Improve intersection reduction and CFA for truthy, equality, and typeof checks #49119

ahejlsberg · 2022-05-15T19:20:51Z

This PR introduces a number of changes affecting control flow analysis of truthy, equality, and typeof checks involving type unknown and unconstrained type variables in --strictNullChecks mode. Key to these changes is the fact that {}, the empty object type literal, is a supertype of all types except null and undefined. Thus, {} | null | undefined is effectively equivalent to unknown, and for an arbitrary type T, the intersection T & {} represents the non-nullable form of T.

The PR introduces the following new behaviors:

An unconstrained type parameter is no longer assignable to {}.
The predefined type NonNullable<T> is now an alias for T & {}.
An intersection T & {}, where T is non-generic and not null or undefined, reduces to just T (null & {} and undefined & {} already reduce to never). See below for exceptions for string & {}, number & {}, and bigint & {}.
An intersection undefined & void reduces to just undefined.
Any type is assignable to a union type that contains {}, null, and undefined.
In control flow analysis, unknown behaves similarly to the union type {} | null | undefined.
In control flow analysis of truthy checks, generic types are intersected with {} in the true branch.
In control flow analysis of equality comparisons with null or undefined, generic types are intersected with {}, {} | null, or {} | undefined in the false branch.
In control flow analysis of typeof x === "object" expressions, generic types are intersected with object and/or null in the true branch (typeof checks for other types already produce intersections in a similar manner).

Some examples:

type T1 = {} & string;  // string
type T2 = {} & 'a';  // 'a'
type T3 = {} & object;  // object
type T4 = {} & { x: number };  // { x: number }
type T5 = {} & null;  // never
type T6 = {} & undefined;  // never
type T7 = undefined & void;  // undefined

function f1(u: unknown) {
    let x1: {} = u;  // Error
    let x2: {} | null | undefined = u;  // Ok
    let x3: {} | { x: string } | null | undefined = u;  // Ok
}

function f2(x: unknown) {
    if (x) {
        x;  // {}
    }
    else {
        x;  // unknown
    }
}

function f3<T>(x: T) {
    if (x) {
        x;  // T & {}
    }
    else {
        x;  // T
    }
}

function f4(x: unknown) {
    if (x !== undefined) {
        x;  // {} | null
    }
    else {
        x;  // undefined
    }
    if (x !== null) {
        x;  // {} | undefined
    }
    else {
        x;  // null
    }
    if (x !== undefined && x !== null) {
        x;  // {}
    }
    else {
        x;  // null | undefined
    }
    if (x != undefined) {
        x;  // {}
    }
    else {
        x;  // null | undefined
    }
    if (x != null) {
        x;  // {}
    }
    else {
        x;  // null | undefined
    }
}

function f5<T>(x: T) {
    if (x !== undefined) {
        x;  // T & ({} | null)
    }
    else {
        x;  // T
    }
    if (x !== null) {
        x;  // T & ({} | undefined)
    }
    else {
        x;  // T
    }
    if (x !== undefined && x !== null) {
        x;  // {}
    }
    else {
        x;  // T
    }
    if (x != undefined) {
        x;  // {}
    }
    else {
        x;  // T
    }
    if (x != null) {
        x;  // {}
    }
    else {
        x;  // T
    }
}

function f6<T>(x: T) {
    if (typeof x === "object") {
        x;  // T & object | T & null
    }
    if (x && typeof x === "object") {
        x;  // T & object
    }
    if (typeof x === "object" && x) {
        x;  // T & object
    }
}

function ensureNotNull<T>(x: T) {
    if (x === null) throw Error();
    return x;  // T & ({} | undefined)
}

function ensureNotUndefined<T>(x: T) {
    if (x === undefined) throw Error();
    return x;  // T & ({} | null)
}

function ensureNotNullOrUndefined<T>(x: T) {
    return ensureNotUndefined(ensureNotNull(x));  // T & {}
}

function f7(a: string | undefined, b: number | null | undefined) {
    let a1 = ensureNotNullOrUndefined(a);  // string
    let b1 = ensureNotNullOrUndefined(b);  // number
}

Note the manner in which types are properly inferred, combined, and reduced in the ensureNotXXX functions. This contrasts with the NonNullable<T> conditional type provided in lib.d.ts, which unfortunately combines and reduces poorly. For example, NonNullable<NonNullable<T>> doesn't inherently reduce to NonNullable<T>, sometimes leading to needlessly complex types. For this and other reasons we intend to investigate switching NonNullable<T> to be an alias for T & {}.

For backwards compatibility, special exceptions to the T & {} type reduction rules existing for intersections written explicitly as string & {}, number & {}, and bigint & {} (as opposed to created through instantiation of a generic type T & {}). These types are used in a few frameworks (e.g. react and csstype) to construct types that permit any string, number, or bigint, but has statement completion hints for common literal values. For example:

type Alignment = string & {} | "left" | "center" | "right";

The special string & {} type prevents subtype reduction from taking place in the union type, thus preserving the literal types, but otherwise any string value is assignable to the type.

This PR reinstatates #48366 (which was removed from 4.7 due to concerns over breaking changes).

Fixes #23368.
Fixes #31908.
Fixes #32347.
Fixes #43997.
Fixes #44446.
Fixes #48048.
Fixes #48468.
Fixes #48691.
Fixes #49005.
Fixes #49191.

ahejlsberg · 2022-05-15T19:21:48Z

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

typescript-bot · 2022-05-15T19:21:50Z

Heya @ahejlsberg, I've started to run the abridged perf test suite on this PR at 39326d7. You can monitor the build here.

Update: The results are in!

typescript-bot · 2022-05-15T19:21:50Z

Heya @ahejlsberg, I've started to run the parallelized Definitely Typed test suite on this PR at 39326d7. You can monitor the build here.

typescript-bot · 2022-05-15T19:21:50Z

Heya @ahejlsberg, I've started to run the extended test suite on this PR at 39326d7. You can monitor the build here.

typescript-bot · 2022-05-15T19:21:50Z

Heya @ahejlsberg, I've started to run the diff-based community code test suite on this PR at 39326d7. You can monitor the build here.

Update: The results are in!

typescript-bot · 2022-05-15T19:34:56Z

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

Here they are:

Comparison Report - main..refs/pull/49119/merge

[async]

1 of 1 projects failed to build with the old tsc

/mnt/ts_downloads/async/tsconfig.json

error TS2339: Property 'iterator' does not exist on type 'never'.
- /mnt/ts_downloads/async/node_modules/async/dist/async.js(477,61)
- /mnt/ts_downloads/async/node_modules/async/internal/getIterator.js(11,61)

typescript-bot · 2022-05-15T19:36:09Z

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

Here they are:

Comparison Report - main..49119

_Metric	_main	₄₉₁₁₉	_Delta	_Best	_Worst
_{Angular - node (v14.15.1, x64)}
_{Memory used}	_{333,610k (± 0.01%)}	_{333,600k (± 0.01%)}	_{-9k (- 0.00%)}	_333,548k	_333,664k
_{Parse Time}	_{2.04s (± 0.44%)}	_{2.07s (± 0.96%)}	_{+0.02s (+ 1.08%)}	_2.04s	_2.13s
_{Bind Time}	_{0.88s (± 0.95%)}	_{0.88s (± 0.78%)}	_{0.00s ( 0.00%)}	_0.86s	_0.89s
_{Check Time}	_{5.65s (± 0.55%)}	_{5.69s (± 0.54%)}	_{+0.03s (+ 0.58%)}	_5.61s	_5.76s
_{Emit Time}	_{6.29s (± 0.74%)}	_{6.37s (± 0.93%)}	_{+0.08s (+ 1.34%)}	_6.19s	_6.49s
_{Total Time}	_{14.86s (± 0.49%)}	_{15.00s (± 0.62%)}	_{+0.14s (+ 0.94%)}	_14.70s	_15.15s
_{Compiler-Unions - node (v14.15.1, x64)}
_{Memory used}	_{192,272k (± 0.01%)}	_{192,173k (± 0.12%)}	_{-99k (- 0.05%)}	_191,218k	_192,363k
_{Parse Time}	_{0.85s (± 0.87%)}	_{0.85s (± 0.35%)}	_{-0.00s (- 0.24%)}	_0.84s	_0.85s
_{Bind Time}	_{0.56s (± 0.84%)}	_{0.56s (± 0.84%)}	_{+0.00s (+ 0.54%)}	_0.55s	_0.57s
_{Check Time}	_{7.55s (± 0.47%)}	_{7.61s (± 0.68%)}	_{+0.06s (+ 0.78%)}	_7.52s	_7.75s
_{Emit Time}	_{2.50s (± 0.66%)}	_{2.51s (± 0.89%)}	_{+0.01s (+ 0.28%)}	_2.47s	_2.58s
_{Total Time}	_{11.46s (± 0.28%)}	_{11.53s (± 0.54%)}	_{+0.06s (+ 0.56%)}	_11.43s	_11.74s
_{Monaco - node (v14.15.1, x64)}
_{Memory used}	_{325,609k (± 0.00%)}	_{325,639k (± 0.00%)}	_{+30k (+ 0.01%)}	_325,603k	_325,665k
_{Parse Time}	_{1.56s (± 0.40%)}	_{1.57s (± 0.85%)}	_{+0.02s (+ 1.03%)}	_1.55s	_1.61s
_{Bind Time}	_{0.78s (± 1.15%)}	_{0.78s (± 0.71%)}	_{+0.00s (+ 0.26%)}	_0.77s	_0.79s
_{Check Time}	_{5.54s (± 0.51%)}	_{5.54s (± 0.36%)}	_{+0.01s (+ 0.13%)}	_5.51s	_5.58s
_{Emit Time}	_{3.31s (± 0.47%)}	_{3.33s (± 0.75%)}	_{+0.02s (+ 0.51%)}	_3.27s	_3.37s
_{Total Time}	_{11.18s (± 0.26%)}	_{11.22s (± 0.24%)}	_{+0.05s (+ 0.42%)}	_11.15s	_11.26s
_{TFS - node (v14.15.1, x64)}
_{Memory used}	_{289,123k (± 0.01%)}	_{289,109k (± 0.01%)}	_{-14k (- 0.00%)}	_289,052k	_289,157k
_{Parse Time}	_{1.36s (± 1.72%)}	_{1.37s (± 0.73%)}	_{+0.01s (+ 0.51%)}	_1.35s	_1.40s
_{Bind Time}	_{0.72s (± 0.31%)}	_{0.72s (± 0.55%)}	_{+0.00s (+ 0.00%)}	_0.71s	_0.73s
_{Check Time}	_{5.21s (± 0.57%)}	_{5.21s (± 0.44%)}	_{+0.00s (+ 0.08%)}	_5.17s	_5.26s
_{Emit Time}	_{3.54s (± 1.90%)}	_{3.60s (± 1.11%)}	_{+0.06s (+ 1.70%)}	_3.44s	_3.64s
_{Total Time}	_{10.83s (± 0.73%)}	_{10.90s (± 0.41%)}	_{+0.07s (+ 0.65%)}	_10.77s	_11.01s
_{material-ui - node (v14.15.1, x64)}
_{Memory used}	_{445,620k (± 0.06%)}	_{445,758k (± 0.00%)}	_{+138k (+ 0.03%)}	_445,724k	_445,788k
_{Parse Time}	_{1.88s (± 0.59%)}	_{1.88s (± 0.59%)}	_{0.00s ( 0.00%)}	_1.86s	_1.91s
_{Bind Time}	_{0.70s (± 0.68%)}	_{0.70s (± 0.68%)}	_{0.00s ( 0.00%)}	_0.69s	_0.71s
_{Check Time}	_{13.12s (± 0.84%)}	_{13.15s (± 0.63%)}	_{+0.03s (+ 0.23%)}	_12.95s	_13.31s
_{Emit Time}	_{0.00s (± 0.00%)}	_{0.00s (± 0.00%)}	_{0.00s ( NaN%)}	_0.00s	_0.00s
_{Total Time}	_{15.70s (± 0.73%)}	_{15.73s (± 0.54%)}	_{+0.03s (+ 0.21%)}	_15.52s	_15.91s
_{xstate - node (v14.15.1, x64)}
_{Memory used}	_{535,261k (± 0.00%)}	_{535,348k (± 0.00%)}	_{+87k (+ 0.02%)}	_535,298k	_535,383k
_{Parse Time}	_{2.58s (± 0.44%)}	_{2.60s (± 0.57%)}	_{+0.02s (+ 0.77%)}	_2.57s	_2.64s
_{Bind Time}	_{1.15s (± 0.65%)}	_{1.16s (± 1.25%)}	_{+0.01s (+ 1.13%)}	_1.14s	_1.20s
_{Check Time}	_{1.52s (± 0.48%)}	_{1.52s (± 0.45%)}	_{+0.00s (+ 0.20%)}	_1.51s	_1.54s
_{Emit Time}	_{0.07s (± 0.00%)}	_{0.07s (± 0.00%)}	_{0.00s ( 0.00%)}	_0.07s	_0.07s
_{Total Time}	_{5.32s (± 0.20%)}	_{5.36s (± 0.40%)}	_{+0.04s (+ 0.75%)}	_5.32s	_5.42s

System

_{Machine Name}	_ts-ci-ubuntu
_Platform	_{linux 4.4.0-210-generic}
_Architecture	_x64
_{Available Memory}	_{16 GB}
_{Available Memory}	_{1 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	₄₉₁₁₉	₁₀
_Baseline	_main	₁₀

Developer Information:

Download Benchmark

ahejlsberg · 2022-05-15T23:45:14Z

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

typescript-bot · 2022-05-15T23:45:16Z

Heya @ahejlsberg, I've started to run the abridged perf test suite on this PR at 986963c. You can monitor the build here.

Update: The results are in!

typescript-bot · 2022-05-15T23:45:16Z

Heya @ahejlsberg, I've started to run the parallelized Definitely Typed test suite on this PR at 986963c. You can monitor the build here.

typescript-bot · 2022-05-15T23:45:16Z

Heya @ahejlsberg, I've started to run the diff-based community code test suite on this PR at 986963c. You can monitor the build here.

typescript-bot · 2022-05-15T23:45:16Z

Heya @ahejlsberg, I've started to run the extended test suite on this PR at 986963c. You can monitor the build here.

typescript-bot · 2022-05-15T23:59:23Z

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

Here they are:

Comparison Report - main..49119

_Metric	_main	₄₉₁₁₉	_Delta	_Best	_Worst
_{Angular - node (v14.15.1, x64)}
_{Memory used}	_{333,610k (± 0.01%)}	_{333,609k (± 0.00%)}	_{-1k (- 0.00%)}	_333,591k	_333,642k
_{Parse Time}	_{2.04s (± 0.44%)}	_{2.04s (± 0.46%)}	_{-0.00s (- 0.10%)}	_2.02s	_2.06s
_{Bind Time}	_{0.88s (± 0.95%)}	_{0.87s (± 0.46%)}	_{-0.00s (- 0.46%)}	_0.86s	_0.88s
_{Check Time}	_{5.65s (± 0.55%)}	_{5.65s (± 0.39%)}	_{-0.00s (- 0.02%)}	_5.60s	_5.69s
_{Emit Time}	_{6.29s (± 0.74%)}	_{6.35s (± 0.88%)}	_{+0.06s (+ 0.97%)}	_6.27s	_6.49s
_{Total Time}	_{14.86s (± 0.49%)}	_{14.91s (± 0.44%)}	_{+0.05s (+ 0.35%)}	_14.78s	_15.04s
_{Compiler-Unions - node (v14.15.1, x64)}
_{Memory used}	_{192,272k (± 0.01%)}	_{192,279k (± 0.02%)}	_{+7k (+ 0.00%)}	_192,180k	_192,344k
_{Parse Time}	_{0.85s (± 0.87%)}	_{0.85s (± 0.73%)}	_{-0.00s (- 0.12%)}	_0.84s	_0.86s
_{Bind Time}	_{0.56s (± 0.84%)}	_{0.56s (± 0.65%)}	_{+0.00s (+ 0.71%)}	_0.56s	_0.57s
_{Check Time}	_{7.55s (± 0.47%)}	_{7.55s (± 0.40%)}	_{-0.00s (- 0.03%)}	_7.50s	_7.63s
_{Emit Time}	_{2.50s (± 0.66%)}	_{2.50s (± 0.75%)}	_{+0.00s (+ 0.12%)}	_2.46s	_2.54s
_{Total Time}	_{11.46s (± 0.28%)}	_{11.46s (± 0.35%)}	_{+0.00s (+ 0.02%)}	_11.39s	_11.59s
_{Monaco - node (v14.15.1, x64)}
_{Memory used}	_{325,609k (± 0.00%)}	_{325,627k (± 0.01%)}	_{+18k (+ 0.01%)}	_325,586k	_325,688k
_{Parse Time}	_{1.56s (± 0.40%)}	_{1.57s (± 0.67%)}	_{+0.01s (+ 0.90%)}	_1.56s	_1.60s
_{Bind Time}	_{0.78s (± 1.15%)}	_{0.77s (± 0.72%)}	_{-0.00s (- 0.52%)}	_0.76s	_0.78s
_{Check Time}	_{5.54s (± 0.51%)}	_{5.59s (± 0.32%)}	_{+0.06s (+ 0.99%)}	_5.54s	_5.63s
_{Emit Time}	_{3.31s (± 0.47%)}	_{3.35s (± 0.75%)}	_{+0.04s (+ 1.18%)}	_3.30s	_3.40s
_{Total Time}	_{11.18s (± 0.26%)}	_{11.29s (± 0.37%)}	_{+0.11s (+ 0.98%)}	_11.20s	_11.36s
_{TFS - node (v14.15.1, x64)}
_{Memory used}	_{289,123k (± 0.01%)}	_{289,132k (± 0.00%)}	_{+8k (+ 0.00%)}	_289,103k	_289,147k
_{Parse Time}	_{1.36s (± 1.72%)}	_{1.36s (± 1.10%)}	_{-0.01s (- 0.44%)}	_1.31s	_1.38s
_{Bind Time}	_{0.72s (± 0.31%)}	_{0.72s (± 0.50%)}	_{+0.00s (+ 0.42%)}	_0.72s	_0.73s
_{Check Time}	_{5.21s (± 0.57%)}	_{5.21s (± 0.29%)}	_{+0.00s (+ 0.02%)}	_5.18s	_5.24s
_{Emit Time}	_{3.54s (± 1.90%)}	_{3.56s (± 1.93%)}	_{+0.03s (+ 0.76%)}	_3.41s	_3.65s
_{Total Time}	_{10.83s (± 0.73%)}	_{10.85s (± 0.69%)}	_{+0.02s (+ 0.22%)}	_10.67s	_10.97s
_{material-ui - node (v14.15.1, x64)}
_{Memory used}	_{445,620k (± 0.06%)}	_{445,722k (± 0.01%)}	_{+102k (+ 0.02%)}	_445,618k	_445,786k
_{Parse Time}	_{1.88s (± 0.59%)}	_{1.88s (± 0.56%)}	_{-0.01s (- 0.37%)}	_1.86s	_1.91s
_{Bind Time}	_{0.70s (± 0.68%)}	_{0.70s (± 0.74%)}	_{+0.00s (+ 0.57%)}	_0.69s	_0.71s
_{Check Time}	_{13.12s (± 0.84%)}	_{13.11s (± 0.61%)}	_{-0.01s (- 0.08%)}	_12.96s	_13.36s
_{Emit Time}	_{0.00s (± 0.00%)}	_{0.00s (± 0.00%)}	_{0.00s ( NaN%)}	_0.00s	_0.00s
_{Total Time}	_{15.70s (± 0.73%)}	_{15.69s (± 0.53%)}	_{-0.01s (- 0.07%)}	_15.52s	_15.95s
_{xstate - node (v14.15.1, x64)}
_{Memory used}	_{535,261k (± 0.00%)}	_{535,395k (± 0.00%)}	_{+134k (+ 0.03%)}	_535,367k	_535,423k
_{Parse Time}	_{2.58s (± 0.44%)}	_{2.60s (± 0.58%)}	_{+0.02s (+ 0.77%)}	_2.57s	_2.63s
_{Bind Time}	_{1.15s (± 0.65%)}	_{1.15s (± 1.04%)}	_{+0.00s (+ 0.26%)}	_1.13s	_1.19s
_{Check Time}	_{1.52s (± 0.48%)}	_{1.52s (± 0.70%)}	_{+0.00s (+ 0.20%)}	_1.51s	_1.55s
_{Emit Time}	_{0.07s (± 0.00%)}	_{0.07s (± 0.00%)}	_{0.00s ( 0.00%)}	_0.07s	_0.07s
_{Total Time}	_{5.32s (± 0.20%)}	_{5.35s (± 0.42%)}	_{+0.03s (+ 0.53%)}	_5.30s	_5.39s

System

_{Machine Name}	_ts-ci-ubuntu
_Platform	_{linux 4.4.0-210-generic}
_Architecture	_x64
_{Available Memory}	_{16 GB}
_{Available Memory}	_{1 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	₄₉₁₁₉	₁₀
_Baseline	_main	₁₀

Developer Information:

Download Benchmark

ahejlsberg · 2022-05-16T13:58:52Z

@user test this inline

jcalz · 2022-09-17T18:21:50Z

Is there a reason why this narrowing wasn't implemented for typeof x === "undefined" the way it was for x === undefined? See this SO question

jakebailey · 2022-09-19T21:33:06Z

I feel like that's an oversight and probably deserves its own issue. (But, I'm not Anders 😄)

Andarist · 2023-02-01T10:39:44Z

@jcalz what you reported here, in your last comment, was just fixed 2 days ago in #52456

uid11 · 2023-09-28T10:39:08Z

It seems that in the examples in the main message in the function f5<T> the type parameter T is missing in a couple of places:

function f5<T>(x: T) {
    ...
    if (x !== undefined && x !== null) {
        x;  // {} -- should be T & {}
    }
    else {
        x;  // T
    }
    if (x != undefined) {
        x;  // {} -- should be NonNullable<T>
    }
    else {
        x;  // T
    }
    if (x != null) {
        x;  // {} -- should be NonNullable<T>
    }
    else {
        x;  // T
    }
}

But this is clear from the context and will not confuse anyone too much, I think.

ahejlsberg added 5 commits May 5, 2022 08:31

Improve reduction of intersection types

ce23b8d

Accept new baselines

ffe147e

Merge branch 'main' into improveIntersectionReduction

a95de48

Improve CFA for truthy, equality, and typeof checks

29edef1

Accept new baselines

39326d7

typescript-bot assigned ahejlsberg May 15, 2022

typescript-bot added Author: Team For Uncommitted Bug PR for untriaged, rejected, closed or missing bug labels May 15, 2022

ahejlsberg added 4 commits May 15, 2022 13:12

Remove special case for Function type

d0b7ec8

Merge branch 'main' into improveIntersectionReduction

a25388d

Don't reduce intersections of form {...} & object

95c3c56

Accept new baselines

986963c

DanielRosenwasser mentioned this pull request May 16, 2022

Design Meeting Notes, 5/13/2022 #49137

Closed

ahejlsberg added 3 commits May 16, 2022 14:16

Anything is assignable to unknown-like union

c400181

Accept new baselines

f1ebcdd

Tweak subtype check

73c91fd

JLHwung mentioned this pull request Aug 29, 2022

Performance issue on updating Babel monorepo typescript from 4.7.4 to 4.8.2 #50515

Closed

jakebailey mentioned this pull request Aug 30, 2022

[regression 4.8] type narrowed too far; valid cases considered unreachable #50527

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jcalz mentioned this pull request Aug 31, 2022

unknown type is narrowed to {} in strict equality condition since 4.8 #50567

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andrewbranch mentioned this pull request Sep 1, 2022

Use bidirectional comparability in narrowing #50592

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BPScott mentioned this pull request Sep 6, 2022

Typescript 4.9 Shopify/quilt#2409

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PointSingularity mentioned this pull request Sep 7, 2022

MantineThemeColors are possibly "undefined" (loses types on TypeScript v4.8.2) mantinedev/mantine#2364

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maxijonson mentioned this pull request Sep 8, 2022

Since 4.8.2, union discrimination fails with (string & {}) when noUncheckedIndexedAccess is true #50683

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WhiteMinds mentioned this pull request Sep 13, 2022

Typescript 4.8.2 does not like the type definitions from sequelize 6.21.4 sequelize/sequelize#14934

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zuopf769 mentioned this pull request Sep 19, 2022

微软宣布 TypeScript 4.8 正式发布 retech-fe/weekly#59

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jakebailey mentioned this pull request Oct 21, 2022

tsserver and intellisense hang indefinitely on "loading intellisense status" and "loading..." when using assertion function and complex conditional type #51188

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jakebailey mentioned this pull request Feb 1, 2023

await Promise.all fails to resolve due to optional chaining in JSX #52475

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Andarist mentioned this pull request Feb 15, 2023

Make special intersections order-independent #52782

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andrewbranch mentioned this pull request Mar 1, 2023

"Special" intersections (such as string & {}) are no longer order-independent since 4.8 #53043

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JoniJnm mentioned this pull request Mar 10, 2023

NonNullable behaves differently when passing a property type from this #36061

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jakebailey mentioned this pull request Jul 11, 2023

this type is not assignable to NonNullable<this> #22934

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This was referenced Jul 18, 2023

Unconstrained generics are incorrectly assignable to _any_ "Partial" type #30634

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Enable @typescript-eslint/ban-types #55133

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Andarist mentioned this pull request Aug 13, 2023

Incorrect post-narrowing merge of typeof symbol | {} | (() => void) #45467

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jcalz mentioned this pull request Dec 6, 2023

Empty types and types with never as a key behave differently #56691

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Andarist mentioned this pull request Jan 7, 2024

Extend isEmptyAnonymousObjectType with support for non-generic mapped types #56974

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Andarist mentioned this pull request Jan 24, 2024

NonNullable doesn't work on mapped types instantiated with null/undefined #57151

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Andarist mentioned this pull request Mar 7, 2024

Fixed excess and common property checks with NoInfer #57673

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jakebailey mentioned this pull request Mar 15, 2024

Remove nonNullUnknownType #57665

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This was referenced Mar 17, 2024

Enhancement: [ban-types] Split the {} ban into a separate, better-phrased rule typescript-eslint/typescript-eslint#8700

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ESM X.test which have zero export statement, should be sub type of ESM X which have at least one export statement #57735

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jakebailey mentioned this pull request Apr 16, 2024

TypeScript 4.6 regression #48118

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Improve intersection reduction and CFA for truthy, equality, and typeof checks #49119

Improve intersection reduction and CFA for truthy, equality, and typeof checks #49119

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[async]

/mnt/ts_downloads/async/tsconfig.json

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uid11 commented Sep 28, 2023

Improve intersection reduction and CFA for truthy, equality, and typeof checks #49119

Improve intersection reduction and CFA for truthy, equality, and typeof checks #49119

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[async]

/mnt/ts_downloads/async/tsconfig.json

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