allow type narrowing with NonNullExpression

[uhyo (uhyo)]

Happy hacktoberfest! 🎃🥳

Fixes #36958.

Example

Code

const m = ''.match('');
m! && m[0];
m?.[0]! && m[0];

Current Behavior (TS 4.1 Beta)

src/36958.ts:2:7 - error TS2531: Object is possibly 'null'.

2 m! && m[0];
        ~

src/36958.ts:3:12 - error TS2531: Object is possibly 'null'.

3 m?.[0]! && m[0];
             ~


Found 2 errors.

New Behavior

(no errors)

Details & Discussion

This PR enables type narrowing when condition is a NonNullExpression.

The original issue includes following example, but this PR does not fix that case.

m?.[0].length! > 0 && m[0];

To fix this case, we have to take expr > 0 and similar expressions into consideration, which I think is too complex compared to the outcome. How do you think?

[Wesley Wigham (weswigham)]

TypeScript Bot (@typescript-bot) perf test this

[TypeScript Bot (typescript-bot)]

Heya Wesley Wigham (@weswigham), I've started to run the perf test suite on this PR at 58781b0. You can monitor the build here.

Update: The results are in!

[Wesley Wigham (weswigham)]

Assuming the perf tests come back OK (always a good idea to check with control flow changes), this looks great to me.

[Wesley Wigham (weswigham)]

Nathan Shively-Sanders (@sandersn) Anders Hejlsberg (@ahejlsberg) should this be 4.1 or 4.2 bound?

[Nathan Shively-Sanders (sandersn)]

I'd lean 4.2, but it's a small change so if the perf results come back clean, 4.1 would be OK too.

[Anders Hejlsberg (ahejlsberg)]

If perf looks good I'm fine with having this in 4.1.

[TypeScript Bot (typescript-bot)]

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

Here they are:

Comparison Report - master..41075

Metric	master	41075	Delta	Best	Worst
Angular - node (v10.16.3, x64)
Memory used	350,582k (± 0.02%)	350,589k (± 0.02%)	+7k (+ 0.00%)	350,422k	350,739k
Parse Time	2.07s (± 0.39%)	2.08s (± 0.64%)	+0.01s (+ 0.34%)	2.04s	2.10s
Bind Time	0.84s (± 0.83%)	0.84s (± 0.59%)	+0.00s (+ 0.48%)	0.84s	0.86s
Check Time	4.97s (± 0.47%)	4.98s (± 0.33%)	+0.00s (+ 0.08%)	4.95s	5.03s
Emit Time	5.30s (± 0.61%)	5.31s (± 0.65%)	+0.01s (+ 0.13%)	5.26s	5.40s
Total Time	13.19s (± 0.32%)	13.21s (± 0.26%)	+0.02s (+ 0.17%)	13.15s	13.30s
Monaco - node (v10.16.3, x64)
Memory used	354,616k (± 0.02%)	354,630k (± 0.02%)	+14k (+ 0.00%)	354,490k	354,755k
Parse Time	1.60s (± 0.51%)	1.60s (± 0.19%)	-0.00s (- 0.31%)	1.59s	1.60s
Bind Time	0.72s (± 0.72%)	0.72s (± 0.62%)	-0.00s (- 0.42%)	0.71s	0.73s
Check Time	5.13s (± 0.65%)	5.10s (± 0.44%)	-0.03s (- 0.58%)	5.05s	5.16s
Emit Time	2.82s (± 0.79%)	2.80s (± 0.77%)	-0.02s (- 0.57%)	2.75s	2.86s
Total Time	10.27s (± 0.43%)	10.21s (± 0.37%)	-0.05s (- 0.51%)	10.14s	10.28s
TFS - node (v10.16.3, x64)
Memory used	307,880k (± 0.02%)	307,845k (± 0.02%)	-35k (- 0.01%)	307,733k	308,004k
Parse Time	1.24s (± 0.54%)	1.24s (± 0.54%)	-0.00s (- 0.24%)	1.22s	1.25s
Bind Time	0.68s (± 0.88%)	0.67s (± 0.54%)	-0.00s (- 0.30%)	0.67s	0.68s
Check Time	4.58s (± 0.47%)	4.56s (± 0.33%)	-0.03s (- 0.61%)	4.52s	4.59s
Emit Time	2.92s (± 0.69%)	2.93s (± 0.85%)	+0.01s (+ 0.41%)	2.87s	2.96s
Total Time	9.42s (± 0.35%)	9.40s (± 0.30%)	-0.02s (- 0.22%)	9.33s	9.45s
material-ui - node (v10.16.3, x64)
Memory used	489,312k (± 0.01%)	489,331k (± 0.02%)	+19k (+ 0.00%)	489,161k	489,527k
Parse Time	2.07s (± 0.46%)	2.06s (± 0.44%)	-0.01s (- 0.34%)	2.04s	2.08s
Bind Time	0.65s (± 0.72%)	0.65s (± 0.68%)	+0.00s (+ 0.31%)	0.64s	0.66s
Check Time	13.51s (± 0.77%)	13.48s (± 0.45%)	-0.02s (- 0.17%)	13.35s	13.65s
Emit Time	0.00s (± 0.00%)	0.00s (± 0.00%)	0.00s ( NaN%)	0.00s	0.00s
Total Time	16.22s (± 0.68%)	16.20s (± 0.39%)	-0.02s (- 0.15%)	16.04s	16.37s
Angular - node (v12.1.0, x64)
Memory used	327,745k (± 0.03%)	327,770k (± 0.02%)	+26k (+ 0.01%)	327,658k	327,946k
Parse Time	2.06s (± 0.87%)	2.08s (± 0.70%)	+0.02s (+ 1.22%)	2.05s	2.12s
Bind Time	0.81s (± 0.69%)	0.81s (± 0.92%)	+0.01s (+ 0.62%)	0.80s	0.83s
Check Time	4.90s (± 0.31%)	4.94s (± 0.92%)	+0.04s (+ 0.76%)	4.84s	5.05s
Emit Time	5.48s (± 0.57%)	5.53s (± 0.54%)	+0.05s (+ 0.88%)	5.46s	5.59s
Total Time	13.24s (± 0.29%)	13.36s (± 0.54%)	+0.11s (+ 0.84%)	13.20s	13.46s
Monaco - node (v12.1.0, x64)
Memory used	336,763k (± 0.01%)	336,779k (± 0.03%)	+15k (+ 0.00%)	336,624k	337,086k
Parse Time	1.58s (± 0.81%)	1.59s (± 0.82%)	+0.01s (+ 0.38%)	1.55s	1.61s
Bind Time	0.70s (± 0.74%)	0.70s (± 0.95%)	+0.00s (+ 0.57%)	0.69s	0.72s
Check Time	4.92s (± 0.35%)	4.91s (± 0.66%)	-0.01s (- 0.22%)	4.84s	4.97s
Emit Time	2.87s (± 0.93%)	2.88s (± 0.92%)	+0.00s (+ 0.03%)	2.82s	2.94s
Total Time	10.07s (± 0.34%)	10.08s (± 0.50%)	+0.00s (+ 0.03%)	9.98s	10.17s
TFS - node (v12.1.0, x64)
Memory used	292,055k (± 0.02%)	292,057k (± 0.01%)	+1k (+ 0.00%)	291,971k	292,161k
Parse Time	1.25s (± 0.56%)	1.25s (± 0.72%)	-0.00s (- 0.40%)	1.23s	1.27s
Bind Time	0.65s (± 1.03%)	0.64s (± 0.53%)	-0.00s (- 0.62%)	0.64s	0.65s
Check Time	4.51s (± 0.59%)	4.49s (± 0.35%)	-0.02s (- 0.40%)	4.46s	4.53s
Emit Time	2.95s (± 0.57%)	2.96s (± 0.81%)	+0.01s (+ 0.31%)	2.90s	3.02s
Total Time	9.35s (± 0.34%)	9.34s (± 0.40%)	-0.02s (- 0.16%)	9.26s	9.45s
material-ui - node (v12.1.0, x64)
Memory used	467,316k (± 0.01%)	467,269k (± 0.05%)	-48k (- 0.01%)	466,279k	467,525k
Parse Time	2.09s (± 0.42%)	2.08s (± 0.63%)	-0.01s (- 0.38%)	2.06s	2.11s
Bind Time	0.64s (± 0.69%)	0.65s (± 0.58%)	+0.00s (+ 0.47%)	0.64s	0.65s
Check Time	11.99s (± 0.48%)	12.05s (± 0.62%)	+0.06s (+ 0.50%)	11.93s	12.24s
Emit Time	0.00s (± 0.00%)	0.00s (± 0.00%)	0.00s ( NaN%)	0.00s	0.00s
Total Time	14.72s (± 0.39%)	14.77s (± 0.46%)	+0.05s (+ 0.35%)	14.67s	14.94s
Angular - node (v8.9.0, x64)
Memory used	353,022k (± 0.02%)	352,946k (± 0.02%)	-76k (- 0.02%)	352,786k	353,098k
Parse Time	2.65s (± 0.38%)	2.64s (± 0.20%)	-0.01s (- 0.26%)	2.63s	2.65s
Bind Time	0.88s (± 0.80%)	0.88s (± 0.75%)	+0.00s (+ 0.11%)	0.87s	0.90s
Check Time	5.60s (± 0.51%)	5.61s (± 0.44%)	+0.01s (+ 0.14%)	5.55s	5.67s
Emit Time	6.36s (± 0.79%)	6.41s (± 0.91%)	+0.05s (+ 0.82%)	6.26s	6.54s
Total Time	15.49s (± 0.46%)	15.54s (± 0.42%)	+0.05s (+ 0.33%)	15.35s	15.69s
Monaco - node (v8.9.0, x64)
Memory used	358,439k (± 0.02%)	358,435k (± 0.01%)	-4k (- 0.00%)	358,314k	358,580k
Parse Time	1.93s (± 0.29%)	1.92s (± 0.31%)	-0.00s (- 0.21%)	1.91s	1.94s
Bind Time	0.90s (± 1.15%)	0.90s (± 1.04%)	-0.00s (- 0.22%)	0.88s	0.92s
Check Time	5.66s (± 0.73%)	5.63s (± 0.66%)	-0.03s (- 0.55%)	5.56s	5.71s
Emit Time	3.36s (± 1.46%)	3.36s (± 1.20%)	+0.00s (+ 0.06%)	3.24s	3.44s
Total Time	11.85s (± 0.68%)	11.82s (± 0.57%)	-0.04s (- 0.31%)	11.63s	11.95s
TFS - node (v8.9.0, x64)
Memory used	310,265k (± 0.02%)	310,249k (± 0.01%)	-16k (- 0.01%)	310,128k	310,327k
Parse Time	1.57s (± 0.49%)	1.57s (± 0.49%)	-0.01s (- 0.38%)	1.55s	1.58s
Bind Time	0.68s (± 0.54%)	0.68s (± 0.53%)	-0.00s (- 0.15%)	0.68s	0.69s
Check Time	5.35s (± 0.49%)	5.33s (± 0.60%)	-0.02s (- 0.37%)	5.27s	5.43s
Emit Time	2.98s (± 0.53%)	2.97s (± 1.55%)	-0.01s (- 0.30%)	2.89s	3.12s
Total Time	10.59s (± 0.34%)	10.55s (± 0.53%)	-0.04s (- 0.39%)	10.46s	10.70s
material-ui - node (v8.9.0, x64)
Memory used	496,221k (± 0.02%)	496,190k (± 0.02%)	-32k (- 0.01%)	496,028k	496,374k
Parse Time	2.49s (± 0.52%)	2.49s (± 0.35%)	-0.00s (- 0.08%)	2.47s	2.51s
Bind Time	0.82s (± 0.99%)	0.81s (± 1.61%)	-0.01s (- 1.10%)	0.78s	0.84s
Check Time	17.99s (± 1.03%)	17.93s (± 1.19%)	-0.07s (- 0.38%)	17.48s	18.36s
Emit Time	0.00s (± 0.00%)	0.00s (± 0.00%)	0.00s ( NaN%)	0.00s	0.00s
Total Time	21.31s (± 0.91%)	21.23s (± 0.94%)	-0.08s (- 0.37%)	20.81s	21.65s
Angular - node (v8.9.0, x86)
Memory used	202,046k (± 0.01%)	202,098k (± 0.02%)	+52k (+ 0.03%)	201,974k	202,199k
Parse Time	2.54s (± 0.50%)	2.54s (± 0.76%)	+0.00s (+ 0.04%)	2.51s	2.59s
Bind Time	1.01s (± 0.59%)	1.02s (± 0.95%)	+0.01s (+ 0.49%)	1.00s	1.04s
Check Time	5.08s (± 0.68%)	5.04s (± 0.52%)	-0.03s (- 0.63%)	4.98s	5.09s
Emit Time	6.12s (± 1.11%)	6.09s (± 0.52%)	-0.03s (- 0.44%)	6.01s	6.17s
Total Time	14.75s (± 0.57%)	14.70s (± 0.35%)	-0.05s (- 0.34%)	14.60s	14.81s
Monaco - node (v8.9.0, x86)
Memory used	202,968k (± 0.01%)	202,939k (± 0.03%)	-29k (- 0.01%)	202,775k	203,048k
Parse Time	1.96s (± 0.42%)	1.97s (± 0.68%)	+0.00s (+ 0.10%)	1.94s	1.99s
Bind Time	0.72s (± 0.77%)	0.71s (± 0.83%)	-0.00s (- 0.56%)	0.70s	0.73s
Check Time	5.75s (± 1.42%)	5.72s (± 1.63%)	-0.03s (- 0.50%)	5.46s	5.86s
Emit Time	2.77s (± 2.22%)	2.81s (± 3.32%)	+0.04s (+ 1.41%)	2.71s	3.06s
Total Time	11.20s (± 0.37%)	11.21s (± 0.25%)	+0.01s (+ 0.09%)	11.15s	11.27s
TFS - node (v8.9.0, x86)
Memory used	177,412k (± 0.02%)	177,352k (± 0.01%)	-60k (- 0.03%)	177,319k	177,414k
Parse Time	1.61s (± 1.05%)	1.61s (± 0.55%)	-0.00s (- 0.06%)	1.59s	1.63s
Bind Time	0.65s (± 1.19%)	0.65s (± 0.56%)	-0.01s (- 0.77%)	0.64s	0.65s
Check Time	4.87s (± 0.59%)	4.85s (± 0.57%)	-0.02s (- 0.33%)	4.78s	4.92s
Emit Time	2.82s (± 1.15%)	2.82s (± 0.66%)	-0.00s (- 0.04%)	2.76s	2.85s
Total Time	9.95s (± 0.54%)	9.92s (± 0.42%)	-0.02s (- 0.24%)	9.84s	9.99s
material-ui - node (v8.9.0, x86)
Memory used	279,261k (± 0.01%)	279,281k (± 0.01%)	+20k (+ 0.01%)	279,228k	279,349k
Parse Time	2.55s (± 0.66%)	2.55s (± 0.75%)	+0.00s (+ 0.04%)	2.52s	2.61s
Bind Time	0.72s (± 4.79%)	0.72s (± 4.81%)	-0.00s (- 0.00%)	0.69s	0.85s
Check Time	16.40s (± 0.70%)	16.48s (± 0.66%)	+0.07s (+ 0.44%)	16.23s	16.76s
Emit Time	0.00s (± 0.00%)	0.00s (± 0.00%)	0.00s ( NaN%)	0.00s	0.00s
Total Time	19.68s (± 0.61%)	19.75s (± 0.51%)	+0.07s (+ 0.38%)	19.54s	20.00s

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	41075	10
Baseline	master	10