Properly handle null and undefined in getCommonSupertype

[Anders Hejlsberg (ahejlsberg)]

This is an alternative fix for #49938 that supercedes #49981.

Jake Bailey (@jakebailey) I found it easier to put up a new PR. I've copied the tests from #49981. This PR more uniformly lifts undefined and null from the inference candidates and then adds them back later, plus it's a bit better at avoiding duplicate work. For example, it handles this case that otherwise is an error:

letv=null!;declarefunctionfoo<T>(x: T,y: T): T;constx=foo(vas'a'|undefined,vas'b');

[Anders Hejlsberg (ahejlsberg)]

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 faster
TypeScript Bot (@typescript-bot) pack this

[Anders Hejlsberg (ahejlsberg)]

TypeScript Bot (@typescript-bot) test this

[TypeScript Bot (typescript-bot)]

Heya Anders Hejlsberg (@ahejlsberg), I've started to run the extended test suite on this PR at d4a239c. You can monitor the build here.

[Anders Hejlsberg (ahejlsberg)]

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

[TypeScript Bot (typescript-bot)]

Heya Anders Hejlsberg (@ahejlsberg), I've started to run the diff-based user code test suite on this PR at d4a239c. 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 abridged perf test suite on this PR at d4a239c. 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 d4a239c. You can monitor the build here.

[Anders Hejlsberg (ahejlsberg)]

TypeScript Bot (@typescript-bot) pack this

[TypeScript Bot (typescript-bot)]

Heya Anders Hejlsberg (@ahejlsberg), I've started to run the tarball bundle task on this PR at d4a239c. You can monitor the build here.

[TypeScript Bot (typescript-bot)]

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

Here they are:

Comparison Report - main..50021

Metric	main	50021	Delta	Best	Worst
Angular - node (v14.15.1, x64)
Memory used	335,938k (± 0.01%)	335,962k (± 0.01%)	+24k (+ 0.01%)	335,871k	336,005k
Parse Time	2.06s (± 0.65%)	2.06s (± 0.46%)	-0.01s (- 0.39%)	2.04s	2.08s
Bind Time	0.90s (± 1.30%)	0.90s (± 0.72%)	-0.00s (- 0.11%)	0.89s	0.91s
Check Time	5.82s (± 0.41%)	5.83s (± 0.41%)	+0.01s (+ 0.19%)	5.77s	5.89s
Emit Time	6.38s (± 0.63%)	6.38s (± 0.63%)	-0.01s (- 0.08%)	6.27s	6.43s
Total Time	15.17s (± 0.37%)	15.16s (± 0.43%)	-0.01s (- 0.05%)	14.98s	15.24s
Compiler-Unions - node (v14.15.1, x64)
Memory used	193,129k (± 0.01%)	193,453k (± 0.38%)	+324k (+ 0.17%)	193,001k	196,437k
Parse Time	0.85s (± 0.68%)	0.84s (± 0.43%)	-0.00s (- 0.35%)	0.84s	0.85s
Bind Time	0.57s (± 1.01%)	0.57s (± 1.13%)	+0.00s (+ 0.35%)	0.56s	0.59s
Check Time	6.71s (± 0.80%)	6.73s (± 0.58%)	+0.03s (+ 0.39%)	6.64s	6.83s
Emit Time	2.49s (± 0.87%)	2.49s (± 0.82%)	+0.01s (+ 0.28%)	2.46s	2.55s
Total Time	10.61s (± 0.54%)	10.64s (± 0.38%)	+0.03s (+ 0.29%)	10.54s	10.74s
Monaco - node (v14.15.1, x64)
Memory used	325,664k (± 0.01%)	325,647k (± 0.01%)	-17k (- 0.01%)	325,601k	325,702k
Parse Time	1.58s (± 0.48%)	1.59s (± 0.70%)	+0.01s (+ 0.63%)	1.56s	1.61s
Bind Time	0.78s (± 0.71%)	0.79s (± 1.06%)	+0.00s (+ 0.38%)	0.77s	0.81s
Check Time	5.71s (± 0.46%)	5.67s (± 0.36%)	-0.03s (- 0.56%)	5.64s	5.73s
Emit Time	3.36s (± 0.58%)	3.34s (± 0.75%)	-0.02s (- 0.60%)	3.28s	3.40s
Total Time	11.42s (± 0.36%)	11.38s (± 0.34%)	-0.04s (- 0.32%)	11.34s	11.51s
TFS - node (v14.15.1, x64)
Memory used	288,822k (± 0.01%)	288,845k (± 0.01%)	+23k (+ 0.01%)	288,795k	288,931k
Parse Time	1.33s (± 1.04%)	1.33s (± 1.76%)	+0.00s (+ 0.23%)	1.29s	1.39s
Bind Time	0.77s (± 4.36%)	0.77s (± 4.05%)	-0.00s (- 0.00%)	0.73s	0.85s
Check Time	5.36s (± 0.26%)	5.33s (± 0.50%)	-0.03s (- 0.54%)	5.27s	5.39s
Emit Time	3.54s (± 1.81%)	3.62s (± 1.92%)	+0.08s (+ 2.18%)	3.46s	3.73s
Total Time	10.99s (± 0.57%)	11.04s (± 0.73%)	+0.05s (+ 0.48%)	10.82s	11.17s
material-ui - node (v14.15.1, x64)
Memory used	446,711k (± 0.01%)	446,730k (± 0.01%)	+19k (+ 0.00%)	446,661k	446,786k
Parse Time	1.88s (± 0.62%)	1.88s (± 0.64%)	-0.00s (- 0.05%)	1.85s	1.91s
Bind Time	0.72s (± 1.23%)	0.72s (± 0.97%)	-0.01s (- 0.83%)	0.71s	0.74s
Check Time	13.18s (± 0.51%)	13.24s (± 0.58%)	+0.07s (+ 0.51%)	13.11s	13.44s
Emit Time	0.00s (± 0.00%)	0.00s (± 0.00%)	0.00s ( NaN%)	0.00s	0.00s
Total Time	15.78s (± 0.47%)	15.85s (± 0.52%)	+0.06s (+ 0.39%)	15.70s	16.04s
xstate - node (v14.15.1, x64)
Memory used	541,295k (± 0.01%)	541,308k (± 0.00%)	+13k (+ 0.00%)	541,260k	541,341k
Parse Time	2.60s (± 0.29%)	2.61s (± 0.32%)	+0.01s (+ 0.35%)	2.58s	2.62s
Bind Time	1.15s (± 1.24%)	1.14s (± 1.57%)	-0.01s (- 0.61%)	1.10s	1.20s
Check Time	1.56s (± 0.49%)	1.56s (± 0.72%)	-0.00s (- 0.06%)	1.53s	1.58s
Emit Time	0.07s (± 4.66%)	0.07s (± 4.13%)	-0.00s (- 1.37%)	0.07s	0.08s
Total Time	5.38s (± 0.36%)	5.38s (± 0.41%)	+0.01s (+ 0.11%)	5.35s	5.46s

System

Machine Name	ts-ci-ubuntu
Platform	linux 4.4.0-210-generic
Architecture	x64
Available Memory	16 GB
Available Memory	15 GB
CPUs	4 × Intel(R) Core(TM) i7-4770 CPU @ 3.40GHz

Hosts

• node (v14.15.1, x64)

Scenarios

• Angular - node (v14.15.1, x64)
• Compiler-Unions - node (v14.15.1, x64)
• Monaco - node (v14.15.1, x64)
• TFS - node (v14.15.1, x64)
• material-ui - node (v14.15.1, x64)
• xstate - node (v14.15.1, x64)

Benchmark	Name	Iterations
Current	50021	10
Baseline	main	10

Developer Information:

Download Benchmark

[TypeScript Bot (typescript-bot)]

Heya Anders Hejlsberg (@ahejlsberg), I've run the RWC suite on this PR - assuming you're on the TS core team, you can view the resulting diff here.

[TypeScript Bot (typescript-bot)]

Anders Hejlsberg (@ahejlsberg)
Great news! no new errors were found between main..refs/pull/50021/merge

[TypeScript Bot (typescript-bot)]

Hey Anders Hejlsberg (@ahejlsberg), I've packed this into an installable tgz. You can install it for testing by referencing it in your package.json like so:

{
"devDependencies": {
"typescript": "https://typescript.visualstudio.com/cf7ac146-d525-443c-b23c-0d58337efebc/_apis/build/builds/130297/artifacts?artifactName=tgz&fileId=5B6A9298038EC2E4EEE17420D8BA1C609540E927E60F49CC71CBE61DF68A3F3902&fileName=/typescript-4.8.0-insiders.20220723.tgz"
}
}

and then running npm install.

---

There is also a playground for this build and an npm module you can use via "typescript": "npm:@typescript-deploys/pr-build@4.8.0-pr-50021-12".;

[Anders Hejlsberg (ahejlsberg)]

Tests and performance all look good. No new errors, but one error went away in RWC because of better inference. I think this is a good fix.

[Anders Hejlsberg (ahejlsberg)]

Latest commit adds more tests that now succeed but previously failed.

[Jake Bailey (jakebailey)]

Looks great. I should have known that literals needed the same treatment!

(filterType is another helper I need to commit to memory as existing.)