TypeScript Infer type arguments on instance check

Fixes #17473 - Infer constrained generic parameters after instanceof check Fixes #46668 - Private field check narrows generic class too far

This is an updated and ready-to-be-reviewed recreation of my previous #49863. Please see that PR for a longer description of the problem and the proposed solution, as I don't want to duplicate it all here unnecessarily. In short, when instantiating the type of a class for an instance check, TypeScript would populate all type arguments with any no matter the constraint on the type parameter or the strictness settings. This change factors in the compiler strictness as well as the constraints and variances of the type parameters to "infer" the type arguments.

This does NOT handle #57317, per @Andarist on #57323 but I have included that test case here as these changes do introduce new behavior to that case (any to unknown). I can remove if it feels irrelevant to these changes.

Breaking Changes

From the last PR, I have resolved to use the compiler option strictInstanceOfTypeParameters to gate these otherwise breaking changes. However, there was some discussion about the possibility of not hiding these changes behind a compiler option. I can test enabling these changes for all, similar to what I did last time.

Apr 01 '24 21:04 molisani

Looks like you're introducing a change to the public API surface area. If this includes breaking changes, please document them on our wiki's API Breaking Changes page.

Also, please make sure @DanielRosenwasser and @RyanCavanaugh are aware of the changes, just as a heads up.

Apr 01 '24 21:04 typescript-bot

The TypeScript team hasn't accepted the linked issue #17473. If you can get it accepted, this PR will have a better chance of being reviewed.

Apr 01 '24 21:04 typescript-bot

The TypeScript team hasn't accepted the linked issue #17473. If you can get it accepted, this PR will have a better chance of being reviewed.

Apr 01 '24 21:04 typescript-bot

@typescript-bot test it

Apr 02 '24 07:04 jakebailey

Starting jobs; this comment will be updated as builds start and complete.

Command	Status	Results
`test top400`	✅ Started	👀 Results
`user test this`	✅ Started	👀 Results
`run dt`	✅ Started	✅ Results
`perf test this faster`	✅ Started	👀 Results

Apr 02 '24 07:04 typescript-bot

Hey @jakebailey, the results of running the DT tests are ready.

Everything looks the same!

You can check the log here.

Apr 02 '24 07:04 typescript-bot

@jakebailey Here are the results of running the user tests comparing main and refs/pull/58028/merge:

Something interesting changed - please have a look.

Details

puppeteer

packages/puppeteer-core/tsconfig.json

[NEW] error TS2345: Argument of type 'JSHandle<unknown>' is not assignable to parameter of type 'JSHandle<Node>'.
[NEW] error TS2345: Argument of type 'ExecutionContext' is not assignable to parameter of type 'never'.
- packages/puppeteer-core/src/cdp/ExecutionContext.ts#L315 in packages/puppeteer-core/src/tsconfig.esm.json
- packages/puppeteer-core/src/cdp/ExecutionContext.ts#L315 in packages/puppeteer-core/src/tsconfig.cjs.json
[NEW] error TS2345: Argument of type 'this' is not assignable to parameter of type 'never'.
- packages/puppeteer-core/src/bidi/Realm.ts#L198 in packages/puppeteer-core/src/tsconfig.esm.json
- packages/puppeteer-core/src/bidi/Realm.ts#L198 in packages/puppeteer-core/src/tsconfig.cjs.json

type-fest

tsconfig.json

[NEW] error TS2417: Class static side 'typeof Building' incorrectly extends base class static side '{ prototype: Pick<BuildingType, keyof BuildingType>; }'.
- test-d/abstract-class.ts#L83

Apr 02 '24 07:04 typescript-bot

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

Here they are:

tsc

Comparison Report - baseline..pr

_Metric	_baseline	_pr	_Delta	_Best	_Worst	_p-value
_{Angular - node (v18.15.0, x64)}
_{Memory used}	_{295,704k (± 0.01%)}	_{295,730k (± 0.01%)}	_~	_295,709k	_295,764k	_{p=0.093 n=6}
_{Parse Time}	_{2.66s (± 0.15%)}	_{2.64s (± 0.34%)}	_{-0.02s (- 0.69%)}	_2.63s	_2.65s	_{p=0.006 n=6}
_{Bind Time}	_{0.84s (± 0.90%)}	_{0.83s (± 0.49%)}	_~	_0.83s	_0.84s	_{p=0.100 n=6}
_{Check Time}	_{8.24s (± 0.35%)}	_{8.25s (± 0.31%)}	_~	_8.20s	_8.28s	_{p=0.570 n=6}
_{Emit Time}	_{7.04s (± 0.17%)}	_{7.04s (± 0.40%)}	_~	_7.02s	_7.08s	_{p=0.870 n=6}
_{Total Time}	_{18.76s (± 0.17%)}	_{18.76s (± 0.30%)}	_~	_18.68s	_18.85s	_{p=0.936 n=6}
_{Compiler-Unions - node (v18.15.0, x64)}
_{Memory used}	_{193,284k (± 0.93%)}	_{192,703k (± 0.74%)}	_~	_192,070k	_195,619k	_{p=0.689 n=6}
_{Parse Time}	_{1.36s (± 0.86%)}	_{1.37s (± 0.89%)}	_~	_1.35s	_1.38s	_{p=0.507 n=6}
_{Bind Time}	_{0.73s (± 0.56%)}	_{0.73s (± 0.56%)}	_~	_0.72s	_0.73s	_{p=1.000 n=6}
_{Check Time}	_{9.52s (± 0.20%)}	_{9.54s (± 0.37%)}	_~	_9.48s	_9.59s	_{p=0.090 n=6}
_{Emit Time}	_{2.63s (± 0.75%)}	_{2.63s (± 0.56%)}	_~	_2.60s	_2.64s	_{p=1.000 n=6}
_{Total Time}	_{14.23s (± 0.13%)}	_{14.26s (± 0.38%)}	_~	_14.16s	_14.32s	_{p=0.063 n=6}
_{Monaco - node (v18.15.0, x64)}
_{Memory used}	_{347,408k (± 0.01%)}	_{347,418k (± 0.01%)}	_~	_347,390k	_347,446k	_{p=0.470 n=6}
_{Parse Time}	_{2.48s (± 0.40%)}	_{2.48s (± 0.40%)}	_~	_2.47s	_2.49s	_{p=1.000 n=6}
_{Bind Time}	_{0.93s (± 0.44%)}	_{0.93s (± 0.44%)}	_~	_0.92s	_0.93s	_{p=1.000 n=6}
_{Check Time}	_{7.02s (± 0.30%)}	_{7.03s (± 0.39%)}	_~	_6.99s	_7.07s	_{p=0.329 n=6}
_{Emit Time}	_{4.06s (± 0.20%)}	_{4.06s (± 0.27%)}	_~	_4.04s	_4.07s	_{p=0.448 n=6}
_{Total Time}	_{14.48s (± 0.16%)}	_{14.50s (± 0.17%)}	_~	_14.48s	_14.55s	_{p=0.165 n=6}
_{TFS - node (v18.15.0, x64)}
_{Memory used}	_{302,767k (± 0.01%)}	_{302,789k (± 0.01%)}	_~	_302,751k	_302,821k	_{p=0.171 n=6}
_{Parse Time}	_{2.40s (± 0.83%)}	_{2.39s (± 0.67%)}	_~	_2.36s	_2.40s	_{p=0.193 n=6}
_{Bind Time}	_{1.19s (± 0.34%)}	_{1.19s (± 0.00%)}	_~	_1.19s	_1.19s	_{p=0.405 n=6}
_{Check Time}	_{7.50s (± 0.31%)}	_{7.52s (± 0.20%)}	_~	_7.50s	_7.54s	_{p=0.256 n=6}
_{Emit Time}	_{4.25s (± 0.84%)}	_{4.28s (± 0.40%)}	_~	_4.25s	_4.30s	_{p=0.257 n=6}
_{Total Time}	_{15.34s (± 0.14%)}	_{15.38s (± 0.15%)}	_~	_15.35s	_15.40s	_{p=0.072 n=6}
_{material-ui - node (v18.15.0, x64)}
_{Memory used}	_{510,199k (± 0.01%)}	_{510,160k (± 0.01%)}	_~	_510,115k	_510,249k	_{p=0.229 n=6}
_{Parse Time}	_{3.92s (± 0.13%)}	_{3.94s (± 0.44%)}	_~	_3.92s	_3.97s	_{p=0.051 n=6}
_{Bind Time}	_{1.46s (± 1.14%)}	_{1.46s (± 0.52%)}	_~	_1.45s	_1.47s	_{p=1.000 n=6}
_{Check Time}	_{25.50s (± 0.64%)}	_{25.45s (± 0.47%)}	_~	_25.30s	_25.57s	_{p=0.687 n=6}
_{Emit Time}	_{0.00s (± 0.00%)}	_{0.00s (± 0.00%)}	_~	_0.00s	_0.00s	_{p=1.000 n=6}
_{Total Time}	_{30.88s (± 0.52%)}	_{30.85s (± 0.37%)}	_~	_30.71s	_30.97s	_{p=1.000 n=6}
_{mui-docs - node (v18.15.0, x64)}
_{Memory used}	_{1,745,032k (± 0.00%)}	_{1,745,037k (± 0.00%)}	_~	_1,744,985k	_1,745,076k	_{p=0.689 n=6}
_{Parse Time}	_{6.61s (± 0.82%)}	_{6.64s (± 0.93%)}	_~	_6.58s	_6.74s	_{p=0.572 n=6}
_{Bind Time}	_{2.37s (± 0.79%)}	_{2.37s (± 0.82%)}	_~	_2.34s	_2.39s	_{p=0.870 n=6}
_{Check Time}	_{56.67s (± 0.46%)}	_{56.78s (± 0.32%)}	_~	_56.64s	_57.13s	_{p=0.575 n=6}
_{Emit Time}	_{0.13s (± 3.87%)}	_{0.13s (± 3.87%)}	_~	_0.13s	_0.14s	_{p=1.000 n=6}
_{Total Time}	_{65.78s (± 0.42%)}	_{65.93s (± 0.24%)}	_~	_65.78s	_66.24s	_{p=0.261 n=6}
_{self-build-src - node (v18.15.0, x64)}
_{Memory used}	_{2,400,790k (± 0.03%)}	_{2,400,711k (± 0.03%)}	_~	_2,399,987k	_2,401,858k	_{p=0.810 n=6}
_{Parse Time}	_{6.07s (± 0.54%)}	_{6.04s (± 1.19%)}	_~	_5.95s	_6.13s	_{p=0.810 n=6}
_{Bind Time}	_{2.25s (± 1.51%)}	_{2.26s (± 0.92%)}	_~	_2.23s	_2.29s	_{p=0.810 n=6}
_{Check Time}	_{39.98s (± 0.25%)}	_{40.02s (± 0.62%)}	_~	_39.84s	_40.48s	_{p=0.471 n=6}
_{Emit Time}	_{3.15s (± 0.68%)}	_{3.17s (± 1.00%)}	_~	_3.11s	_3.20s	_{p=0.196 n=6}
_{Total Time}	_{51.47s (± 0.16%)}	_{51.51s (± 0.64%)}	_~	_51.22s	_52.07s	_{p=0.471 n=6}
_{self-compiler - node (v18.15.0, x64)}
_{Memory used}	_{416,189k (± 0.00%)}	_{416,323k (± 0.01%)}	_{+134k (+ 0.03%)}	_416,302k	_416,356k	_{p=0.005 n=6}
_{Parse Time}	_{3.35s (± 0.58%)}	_{3.36s (± 0.95%)}	_~	_3.33s	_3.42s	_{p=0.627 n=6}
_{Bind Time}	_{1.30s (± 0.90%)}	_{1.31s (± 0.96%)}	_~	_1.30s	_1.33s	_{p=0.278 n=6}
_{Check Time}	_{18.23s (± 0.28%)}	_{18.19s (± 0.29%)}	_~	_18.12s	_18.26s	_{p=0.261 n=6}
_{Emit Time}	_{1.34s (± 2.03%)}	_{1.35s (± 1.58%)}	_~	_1.32s	_1.37s	_{p=0.627 n=6}
_{Total Time}	_{24.22s (± 0.27%)}	_{24.21s (± 0.17%)}	_~	_24.14s	_24.26s	_{p=0.872 n=6}
_{vscode - node (v18.15.0, x64)}
_{Memory used}	_{2,898,944k (± 0.00%)}	_{2,899,520k (± 0.00%)}	_{+576k (+ 0.02%)}	_2,899,329k	_2,899,637k	_{p=0.005 n=6}
_{Parse Time}	_{12.91s (± 0.11%)}	_{12.97s (± 0.54%)}	_~	_12.90s	_13.07s	_{p=0.462 n=6}
_{Bind Time}	_{4.14s (± 0.54%)}	_{4.14s (± 0.37%)}	_~	_4.11s	_4.15s	_{p=0.505 n=6}
_{Check Time}	_{72.13s (± 0.56%)}	_{71.99s (± 0.83%)}	_~	_71.47s	_73.12s	_{p=0.336 n=6}
_{Emit Time}	_{20.10s (± 8.33%)}	_{20.00s (± 7.87%)}	_~	_19.29s	_23.21s	_{p=0.422 n=6}
_{Total Time}	_{109.29s (± 1.83%)}	_{109.09s (± 1.98%)}	_~	_107.93s	_113.46s	_{p=0.378 n=6}
_{webpack - node (v18.15.0, x64)}
_{Memory used}	_{408,878k (± 0.01%)}	_{409,310k (± 0.01%)}	_{+433k (+ 0.11%)}	_409,244k	_409,399k	_{p=0.005 n=6}
_{Parse Time}	_{3.87s (± 0.34%)}	_{3.87s (± 0.48%)}	_~	_3.85s	_3.90s	_{p=1.000 n=6}
_{Bind Time}	_{1.68s (± 0.69%)}	_{1.69s (± 0.61%)}	_~	_1.67s	_1.70s	_{p=0.491 n=6}
_{Check Time}	_{16.80s (± 0.36%)}	_{16.85s (± 0.24%)}	_~	_16.80s	_16.91s	_{p=0.091 n=6}
_{Emit Time}	_{0.00s (± 0.00%)}	_{0.00s (± 0.00%)}	_~	_0.00s	_0.00s	_{p=1.000 n=6}
_{Total Time}	_{22.35s (± 0.29%)}	_{22.41s (± 0.18%)}	_~	_22.36s	_22.48s	_{p=0.149 n=6}
_{xstate - node (v18.15.0, x64)}
_{Memory used}	_{513,462k (± 0.01%)}	_{513,501k (± 0.02%)}	_~	_513,365k	_513,659k	_{p=0.230 n=6}
_{Parse Time}	_{3.98s (± 0.61%)}	_{3.97s (± 0.33%)}	_~	_3.95s	_3.98s	_{p=0.744 n=6}
_{Bind Time}	_{1.88s (± 1.46%)}	_{1.89s (± 1.60%)}	_~	_1.85s	_1.93s	_{p=0.745 n=6}
_{Check Time}	_{3.44s (± 0.66%)}	_{3.45s (± 1.28%)}	_~	_3.39s	_3.50s	_{p=0.808 n=6}
_{Emit Time}	_{0.09s (± 5.95%)}	_{0.08s (± 4.99%)}	_~	_0.08s	_0.09s	_{p=0.112 n=6}
_{Total Time}	_{9.38s (± 0.50%)}	_{9.39s (± 0.72%)}	_~	_9.31s	_9.47s	_{p=0.520 n=6}

System info unknown

Hosts

node (v18.15.0, x64)

Scenarios

Angular - node (v18.15.0, x64)
Compiler-Unions - node (v18.15.0, x64)
Monaco - node (v18.15.0, x64)
TFS - node (v18.15.0, x64)
material-ui - node (v18.15.0, x64)
mui-docs - node (v18.15.0, x64)
self-build-src - node (v18.15.0, x64)
self-compiler - node (v18.15.0, x64)
vscode - node (v18.15.0, x64)
webpack - node (v18.15.0, x64)
xstate - node (v18.15.0, x64)

_Benchmark	_Name	_Iterations
_Current	_pr	₆
_Baseline	_baseline	₆

Developer Information:

Download Benchmarks

Apr 02 '24 07:04 typescript-bot

@jakebailey Here are the results of running the top 400 repos comparing main and refs/pull/58028/merge:

Something interesting changed - please have a look.

Details

apollographql/apollo-client

1 of 12 projects failed to build with the old tsc and were ignored

tsconfig.json

error TS2345: Argument of type 'ApolloClient<unknown>' is not assignable to parameter of type 'ApolloClient<object> & { [suspenseCacheSymbol]?: SuspenseCache | undefined; }'.
- src/testing/matchers/toHaveSuspenseCacheEntryUsing.ts#L26
error TS2345: Argument of type 'any' is not assignable to parameter of type 'never'.
- src/utilities/caching/caches.ts#L39
- src/utilities/caching/caches.ts#L73

src/tsconfig.json

error TS2345: Argument of type 'ApolloClient<unknown>' is not assignable to parameter of type 'ApolloClient<object> & { [suspenseCacheSymbol]?: SuspenseCache | undefined; }'.
- src/testing/matchers/toHaveSuspenseCacheEntryUsing.ts#L26
error TS2345: Argument of type 'any' is not assignable to parameter of type 'never'.
- src/utilities/caching/caches.ts#L39
- src/utilities/caching/caches.ts#L73

colinhacks/zod

tsconfig.json

error TS2345: Argument of type 'any[]' is not assignable to parameter of type '[] | [ZodTypeAny, ...ZodTypeAny[]]'.
- src/types.ts#L2246
error TS2322: Type 'unknown' is not assignable to type 'Primitive'.
- src/types.ts#L2900

configs/tsconfig.types.json

error TS2345: Argument of type 'any[]' is not assignable to parameter of type '[] | [ZodTypeAny, ...ZodTypeAny[]]'.
- src/types.ts#L2246
error TS2322: Type 'unknown' is not assignable to type 'Primitive'.
- src/types.ts#L2900

configs/tsconfig.test.json

error TS2345: Argument of type 'any[]' is not assignable to parameter of type '[] | [ZodTypeAny, ...ZodTypeAny[]]'.
- src/types.ts#L2246
error TS2322: Type 'unknown' is not assignable to type 'Primitive'.
- src/types.ts#L2900

configs/tsconfig.esm.json

error TS2345: Argument of type 'any[]' is not assignable to parameter of type '[] | [ZodTypeAny, ...ZodTypeAny[]]'.
- src/types.ts#L2246
error TS2322: Type 'unknown' is not assignable to type 'Primitive'.
- src/types.ts#L2900

configs/tsconfig.cjs.json

error TS2345: Argument of type 'any[]' is not assignable to parameter of type '[] | [ZodTypeAny, ...ZodTypeAny[]]'.
- src/types.ts#L2246
error TS2322: Type 'unknown' is not assignable to type 'Primitive'.
- src/types.ts#L2900

desktop/desktop

1 of 4 projects failed to build with the old tsc and were ignored

tsconfig.json

error TS2322: Type '(item: ICloneableRepositoryListItem, matches: IMatches) => JSX.Element' is not assignable to type '((item: IFilterListItem, matches: IMatches) => Element | null) | ((item: IFilterListItem, matches: IMatches) => Element | null)'.
- app/src/ui/clone-repository/cloneable-repository-filter-list.tsx#L176
error TS2322: Type '(item: ICloneableRepositoryListItem | null) => void' is not assignable to type '((selectedItem: IFilterListItem | null, source: SelectionSource) => void) | ((selectedItem: IFilterListItem | null, source: SelectionSource) => void) | undefined'.
- app/src/ui/clone-repository/cloneable-repository-filter-list.tsx#L178
error TS2322: Type '((item: ICloneableRepositoryListItem, source: ClickSource) => void) | undefined' is not assignable to type '((item: IFilterListItem, source: ClickSource) => void) | ((item: IFilterListItem, source: ClickSource) => void) | undefined'.
- app/src/ui/clone-repository/cloneable-repository-filter-list.tsx#L185
error TS2322: Type '(item: IRepositoryListItem, matches: IMatches) => JSX.Element' is not assignable to type '((item: IFilterListItem, matches: IMatches) => Element | null) | ((item: IFilterListItem, matches: IMatches) => Element | null)'.
- app/src/ui/repositories-list/repositories-list.tsx#L255
error TS2322: Type '(item: IRepositoryListItem) => void' is not assignable to type '((item: IFilterListItem, source: ClickSource) => void) | ((item: IFilterListItem, source: ClickSource) => void) | undefined'.
- app/src/ui/repositories-list/repositories-list.tsx#L257
error TS2322: Type '(item: IRepositoryListItem, event: React.MouseEvent<HTMLDivElement>) => void' is not assignable to type '((item: IFilterListItem, event: MouseEvent<HTMLDivElement, MouseEvent>) => void) | ((item: IFilterListItem, event: MouseEvent<...>) => void) | undefined'.
- app/src/ui/repositories-list/repositories-list.tsx#L265
error TS2322: Type '(item: IRepositoryListItem) => string' is not assignable to type '(item: IFilterListItem) => string | undefined'.
- app/src/ui/repositories-list/repositories-list.tsx#L267

google/blockly

2 of 3 projects failed to build with the old tsc and were ignored

tsconfig.json

error TS2322: Type 'unknown' is not assignable to type 'T | null'.
- core/field.ts#L220
error TS2345: Argument of type 'typeof FieldAngle' is not assignable to parameter of type 'FieldProto'.
- core/field_angle.ts#L526
error TS2345: Argument of type 'typeof FieldCheckbox' is not assignable to parameter of type 'FieldProto'.
- core/field_checkbox.ts#L103
- core/field_checkbox.ts#L236
error TS2345: Argument of type 'typeof FieldColour' is not assignable to parameter of type 'FieldProto'.
- core/field_colour.ts#L654
error TS2345: Argument of type 'typeof FieldDropdown' is not assignable to parameter of type 'FieldProto'.
- core/field_dropdown.ts#L176
- core/field_dropdown.ts#L862
error TS2345: Argument of type 'typeof FieldImage' is not assignable to parameter of type 'FieldProto'.
- core/field_image.ts#L274
error TS2345: Argument of type 'typeof FieldLabel' is not assignable to parameter of type 'FieldProto'.
- core/field_label.ts#L128
error TS2345: Argument of type 'typeof FieldLabelSerializable' is not assignable to parameter of type 'FieldProto'.
- core/field_label_serializable.ts#L73
error TS2345: Argument of type 'typeof FieldMultilineInput' is not assignable to parameter of type 'FieldProto'.
- core/field_multilineinput.ts#L130
- core/field_multilineinput.ts#L477
error TS2345: Argument of type 'typeof FieldNumber' is not assignable to parameter of type 'FieldProto'.
- core/field_number.ts#L332
error TS2345: Argument of type 'typeof FieldTextInput' is not assignable to parameter of type 'FieldProto'.
- core/field_textinput.ts#L84
error TS2345: Argument of type 'typeof FieldVariable' is not assignable to parameter of type 'FieldProto'.

graphile/crystal

7 of 10 projects failed to build with the old tsc and were ignored

utils/lru/tests/tsconfig.json

error TS2322: Type '(key: unknown) => unknown' is not assignable to type '(key: KeyType) => ValueType | undefined'.
- utils/lru/src/index.ts#L167 in utils/lru/tsconfig.json

honojs/hono

3 of 5 projects failed to build with the old tsc and were ignored

tsconfig.json

error TS2345: Argument of type 'C & Context<Env, string, never>' is not assignable to parameter of type 'Context<E, any, {}>'.
- src/compose.ts#L41
- src/compose.ts#L51

tsconfig.build.json

error TS2345: Argument of type 'C & Context<Env, string, never>' is not assignable to parameter of type 'Context<E, any, {}>'.
- src/compose.ts#L41
- src/compose.ts#L51

jquense/yup

1 of 2 projects failed to build with the old tsc and were ignored

tsconfig.json

error TS2322: Type '{ (enums: readonly (Reference<unknown> | U)[], message?: Message<{ values: any; }> | undefined): Schema<unknown, unknown, unknown, Flags>; (enums: readonly unknown[], message: Message<{ values: any; }>): any; }' is not assignable to type '{ (enums: readonly (Reference<unknown> | U)[], message?: Message<{ values: any; }> | undefined): Schema<any, any, any, "">; (enums: readonly any[], message: Message<{ values: any; }>): any; }'.
- src/schema.ts#L1000
error TS2322: Type '(enums: readonly (Reference<unknown> | Maybe)[], message?: Message<{ values: any; }>) => Schema<unknown, unknown, unknown, Flags>' is not assignable to type '(enums: readonly (Reference<unknown> | Maybe)[], message?: Message<{ values: any; }>) => Schema<any, any, any, "">'.
- src/schema.ts#L1003

microsoft/vscode

4 of 54 projects failed to build with the old tsc and were ignored

src/tsconfig.tsec.json

error TS2345: Argument of type 'ElementsDragAndDropData<unknown, unknown>' is not assignable to parameter of type 'ElementsDragAndDropData<ITreeNode<unknown, unknown>, unknown>'.
- src/vs/base/browser/ui/tree/abstractTree.ts#L57
error TS2345: Argument of type 'ElementsDragAndDropData<unknown, unknown>' is not assignable to parameter of type 'ElementsDragAndDropData<IAsyncDataTreeNode<unknown, unknown>, unknown>'.
- src/vs/base/browser/ui/tree/asyncDataTree.ts#L177
error TS18046: 'oe' is of type 'unknown'.
error TS18046: 'e' is of type 'unknown'.
- src/vs/workbench/contrib/terminal/browser/terminalTabsList.ts#L691

src/tsconfig.monaco.json

error TS2345: Argument of type 'ElementsDragAndDropData<unknown, unknown>' is not assignable to parameter of type 'ElementsDragAndDropData<ITreeNode<unknown, unknown>, unknown>'.
- src/vs/base/browser/ui/tree/abstractTree.ts#L57
error TS2345: Argument of type 'ElementsDragAndDropData<unknown, unknown>' is not assignable to parameter of type 'ElementsDragAndDropData<IAsyncDataTreeNode<unknown, unknown>, unknown>'.
- src/vs/base/browser/ui/tree/asyncDataTree.ts#L177

src/tsconfig.json

error TS2345: Argument of type 'ElementsDragAndDropData<unknown, unknown>' is not assignable to parameter of type 'ElementsDragAndDropData<ITreeNode<unknown, unknown>, unknown>'.
- src/vs/base/browser/ui/tree/abstractTree.ts#L57
error TS2345: Argument of type 'ElementsDragAndDropData<unknown, unknown>' is not assignable to parameter of type 'ElementsDragAndDropData<IAsyncDataTreeNode<unknown, unknown>, unknown>'.
- src/vs/base/browser/ui/tree/asyncDataTree.ts#L177
error TS18046: 'oe' is of type 'unknown'.
error TS18046: 'e' is of type 'unknown'.
- src/vs/workbench/contrib/terminal/browser/terminalTabsList.ts#L691

neoclide/coc.nvim

tsconfig.json

error TS2339: Property 'retry' does not exist on type 'unknown'.
- src/language-client/client.ts#L1087

ReactiveX/rxjs

13 of 16 projects failed to build with the old tsc and were ignored

packages/observable/tsconfig.json

error TS2345: Argument of type 'Subscriber<T> | (Partial<Observer<T>> & Subscriber<never>) | (((value: T) => void) & Subscriber<never>)' is not assignable to parameter of type 'Subscriber<T>'.
- packages/observable/src/observable.ts#L697

sindresorhus/got

tsconfig.json

error TS2769: No overload matches this call.
- test/error.ts#L128

sindresorhus/type-fest

tsconfig.json

error TS2417: Class static side 'typeof Building' incorrectly extends base class static side '{ prototype: Pick<BuildingType, keyof BuildingType>; }'.
- test-d/abstract-class.ts#L83

theatre-js/theatre

16 of 24 projects failed to build with the old tsc and were ignored

packages/dataverse-experiments/tsconfig.json

error TS2322: Type '(V | IDerivation<V>) & AbstractDerivation<unknown>' is not assignable to type 'IDerivation<V> | null | undefined'.
- packages/dataverse-experiments/src/derivations/flatMap.ts#L43 in packages/dataverse-experiments/tsconfig.json
error TS2416: Property '_recalculate' in type 'FlatMapDerivation<V, DepType>' is not assignable to the same property in base type 'AbstractDerivation<V>'.
- packages/dataverse-experiments/src/derivations/flatMap.ts#L61 in packages/dataverse-experiments/tsconfig.json

Apr 02 '24 08:04 typescript-bot

Wow, it broke approximately everything 😅

Apr 02 '24 15:04 fatcerberus

Not surprising if you've seen #49863.

Notably, this new PR adds a strict mode setting. That's what made DT clean, as DT does not set strict=true, but rather enables specific strict mode options. (Been on my todo list to look into change that for a while.)

Apr 02 '24 15:04 jakebailey

@jakebailey If you pack this I can make playground reproductions of some of these errors.

And let me know if you want to test turning it on by default 😅

Apr 02 '24 17:04 molisani

@typescript-bot pack this

Apr 02 '24 17:04 jakebailey

Starting jobs; this comment will be updated as builds start and complete.

Command	Status	Results
`pack this`	✅ Started	✅ Results

Apr 02 '24 17:04 typescript-bot

Hey @jakebailey, 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/160908/artifacts?artifactName=tgz&fileId=887091D6EC182401D9A7B148E7615E05FC9A1E5F8637C385DC2D7778C222C73C02&fileName=/typescript-5.5.0-insiders.20240402.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/[email protected]".;

Apr 02 '24 17:04 typescript-bot

There are a decent number of errors where some type that was any is now unknown. Most of these could be fixed by adding/modifying a constraint or adding a type cast. The strangest errors showed up when prototype was used/declared manually. I've compiled a collection of some errors that weren't clear to me on first glance:

A) Extracting `prototype` directly is now too restrictive

From: google/blockly Playground - This code used Pick<typeof Class, "prototype"> as a shorthand to capture the prototype, but this is now the most restrictive version. In order to loosen the type, it needs to be manually declared with whatever type argument is most correct.

B) `new.target.prototype` doesn't capture local type parameters

From: google/blockly Playground - This is now a valid error, as there is no guarantee that every instance of this class has a type argument that matches DEFAULT_VALUE.

C) Subclass doesn't share instance of type in manual prototype declaration

From: sindresorhus/type-fest Playground - I'm not exactly sure why this is going wrong. It seems like the concern about it being a different subtype is not warranted, but I can't say for sure. This one is definitely the most worrying of what I've seen, as I wouldn't expect class X extends Y {} to give me an error.

Apr 02 '24 19:04 molisani

Hi there @molisani, are there plans to resurrect this? Would be a great addition!

Jun 07 '25 20:06 nmattia

I would definitely be interested in refreshing and landing this, but I don't know what the appetite is from the TypeScript team given that it would lead to a lot of breakage and the codebase is currently being migrated to the golang rewrite. Will defer to @jakebailey or @sandersn for a recommendation.

Jun 09 '25 14:06 molisani

I'd guess it's worth keeping around but we are all still heads-down on porting at the moment. I think it's likely that we'd need to discuss it at a design meeting as well, to decide on the question of breaks vs flags.

Jun 09 '25 22:06 sandersn

Infer type arguments on instance check

Breaking Changes

tsc

A) Extracting prototype directly is now too restrictive

B) new.target.prototype doesn't capture local type parameters

C) Subclass doesn't share instance of type in manual prototype declaration

A) Extracting `prototype` directly is now too restrictive

B) `new.target.prototype` doesn't capture local type parameters