Consistent narrowing by discriminant

[Anders Hejlsberg (ahejlsberg)]

With this PR we fix inconsistencies in our narrowing logic for discriminated unions. Previously we required the declared type of a reference to be a union type before we'd narrow by discriminants. This meant narrowing by discriminant wouldn't work in conjunction with user defined type predicate narrowing, with the notable (and inconsistent) exception of switch statements. We now consistently allow narrowing by discriminant of a reference with a declared type that isn't a union but a control flow type that is (which, for example, might result from first narrowing an unknown to a union type using a user defined type predicate and then narrowing the union type by a discriminant).

Fixes#30557.
Fixes#36777.

[Anders Hejlsberg (ahejlsberg)]

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

[TypeScript Bot (typescript-bot)]

Heya Anders Hejlsberg (@ahejlsberg), I've started to run the parallelized community code test suite on this PR at 88025e6. You can monitor the build here.

[TypeScript Bot (typescript-bot)]

Heya Anders Hejlsberg (@ahejlsberg), I've started to run the perf test suite on this PR at 88025e6. You can monitor the build here.

Update: The results are in!

[TypeScript Bot (typescript-bot)]

Heya Anders Hejlsberg (@ahejlsberg), I've started to run the parallelized Definitely Typed test suite on this PR at 88025e6. You can monitor the build here.

[TypeScript Bot (typescript-bot)]

Heya Anders Hejlsberg (@ahejlsberg), I've started to run the extended test suite on this PR at 88025e6. You can monitor the build here.

[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.

[TypeScript Bot (typescript-bot)]

Anders Hejlsberg (@ahejlsberg)
The results of the perf run you requested are in!

Here they are:

Comparison Report - master..38311

Metric	master	38311	Delta	Best	Worst
Angular - node (v10.16.3, x64)
Memory used	328,207k (± 0.02%)	327,547k (± 0.03%)	-661k (- 0.20%)	327,354k	327,707k
Parse Time	1.65s (± 0.57%)	1.64s (± 0.62%)	-0.01s (- 0.67%)	1.61s	1.66s
Bind Time	0.91s (± 0.44%)	0.90s (± 1.16%)	-0.01s (- 1.43%)	0.88s	0.92s
Check Time	4.83s (± 0.44%)	4.81s (± 0.56%)	-0.01s (- 0.23%)	4.75s	4.86s
Emit Time	5.44s (± 0.84%)	5.42s (± 0.53%)	-0.01s (- 0.26%)	5.37s	5.52s
Total Time	12.83s (± 0.42%)	12.77s (± 0.32%)	-0.05s (- 0.42%)	12.70s	12.87s
Monaco - node (v10.16.3, x64)
Memory used	327,218k (± 0.02%)	327,242k (± 0.02%)	+24k (+ 0.01%)	327,120k	327,366k
Parse Time	1.28s (± 0.55%)	1.28s (± 0.71%)	-0.00s (- 0.00%)	1.26s	1.30s
Bind Time	0.79s (± 0.63%)	0.79s (± 0.47%)	0.00s ( 0.00%)	0.78s	0.79s
Check Time	4.83s (± 0.51%)	4.80s (± 0.49%)	-0.03s (- 0.70%)	4.75s	4.84s
Emit Time	2.95s (± 0.85%)	2.93s (± 0.79%)	-0.02s (- 0.74%)	2.86s	2.97s
Total Time	9.85s (± 0.38%)	9.79s (± 0.44%)	-0.06s (- 0.57%)	9.68s	9.88s
TFS - node (v10.16.3, x64)
Memory used	292,293k (± 0.02%)	292,293k (± 0.02%)	+0k (+ 0.00%)	292,172k	292,454k
Parse Time	0.97s (± 0.67%)	0.97s (± 0.78%)	-0.00s (- 0.21%)	0.94s	0.98s
Bind Time	0.75s (± 0.94%)	0.76s (± 0.79%)	+0.01s (+ 0.93%)	0.75s	0.77s
Check Time	4.34s (± 0.61%)	4.35s (± 0.58%)	+0.01s (+ 0.21%)	4.29s	4.41s
Emit Time	3.11s (± 0.61%)	3.08s (± 1.02%)	-0.03s (- 0.90%)	3.00s	3.13s
Total Time	9.16s (± 0.39%)	9.15s (± 0.51%)	-0.01s (- 0.10%)	9.06s	9.23s
material-ui - node (v10.16.3, x64)
Memory used	449,256k (± 0.01%)	449,062k (± 0.01%)	-195k (- 0.04%)	448,923k	449,162k
Parse Time	1.79s (± 0.67%)	1.78s (± 0.60%)	-0.01s (- 0.28%)	1.77s	1.82s
Bind Time	0.70s (± 0.88%)	0.70s (± 1.00%)	-0.00s (- 0.00%)	0.69s	0.72s
Check Time	12.71s (± 1.05%)	12.65s (± 0.76%)	-0.06s (- 0.47%)	12.45s	12.82s
Emit Time	0.00s (± 0.00%)	0.00s (± 0.00%)	0.00s ( NaN%)	0.00s	0.00s
Total Time	15.20s (± 0.94%)	15.13s (± 0.65%)	-0.07s (- 0.44%)	14.93s	15.29s
Angular - node (v12.1.0, x64)
Memory used	303,676k (± 0.01%)	303,182k (± 0.02%)	-494k (- 0.16%)	302,966k	303,294k
Parse Time	1.58s (± 0.60%)	1.58s (± 0.52%)	0.00s ( 0.00%)	1.57s	1.61s
Bind Time	0.89s (± 0.50%)	0.89s (± 0.86%)	-0.00s (- 0.34%)	0.87s	0.90s
Check Time	4.70s (± 0.60%)	4.69s (± 0.46%)	-0.01s (- 0.21%)	4.64s	4.74s
Emit Time	5.55s (± 0.68%)	5.54s (± 0.58%)	-0.00s (- 0.04%)	5.49s	5.62s
Total Time	12.72s (± 0.40%)	12.71s (± 0.41%)	-0.01s (- 0.11%)	12.59s	12.84s
Monaco - node (v12.1.0, x64)
Memory used	307,171k (± 0.02%)	307,179k (± 0.02%)	+8k (+ 0.00%)	307,104k	307,360k
Parse Time	1.23s (± 0.83%)	1.22s (± 0.48%)	-0.01s (- 0.98%)	1.20s	1.23s
Bind Time	0.76s (± 1.09%)	0.76s (± 0.99%)	-0.01s (- 1.05%)	0.75s	0.78s
Check Time	4.65s (± 0.53%)	4.64s (± 0.59%)	-0.00s (- 0.02%)	4.57s	4.69s
Emit Time	3.01s (± 1.49%)	3.00s (± 0.79%)	-0.01s (- 0.43%)	2.95s	3.06s
Total Time	9.65s (± 0.56%)	9.62s (± 0.48%)	-0.04s (- 0.37%)	9.49s	9.71s
TFS - node (v12.1.0, x64)
Memory used	274,546k (± 0.02%)	274,522k (± 0.02%)	-24k (- 0.01%)	274,393k	274,634k
Parse Time	0.94s (± 1.50%)	0.93s (± 0.70%)	-0.01s (- 1.59%)	0.92s	0.94s
Bind Time	0.73s (± 0.96%)	0.72s (± 0.47%)	-0.01s (- 1.09%)	0.72s	0.73s
Check Time	4.27s (± 0.40%)	4.24s (± 0.51%)	-0.03s (- 0.63%)	4.20s	4.28s
Emit Time	3.15s (± 0.70%)	3.11s (± 1.04%)	-0.04s (- 1.27%)	3.06s	3.21s
Total Time	9.10s (± 0.31%)	9.01s (± 0.51%)	-0.09s (- 0.95%)	8.91s	9.14s
material-ui - node (v12.1.0, x64)
Memory used	426,512k (± 0.07%)	426,448k (± 0.01%)	-64k (- 0.02%)	426,355k	426,552k
Parse Time	1.77s (± 0.37%)	1.76s (± 0.42%)	-0.01s (- 0.68%)	1.74s	1.77s
Bind Time	0.65s (± 0.92%)	0.65s (± 0.92%)	-0.00s (- 0.00%)	0.63s	0.66s
Check Time	11.28s (± 1.07%)	11.20s (± 0.67%)	-0.08s (- 0.69%)	11.09s	11.43s
Emit Time	0.00s (± 0.00%)	0.00s (± 0.00%)	0.00s ( NaN%)	0.00s	0.00s
Total Time	13.69s (± 0.88%)	13.61s (± 0.58%)	-0.09s (- 0.65%)	13.50s	13.85s
Angular - node (v8.9.0, x64)
Memory used	323,133k (± 0.02%)	322,654k (± 0.02%)	-478k (- 0.15%)	322,561k	322,774k
Parse Time	2.13s (± 0.41%)	2.11s (± 0.61%)	-0.02s (- 0.85%)	2.08s	2.14s
Bind Time	0.94s (± 0.85%)	0.94s (± 1.14%)	+0.00s (+ 0.32%)	0.92s	0.97s
Check Time	5.50s (± 0.97%)	5.44s (± 1.75%)	-0.06s (- 1.13%)	5.25s	5.61s
Emit Time	6.32s (± 0.91%)	6.33s (± 1.32%)	+0.01s (+ 0.19%)	6.21s	6.59s
Total Time	14.88s (± 0.44%)	14.83s (± 0.56%)	-0.06s (- 0.39%)	14.66s	14.99s
Monaco - node (v8.9.0, x64)
Memory used	325,844k (± 0.02%)	325,803k (± 0.02%)	-41k (- 0.01%)	325,693k	325,954k
Parse Time	1.55s (± 0.37%)	1.55s (± 0.40%)	-0.00s (- 0.13%)	1.54s	1.57s
Bind Time	0.94s (± 2.14%)	0.91s (± 1.15%)	-0.02s (- 2.35%)	0.89s	0.94s
Check Time	5.43s (± 0.74%)	5.42s (± 0.67%)	-0.01s (- 0.15%)	5.33s	5.51s
Emit Time	3.48s (± 0.86%)	3.52s (± 0.62%)	+0.03s (+ 0.98%)	3.45s	3.55s
Total Time	11.40s (± 0.48%)	11.40s (± 0.42%)	+0.00s (+ 0.00%)	11.25s	11.48s
TFS - node (v8.9.0, x64)
Memory used	291,814k (± 0.02%)	291,841k (± 0.01%)	+27k (+ 0.01%)	291,725k	291,961k
Parse Time	1.26s (± 0.74%)	1.26s (± 0.38%)	+0.00s (+ 0.08%)	1.25s	1.27s
Bind Time	0.76s (± 0.59%)	0.76s (± 0.96%)	-0.00s (- 0.00%)	0.74s	0.77s
Check Time	5.14s (± 1.38%)	4.97s (± 1.19%)	🟩-0.17s (- 3.31%)	4.88s	5.16s
Emit Time	3.20s (± 2.47%)	3.32s (± 2.37%)	+0.12s (+ 3.72%)	3.11s	3.46s
Total Time	10.36s (± 0.34%)	10.31s (± 0.53%)	-0.05s (- 0.48%)	10.20s	10.45s
material-ui - node (v8.9.0, x64)
Memory used	452,144k (± 0.01%)	451,882k (± 0.01%)	-261k (- 0.06%)	451,803k	452,035k
Parse Time	2.13s (± 0.58%)	2.13s (± 0.54%)	+0.00s (+ 0.19%)	2.10s	2.15s
Bind Time	0.83s (± 1.08%)	0.82s (± 0.70%)	-0.00s (- 0.36%)	0.81s	0.84s
Check Time	16.75s (± 0.88%)	16.79s (± 1.25%)	+0.04s (+ 0.23%)	16.38s	17.27s
Emit Time	0.00s (± 0.00%)	0.00s (± 0.00%)	0.00s ( NaN%)	0.00s	0.00s
Total Time	19.71s (± 0.71%)	19.74s (± 1.07%)	+0.03s (+ 0.17%)	19.32s	20.23s
Angular - node (v8.9.0, x86)
Memory used	186,102k (± 0.03%)	185,870k (± 0.02%)	-231k (- 0.12%)	185,793k	185,964k
Parse Time	2.07s (± 1.13%)	2.05s (± 0.36%)	-0.02s (- 1.06%)	2.04s	2.07s
Bind Time	1.09s (± 0.51%)	1.08s (± 0.51%)	-0.01s (- 0.55%)	1.07s	1.09s
Check Time	5.02s (± 0.61%)	5.04s (± 0.43%)	+0.02s (+ 0.36%)	4.99s	5.08s
Emit Time	6.14s (± 1.25%)	6.09s (± 0.66%)	-0.06s (- 0.93%)	5.98s	6.18s
Total Time	14.32s (± 0.66%)	14.26s (± 0.31%)	-0.06s (- 0.43%)	14.17s	14.35s
Monaco - node (v8.9.0, x86)
Memory used	185,618k (± 0.02%)	185,643k (± 0.02%)	+25k (+ 0.01%)	185,593k	185,721k
Parse Time	1.61s (± 0.77%)	1.60s (± 0.62%)	-0.01s (- 0.62%)	1.58s	1.62s
Bind Time	0.78s (± 0.99%)	0.78s (± 0.77%)	-0.01s (- 0.77%)	0.76s	0.79s
Check Time	5.46s (± 0.44%)	5.47s (± 0.76%)	+0.01s (+ 0.11%)	5.40s	5.58s
Emit Time	2.89s (± 0.68%)	2.89s (± 0.97%)	+0.01s (+ 0.21%)	2.85s	2.96s
Total Time	10.73s (± 0.26%)	10.73s (± 0.48%)	-0.00s (- 0.03%)	10.63s	10.82s
TFS - node (v8.9.0, x86)
Memory used	167,174k (± 0.01%)	167,146k (± 0.01%)	-28k (- 0.02%)	167,086k	167,207k
Parse Time	1.30s (± 0.53%)	1.29s (± 0.51%)	-0.01s (- 0.39%)	1.28s	1.31s
Bind Time	0.72s (± 1.23%)	0.72s (± 1.01%)	-0.01s (- 0.83%)	0.70s	0.74s
Check Time	4.71s (± 0.53%)	4.70s (± 0.72%)	-0.01s (- 0.13%)	4.64s	4.79s
Emit Time	3.07s (± 3.39%)	3.03s (± 1.85%)	-0.04s (- 1.21%)	2.93s	3.21s
Total Time	9.79s (± 0.99%)	9.74s (± 0.79%)	-0.06s (- 0.57%)	9.64s	9.96s
material-ui - node (v8.9.0, x86)
Memory used	256,117k (± 0.02%)	255,969k (± 0.02%)	-148k (- 0.06%)	255,874k	256,134k
Parse Time	2.20s (± 0.59%)	2.18s (± 0.65%)	-0.01s (- 0.64%)	2.16s	2.21s
Bind Time	0.70s (± 1.57%)	0.69s (± 0.86%)	-0.01s (- 1.14%)	0.68s	0.71s
Check Time	15.32s (± 1.08%)	15.26s (± 0.64%)	-0.06s (- 0.38%)	15.03s	15.46s
Emit Time	0.00s (± 0.00%)	0.00s (± 0.00%)	0.00s ( NaN%)	0.00s	0.00s
Total Time	18.22s (± 0.96%)	18.14s (± 0.55%)	-0.07s (- 0.40%)	17.91s	18.36s

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	38311	10
Baseline	master	10

[Anders Hejlsberg (ahejlsberg)]

Tests all look good (nothing but preexisting conditions).

[Wesley Wigham (weswigham)]

Does this obsolete #33434 ? #30593?

[Jack Williams (jack-williams)]

Wesley Wigham (@weswigham) I think it pretty much replaces the second: this is so much simpler. I don’t believe this is quite as general as the other PR aims to be, but I went through all the duplicates on the original issue and this fixes them.

I think my only comment here is whether it’s worth filter the declared type for non-object types. I’m not sure this approach works if the declared type is something like object | undefined.

The first PR you link was some tidying I haven’t updated yet (sorry). I don’t think it’s changed by this.