Merge pull request #29082 from Microsoft/widenIntersectionTypes

Properly widen intersection types

Author: ahejlsberg

src/compiler/checker.ts

@@ -13597,6 +13597,9 @@ namespace ts {
                     // union includes empty object types (e.g. reducing {} | string to just {}).
                     return getUnionType(widenedTypes, some(widenedTypes, isEmptyObjectType) ? UnionReduction.Subtype : UnionReduction.Literal);
                 }
+                if (type.flags & TypeFlags.Intersection) {
+                    return getIntersectionType(sameMap((<IntersectionType>type).types, getWidenedType));
+                }
                 if (isArrayType(type) || isTupleType(type)) {
                     return createTypeReference((<TypeReference>type).target, sameMap((<TypeReference>type).typeArguments, getWidenedType));
                 }

tests/baselines/reference/literalTypeWidening.js

@@ -128,11 +128,38 @@ export type LangCode = keyof typeof langCodeSet
 export const langCodes = keys(langCodeSet)
 
 const arr: Obj[] = langCodes.map(code => ({ code }))
+
+// Repro from #29081
+
+function test<T extends { a: string, b: string }>(obj: T): T {
+    let { a, ...rest } = obj;
+    return { a: 'hello', ...rest } as T;
+}
 
 
 //// [literalTypeWidening.js]
 "use strict";
 // Widening vs. non-widening literal types
+var __assign = (this && this.__assign) || function () {
+    __assign = Object.assign || function(t) {
+        for (var s, i = 1, n = arguments.length; i < n; i++) {
+            s = arguments[i];
+            for (var p in s) if (Object.prototype.hasOwnProperty.call(s, p))
+                t[p] = s[p];
+        }
+        return t;
+    };
+    return __assign.apply(this, arguments);
+};
+var __rest = (this && this.__rest) || function (s, e) {
+    var t = {};
+    for (var p in s) if (Object.prototype.hasOwnProperty.call(s, p) && e.indexOf(p) < 0)
+        t[p] = s[p];
+    if (s != null && typeof Object.getOwnPropertySymbols === "function")
+        for (var i = 0, p = Object.getOwnPropertySymbols(s); i < p.length; i++) if (e.indexOf(p[i]) < 0)
+            t[p[i]] = s[p[i]];
+    return t;
+};
 exports.__esModule = true;
 function f1() {
     var c1 = "hello"; // Widening type "hello"
@@ -233,3 +260,8 @@ exports.keys = keys;
 var langCodeSet = Set('fr', 'en', 'es', 'it', 'nl');
 exports.langCodes = keys(langCodeSet);
 var arr = exports.langCodes.map(function (code) { return ({ code: code }); });
+// Repro from #29081
+function test(obj) {
+    var a = obj.a, rest = __rest(obj, ["a"]);
+    return __assign({ a: 'hello' }, rest);
+}

tests/baselines/reference/literalTypeWidening.symbols

@@ -400,3 +400,25 @@ const arr: Obj[] = langCodes.map(code => ({ code }))
 >code : Symbol(code, Decl(literalTypeWidening.ts, 128, 33))
 >code : Symbol(code, Decl(literalTypeWidening.ts, 128, 43))
 
+// Repro from #29081
+
+function test<T extends { a: string, b: string }>(obj: T): T {
+>test : Symbol(test, Decl(literalTypeWidening.ts, 128, 52))
+>T : Symbol(T, Decl(literalTypeWidening.ts, 132, 14))
+>a : Symbol(a, Decl(literalTypeWidening.ts, 132, 25))
+>b : Symbol(b, Decl(literalTypeWidening.ts, 132, 36))
+>obj : Symbol(obj, Decl(literalTypeWidening.ts, 132, 50))
+>T : Symbol(T, Decl(literalTypeWidening.ts, 132, 14))
+>T : Symbol(T, Decl(literalTypeWidening.ts, 132, 14))
+
+    let { a, ...rest } = obj;
+>a : Symbol(a, Decl(literalTypeWidening.ts, 133, 9))
+>rest : Symbol(rest, Decl(literalTypeWidening.ts, 133, 12))
+>obj : Symbol(obj, Decl(literalTypeWidening.ts, 132, 50))
+
+    return { a: 'hello', ...rest } as T;
+>a : Symbol(a, Decl(literalTypeWidening.ts, 134, 12))
+>rest : Symbol(rest, Decl(literalTypeWidening.ts, 133, 12))
+>T : Symbol(T, Decl(literalTypeWidening.ts, 132, 14))
+}
+

tests/baselines/reference/literalTypeWidening.types

@@ -433,3 +433,24 @@ const arr: Obj[] = langCodes.map(code => ({ code }))
 >{ code } : { code: "fr" | "en" | "es" | "it" | "nl"; }
 >code : "fr" | "en" | "es" | "it" | "nl"
 
+// Repro from #29081
+
+function test<T extends { a: string, b: string }>(obj: T): T {
+>test : <T extends { a: string; b: string; }>(obj: T) => T
+>a : string
+>b : string
+>obj : T
+
+    let { a, ...rest } = obj;
+>a : string
+>rest : Pick<T, Exclude<keyof T, "a">>
+>obj : T
+
+    return { a: 'hello', ...rest } as T;
+>{ a: 'hello', ...rest } as T : T
+>{ a: 'hello', ...rest } : { a: string; } & Pick<T, Exclude<keyof T, "a">>
+>a : string
+>'hello' : "hello"
+>rest : Pick<T, Exclude<keyof T, "a">>
+}
+

tests/cases/conformance/types/literal/literalTypeWidening.ts

@@ -127,3 +127,10 @@ export type LangCode = keyof typeof langCodeSet
 export const langCodes = keys(langCodeSet)
 
 const arr: Obj[] = langCodes.map(code => ({ code }))
+
+// Repro from #29081
+
+function test<T extends { a: string, b: string }>(obj: T): T {
+    let { a, ...rest } = obj;
+    return { a: 'hello', ...rest } as T;
+}