Allow narrowing for any left-hand in operand

[gabritto]

Extends a more restrictive fix already in place for #42639.

Previously, narrowing of an in expression happens if the expression satisfy two constraints:

• In the binder: isNarrowableInOperands is a syntactic constraint that allows narrowing of an expression if the right in operand is a narrowing expression, and the left in operand is a string literal (e.g. if ('prop' in c) { ... }).
• In the checker: narrowBinaryExpression only calls narrowByInKeyword if the left in operand's type is a string literal type.

An already merged PR (#44893) relaxed the binder constraint to allow narrowing in cases the left in operand is an identifier, to address scenarios such as:

type A = { a: number };
type B = { b: string };
declare c: A | B;

if ("a" in c) {
    c; // c has type `A` here
}

const a = "a";
if (a in c) {
    c; // c should also have type `A` here; previously it had type `A | B`
}

This PR further relaxes the constraint in the binder for narrowing in expressions, by no longer placing any syntactic constraint on the left in operand expression. This means that an in expression is considered narrowable by the binder if the right expression is narrowing:

type A = { a: number };
type B = { b: string };
declare c: A | B;

if ("a" in c) {
    c; // c has type `A` here
}

const a = "a";
if (a in c) {
    c; // c has type `A` here
}

let stringA: string = "a";
if ((stringA as "a") in c) {
    c; // c now has type `A` here too
}

if ((stringA as ("a" | "b")) in c) {
    c; // c has type `A | B`; not narrowed because the left expression has type `"a" | "b"`, i.e. not a string literal type
}

Concerns:
From what I can tell, a possible concern would be performance, since this PR makes it so the checker attempts to narrow more types of in expressions, but the impact may be negligible.
A caveat here (brought up by @andrewbranch) regarding perf tests is that, since the checker currently doesn't narrow those kinds of expressions, real world code is unlikely to have those kinds of expressions.

[typescript-bot]

This PR doesn't have any linked issues. Please open an issue that references this PR. From there we can discuss and prioritise.

[typescript-bot]

This PR doesn't have any linked issues. Please open an issue that references this PR. From there we can discuss and prioritise.

[andrewbranch]

@typescript-bot perf test this
@typescript-bot test this
@typescript-bot user test this

[typescript-bot]

Heya @andrewbranch, I've started to run the perf test suite on this PR at b4f2f8c. You can monitor the build here.

Update: The results are in!

[typescript-bot]

Heya @andrewbranch, I've started to run the parallelized community code test suite on this PR at b4f2f8c. You can monitor the build here.

[typescript-bot]

Heya @andrewbranch, I've started to run the extended test suite on this PR at b4f2f8c. You can monitor the build here.

[andrewbranch]

@typescript-bot user test this inline

[typescript-bot]

Heya @andrewbranch, I've started to run the inline community code test suite on this PR at b4f2f8c. You can monitor the build here.

Update: The results are in!

[typescript-bot]

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

Here they are:

Comparison Report - main..45152

Metric	main	45152	Delta	Best	Worst
Angular - node (v10.16.3, x64)
Memory used	348,498k (± 0.03%)	348,551k (± 0.02%)	+53k (+ 0.02%)	348,389k	348,681k
Parse Time	1.81s (± 0.57%)	1.80s (± 0.26%)	-0.01s (- 0.66%)	1.79s	1.81s
Bind Time	0.84s (± 0.90%)	0.84s (± 0.56%)	-0.00s (- 0.12%)	0.83s	0.85s
Check Time	5.37s (± 0.72%)	5.36s (± 0.53%)	-0.01s (- 0.24%)	5.30s	5.42s
Emit Time	5.85s (± 0.54%)	5.80s (± 0.68%)	-0.05s (- 0.89%)	5.73s	5.93s
Total Time	13.88s (± 0.47%)	13.80s (± 0.49%)	-0.08s (- 0.58%)	13.68s	14.01s
Compiler-Unions - node (v10.16.3, x64)
Memory used	203,376k (± 0.02%)	203,369k (± 0.03%)	-8k (- 0.00%)	203,194k	203,456k
Parse Time	0.78s (± 0.95%)	0.78s (± 0.60%)	-0.00s (- 0.38%)	0.77s	0.79s
Bind Time	0.53s (± 1.27%)	0.53s (± 1.13%)	-0.00s (- 0.19%)	0.51s	0.54s
Check Time	7.83s (± 0.69%)	7.81s (± 0.77%)	-0.02s (- 0.24%)	7.68s	7.99s
Emit Time	2.43s (± 0.51%)	2.43s (± 0.63%)	-0.00s (- 0.04%)	2.39s	2.46s
Total Time	11.56s (± 0.51%)	11.54s (± 0.50%)	-0.02s (- 0.21%)	11.44s	11.74s
Monaco - node (v10.16.3, x64)
Memory used	340,535k (± 0.03%)	340,559k (± 0.01%)	+24k (+ 0.01%)	340,500k	340,636k
Parse Time	1.47s (± 1.01%)	1.47s (± 0.40%)	-0.00s (- 0.20%)	1.46s	1.48s
Bind Time	0.75s (± 0.97%)	0.74s (± 0.65%)	-0.01s (- 1.47%)	0.73s	0.75s
Check Time	5.38s (± 0.74%)	5.37s (± 0.48%)	-0.02s (- 0.37%)	5.30s	5.41s
Emit Time	3.16s (± 0.86%)	3.16s (± 0.78%)	-0.00s (- 0.09%)	3.12s	3.23s
Total Time	10.76s (± 0.37%)	10.73s (± 0.43%)	-0.04s (- 0.33%)	10.62s	10.83s
TFS - node (v10.16.3, x64)
Memory used	304,022k (± 0.02%)	303,969k (± 0.02%)	-52k (- 0.02%)	303,838k	304,132k
Parse Time	1.19s (± 0.52%)	1.19s (± 0.81%)	+0.00s (+ 0.17%)	1.17s	1.21s
Bind Time	0.71s (± 0.70%)	0.71s (± 0.78%)	-0.00s (- 0.42%)	0.70s	0.72s
Check Time	4.90s (± 0.40%)	4.87s (± 0.51%)	-0.03s (- 0.63%)	4.81s	4.92s
Emit Time	3.32s (± 0.79%)	3.30s (± 0.73%)	-0.03s (- 0.75%)	3.23s	3.34s
Total Time	10.12s (± 0.34%)	10.07s (± 0.43%)	-0.05s (- 0.53%)	9.94s	10.13s
material-ui - node (v10.16.3, x64)
Memory used	469,690k (± 0.01%)	469,634k (± 0.02%)	-56k (- 0.01%)	469,413k	469,773k
Parse Time	1.74s (± 0.57%)	1.74s (± 0.61%)	-0.01s (- 0.29%)	1.71s	1.76s
Bind Time	0.66s (± 0.79%)	0.66s (± 1.59%)	-0.00s (- 0.15%)	0.63s	0.68s
Check Time	14.22s (± 0.78%)	14.14s (± 0.38%)	-0.08s (- 0.56%)	14.03s	14.25s
Emit Time	0.00s (± 0.00%)	0.00s (± 0.00%)	0.00s ( NaN%)	0.00s	0.00s
Total Time	16.62s (± 0.69%)	16.54s (± 0.35%)	-0.09s (- 0.51%)	16.42s	16.67s
Angular - node (v12.1.0, x64)
Memory used	326,625k (± 0.02%)	326,506k (± 0.09%)	-118k (- 0.04%)	325,358k	326,811k
Parse Time	1.80s (± 0.66%)	1.78s (± 0.73%)	-0.01s (- 0.78%)	1.75s	1.81s
Bind Time	0.83s (± 1.30%)	0.82s (± 1.00%)	-0.01s (- 0.60%)	0.81s	0.85s
Check Time	5.19s (± 0.58%)	5.19s (± 0.47%)	-0.01s (- 0.13%)	5.15s	5.27s
Emit Time	6.07s (± 0.41%)	6.08s (± 0.69%)	+0.01s (+ 0.25%)	5.98s	6.18s
Total Time	13.89s (± 0.33%)	13.88s (± 0.39%)	-0.02s (- 0.12%)	13.73s	13.98s
Compiler-Unions - node (v12.1.0, x64)
Memory used	190,734k (± 0.10%)	190,850k (± 0.03%)	+115k (+ 0.06%)	190,734k	190,931k
Parse Time	0.78s (± 0.83%)	0.77s (± 0.52%)	-0.01s (- 0.90%)	0.76s	0.78s
Bind Time	0.53s (± 0.75%)	0.53s (± 1.09%)	+0.00s (+ 0.38%)	0.52s	0.55s
Check Time	7.33s (± 0.47%)	7.28s (± 0.51%)	-0.04s (- 0.55%)	7.18s	7.35s
Emit Time	2.45s (± 1.02%)	2.44s (± 0.63%)	-0.01s (- 0.57%)	2.40s	2.48s
Total Time	11.09s (± 0.42%)	11.03s (± 0.43%)	-0.06s (- 0.53%)	10.91s	11.13s
Monaco - node (v12.1.0, x64)
Memory used	323,695k (± 0.01%)	323,714k (± 0.02%)	+19k (+ 0.01%)	323,555k	323,834k
Parse Time	1.44s (± 0.70%)	1.43s (± 0.77%)	-0.00s (- 0.21%)	1.41s	1.46s
Bind Time	0.73s (± 0.82%)	0.72s (± 0.66%)	-0.00s (- 0.41%)	0.71s	0.73s
Check Time	5.26s (± 0.54%)	5.25s (± 0.59%)	-0.00s (- 0.06%)	5.21s	5.33s
Emit Time	3.20s (± 0.49%)	3.19s (± 0.82%)	-0.01s (- 0.25%)	3.14s	3.27s
Total Time	10.62s (± 0.34%)	10.60s (± 0.40%)	-0.02s (- 0.17%)	10.50s	10.68s
TFS - node (v12.1.0, x64)
Memory used	288,644k (± 0.03%)	288,668k (± 0.02%)	+24k (+ 0.01%)	288,536k	288,812k
Parse Time	1.21s (± 0.49%)	1.21s (± 0.79%)	-0.01s (- 0.66%)	1.18s	1.22s
Bind Time	0.70s (± 1.27%)	0.70s (± 0.85%)	-0.01s (- 1.28%)	0.68s	0.71s
Check Time	4.84s (± 0.44%)	4.84s (± 0.53%)	-0.00s (- 0.06%)	4.79s	4.91s
Emit Time	3.38s (± 1.07%)	3.36s (± 1.00%)	-0.02s (- 0.53%)	3.30s	3.47s
Total Time	10.13s (± 0.40%)	10.09s (± 0.53%)	-0.04s (- 0.38%)	9.99s	10.27s
material-ui - node (v12.1.0, x64)
Memory used	448,401k (± 0.01%)	448,447k (± 0.01%)	+46k (+ 0.01%)	448,329k	448,559k
Parse Time	1.72s (± 0.52%)	1.72s (± 0.82%)	-0.00s (- 0.23%)	1.69s	1.76s
Bind Time	0.66s (± 0.57%)	0.65s (± 1.30%)	-0.00s (- 0.61%)	0.63s	0.67s
Check Time	12.86s (± 0.53%)	12.72s (± 0.32%)	-0.14s (- 1.07%)	12.64s	12.81s
Emit Time	0.00s (± 0.00%)	0.00s (± 0.00%)	0.00s ( NaN%)	0.00s	0.00s
Total Time	15.24s (± 0.48%)	15.09s (± 0.28%)	-0.15s (- 0.98%)	15.00s	15.18s
Angular - node (v14.15.1, x64)
Memory used	325,716k (± 0.01%)	325,734k (± 0.01%)	+19k (+ 0.01%)	325,644k	325,776k
Parse Time	1.82s (± 0.34%)	1.81s (± 0.90%)	-0.01s (- 0.27%)	1.79s	1.87s
Bind Time	0.88s (± 0.96%)	0.86s (± 0.42%)	-0.02s (- 1.93%)	0.86s	0.87s
Check Time	5.27s (± 0.43%)	5.23s (± 0.39%)	-0.04s (- 0.78%)	5.18s	5.26s
Emit Time	6.21s (± 1.05%)	6.16s (± 0.75%)	-0.05s (- 0.76%)	6.08s	6.28s
Total Time	14.17s (± 0.53%)	14.07s (± 0.40%)	-0.10s (- 0.73%)	13.97s	14.19s
Compiler-Unions - node (v14.15.1, x64)
Memory used	191,124k (± 0.63%)	191,118k (± 0.63%)	-6k (- 0.00%)	189,448k	192,776k
Parse Time	0.81s (± 0.83%)	0.80s (± 1.11%)	-0.00s (- 0.37%)	0.79s	0.83s
Bind Time	0.56s (± 0.65%)	0.56s (± 0.72%)	-0.00s (- 0.89%)	0.55s	0.57s
Check Time	7.50s (± 0.56%)	7.45s (± 0.58%)	-0.05s (- 0.69%)	7.35s	7.56s
Emit Time	2.42s (± 0.73%)	2.42s (± 0.66%)	+0.00s (+ 0.04%)	2.38s	2.46s
Total Time	11.30s (± 0.47%)	11.23s (± 0.50%)	-0.06s (- 0.55%)	11.10s	11.36s
Monaco - node (v14.15.1, x64)
Memory used	322,488k (± 0.01%)	322,496k (± 0.01%)	+8k (+ 0.00%)	322,452k	322,540k
Parse Time	1.50s (± 0.51%)	1.48s (± 0.98%)	-0.01s (- 0.80%)	1.46s	1.53s
Bind Time	0.76s (± 0.59%)	0.76s (± 0.81%)	+0.00s (+ 0.40%)	0.75s	0.77s
Check Time	5.22s (± 0.50%)	5.17s (± 0.47%)	-0.05s (- 1.01%)	5.13s	5.25s
Emit Time	3.24s (± 0.83%)	3.21s (± 0.52%)	-0.03s (- 1.05%)	3.17s	3.24s
Total Time	10.71s (± 0.45%)	10.62s (± 0.44%)	-0.10s (- 0.89%)	10.56s	10.74s
TFS - node (v14.15.1, x64)
Memory used	287,658k (± 0.01%)	287,656k (± 0.01%)	-1k (- 0.00%)	287,615k	287,716k
Parse Time	1.23s (± 1.43%)	1.26s (± 1.33%)	+0.02s (+ 2.03%)	1.22s	1.30s
Bind Time	0.75s (± 3.33%)	0.72s (± 0.92%)	🟩-0.03s (- 3.61%)	0.71s	0.74s
Check Time	4.82s (± 0.43%)	4.82s (± 0.54%)	+0.00s (+ 0.02%)	4.74s	4.87s
Emit Time	3.45s (± 0.74%)	3.46s (± 0.95%)	+0.02s (+ 0.55%)	3.40s	3.58s
Total Time	10.24s (± 0.36%)	10.26s (± 0.46%)	+0.02s (+ 0.20%)	10.19s	10.40s
material-ui - node (v14.15.1, x64)
Memory used	446,859k (± 0.00%)	446,855k (± 0.00%)	-4k (- 0.00%)	446,802k	446,894k
Parse Time	1.76s (± 0.46%)	1.76s (± 0.43%)	-0.01s (- 0.40%)	1.74s	1.77s
Bind Time	0.69s (± 0.68%)	0.69s (± 1.06%)	-0.00s (- 0.29%)	0.68s	0.71s
Check Time	13.00s (± 0.88%)	12.86s (± 0.45%)	-0.14s (- 1.06%)	12.72s	13.01s
Emit Time	0.00s (± 0.00%)	0.00s (± 0.00%)	0.00s ( NaN%)	0.00s	0.00s
Total Time	15.45s (± 0.76%)	15.30s (± 0.41%)	-0.14s (- 0.93%)	15.16s	15.46s

System

Machine Name	ts-ci-ubuntu
Platform	linux 4.4.0-206-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 (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	45152	10
Baseline	main	10

Developer Information:

Download Benchmark

[typescript-bot]

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

[typescript-bot]

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

Here they are:

Comparison Report - main..refs/pull/45152/merge

[ahejlsberg]

Approved with the suggested change.

[DanielRosenwasser]

A while back we put in place a restriction to ensure that assertion functions had to be fully annotated so that they couldn't trigger further CFA computation when trying to resolve them (#33622).

It's been a while, so @ahejlsberg do you have an example of when this could happen? Just want to make sure there's nothing we're missing here.

[DanielRosenwasser]

Thinking about it some more, I think this is probably fine.