Fix TS2783 false positive for union types in object spread expressions

src/compiler/checker.ts

@@ -33858,7 +33858,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
 
     function checkSpreadPropOverrides(type: Type, props: SymbolTable, spread: SpreadAssignment | JsxSpreadAttribute) {
         for (const right of getPropertiesOfType(type)) {
-            if (!(right.flags & SymbolFlags.Optional)) {
+            if (!(right.flags & SymbolFlags.Optional) && !(getCheckFlags(right) & CheckFlags.Partial)) {
                 const left = props.get(right.escapedName);
                 if (left) {
                     const diagnostic = error(left.valueDeclaration, Diagnostics._0_is_specified_more_than_once_so_this_usage_will_be_overwritten, unescapeLeadingUnderscores(left.escapedName));

tests/baselines/reference/spreadUnionPropOverride.errors.txt

@@ -0,0 +1,81 @@
+spreadUnionPropOverride.ts(30,5): error TS2783: 'x' is specified more than once, so this usage will be overwritten.
+spreadUnionPropOverride.ts(46,5): error TS2783: 'a' is specified more than once, so this usage will be overwritten.
+spreadUnionPropOverride.ts(63,5): error TS2783: 'name' is specified more than once, so this usage will be overwritten.
+
+
+==== spreadUnionPropOverride.ts (3 errors) ====
+    // Repro from #62655
+    type Thing = {
+        id: string;
+        label: string;
+    };
+
+    const things: Thing[] = [];
+
+    function find(id: string): undefined | Thing {
+        return things.find(thing => thing.id === id);
+    }
+
+    declare function fun(thing: Thing): void;
+
+    fun({
+        id: 'foo',
+        ...find('foo') ?? {
+            label: 'Foo',
+        },
+    });
+
+    // Should not error when spreading a union where one type doesn't have the property
+    const obj1 = {
+        x: 1,
+        ...(Math.random() > 0.5 ? { y: 2 } : { y: 2, x: 3 }),
+    }; // OK - x might be overwritten
+
+    // Should error when the property is in all constituents
+    const obj2 = {
+        x: 1,
+        ~~~~
+!!! error TS2783: 'x' is specified more than once, so this usage will be overwritten.
+!!! related TS2785 spreadUnionPropOverride.ts:31:5: This spread always overwrites this property.
+        ...(Math.random() > 0.5 ? { x: 2, y: 3 } : { x: 4, z: 5 }),
+    }; // Error - x is always overwritten
+
+    // Should not error with optional property in union
+    type Partial1 = { a: string; b?: number };
+    type Partial2 = { a: string; c: boolean };
+    declare const partial: Partial1 | Partial2;
+
+    const obj3 = {
+        b: 42,
+        ...partial,
+    }; // OK - b is optional in Partial1 and missing in Partial2
+
+    // Should error when property is required in all types
+    const obj4 = {
+        a: "test",
+        ~~~~~~~~~
+!!! error TS2783: 'a' is specified more than once, so this usage will be overwritten.
+!!! related TS2785 spreadUnionPropOverride.ts:47:5: This spread always overwrites this property.
+        ...partial,
+    }; // Error - a is required in both types
+
+    // More complex union case
+    type A = { id: string; name: string };
+    type B = { name: string; age: number };
+    type C = { name: string };
+
+    declare const abc: A | B | C;
+
+    const obj5 = {
+        id: "123",
+        ...abc,
+    }; // OK - id is only in A
+
+    const obj6 = {
+        name: "test",
+        ~~~~~~~~~~~~
+!!! error TS2783: 'name' is specified more than once, so this usage will be overwritten.
+!!! related TS2785 spreadUnionPropOverride.ts:64:5: This spread always overwrites this property.
+        ...abc,
+    }; // Error - name is in all types
+

tests/baselines/reference/spreadUnionPropOverride.js

@@ -0,0 +1,100 @@
+//// [tests/cases/compiler/spreadUnionPropOverride.ts] ////
+
+//// [spreadUnionPropOverride.ts]
+// Repro from #62655
+type Thing = {
+    id: string;
+    label: string;
+};
+
+const things: Thing[] = [];
+
+function find(id: string): undefined | Thing {
+    return things.find(thing => thing.id === id);
+}
+
+declare function fun(thing: Thing): void;
+
+fun({
+    id: 'foo',
+    ...find('foo') ?? {
+        label: 'Foo',
+    },
+});
+
+// Should not error when spreading a union where one type doesn't have the property
+const obj1 = {
+    x: 1,
+    ...(Math.random() > 0.5 ? { y: 2 } : { y: 2, x: 3 }),
+}; // OK - x might be overwritten
+
+// Should error when the property is in all constituents
+const obj2 = {
+    x: 1,
+    ...(Math.random() > 0.5 ? { x: 2, y: 3 } : { x: 4, z: 5 }),
+}; // Error - x is always overwritten
+
+// Should not error with optional property in union
+type Partial1 = { a: string; b?: number };
+type Partial2 = { a: string; c: boolean };
+declare const partial: Partial1 | Partial2;
+
+const obj3 = {
+    b: 42,
+    ...partial,
+}; // OK - b is optional in Partial1 and missing in Partial2
+
+// Should error when property is required in all types
+const obj4 = {
+    a: "test",
+    ...partial,
+}; // Error - a is required in both types
+
+// More complex union case
+type A = { id: string; name: string };
+type B = { name: string; age: number };
+type C = { name: string };
+
+declare const abc: A | B | C;
+
+const obj5 = {
+    id: "123",
+    ...abc,
+}; // OK - id is only in A
+
+const obj6 = {
+    name: "test",
+    ...abc,
+}; // Error - name is in all types
+
+
+//// [spreadUnionPropOverride.js]
+"use strict";
+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 _a;
+var things = [];
+function find(id) {
+    return things.find(function (thing) { return thing.id === id; });
+}
+fun(__assign({ id: 'foo' }, (_a = find('foo')) !== null && _a !== void 0 ? _a : {
+    label: 'Foo',
+}));
+// Should not error when spreading a union where one type doesn't have the property
+var obj1 = __assign({ x: 1 }, (Math.random() > 0.5 ? { y: 2 } : { y: 2, x: 3 })); // OK - x might be overwritten
+// Should error when the property is in all constituents
+var obj2 = __assign({ x: 1 }, (Math.random() > 0.5 ? { x: 2, y: 3 } : { x: 4, z: 5 })); // Error - x is always overwritten
+var obj3 = __assign({ b: 42 }, partial); // OK - b is optional in Partial1 and missing in Partial2
+// Should error when property is required in all types
+var obj4 = __assign({ a: "test" }, partial); // Error - a is required in both types
+var obj5 = __assign({ id: "123" }, abc); // OK - id is only in A
+var obj6 = __assign({ name: "test" }, abc); // Error - name is in all types

tests/baselines/reference/spreadUnionPropOverride.symbols

@@ -0,0 +1,172 @@
+//// [tests/cases/compiler/spreadUnionPropOverride.ts] ////
+
+=== spreadUnionPropOverride.ts ===
+// Repro from #62655
+type Thing = {
+>Thing : Symbol(Thing, Decl(spreadUnionPropOverride.ts, 0, 0))
+
+    id: string;
+>id : Symbol(id, Decl(spreadUnionPropOverride.ts, 1, 14))
+
+    label: string;
+>label : Symbol(label, Decl(spreadUnionPropOverride.ts, 2, 15))
+
+};
+
+const things: Thing[] = [];
+>things : Symbol(things, Decl(spreadUnionPropOverride.ts, 6, 5))
+>Thing : Symbol(Thing, Decl(spreadUnionPropOverride.ts, 0, 0))
+
+function find(id: string): undefined | Thing {
+>find : Symbol(find, Decl(spreadUnionPropOverride.ts, 6, 27))
+>id : Symbol(id, Decl(spreadUnionPropOverride.ts, 8, 14))
+>Thing : Symbol(Thing, Decl(spreadUnionPropOverride.ts, 0, 0))
+
+    return things.find(thing => thing.id === id);
+>things.find : Symbol(Array.find, Decl(lib.es2015.core.d.ts, --, --), Decl(lib.es2015.core.d.ts, --, --))
+>things : Symbol(things, Decl(spreadUnionPropOverride.ts, 6, 5))
+>find : Symbol(Array.find, Decl(lib.es2015.core.d.ts, --, --), Decl(lib.es2015.core.d.ts, --, --))
+>thing : Symbol(thing, Decl(spreadUnionPropOverride.ts, 9, 23))
+>thing.id : Symbol(id, Decl(spreadUnionPropOverride.ts, 1, 14))
+>thing : Symbol(thing, Decl(spreadUnionPropOverride.ts, 9, 23))
+>id : Symbol(id, Decl(spreadUnionPropOverride.ts, 1, 14))
+>id : Symbol(id, Decl(spreadUnionPropOverride.ts, 8, 14))
+}
+
+declare function fun(thing: Thing): void;
+>fun : Symbol(fun, Decl(spreadUnionPropOverride.ts, 10, 1))
+>thing : Symbol(thing, Decl(spreadUnionPropOverride.ts, 12, 21))
+>Thing : Symbol(Thing, Decl(spreadUnionPropOverride.ts, 0, 0))
+
+fun({
+>fun : Symbol(fun, Decl(spreadUnionPropOverride.ts, 10, 1))
+
+    id: 'foo',
+>id : Symbol(id, Decl(spreadUnionPropOverride.ts, 14, 5))
+
+    ...find('foo') ?? {
+>find : Symbol(find, Decl(spreadUnionPropOverride.ts, 6, 27))
+
+        label: 'Foo',
+>label : Symbol(label, Decl(spreadUnionPropOverride.ts, 16, 23))
+
+    },
+});
+
+// Should not error when spreading a union where one type doesn't have the property
+const obj1 = {
+>obj1 : Symbol(obj1, Decl(spreadUnionPropOverride.ts, 22, 5))
+
+    x: 1,
+>x : Symbol(x, Decl(spreadUnionPropOverride.ts, 22, 14))
+
+    ...(Math.random() > 0.5 ? { y: 2 } : { y: 2, x: 3 }),
+>Math.random : Symbol(Math.random, Decl(lib.es5.d.ts, --, --))
+>Math : Symbol(Math, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.core.d.ts, --, --), Decl(lib.es2015.symbol.wellknown.d.ts, --, --))
+>random : Symbol(Math.random, Decl(lib.es5.d.ts, --, --))
+>y : Symbol(y, Decl(spreadUnionPropOverride.ts, 24, 31))
+>y : Symbol(y, Decl(spreadUnionPropOverride.ts, 24, 42))
+>x : Symbol(x, Decl(spreadUnionPropOverride.ts, 24, 48))
+
+}; // OK - x might be overwritten
+
+// Should error when the property is in all constituents
+const obj2 = {
+>obj2 : Symbol(obj2, Decl(spreadUnionPropOverride.ts, 28, 5))
+
+    x: 1,
+>x : Symbol(x, Decl(spreadUnionPropOverride.ts, 28, 14))
+
+    ...(Math.random() > 0.5 ? { x: 2, y: 3 } : { x: 4, z: 5 }),
+>Math.random : Symbol(Math.random, Decl(lib.es5.d.ts, --, --))
+>Math : Symbol(Math, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.core.d.ts, --, --), Decl(lib.es2015.symbol.wellknown.d.ts, --, --))
+>random : Symbol(Math.random, Decl(lib.es5.d.ts, --, --))
+>x : Symbol(x, Decl(spreadUnionPropOverride.ts, 30, 31))
+>y : Symbol(y, Decl(spreadUnionPropOverride.ts, 30, 37))
+>x : Symbol(x, Decl(spreadUnionPropOverride.ts, 30, 48))
+>z : Symbol(z, Decl(spreadUnionPropOverride.ts, 30, 54))
+
+}; // Error - x is always overwritten
+
+// Should not error with optional property in union
+type Partial1 = { a: string; b?: number };
+>Partial1 : Symbol(Partial1, Decl(spreadUnionPropOverride.ts, 31, 2))
+>a : Symbol(a, Decl(spreadUnionPropOverride.ts, 34, 17))
+>b : Symbol(b, Decl(spreadUnionPropOverride.ts, 34, 28))
+
+type Partial2 = { a: string; c: boolean };
+>Partial2 : Symbol(Partial2, Decl(spreadUnionPropOverride.ts, 34, 42))
+>a : Symbol(a, Decl(spreadUnionPropOverride.ts, 35, 17))
+>c : Symbol(c, Decl(spreadUnionPropOverride.ts, 35, 28))
+
+declare const partial: Partial1 | Partial2;
+>partial : Symbol(partial, Decl(spreadUnionPropOverride.ts, 36, 13))
+>Partial1 : Symbol(Partial1, Decl(spreadUnionPropOverride.ts, 31, 2))
+>Partial2 : Symbol(Partial2, Decl(spreadUnionPropOverride.ts, 34, 42))
+
+const obj3 = {
+>obj3 : Symbol(obj3, Decl(spreadUnionPropOverride.ts, 38, 5))
+
+    b: 42,
+>b : Symbol(b, Decl(spreadUnionPropOverride.ts, 38, 14))
+
+    ...partial,
+>partial : Symbol(partial, Decl(spreadUnionPropOverride.ts, 36, 13))
+
+}; // OK - b is optional in Partial1 and missing in Partial2
+
+// Should error when property is required in all types
+const obj4 = {
+>obj4 : Symbol(obj4, Decl(spreadUnionPropOverride.ts, 44, 5))
+
+    a: "test",
+>a : Symbol(a, Decl(spreadUnionPropOverride.ts, 44, 14))
+
+    ...partial,
+>partial : Symbol(partial, Decl(spreadUnionPropOverride.ts, 36, 13))
+
+}; // Error - a is required in both types
+
+// More complex union case
+type A = { id: string; name: string };
+>A : Symbol(A, Decl(spreadUnionPropOverride.ts, 47, 2))
+>id : Symbol(id, Decl(spreadUnionPropOverride.ts, 50, 10))
+>name : Symbol(name, Decl(spreadUnionPropOverride.ts, 50, 22))
+
+type B = { name: string; age: number };
+>B : Symbol(B, Decl(spreadUnionPropOverride.ts, 50, 38))
+>name : Symbol(name, Decl(spreadUnionPropOverride.ts, 51, 10))
+>age : Symbol(age, Decl(spreadUnionPropOverride.ts, 51, 24))
+
+type C = { name: string };
+>C : Symbol(C, Decl(spreadUnionPropOverride.ts, 51, 39))
+>name : Symbol(name, Decl(spreadUnionPropOverride.ts, 52, 10))
+
+declare const abc: A | B | C;
+>abc : Symbol(abc, Decl(spreadUnionPropOverride.ts, 54, 13))
+>A : Symbol(A, Decl(spreadUnionPropOverride.ts, 47, 2))
+>B : Symbol(B, Decl(spreadUnionPropOverride.ts, 50, 38))
+>C : Symbol(C, Decl(spreadUnionPropOverride.ts, 51, 39))
+
+const obj5 = {
+>obj5 : Symbol(obj5, Decl(spreadUnionPropOverride.ts, 56, 5))
+
+    id: "123",
+>id : Symbol(id, Decl(spreadUnionPropOverride.ts, 56, 14))
+
+    ...abc,
+>abc : Symbol(abc, Decl(spreadUnionPropOverride.ts, 54, 13))
+
+}; // OK - id is only in A
+
+const obj6 = {
+>obj6 : Symbol(obj6, Decl(spreadUnionPropOverride.ts, 61, 5))
+
+    name: "test",
+>name : Symbol(name, Decl(spreadUnionPropOverride.ts, 61, 14))
+
+    ...abc,
+>abc : Symbol(abc, Decl(spreadUnionPropOverride.ts, 54, 13))
+
+}; // Error - name is in all types
+