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fix(64231): avoid parsing async() calls as typed arrows in conditionals #64233

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3ffd995
fix(64231): avoid parsing async() calls as typed arrows in conditionals
a-tarasyuk Sep 10, 2026
00e82d9
Merge branch 'main' into fix/64231
a-tarasyuk Sep 11, 2026
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11 changes: 6 additions & 5 deletions tsc/internal/parser/parser.go
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Original file line number Diff line number Diff line change
Expand Up @@ -4263,7 +4263,8 @@ func (p *Parser) isParenthesizedArrowFunctionExpression() core.Tristate {
}

func (p *Parser) nextIsParenthesizedArrowFunctionExpression() core.Tristate {
if p.token == ast.KindAsyncKeyword {
isAsync := p.token == ast.KindAsyncKeyword
if isAsync {
p.nextToken()
if p.hasPrecedingLineBreak() {
return core.TSFalse
Expand All @@ -4277,12 +4278,12 @@ func (p *Parser) nextIsParenthesizedArrowFunctionExpression() core.Tristate {
if first == ast.KindOpenParenToken {
if second == ast.KindCloseParenToken {
// Simple cases: "() =>", "(): ", and "() {".
// This is an arrow function with no parameters.
// The last one is not actually an arrow function,
// but this is probably what the user intended.
third := p.nextToken()
switch third {
case ast.KindEqualsGreaterThanToken, ast.KindColonToken, ast.KindOpenBraceToken:
switch p.nextToken() {
case ast.KindColonToken:
return core.IfElse(isAsync, core.TSUnknown, core.TSTrue)
case ast.KindEqualsGreaterThanToken, ast.KindOpenBraceToken:
return core.TSTrue
}
return core.TSFalse
Expand Down
29 changes: 29 additions & 0 deletions tsc/testdata/baselines/reference/compiler/parenthesizedAsyncArrowFunction.js
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Expand Up @@ -4,6 +4,22 @@
// Repro from #20096

let foo = (async bar => bar);

const a = true;
const b = 1;

function async(): number {
return b;
}

const f1 = a ? async() : 0;
const f2 = a ? async() : x => x;
const f3 = a ? a ? async() : 0 : b;
const f4 = a ? x => async() : x => x;
const f5 = a ? async (): Promise<number> => b : () => b;
const f6 = a ? async (): Promise<number> => { return b; } : () => b;
const f7 = a ? async (): Promise<number> => a ? async() : 0 : () => b;
const f8 = a ? (): number => b : () => b;


//// [parenthesizedAsyncArrowFunction.js]
Expand All @@ -19,3 +35,16 @@ var __awaiter = (this && this.__awaiter) || function (thisArg, _arguments, P, ge
});
};
let foo = ((bar) => __awaiter(void 0, void 0, void 0, function* () { return bar; }));
const a = true;
const b = 1;
function async() {
return b;
}
const f1 = a ? async() : 0;
const f2 = a ? async() : x => x;
const f3 = a ? a ? async() : 0 : b;
const f4 = a ? x => async() : x => x;
const f5 = a ? () => __awaiter(void 0, void 0, void 0, function* () { return b; }) : () => b;
const f6 = a ? () => __awaiter(void 0, void 0, void 0, function* () { return b; }) : () => b;
const f7 = a ? () => __awaiter(void 0, void 0, void 0, function* () { return a ? async() : 0; }) : () => b;
const f8 = a ? () => b : () => b;
68 changes: 68 additions & 0 deletions tsc/testdata/baselines/reference/compiler/parenthesizedAsyncArrowFunction.symbols
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Expand Up @@ -8,3 +8,71 @@ let foo = (async bar => bar);
>bar : Symbol(bar, Decl(parenthesizedAsyncArrowFunction.ts, 2, 16))
>bar : Symbol(bar, Decl(parenthesizedAsyncArrowFunction.ts, 2, 16))

const a = true;
>a : Symbol(a, Decl(parenthesizedAsyncArrowFunction.ts, 4, 5))

const b = 1;
>b : Symbol(b, Decl(parenthesizedAsyncArrowFunction.ts, 5, 5))

function async(): number {
>async : Symbol(async, Decl(parenthesizedAsyncArrowFunction.ts, 5, 12))

return b;
>b : Symbol(b, Decl(parenthesizedAsyncArrowFunction.ts, 5, 5))
}

const f1 = a ? async() : 0;
>f1 : Symbol(f1, Decl(parenthesizedAsyncArrowFunction.ts, 11, 5))
>a : Symbol(a, Decl(parenthesizedAsyncArrowFunction.ts, 4, 5))
>async : Symbol(async, Decl(parenthesizedAsyncArrowFunction.ts, 5, 12))

const f2 = a ? async() : x => x;
>f2 : Symbol(f2, Decl(parenthesizedAsyncArrowFunction.ts, 12, 5))
>a : Symbol(a, Decl(parenthesizedAsyncArrowFunction.ts, 4, 5))
>async : Symbol(async, Decl(parenthesizedAsyncArrowFunction.ts, 5, 12))
>x : Symbol(x, Decl(parenthesizedAsyncArrowFunction.ts, 12, 24))
>x : Symbol(x, Decl(parenthesizedAsyncArrowFunction.ts, 12, 24))

const f3 = a ? a ? async() : 0 : b;
>f3 : Symbol(f3, Decl(parenthesizedAsyncArrowFunction.ts, 13, 5))
>a : Symbol(a, Decl(parenthesizedAsyncArrowFunction.ts, 4, 5))
>a : Symbol(a, Decl(parenthesizedAsyncArrowFunction.ts, 4, 5))
>async : Symbol(async, Decl(parenthesizedAsyncArrowFunction.ts, 5, 12))
>b : Symbol(b, Decl(parenthesizedAsyncArrowFunction.ts, 5, 5))

const f4 = a ? x => async() : x => x;
>f4 : Symbol(f4, Decl(parenthesizedAsyncArrowFunction.ts, 14, 5))
>a : Symbol(a, Decl(parenthesizedAsyncArrowFunction.ts, 4, 5))
>x : Symbol(x, Decl(parenthesizedAsyncArrowFunction.ts, 14, 14))
>async : Symbol(async, Decl(parenthesizedAsyncArrowFunction.ts, 5, 12))
>x : Symbol(x, Decl(parenthesizedAsyncArrowFunction.ts, 14, 29))
>x : Symbol(x, Decl(parenthesizedAsyncArrowFunction.ts, 14, 29))

const f5 = a ? async (): Promise<number> => b : () => b;
>f5 : Symbol(f5, Decl(parenthesizedAsyncArrowFunction.ts, 15, 5))
>a : Symbol(a, Decl(parenthesizedAsyncArrowFunction.ts, 4, 5))
>Promise : Symbol(Promise, Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --), Decl(lib.es2015.promise.d.ts, --, --), Decl(lib.es2015.symbol.wellknown.d.ts, --, --))
>b : Symbol(b, Decl(parenthesizedAsyncArrowFunction.ts, 5, 5))
>b : Symbol(b, Decl(parenthesizedAsyncArrowFunction.ts, 5, 5))

const f6 = a ? async (): Promise<number> => { return b; } : () => b;
>f6 : Symbol(f6, Decl(parenthesizedAsyncArrowFunction.ts, 16, 5))
>a : Symbol(a, Decl(parenthesizedAsyncArrowFunction.ts, 4, 5))
>Promise : Symbol(Promise, Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --), Decl(lib.es2015.promise.d.ts, --, --), Decl(lib.es2015.symbol.wellknown.d.ts, --, --))
>b : Symbol(b, Decl(parenthesizedAsyncArrowFunction.ts, 5, 5))
>b : Symbol(b, Decl(parenthesizedAsyncArrowFunction.ts, 5, 5))

const f7 = a ? async (): Promise<number> => a ? async() : 0 : () => b;
>f7 : Symbol(f7, Decl(parenthesizedAsyncArrowFunction.ts, 17, 5))
>a : Symbol(a, Decl(parenthesizedAsyncArrowFunction.ts, 4, 5))
>Promise : Symbol(Promise, Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --), Decl(lib.es2015.promise.d.ts, --, --), Decl(lib.es2015.symbol.wellknown.d.ts, --, --))
>a : Symbol(a, Decl(parenthesizedAsyncArrowFunction.ts, 4, 5))
>async : Symbol(async, Decl(parenthesizedAsyncArrowFunction.ts, 5, 12))
>b : Symbol(b, Decl(parenthesizedAsyncArrowFunction.ts, 5, 5))

const f8 = a ? (): number => b : () => b;
>f8 : Symbol(f8, Decl(parenthesizedAsyncArrowFunction.ts, 18, 5))
>a : Symbol(a, Decl(parenthesizedAsyncArrowFunction.ts, 4, 5))
>b : Symbol(b, Decl(parenthesizedAsyncArrowFunction.ts, 5, 5))
>b : Symbol(b, Decl(parenthesizedAsyncArrowFunction.ts, 5, 5))

96 changes: 96 additions & 0 deletions tsc/testdata/baselines/reference/compiler/parenthesizedAsyncArrowFunction.types
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Expand Up @@ -10,3 +10,99 @@ let foo = (async bar => bar);
>bar : any
>bar : any

const a = true;
>a : true
>true : true

const b = 1;
>b : 1
>1 : 1

function async(): number {
>async : () => number

return b;
>b : 1
}

const f1 = a ? async() : 0;
>f1 : number
>a ? async() : 0 : number
>a : true
>async() : number
>async : () => number
>0 : 0

const f2 = a ? async() : x => x;
>f2 : number | ((x: any) => any)
>a ? async() : x => x : number | ((x: any) => any)
>a : true
>async() : number
>async : () => number
>x => x : (x: any) => any
>x : any
>x : any

const f3 = a ? a ? async() : 0 : b;
>f3 : number
>a ? a ? async() : 0 : b : number
>a : true
>a ? async() : 0 : number
>a : true
>async() : number
>async : () => number
>0 : 0
>b : 1

const f4 = a ? x => async() : x => x;
>f4 : (x: any) => any
>a ? x => async() : x => x : (x: any) => any
>a : true
>x => async() : (x: any) => number
>x : any
>async() : number
>async : () => number
>x => x : (x: any) => any
>x : any
>x : any

const f5 = a ? async (): Promise<number> => b : () => b;
>f5 : (() => Promise<number>) | (() => number)
>a ? async (): Promise<number> => b : () => b : (() => Promise<number>) | (() => number)
>a : true
>async (): Promise<number> => b : () => Promise<number>
>b : 1
>() => b : () => number
>b : 1

const f6 = a ? async (): Promise<number> => { return b; } : () => b;
>f6 : (() => Promise<number>) | (() => number)
>a ? async (): Promise<number> => { return b; } : () => b : (() => Promise<number>) | (() => number)
>a : true
>async (): Promise<number> => { return b; } : () => Promise<number>
>b : 1
>() => b : () => number
>b : 1

const f7 = a ? async (): Promise<number> => a ? async() : 0 : () => b;
>f7 : (() => Promise<number>) | (() => number)
>a ? async (): Promise<number> => a ? async() : 0 : () => b : (() => Promise<number>) | (() => number)
>a : true
>async (): Promise<number> => a ? async() : 0 : () => Promise<number>
>a ? async() : 0 : number
>a : true
>async() : number
>async : () => number
>0 : 0
>() => b : () => number
>b : 1

const f8 = a ? (): number => b : () => b;
>f8 : () => number
>a ? (): number => b : () => b : () => number
>a : true
>(): number => b : () => number
>b : 1
>() => b : () => number
>b : 1

16 changes: 15 additions & 1 deletion tsc/testdata/baselines/reference/conformance/asyncArrowFunction_allowJs.errors.txt
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Expand Up @@ -45,4 +45,18 @@ file.js(22,12): error TS7006: Parameter 'p' implicitly has an 'any' type.
// Error (good)
f(async () => {
return 0
})
})

const g = true;

function async() {
return 1;
}

const f1 = g ? async() : 0;
/** @type {number | ((x: number) => number)} */
const f2 = g ? async() : x => x;
const f3 = g ? g ? async() : 0 : 1;
/** @type {(x: number) => number} */
const f4 = g ? x => async() : x => x;

38 changes: 38 additions & 0 deletions tsc/testdata/baselines/reference/conformance/asyncArrowFunction_allowJs.symbols
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Expand Up @@ -38,3 +38,41 @@ f(async () => {

return 0
})

const g = true;
>g : Symbol(g, Decl(file.js, 28, 5))

function async() {
>async : Symbol(async, Decl(file.js, 28, 15))

return 1;
}

const f1 = g ? async() : 0;
>f1 : Symbol(f1, Decl(file.js, 34, 5))
>g : Symbol(g, Decl(file.js, 28, 5))
>async : Symbol(async, Decl(file.js, 28, 15))

/** @type {number | ((x: number) => number)} */
const f2 = g ? async() : x => x;
>f2 : Symbol(f2, Decl(file.js, 36, 5))
>g : Symbol(g, Decl(file.js, 28, 5))
>async : Symbol(async, Decl(file.js, 28, 15))
>x : Symbol(x, Decl(file.js, 36, 24))
>x : Symbol(x, Decl(file.js, 36, 24))

const f3 = g ? g ? async() : 0 : 1;
>f3 : Symbol(f3, Decl(file.js, 37, 5))
>g : Symbol(g, Decl(file.js, 28, 5))
>g : Symbol(g, Decl(file.js, 28, 5))
>async : Symbol(async, Decl(file.js, 28, 15))

/** @type {(x: number) => number} */
const f4 = g ? x => async() : x => x;
>f4 : Symbol(f4, Decl(file.js, 39, 5))
>g : Symbol(g, Decl(file.js, 28, 5))
>x : Symbol(x, Decl(file.js, 39, 14))
>async : Symbol(async, Decl(file.js, 28, 15))
>x : Symbol(x, Decl(file.js, 39, 29))
>x : Symbol(x, Decl(file.js, 39, 29))

55 changes: 55 additions & 0 deletions tsc/testdata/baselines/reference/conformance/asyncArrowFunction_allowJs.types
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Expand Up @@ -51,3 +51,58 @@ f(async () => {
>0 : 0

})

const g = true;
>g : true
>true : true

function async() {
>async : () => number

return 1;
>1 : 1
}

const f1 = g ? async() : 0;
>f1 : number
>g ? async() : 0 : number
>g : true
>async() : number
>async : () => number
>0 : 0

/** @type {number | ((x: number) => number)} */
const f2 = g ? async() : x => x;
>f2 : number | ((x: number) => number)
>g ? async() : x => x : number | ((x: number) => number)
>g : true
>async() : number
>async : () => number
>x => x : (x: number) => number
>x : number
>x : number

const f3 = g ? g ? async() : 0 : 1;
>f3 : number
>g ? g ? async() : 0 : 1 : number
>g : true
>g ? async() : 0 : number
>g : true
>async() : number
>async : () => number
>0 : 0
>1 : 1

/** @type {(x: number) => number} */
const f4 = g ? x => async() : x => x;
>f4 : (x: number) => number
>g ? x => async() : x => x : (x: number) => number
>g : true
>x => async() : (x: number) => number
>x : number
>async() : number
>async : () => number
>x => x : (x: number) => number
>x : number
>x : number

16 changes: 16 additions & 0 deletions tsc/testdata/tests/cases/compiler/parenthesizedAsyncArrowFunction.ts
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Expand Up @@ -3,3 +3,19 @@
// Repro from #20096

let foo = (async bar => bar);

const a = true;
const b = 1;

function async(): number {
return b;
}

const f1 = a ? async() : 0;
const f2 = a ? async() : x => x;
const f3 = a ? a ? async() : 0 : b;
const f4 = a ? x => async() : x => x;
const f5 = a ? async (): Promise<number> => b : () => b;
const f6 = a ? async (): Promise<number> => { return b; } : () => b;
const f7 = a ? async (): Promise<number> => a ? async() : 0 : () => b;
const f8 = a ? (): number => b : () => b;
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