Merge pull request #49029 from DavidSouther/fix/44466-contextual-keyword-assertion

fix(44466): Fixes parsing contextual keyword casts as arrow functions

src/compiler/parser.ts

@@ -4538,6 +4538,10 @@ namespace ts {
                 // isn't actually allowed, but we want to treat it as a lambda so we can provide
                 // a good error message.
                 if (isModifierKind(second) && second !== SyntaxKind.AsyncKeyword && lookAhead(nextTokenIsIdentifier)) {
+                    if (nextToken() === SyntaxKind.AsKeyword) {
+                        // https://github.com/microsoft/TypeScript/issues/44466
+                        return Tristate.False;
+                    }
                     return Tristate.True;
                 }
 

tests/baselines/reference/modifierParenCast.js

@@ -0,0 +1,23 @@
+//// [modifierParenCast.ts]
+let readonly: any = undefined;
+let override: any = undefined;
+let out: any = undefined;
+let declare: any = undefined;
+
+export const a = (readonly as number);
+export const b = (override as number);
+export const c = (out as number);
+export const d = (declare as number);
+
+//// [modifierParenCast.js]
+"use strict";
+Object.defineProperty(exports, "__esModule", { value: true });
+exports.d = exports.c = exports.b = exports.a = void 0;
+var readonly = undefined;
+var override = undefined;
+var out = undefined;
+var declare = undefined;
+exports.a = readonly;
+exports.b = override;
+exports.c = out;
+exports.d = declare;

tests/baselines/reference/modifierParenCast.symbols

@@ -0,0 +1,33 @@
+=== tests/cases/compiler/modifierParenCast.ts ===
+let readonly: any = undefined;
+>readonly : Symbol(readonly, Decl(modifierParenCast.ts, 0, 3))
+>undefined : Symbol(undefined)
+
+let override: any = undefined;
+>override : Symbol(override, Decl(modifierParenCast.ts, 1, 3))
+>undefined : Symbol(undefined)
+
+let out: any = undefined;
+>out : Symbol(out, Decl(modifierParenCast.ts, 2, 3))
+>undefined : Symbol(undefined)
+
+let declare: any = undefined;
+>declare : Symbol(declare, Decl(modifierParenCast.ts, 3, 3))
+>undefined : Symbol(undefined)
+
+export const a = (readonly as number);
+>a : Symbol(a, Decl(modifierParenCast.ts, 5, 12))
+>readonly : Symbol(readonly, Decl(modifierParenCast.ts, 0, 3))
+
+export const b = (override as number);
+>b : Symbol(b, Decl(modifierParenCast.ts, 6, 12))
+>override : Symbol(override, Decl(modifierParenCast.ts, 1, 3))
+
+export const c = (out as number);
+>c : Symbol(c, Decl(modifierParenCast.ts, 7, 12))
+>out : Symbol(out, Decl(modifierParenCast.ts, 2, 3))
+
+export const d = (declare as number);
+>d : Symbol(d, Decl(modifierParenCast.ts, 8, 12))
+>declare : Symbol(declare, Decl(modifierParenCast.ts, 3, 3))
+

tests/baselines/reference/modifierParenCast.types

@@ -0,0 +1,41 @@
+=== tests/cases/compiler/modifierParenCast.ts ===
+let readonly: any = undefined;
+>readonly : any
+>undefined : undefined
+
+let override: any = undefined;
+>override : any
+>undefined : undefined
+
+let out: any = undefined;
+>out : any
+>undefined : undefined
+
+let declare: any = undefined;
+>declare : any
+>undefined : undefined
+
+export const a = (readonly as number);
+>a : number
+>(readonly as number) : number
+>readonly as number : number
+>readonly : any
+
+export const b = (override as number);
+>b : number
+>(override as number) : number
+>override as number : number
+>override : any
+
+export const c = (out as number);
+>c : number
+>(out as number) : number
+>out as number : number
+>out : any
+
+export const d = (declare as number);
+>d : number
+>(declare as number) : number
+>declare as number : number
+>declare : any
+

tests/cases/compiler/modifierParenCast.ts

@@ -0,0 +1,11 @@
+//@target: ES5
+
+let readonly: any = undefined;
+let override: any = undefined;
+let out: any = undefined;
+let declare: any = undefined;
+
+export const a = (readonly as number);
+export const b = (override as number);
+export const c = (out as number);
+export const d = (declare as number);