Instantiation expressions inconsistently trigger incorrect error messages in editor contexts

Type: Bug

1. Attempt to use the Instantiation Expressions in VSCode typescript language

function makeBox<T>(value: T){
  return {value};
}

const makeStringBox = makeBox<string>;
const stringBox = makeStringBox('abc');

1. Observe Red squiggly lines that shouldn’t be there.

VS Code version: Code - Insiders 1.70.0-insider (e9bda7aa4ff76648cfccc1a7bde465443803da71, 2022-08-02T16:56:25.649Z) OS version: Windows_NT x64 10.0.19044 Modes:

System Info

Item	Value
CPUs	Intel® Core™ i9-9900K CPU @ 3.60GHz (16 x 3600)
GPU Status	2d_canvas: enabled canvas_oop_rasterization: disabled_off direct_rendering_display_compositor: disabled_off_ok gpu_compositing: enabled multiple_raster_threads: enabled_on opengl: enabled_on rasterization: enabled raw_draw: disabled_off_ok skia_renderer: enabled_on video_decode: enabled video_encode: enabled vulkan: disabled_off webgl: enabled webgl2: enabled
Load (avg)	undefined
Memory (System)	31.92GB (17.88GB free)
Process Argv
Screen Reader	no
VM	0%

Extensions: none

A/B Experiments

vsliv695:30137379
vsins829:30139715
vsliv368:30146709
vsreu685:30147344
python383:30185418
vspor879:30202332
vspor708:30202333
vspor363:30204092
vslsvsres303:30308271
pythonvspyl392:30422396
pythontb:30258533
pythonptprofiler:30281269
vsdfh931:30280409
vshan820:30294714
pythondataviewer:30285072
vscod805:30301674
bridge0708:30335490
bridge0723:30353136
vsaa593cf:30376535
pythonvs932:30404738
wslgetstarted:30449409
vscscmwlcmt:30465136
cppdebug:30492333
vscaac:30438845
pylanb8912:30522163
vsclangdf:30492506
c4g48928:30535728

I’ve had this issue with both no npm packages installed. With typescript installed only. And with typescript and a tsconfig.json file.

Note: It is incredibly inconsistent. Sometimes it doesn’t happen. Other times changing from the built-in version of typescript to the local version fixes it, sometimes just waiting fixes it. Until you change the code at all (adding/removing whitespace for example) and then it comes back. Installing a different version of typescript removes the error until you change the code as well.

I believe that this is a VSCode centric issue and not a Typescript issue for 2 reasons.

1. Running npx tsc builds the package just fine without any issues from type errors.
2. As seen in this comment, the typescript playground doesn’t show any errors with this. https://github.com/microsoft/TypeScript/pull/47607#issuecomment-1191409426 TS Playground

[xiaoxiangmoe]

Temporary solution:

function makeBox<T>(value: T){
  return {value};
}

const makeStringBox = (makeBox)<string>;
const stringBox = makeStringBox('abc');

[DanielRosenwasser]

Okay, here’s what I believe happens - you can notice in in two ways:

1. You have semantic highlighting enabled (the default in VS Code) or you have inlay hints enabled. These (sometimes) get requested before diagnostics. However, the way semantic classifier queries entities asks for its meaning as a type instead of a value. That triggers an error, and that error gets cached for the subsequent getErr request.
2. The first thing you do after the language server has loaded or after an edit is you try to get quick info on the usage of bar. That triggers the same bad lookup behavior, which reports an error which gets reported in any following diagnostics request.