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Fix TS2783 false positive for union types in object spread expressions (#62656)
Co-authored-by: copilot-swe-agent[bot] <[email protected]> Co-authored-by: RyanCavanaugh <[email protected]> Co-authored-by: Ryan Cavanaugh <[email protected]> Co-authored-by: Ryan Cavanaugh <[email protected]>
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‎src/compiler/checker.ts‎

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -33858,7 +33858,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
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function checkSpreadPropOverrides(type: Type, props: SymbolTable, spread: SpreadAssignment | JsxSpreadAttribute) {
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for (const right of getPropertiesOfType(type)) {
33861-
if (!(right.flags & SymbolFlags.Optional)) {
33861+
if (!(right.flags & SymbolFlags.Optional) && !(getCheckFlags(right) & CheckFlags.Partial)) {
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const left = props.get(right.escapedName);
3386333863
if (left) {
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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

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

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//// [tests/cases/compiler/spreadUnionPropOverride.ts] ////
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//// [spreadUnionPropOverride.ts]
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// Repro from #62655
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type Thing = {
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id: string;
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label: string;
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};
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const things: Thing[] = [];
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function find(id: string): undefined | Thing {
13+
return things.find(thing => thing.id === id);
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}
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declare function fun(thing: Thing): void;
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fun({
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id: 'foo',
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...find('foo') ?? {
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label: 'Foo',
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},
23+
});
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// Should not error when spreading a union where one type doesn't have the property
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const obj1 = {
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x: 1,
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...(Math.random() > 0.5 ? { y: 2 } : { y: 2, x: 3 }),
29+
}; // OK - x might be overwritten
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// Should error when the property is in all constituents
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const obj2 = {
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x: 1,
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...(Math.random() > 0.5 ? { x: 2, y: 3 } : { x: 4, z: 5 }),
35+
}; // Error - x is always overwritten
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// Should not error with optional property in union
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type Partial1 = { a: string; b?: number };
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type Partial2 = { a: string; c: boolean };
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declare const partial: Partial1 | Partial2;
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const obj3 = {
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b: 42,
44+
...partial,
45+
}; // OK - b is optional in Partial1 and missing in Partial2
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// Should error when property is required in all types
48+
const obj4 = {
49+
a: "test",
50+
...partial,
51+
}; // Error - a is required in both types
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// More complex union case
54+
type A = { id: string; name: string };
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type B = { name: string; age: number };
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type C = { name: string };
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declare const abc: A | B | C;
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const obj5 = {
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id: "123",
62+
...abc,
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}; // OK - id is only in A
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const obj6 = {
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name: "test",
67+
...abc,
68+
}; // Error - name is in all types
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//// [spreadUnionPropOverride.js]
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"use strict";
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var __assign = (this && this.__assign) || function () {
74+
__assign = Object.assign || function(t) {
75+
for (var s, i = 1, n = arguments.length; i < n; i++) {
76+
s = arguments[i];
77+
for (var p in s) if (Object.prototype.hasOwnProperty.call(s, p))
78+
t[p] = s[p];
79+
}
80+
return t;
81+
};
82+
return __assign.apply(this, arguments);
83+
};
84+
var _a;
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var things = [];
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function find(id) {
87+
return things.find(function (thing) { return thing.id === id; });
88+
}
89+
fun(__assign({ id: 'foo' }, (_a = find('foo')) !== null && _a !== void 0 ? _a : {
90+
label: 'Foo',
91+
}));
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// Should not error when spreading a union where one type doesn't have the property
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var obj1 = __assign({ x: 1 }, (Math.random() > 0.5 ? { y: 2 } : { y: 2, x: 3 })); // OK - x might be overwritten
94+
// Should error when the property is in all constituents
95+
var obj2 = __assign({ x: 1 }, (Math.random() > 0.5 ? { x: 2, y: 3 } : { x: 4, z: 5 })); // Error - x is always overwritten
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var obj3 = __assign({ b: 42 }, partial); // OK - b is optional in Partial1 and missing in Partial2
97+
// Should error when property is required in all types
98+
var obj4 = __assign({ a: "test" }, partial); // Error - a is required in both types
99+
var obj5 = __assign({ id: "123" }, abc); // OK - id is only in A
100+
var obj6 = __assign({ name: "test" }, abc); // Error - name is in all types

‎tests/baselines/reference/spreadUnionPropOverride.symbols‎

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1+
//// [tests/cases/compiler/spreadUnionPropOverride.ts] ////
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=== spreadUnionPropOverride.ts ===
4+
// Repro from #62655
5+
type Thing = {
6+
>Thing : Symbol(Thing, Decl(spreadUnionPropOverride.ts, 0, 0))
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id: string;
9+
>id : Symbol(id, Decl(spreadUnionPropOverride.ts, 1, 14))
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label: string;
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>label : Symbol(label, Decl(spreadUnionPropOverride.ts, 2, 15))
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};
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const things: Thing[] = [];
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>things : Symbol(things, Decl(spreadUnionPropOverride.ts, 6, 5))
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>Thing : Symbol(Thing, Decl(spreadUnionPropOverride.ts, 0, 0))
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function find(id: string): undefined | Thing {
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>find : Symbol(find, Decl(spreadUnionPropOverride.ts, 6, 27))
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>id : Symbol(id, Decl(spreadUnionPropOverride.ts, 8, 14))
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>Thing : Symbol(Thing, Decl(spreadUnionPropOverride.ts, 0, 0))
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return things.find(thing => thing.id === id);
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>things.find : Symbol(Array.find, Decl(lib.es2015.core.d.ts, --, --), Decl(lib.es2015.core.d.ts, --, --))
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>things : Symbol(things, Decl(spreadUnionPropOverride.ts, 6, 5))
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>find : Symbol(Array.find, Decl(lib.es2015.core.d.ts, --, --), Decl(lib.es2015.core.d.ts, --, --))
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>thing : Symbol(thing, Decl(spreadUnionPropOverride.ts, 9, 23))
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>thing.id : Symbol(id, Decl(spreadUnionPropOverride.ts, 1, 14))
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>thing : Symbol(thing, Decl(spreadUnionPropOverride.ts, 9, 23))
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>id : Symbol(id, Decl(spreadUnionPropOverride.ts, 1, 14))
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>id : Symbol(id, Decl(spreadUnionPropOverride.ts, 8, 14))
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}
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declare function fun(thing: Thing): void;
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>fun : Symbol(fun, Decl(spreadUnionPropOverride.ts, 10, 1))
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>thing : Symbol(thing, Decl(spreadUnionPropOverride.ts, 12, 21))
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>Thing : Symbol(Thing, Decl(spreadUnionPropOverride.ts, 0, 0))
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fun({
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>fun : Symbol(fun, Decl(spreadUnionPropOverride.ts, 10, 1))
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id: 'foo',
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>id : Symbol(id, Decl(spreadUnionPropOverride.ts, 14, 5))
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...find('foo') ?? {
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>find : Symbol(find, Decl(spreadUnionPropOverride.ts, 6, 27))
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label: 'Foo',
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>label : Symbol(label, Decl(spreadUnionPropOverride.ts, 16, 23))
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},
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});
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// Should not error when spreading a union where one type doesn't have the property
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const obj1 = {
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>obj1 : Symbol(obj1, Decl(spreadUnionPropOverride.ts, 22, 5))
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x: 1,
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>x : Symbol(x, Decl(spreadUnionPropOverride.ts, 22, 14))
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...(Math.random() > 0.5 ? { y: 2 } : { y: 2, x: 3 }),
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>Math.random : Symbol(Math.random, Decl(lib.es5.d.ts, --, --))
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>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, --, --))
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>random : Symbol(Math.random, Decl(lib.es5.d.ts, --, --))
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>y : Symbol(y, Decl(spreadUnionPropOverride.ts, 24, 31))
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>y : Symbol(y, Decl(spreadUnionPropOverride.ts, 24, 42))
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>x : Symbol(x, Decl(spreadUnionPropOverride.ts, 24, 48))
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}; // OK - x might be overwritten
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// Should error when the property is in all constituents
74+
const obj2 = {
75+
>obj2 : Symbol(obj2, Decl(spreadUnionPropOverride.ts, 28, 5))
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x: 1,
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>x : Symbol(x, Decl(spreadUnionPropOverride.ts, 28, 14))
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...(Math.random() > 0.5 ? { x: 2, y: 3 } : { x: 4, z: 5 }),
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>Math.random : Symbol(Math.random, Decl(lib.es5.d.ts, --, --))
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>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, --, --))
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>random : Symbol(Math.random, Decl(lib.es5.d.ts, --, --))
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>x : Symbol(x, Decl(spreadUnionPropOverride.ts, 30, 31))
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>y : Symbol(y, Decl(spreadUnionPropOverride.ts, 30, 37))
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>x : Symbol(x, Decl(spreadUnionPropOverride.ts, 30, 48))
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>z : Symbol(z, Decl(spreadUnionPropOverride.ts, 30, 54))
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}; // Error - x is always overwritten
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// Should not error with optional property in union
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type Partial1 = { a: string; b?: number };
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>Partial1 : Symbol(Partial1, Decl(spreadUnionPropOverride.ts, 31, 2))
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>a : Symbol(a, Decl(spreadUnionPropOverride.ts, 34, 17))
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>b : Symbol(b, Decl(spreadUnionPropOverride.ts, 34, 28))
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type Partial2 = { a: string; c: boolean };
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>Partial2 : Symbol(Partial2, Decl(spreadUnionPropOverride.ts, 34, 42))
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>a : Symbol(a, Decl(spreadUnionPropOverride.ts, 35, 17))
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>c : Symbol(c, Decl(spreadUnionPropOverride.ts, 35, 28))
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declare const partial: Partial1 | Partial2;
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>partial : Symbol(partial, Decl(spreadUnionPropOverride.ts, 36, 13))
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>Partial1 : Symbol(Partial1, Decl(spreadUnionPropOverride.ts, 31, 2))
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>Partial2 : Symbol(Partial2, Decl(spreadUnionPropOverride.ts, 34, 42))
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const obj3 = {
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>obj3 : Symbol(obj3, Decl(spreadUnionPropOverride.ts, 38, 5))
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b: 42,
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>b : Symbol(b, Decl(spreadUnionPropOverride.ts, 38, 14))
112+
113+
...partial,
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>partial : Symbol(partial, Decl(spreadUnionPropOverride.ts, 36, 13))
115+
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}; // OK - b is optional in Partial1 and missing in Partial2
117+
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// Should error when property is required in all types
119+
const obj4 = {
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>obj4 : Symbol(obj4, Decl(spreadUnionPropOverride.ts, 44, 5))
121+
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a: "test",
123+
>a : Symbol(a, Decl(spreadUnionPropOverride.ts, 44, 14))
124+
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...partial,
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>partial : Symbol(partial, Decl(spreadUnionPropOverride.ts, 36, 13))
127+
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}; // Error - a is required in both types
129+
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// More complex union case
131+
type A = { id: string; name: string };
132+
>A : Symbol(A, Decl(spreadUnionPropOverride.ts, 47, 2))
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>id : Symbol(id, Decl(spreadUnionPropOverride.ts, 50, 10))
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>name : Symbol(name, Decl(spreadUnionPropOverride.ts, 50, 22))
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type B = { name: string; age: number };
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>B : Symbol(B, Decl(spreadUnionPropOverride.ts, 50, 38))
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>name : Symbol(name, Decl(spreadUnionPropOverride.ts, 51, 10))
139+
>age : Symbol(age, Decl(spreadUnionPropOverride.ts, 51, 24))
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type C = { name: string };
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>C : Symbol(C, Decl(spreadUnionPropOverride.ts, 51, 39))
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>name : Symbol(name, Decl(spreadUnionPropOverride.ts, 52, 10))
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declare const abc: A | B | C;
146+
>abc : Symbol(abc, Decl(spreadUnionPropOverride.ts, 54, 13))
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>A : Symbol(A, Decl(spreadUnionPropOverride.ts, 47, 2))
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>B : Symbol(B, Decl(spreadUnionPropOverride.ts, 50, 38))
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>C : Symbol(C, Decl(spreadUnionPropOverride.ts, 51, 39))
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const obj5 = {
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>obj5 : Symbol(obj5, Decl(spreadUnionPropOverride.ts, 56, 5))
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id: "123",
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>id : Symbol(id, Decl(spreadUnionPropOverride.ts, 56, 14))
156+
157+
...abc,
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>abc : Symbol(abc, Decl(spreadUnionPropOverride.ts, 54, 13))
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}; // OK - id is only in A
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const obj6 = {
163+
>obj6 : Symbol(obj6, Decl(spreadUnionPropOverride.ts, 61, 5))
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name: "test",
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>name : Symbol(name, Decl(spreadUnionPropOverride.ts, 61, 14))
167+
168+
...abc,
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>abc : Symbol(abc, Decl(spreadUnionPropOverride.ts, 54, 13))
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}; // Error - name is in all types
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