham (@weswigham), I've started to run the tarball bundle task on this PR at a42e1ae. You can monitor the build here.

sigh man that merge commit got deleted the moment I deleted the branch. Anyways, from local testing: Yep, this fixes #32003. So long as the type parameter has a default, we'll prefer it in return type inference over a binding pattern.