Consistent narrowing to 'never' in conditional and switch statements

[ahejlsberg]

Fixes #38629.

[ahejlsberg]

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

[typescript-bot]

Heya @ahejlsberg, I've started to run the extended test suite on this PR at 224877d. You can monitor the build here.

[typescript-bot]

Heya @ahejlsberg, I've started to run the parallelized community code test suite on this PR at 224877d. You can monitor the build here.

[typescript-bot]

Heya @ahejlsberg, I've started to run the perf test suite on this PR at 224877d. You can monitor the build here.

Update: The results are in!

[typescript-bot]

Heya @ahejlsberg, I've started to run the parallelized Definitely Typed test suite on this PR at 224877d. You can monitor the build here.

[typescript-bot]

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

Here they are:

Comparison Report - master..39191

Metric	master	39191	Delta	Best	Worst
Angular - node (v10.16.3, x64)
Memory used	340,391k (± 0.01%)	339,870k (± 0.02%)	-521k (- 0.15%)	339,726k	340,059k
Parse Time	1.99s (± 0.62%)	1.99s (± 0.77%)	+0.00s (+ 0.15%)	1.97s	2.03s
Bind Time	0.80s (± 0.74%)	0.81s (± 1.38%)	+0.00s (+ 0.12%)	0.79s	0.84s
Check Time	4.74s (± 0.35%)	4.72s (± 0.36%)	-0.02s (- 0.44%)	4.68s	4.74s
Emit Time	5.22s (± 0.56%)	5.19s (± 0.67%)	-0.03s (- 0.52%)	5.09s	5.25s
Total Time	12.75s (± 0.34%)	12.70s (± 0.42%)	-0.05s (- 0.37%)	12.53s	12.82s
Monaco - node (v10.16.3, x64)
Memory used	338,891k (± 0.01%)	338,952k (± 0.02%)	+62k (+ 0.02%)	338,808k	339,041k
Parse Time	1.57s (± 0.77%)	1.57s (± 0.80%)	+0.00s (+ 0.06%)	1.54s	1.60s
Bind Time	0.70s (± 0.71%)	0.69s (± 0.86%)	-0.00s (- 0.14%)	0.68s	0.71s
Check Time	4.86s (± 0.49%)	4.85s (± 0.75%)	-0.01s (- 0.10%)	4.78s	4.94s
Emit Time	2.75s (± 0.84%)	2.74s (± 0.52%)	-0.00s (- 0.18%)	2.72s	2.77s
Total Time	9.88s (± 0.37%)	9.87s (± 0.53%)	-0.01s (- 0.12%)	9.74s	9.96s
TFS - node (v10.16.3, x64)
Memory used	301,843k (± 0.02%)	301,887k (± 0.03%)	+44k (+ 0.01%)	301,776k	302,081k
Parse Time	1.21s (± 0.58%)	1.21s (± 0.73%)	+0.00s (+ 0.17%)	1.19s	1.23s
Bind Time	0.64s (± 0.92%)	0.65s (± 1.19%)	+0.01s (+ 0.78%)	0.62s	0.66s
Check Time	4.35s (± 0.56%)	4.36s (± 0.30%)	+0.01s (+ 0.21%)	4.33s	4.39s
Emit Time	2.86s (± 1.35%)	2.86s (± 0.74%)	-0.00s (- 0.03%)	2.81s	2.92s
Total Time	9.07s (± 0.62%)	9.09s (± 0.31%)	+0.02s (+ 0.21%)	9.03s	9.14s
material-ui - node (v10.16.3, x64)
Memory used	459,543k (± 0.02%)	459,225k (± 0.02%)	-318k (- 0.07%)	459,105k	459,443k
Parse Time	2.05s (± 0.76%)	2.03s (± 0.70%)	-0.01s (- 0.54%)	2.01s	2.07s
Bind Time	0.66s (± 1.43%)	0.65s (± 1.30%)	-0.01s (- 0.91%)	0.63s	0.67s
Check Time	12.82s (± 0.62%)	12.81s (± 0.62%)	-0.01s (- 0.06%)	12.69s	13.00s
Emit Time	0.00s (± 0.00%)	0.00s (± 0.00%)	0.00s ( NaN%)	0.00s	0.00s
Total Time	15.52s (± 0.57%)	15.49s (± 0.55%)	-0.02s (- 0.14%)	15.37s	15.67s
Angular - node (v12.1.0, x64)
Memory used	317,804k (± 0.03%)	317,289k (± 0.02%)	-515k (- 0.16%)	317,154k	317,436k
Parse Time	1.96s (± 0.78%)	1.98s (± 1.03%)	+0.01s (+ 0.61%)	1.92s	2.01s
Bind Time	0.78s (± 0.60%)	0.78s (± 0.74%)	-0.00s (- 0.00%)	0.77s	0.79s
Check Time	4.61s (± 0.56%)	4.58s (± 0.48%)	-0.03s (- 0.69%)	4.54s	4.65s
Emit Time	5.34s (± 0.48%)	5.37s (± 1.10%)	+0.03s (+ 0.58%)	5.24s	5.52s
Total Time	12.69s (± 0.37%)	12.70s (± 0.56%)	+0.01s (+ 0.06%)	12.53s	12.85s
Monaco - node (v12.1.0, x64)
Memory used	321,481k (± 0.02%)	321,467k (± 0.02%)	-14k (- 0.00%)	321,348k	321,571k
Parse Time	1.54s (± 0.94%)	1.53s (± 0.62%)	-0.00s (- 0.20%)	1.51s	1.55s
Bind Time	0.68s (± 1.70%)	0.67s (± 0.66%)	-0.01s (- 0.74%)	0.66s	0.68s
Check Time	4.65s (± 0.60%)	4.64s (± 0.48%)	-0.01s (- 0.17%)	4.58s	4.70s
Emit Time	2.79s (± 0.82%)	2.79s (± 0.43%)	-0.00s (- 0.04%)	2.77s	2.83s
Total Time	9.66s (± 0.56%)	9.64s (± 0.34%)	-0.02s (- 0.22%)	9.58s	9.75s
TFS - node (v12.1.0, x64)
Memory used	286,349k (± 0.03%)	286,352k (± 0.02%)	+3k (+ 0.00%)	286,179k	286,439k
Parse Time	1.23s (± 0.94%)	1.23s (± 0.74%)	-0.00s (- 0.32%)	1.21s	1.24s
Bind Time	0.63s (± 1.09%)	0.62s (± 1.55%)	-0.00s (- 0.80%)	0.60s	0.65s
Check Time	4.27s (± 0.35%)	4.26s (± 0.36%)	-0.01s (- 0.19%)	4.23s	4.31s
Emit Time	2.93s (± 0.88%)	2.90s (± 0.57%)	-0.04s (- 1.19%)	2.86s	2.94s
Total Time	9.06s (± 0.33%)	9.01s (± 0.31%)	-0.05s (- 0.57%)	8.96s	9.07s
material-ui - node (v12.1.0, x64)
Memory used	437,981k (± 0.02%)	437,678k (± 0.02%)	-302k (- 0.07%)	437,565k	437,882k
Parse Time	2.02s (± 0.52%)	2.02s (± 0.47%)	-0.00s (- 0.10%)	2.00s	2.04s
Bind Time	0.63s (± 0.75%)	0.63s (± 1.16%)	-0.00s (- 0.79%)	0.61s	0.64s
Check Time	11.46s (± 0.61%)	11.53s (± 1.11%)	+0.07s (+ 0.63%)	11.34s	11.86s
Emit Time	0.00s (± 0.00%)	0.00s (± 0.00%)	0.00s ( NaN%)	0.00s	0.00s
Total Time	14.11s (± 0.48%)	14.18s (± 0.93%)	+0.07s (+ 0.47%)	13.96s	14.52s
Angular - node (v8.9.0, x64)
Memory used	336,794k (± 0.01%)	336,446k (± 0.02%)	-348k (- 0.10%)	336,252k	336,561k
Parse Time	2.50s (± 0.53%)	2.49s (± 0.30%)	-0.01s (- 0.28%)	2.47s	2.50s
Bind Time	0.83s (± 0.36%)	0.83s (± 0.69%)	+0.00s (+ 0.24%)	0.82s	0.84s
Check Time	5.30s (± 0.57%)	5.34s (± 0.51%)	+0.04s (+ 0.70%)	5.27s	5.40s
Emit Time	5.86s (± 1.37%)	5.86s (± 1.20%)	+0.00s (+ 0.02%)	5.67s	5.98s
Total Time	14.49s (± 0.74%)	14.52s (± 0.40%)	+0.03s (+ 0.19%)	14.36s	14.63s
Monaco - node (v8.9.0, x64)
Memory used	340,278k (± 0.02%)	340,204k (± 0.02%)	-73k (- 0.02%)	340,118k	340,401k
Parse Time	1.87s (± 0.48%)	1.86s (± 0.78%)	-0.00s (- 0.05%)	1.84s	1.91s
Bind Time	0.87s (± 0.55%)	0.86s (± 0.42%)	-0.00s (- 0.35%)	0.86s	0.87s
Check Time	5.36s (± 0.67%)	5.33s (± 0.43%)	-0.03s (- 0.60%)	5.26s	5.37s
Emit Time	3.22s (± 0.57%)	3.22s (± 0.48%)	-0.00s (- 0.12%)	3.17s	3.25s
Total Time	11.31s (± 0.41%)	11.28s (± 0.36%)	-0.04s (- 0.32%)	11.15s	11.36s
TFS - node (v8.9.0, x64)
Memory used	303,621k (± 0.01%)	303,620k (± 0.02%)	-1k (- 0.00%)	303,508k	303,720k
Parse Time	1.53s (± 0.69%)	1.53s (± 0.42%)	-0.00s (- 0.13%)	1.52s	1.55s
Bind Time	0.65s (± 0.85%)	0.65s (± 0.95%)	-0.00s (- 0.46%)	0.64s	0.66s
Check Time	4.94s (± 1.65%)	4.96s (± 1.65%)	+0.02s (+ 0.32%)	4.82s	5.12s
Emit Time	3.08s (± 3.17%)	3.04s (± 2.72%)	-0.04s (- 1.14%)	2.88s	3.19s
Total Time	10.20s (± 0.61%)	10.18s (± 0.48%)	-0.02s (- 0.21%)	10.04s	10.30s
material-ui - node (v8.9.0, x64)
Memory used	463,645k (± 0.02%)	463,352k (± 0.01%)	-294k (- 0.06%)	463,209k	463,487k
Parse Time	2.37s (± 0.55%)	2.37s (± 0.39%)	-0.01s (- 0.25%)	2.35s	2.39s
Bind Time	0.78s (± 1.15%)	0.77s (± 1.21%)	-0.01s (- 1.03%)	0.75s	0.79s
Check Time	16.96s (± 0.67%)	16.94s (± 1.37%)	-0.01s (- 0.06%)	16.60s	17.56s
Emit Time	0.00s (± 0.00%)	0.00s (± 0.00%)	0.00s ( NaN%)	0.00s	0.00s
Total Time	20.10s (± 0.58%)	20.08s (± 1.13%)	-0.02s (- 0.12%)	19.75s	20.66s
Angular - node (v8.9.0, x86)
Memory used	193,334k (± 0.02%)	193,140k (± 0.02%)	-194k (- 0.10%)	193,039k	193,216k
Parse Time	2.43s (± 0.63%)	2.44s (± 0.53%)	+0.01s (+ 0.25%)	2.41s	2.47s
Bind Time	0.98s (± 0.78%)	0.97s (± 0.87%)	-0.00s (- 0.41%)	0.95s	0.99s
Check Time	4.79s (± 0.44%)	4.81s (± 0.85%)	+0.03s (+ 0.54%)	4.75s	4.92s
Emit Time	5.91s (± 0.88%)	5.98s (± 0.80%)	+0.07s (+ 1.20%)	5.87s	6.08s
Total Time	14.11s (± 0.54%)	14.20s (± 0.54%)	+0.10s (+ 0.68%)	14.03s	14.38s
Monaco - node (v8.9.0, x86)
Memory used	193,294k (± 0.02%)	193,264k (± 0.02%)	-30k (- 0.02%)	193,171k	193,342k
Parse Time	1.92s (± 1.37%)	1.91s (± 1.07%)	-0.01s (- 0.68%)	1.87s	1.96s
Bind Time	0.68s (± 1.21%)	0.68s (± 1.11%)	+0.00s (+ 0.15%)	0.67s	0.71s
Check Time	5.47s (± 0.57%)	5.47s (± 0.54%)	-0.00s (- 0.09%)	5.39s	5.55s
Emit Time	2.66s (± 0.77%)	2.66s (± 1.20%)	-0.01s (- 0.23%)	2.60s	2.75s
Total Time	10.74s (± 0.59%)	10.72s (± 0.66%)	-0.03s (- 0.23%)	10.53s	10.87s
TFS - node (v8.9.0, x86)
Memory used	173,586k (± 0.03%)	173,569k (± 0.02%)	-16k (- 0.01%)	173,462k	173,637k
Parse Time	1.57s (± 0.70%)	1.59s (± 0.82%)	+0.02s (+ 1.02%)	1.56s	1.62s
Bind Time	0.62s (± 1.00%)	0.62s (± 1.20%)	+0.00s (+ 0.16%)	0.61s	0.64s
Check Time	4.62s (± 0.58%)	4.63s (± 0.63%)	+0.00s (+ 0.11%)	4.56s	4.72s
Emit Time	2.79s (± 0.80%)	2.77s (± 0.72%)	-0.02s (- 0.82%)	2.72s	2.80s
Total Time	9.60s (± 0.36%)	9.60s (± 0.45%)	-0.00s (- 0.01%)	9.53s	9.73s
material-ui - node (v8.9.0, x86)
Memory used	262,483k (± 0.02%)	262,299k (± 0.01%)	-183k (- 0.07%)	262,249k	262,369k
Parse Time	2.44s (± 0.79%)	2.43s (± 0.47%)	-0.00s (- 0.21%)	2.40s	2.46s
Bind Time	0.67s (± 1.66%)	0.66s (± 1.10%)	-0.00s (- 0.75%)	0.65s	0.68s
Check Time	15.45s (± 0.51%)	15.44s (± 0.51%)	-0.00s (- 0.03%)	15.26s	15.56s
Emit Time	0.00s (± 0.00%)	0.00s (± 0.00%)	0.00s ( NaN%)	0.00s	0.00s
Total Time	18.55s (± 0.52%)	18.54s (± 0.49%)	-0.02s (- 0.09%)	18.34s	18.67s

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	39191	10
Baseline	master	10

[ahejlsberg]

Tests look good. Differences are all preexisting conditions. No performance impact.