more precise type facts for intersection

[Gabriela Araujo Britto (gabritto)]

Fixes#45801

Brief background

When narrowing a type, we rely on TypeFacts flags that tell us what narrowing facts could be true for a value of a given type. The flags cover the possible results of narrowing using typeof (e.g. TypeFacts.TypeofEQString), comparsions to null or undefined (e.g. TypeFacts.UndefinedOrNull means if (v === null || v === undefined) could be true), or if the value is truthy or falsy (e.g. TypeFacts.Truthy means if (v) { ... } could be true).
To compute the type facts for a type T, we call getTypeFacts(T).

The issue

Up until v4.2, when computing type facts for an intersection type, we ored the facts of each of the intersection type's component type. e.g. getTypeFacts(A & B) = getTypeFacts(A) | getTypeFacts(B).
Starting at v4.3, this changed to an and of the facts of each intersection type's component type, e.g. getTypeFacts(A & B) = getTypeFacts(A) & getTypeFacts(B), to fix cases like the following:

functionf3<T>(x: T&string|T&number){if(typeofx==="string"){x;// Should narrow to T & string// <= 4.2: x: T & string | T & number}else{x;// Should narrow to T & number// <= 4.2: x: T & string | T & number}}

If we have T & number, we know the value can only be of type number (or null or undefined, in non-strict), never of type string. However, we don't know anything about T, so when computing type facts for T, we think it can be anything at all (including of type string). If we or the type facts for T and number, then, we get that T & number could be string. If we and the type facts, we know T & number can't be of type string, because number can't be of type string.

However, in some cases we don't want an and of the type facts. Consider the example from issue #45801:

typeMeta={foo: string}interfaceF{(): string}constx=(a: (F&Meta)|string)=>{if(typeofa==="function"){// ts.version >= 4.3.5: never -- unexpected// ts.version <= 4.2.3: F & Meta -- expecteda;}else{// ts.version >= 4.3.5: string -- expected// ts.version <= 4.2.3: string | (F & Meta) -- unexpecteda;}}

For type F & Meta, we know values of F have to be functions, since F has a call signature declared. But type Meta doesn't, it is a regular object. If we and those facts, we conclude F & Meta cannot be a function, because we don't think values of Meta could be functions (no call signature). So in this case, we probably want to or the type facts.

(Note: We could include TypeFacts.TypeofEQFunction in the flags returned for object types such as Meta above, and keep using and for computing type facts of intersection types. I think we don't want to do that, since we explicitly make that distinction in getTypeFacts's code and it generally seems a useful distinction.)

The possible fix

Considering both examples above, it seems we sometimes know a fact will always be true (i.e. true for all values of a type), e.g. values of type T & number can't be strings (if (typeof v === 'string') can't be true). This contrasts with the other uses of type facts, which are facts that can be true for values of type T, but are not necessarily always true/true for all values.
So that's why sometimes we want to use an and to compute facts of intersection types, and sometimes we want to use an or.

tl;dr

This PR changes the way we compute type facts of intersection types. For each component type, in addition to computing its type facts, we also compute which facts are always true (true for all values of that type) and which are always false.
We then or the regular type facts of the component types, and we also or the always false facts. We then exclude the facts that are always false from the regular facts.
So, in cases like T & number, even though when we or the components' type facts, we include a flag such as TypeFacts.TypeofEQString (because that's one of the flags for T), we will delete it later because TypeFacts.TypeofEQString is always false for type number.

Questions I had

• When is TypeFacts.TypeofEQHostObject always false? It seems typeof v === "xxx" ("xxx" being something other than the usual strings returned by typeof) can only be true if v is a host object (and hosts return a custom typeof for those), or if we don't yet recognize the "xxx" in question (e.g. if there's ever a new Fraction type and typeof v === "fraction"). So it should always be false for known primitives at least.
• Should we care about contradictory types (e.g. string & number) in getTypeFacts or getAlwaysFalseTypeFacts? I'm assuming we shouldn't, because existing code for getTypeFacts doesn't address this, and this looks like something getIntersectionType takes care of.

[Andrew Branch (andrewbranch)]

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

[TypeScript Bot (typescript-bot)]

Heya Andrew Branch (@andrewbranch), I've started to run the extended test suite on this PR at 2489916. You can monitor the build here.

[TypeScript Bot (typescript-bot)]

Heya Andrew Branch (@andrewbranch), I've started to run the perf test suite on this PR at 2489916. You can monitor the build here.

Update: The results are in!

[TypeScript Bot (typescript-bot)]

Heya Andrew Branch (@andrewbranch), I've started to run the parallelized Definitely Typed test suite on this PR at 2489916. You can monitor the build here.

[TypeScript Bot (typescript-bot)]

Heya Andrew Branch (@andrewbranch), I've started to run the inline community code test suite on this PR at 2489916. You can monitor the build here.

Update: The results are in!

[TypeScript Bot (typescript-bot)]

Andrew Branch (@andrewbranch)
Great news! no new errors were found between main..refs/pull/47282/merge

[TypeScript Bot (typescript-bot)]

Andrew Branch (@andrewbranch)
The results of the perf run you requested are in!

Here they are:

Comparison Report - main..47282

Metric	main	47282	Delta	Best	Worst
Angular - node (v10.16.3, x64)
Memory used	355,048k (± 0.02%)	355,060k (± 0.03%)	+12k (+ 0.00%)	354,804k	355,339k
Parse Time	1.95s (± 0.61%)	1.95s (± 0.38%)	-0.00s (- 0.10%)	1.93s	1.96s
Bind Time	0.84s (± 0.73%)	0.84s (± 0.35%)	-0.00s (- 0.36%)	0.83s	0.84s
Check Time	5.55s (± 0.37%)	5.54s (± 0.37%)	-0.02s (- 0.34%)	5.48s	5.58s
Emit Time	5.90s (± 0.70%)	5.90s (± 0.62%)	-0.00s (- 0.07%)	5.85s	6.01s
Total Time	14.25s (± 0.36%)	14.22s (± 0.39%)	-0.03s (- 0.19%)	14.11s	14.39s
Compiler-Unions - node (v10.16.3, x64)
Memory used	204,146k (± 0.02%)	204,305k (± 0.03%)	+160k (+ 0.08%)	204,221k	204,494k
Parse Time	0.79s (± 0.85%)	0.79s (± 0.78%)	+0.00s (+ 0.51%)	0.78s	0.80s
Bind Time	0.52s (± 1.25%)	0.52s (± 1.49%)	+0.00s (+ 0.58%)	0.51s	0.54s
Check Time	7.87s (± 0.53%)	7.89s (± 0.45%)	+0.02s (+ 0.23%)	7.82s	8.01s
Emit Time	2.47s (± 0.69%)	2.48s (± 0.60%)	+0.01s (+ 0.53%)	2.45s	2.51s
Total Time	11.64s (± 0.39%)	11.68s (± 0.36%)	+0.04s (+ 0.36%)	11.58s	11.82s
Monaco - node (v10.16.3, x64)
Memory used	342,515k (± 0.02%)	342,595k (± 0.02%)	+80k (+ 0.02%)	342,486k	342,729k
Parse Time	1.48s (± 0.42%)	1.48s (± 0.55%)	+0.00s (+ 0.07%)	1.46s	1.50s
Bind Time	0.75s (± 0.78%)	0.75s (± 0.80%)	-0.00s (- 0.13%)	0.74s	0.76s
Check Time	5.50s (± 0.51%)	5.53s (± 0.49%)	+0.03s (+ 0.45%)	5.45s	5.58s
Emit Time	3.22s (± 1.31%)	3.22s (± 0.79%)	0.00s ( 0.00%)	3.18s	3.30s
Total Time	10.95s (± 0.39%)	10.98s (± 0.25%)	+0.02s (+ 0.22%)	10.90s	11.02s
TFS - node (v10.16.3, x64)
Memory used	305,631k (± 0.01%)	305,632k (± 0.02%)	+1k (+ 0.00%)	305,431k	305,751k
Parse Time	1.20s (± 0.57%)	1.19s (± 0.50%)	-0.00s (- 0.08%)	1.18s	1.21s
Bind Time	0.71s (± 0.84%)	0.71s (± 0.66%)	+0.00s (+ 0.57%)	0.70s	0.72s
Check Time	5.03s (± 0.53%)	5.06s (± 0.47%)	+0.02s (+ 0.48%)	4.99s	5.11s
Emit Time	3.34s (± 1.57%)	3.40s (± 1.79%)	+0.06s (+ 1.71%)	3.31s	3.58s
Total Time	10.27s (± 0.64%)	10.36s (± 0.77%)	+0.08s (+ 0.82%)	10.20s	10.60s
material-ui - node (v10.16.3, x64)
Memory used	471,429k (± 0.02%)	471,484k (± 0.01%)	+55k (+ 0.01%)	471,340k	471,632k
Parse Time	1.77s (± 0.43%)	1.77s (± 0.37%)	-0.00s (- 0.17%)	1.76s	1.79s
Bind Time	0.66s (± 0.79%)	0.66s (± 0.88%)	-0.00s (- 0.30%)	0.65s	0.67s
Check Time	14.22s (± 0.57%)	14.24s (± 0.61%)	+0.02s (+ 0.12%)	14.08s	14.48s
Emit Time	0.00s (± 0.00%)	0.00s (± 0.00%)	0.00s ( NaN%)	0.00s	0.00s
Total Time	16.65s (± 0.51%)	16.67s (± 0.55%)	+0.01s (+ 0.09%)	16.49s	16.93s
xstate - node (v10.16.3, x64)
Memory used	569,251k (± 0.02%)	572,922k (± 1.39%)	+3,671k (+ 0.64%)	569,102k	605,017k
Parse Time	2.56s (± 0.28%)	2.55s (± 0.40%)	-0.01s (- 0.27%)	2.53s	2.57s
Bind Time	1.01s (± 0.29%)	1.00s (± 0.37%)	-0.00s (- 0.30%)	1.00s	1.01s
Check Time	1.48s (± 0.61%)	1.50s (± 0.90%)	+0.01s (+ 0.95%)	1.47s	1.53s
Emit Time	0.07s (± 0.00%)	0.07s (± 0.00%)	0.00s ( 0.00%)	0.07s	0.07s
Total Time	5.11s (± 0.24%)	5.11s (± 0.33%)	+0.00s (+ 0.02%)	5.08s	5.16s
Angular - node (v12.1.0, x64)
Memory used	332,718k (± 0.09%)	332,914k (± 0.03%)	+196k (+ 0.06%)	332,716k	333,057k
Parse Time	1.94s (± 0.75%)	1.96s (± 0.78%)	+0.01s (+ 0.67%)	1.93s	1.99s
Bind Time	0.82s (± 1.10%)	0.82s (± 0.58%)	-0.00s (- 0.49%)	0.81s	0.83s
Check Time	5.36s (± 0.61%)	5.37s (± 0.48%)	+0.01s (+ 0.22%)	5.33s	5.46s
Emit Time	6.17s (± 1.28%)	6.17s (± 1.34%)	+0.00s (+ 0.02%)	6.08s	6.49s
Total Time	14.29s (± 0.74%)	14.31s (± 0.56%)	+0.02s (+ 0.13%)	14.19s	14.59s
Compiler-Unions - node (v12.1.0, x64)
Memory used	191,687k (± 0.03%)	191,734k (± 0.08%)	+46k (+ 0.02%)	191,165k	191,922k
Parse Time	0.78s (± 0.79%)	0.79s (± 0.76%)	+0.01s (+ 0.77%)	0.77s	0.80s
Bind Time	0.53s (± 0.89%)	0.53s (± 0.89%)	0.00s ( 0.00%)	0.52s	0.54s
Check Time	7.33s (± 0.61%)	7.31s (± 0.37%)	-0.02s (- 0.30%)	7.26s	7.38s
Emit Time	2.47s (± 0.47%)	2.50s (± 0.83%)	+0.02s (+ 0.93%)	2.47s	2.56s
Total Time	11.11s (± 0.42%)	11.12s (± 0.30%)	+0.01s (+ 0.07%)	11.04s	11.20s
Monaco - node (v12.1.0, x64)
Memory used	325,567k (± 0.02%)	325,648k (± 0.03%)	+81k (+ 0.02%)	325,427k	325,797k
Parse Time	1.47s (± 0.79%)	1.47s (± 0.64%)	0.00s ( 0.00%)	1.45s	1.49s
Bind Time	0.73s (± 0.61%)	0.73s (± 0.55%)	-0.00s (- 0.41%)	0.72s	0.74s
Check Time	5.38s (± 0.35%)	5.39s (± 0.55%)	+0.00s (+ 0.09%)	5.32s	5.45s
Emit Time	3.23s (± 0.70%)	3.25s (± 0.62%)	+0.02s (+ 0.62%)	3.22s	3.31s
Total Time	10.81s (± 0.32%)	10.83s (± 0.35%)	+0.02s (+ 0.17%)	10.74s	10.91s
TFS - node (v12.1.0, x64)
Memory used	290,340k (± 0.02%)	290,343k (± 0.01%)	+3k (+ 0.00%)	290,232k	290,433k
Parse Time	1.21s (± 0.61%)	1.22s (± 0.53%)	+0.01s (+ 0.66%)	1.20s	1.23s
Bind Time	0.70s (± 1.19%)	0.69s (± 0.65%)	-0.01s (- 1.15%)	0.68s	0.70s
Check Time	4.96s (± 0.30%)	4.94s (± 0.59%)	-0.02s (- 0.40%)	4.87s	5.00s
Emit Time	3.43s (± 0.63%)	3.40s (± 1.16%)	-0.03s (- 0.84%)	3.32s	3.51s
Total Time	10.30s (± 0.27%)	10.25s (± 0.62%)	-0.05s (- 0.46%)	10.10s	10.43s
material-ui - node (v12.1.0, x64)
Memory used	450,125k (± 0.06%)	450,258k (± 0.02%)	+133k (+ 0.03%)	450,149k	450,451k
Parse Time	1.78s (± 0.39%)	1.77s (± 0.42%)	-0.01s (- 0.62%)	1.76s	1.79s
Bind Time	0.64s (± 0.73%)	0.64s (± 0.81%)	-0.00s (- 0.16%)	0.63s	0.65s
Check Time	12.69s (± 0.52%)	12.71s (± 0.27%)	+0.02s (+ 0.16%)	12.63s	12.76s
Emit Time	0.00s (± 0.00%)	0.00s (± 0.00%)	0.00s ( NaN%)	0.00s	0.00s
Total Time	15.11s (± 0.43%)	15.12s (± 0.22%)	+0.01s (+ 0.08%)	15.04s	15.17s
xstate - node (v12.1.0, x64)
Memory used	542,181k (± 1.90%)	538,809k (± 1.44%)	-3,372k (- 0.62%)	535,116k	570,145k
Parse Time	2.49s (± 0.51%)	2.49s (± 0.52%)	+0.00s (+ 0.12%)	2.48s	2.53s
Bind Time	1.03s (± 0.84%)	1.04s (± 0.93%)	+0.01s (+ 0.68%)	1.02s	1.06s
Check Time	1.43s (± 0.65%)	1.43s (± 0.67%)	-0.00s (- 0.14%)	1.41s	1.45s
Emit Time	0.07s (± 0.00%)	0.07s (± 0.00%)	0.00s ( 0.00%)	0.07s	0.07s
Total Time	5.02s (± 0.29%)	5.03s (± 0.44%)	+0.00s (+ 0.06%)	4.99s	5.09s
Angular - node (v14.15.1, x64)
Memory used	331,252k (± 0.01%)	331,291k (± 0.01%)	+39k (+ 0.01%)	331,250k	331,362k
Parse Time	1.95s (± 0.59%)	1.94s (± 0.39%)	-0.01s (- 0.56%)	1.93s	1.97s
Bind Time	0.86s (± 0.75%)	0.86s (± 0.47%)	-0.00s (- 0.35%)	0.85s	0.87s
Check Time	5.41s (± 0.45%)	5.39s (± 0.31%)	-0.02s (- 0.37%)	5.35s	5.42s
Emit Time	6.16s (± 0.40%)	6.16s (± 0.63%)	+0.00s (+ 0.03%)	6.10s	6.26s
Total Time	14.39s (± 0.24%)	14.36s (± 0.33%)	-0.03s (- 0.20%)	14.28s	14.49s
Compiler-Unions - node (v14.15.1, x64)
Memory used	192,219k (± 0.62%)	192,600k (± 0.58%)	+382k (+ 0.20%)	190,254k	193,661k
Parse Time	0.81s (± 1.09%)	0.81s (± 0.96%)	+0.00s (+ 0.50%)	0.80s	0.83s
Bind Time	0.55s (± 0.73%)	0.55s (± 0.66%)	+0.00s (+ 0.54%)	0.55s	0.56s
Check Time	7.42s (± 0.62%)	7.42s (± 0.38%)	0.00s ( 0.00%)	7.37s	7.50s
Emit Time	2.47s (± 0.79%)	2.48s (± 0.94%)	+0.01s (+ 0.32%)	2.44s	2.56s
Total Time	11.26s (± 0.43%)	11.27s (± 0.24%)	+0.01s (+ 0.11%)	11.21s	11.34s
Monaco - node (v14.15.1, x64)
Memory used	324,483k (± 0.00%)	324,512k (± 0.00%)	+29k (+ 0.01%)	324,470k	324,547k
Parse Time	1.50s (± 0.40%)	1.52s (± 0.82%)	+0.01s (+ 0.80%)	1.50s	1.55s
Bind Time	0.76s (± 0.68%)	0.76s (± 0.85%)	-0.00s (- 0.13%)	0.75s	0.78s
Check Time	5.37s (± 0.43%)	5.37s (± 0.50%)	-0.00s (- 0.04%)	5.30s	5.42s
Emit Time	3.26s (± 0.67%)	3.27s (± 0.44%)	+0.01s (+ 0.34%)	3.24s	3.30s
Total Time	10.89s (± 0.36%)	10.91s (± 0.35%)	+0.02s (+ 0.20%)	10.83s	10.98s
TFS - node (v14.15.1, x64)
Memory used	289,246k (± 0.01%)	289,298k (± 0.01%)	+53k (+ 0.02%)	289,258k	289,333k
Parse Time	1.23s (± 0.74%)	1.23s (± 0.41%)	-0.00s (- 0.33%)	1.21s	1.23s
Bind Time	0.73s (± 0.84%)	0.73s (± 0.61%)	-0.00s (- 0.41%)	0.72s	0.74s
Check Time	4.98s (± 0.60%)	4.97s (± 0.60%)	-0.01s (- 0.14%)	4.89s	5.03s
Emit Time	3.52s (± 0.53%)	3.51s (± 0.62%)	-0.01s (- 0.34%)	3.47s	3.57s
Total Time	10.46s (± 0.35%)	10.44s (± 0.41%)	-0.03s (- 0.25%)	10.33s	10.52s
material-ui - node (v14.15.1, x64)
Memory used	448,434k (± 0.00%)	448,370k (± 0.06%)	-64k (- 0.01%)	447,366k	448,539k
Parse Time	1.84s (± 0.82%)	1.83s (± 0.44%)	-0.01s (- 0.49%)	1.81s	1.84s
Bind Time	0.67s (± 0.54%)	0.68s (± 0.70%)	+0.00s (+ 0.45%)	0.67s	0.69s
Check Time	12.87s (± 0.28%)	12.85s (± 0.34%)	-0.02s (- 0.16%)	12.75s	12.97s
Emit Time	0.00s (± 0.00%)	0.00s (± 0.00%)	0.00s ( NaN%)	0.00s	0.00s
Total Time	15.38s (± 0.28%)	15.35s (± 0.28%)	-0.03s (- 0.18%)	15.27s	15.47s
xstate - node (v14.15.1, x64)
Memory used	532,909k (± 0.00%)	533,039k (± 0.00%)	+130k (+ 0.02%)	532,999k	533,081k
Parse Time	2.55s (± 0.32%)	2.56s (± 0.42%)	+0.01s (+ 0.35%)	2.54s	2.58s
Bind Time	1.15s (± 0.63%)	1.15s (± 1.10%)	+0.00s (+ 0.26%)	1.13s	1.19s
Check Time	1.47s (± 0.46%)	1.48s (± 0.40%)	+0.00s (+ 0.14%)	1.47s	1.49s
Emit Time	0.07s (± 0.00%)	0.07s (± 0.00%)	0.00s ( 0.00%)	0.07s	0.07s
Total Time	5.25s (± 0.20%)	5.26s (± 0.40%)	+0.01s (+ 0.19%)	5.21s	5.30s

System

Machine Name	ts-ci-ubuntu
Platform	linux 4.4.0-210-generic
Architecture	x64
Available Memory	16 GB
Available Memory	8 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)
• xstate - node (v10.16.3, x64)
• xstate - node (v12.1.0, x64)
• xstate - node (v14.15.1, x64)

Benchmark	Name	Iterations
Current	47282	10
Baseline	main	10

Developer Information:

Download Benchmark

[Gabriela Araujo Britto (gabritto)]

ignoreObjects is only going to be true if we are in the middle of computing type facts for an intersection type. In this case, the neutral value returned by getTypeFacts can't be TypeFacts.All (as it was before), because we are oring the type facts. So it should be TypeFacts.None.

[Anders Hejlsberg (ahejlsberg)]

I'm definitely in favor of fixing this issue, but I'm not crazy about adding 175 lines of code to do it. Couldn't we just say that certain type facts for intersections are computed as and and others are computed as or, but otherwise use the existing single function? For example, TypeFacts.TypeofEQString would be an and whereas TypeFacts.TypeofEQFunction would be an or.