fix(45692): merge non-primitive in spread-union (microsoft#45729)

Author: a-tarasyuk

src/compiler/checker.ts

@@ -16013,7 +16013,7 @@ namespace ts {
                         const declarations = concatenate(leftProp.declarations, rightProp.declarations);
                         const flags = SymbolFlags.Property | (leftProp.flags & SymbolFlags.Optional);
                         const result = createSymbol(flags, leftProp.escapedName);
-                        result.type = getUnionType([getTypeOfSymbol(leftProp), removeMissingOrUndefinedType(rightType)]);
+                        result.type = getUnionType([getTypeOfSymbol(leftProp), removeMissingOrUndefinedType(rightType)], UnionReduction.Subtype);
                         result.leftSpread = leftProp;
                         result.rightSpread = rightProp;
                         result.declarations = declarations;

tests/baselines/reference/spreadUnion4.js

@@ -0,0 +1,20 @@
+//// [spreadUnion4.ts]
+declare const a: { x: () => void }
+declare const b: { x?: () => void }
+
+const c = { ...a, ...b };
+
+
+//// [spreadUnion4.js]
+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 c = __assign(__assign({}, a), b);

tests/baselines/reference/spreadUnion4.symbols

@@ -0,0 +1,14 @@
+=== tests/cases/conformance/types/spread/spreadUnion4.ts ===
+declare const a: { x: () => void }
+>a : Symbol(a, Decl(spreadUnion4.ts, 0, 13))
+>x : Symbol(x, Decl(spreadUnion4.ts, 0, 18))
+
+declare const b: { x?: () => void }
+>b : Symbol(b, Decl(spreadUnion4.ts, 1, 13))
+>x : Symbol(x, Decl(spreadUnion4.ts, 1, 18))
+
+const c = { ...a, ...b };
+>c : Symbol(c, Decl(spreadUnion4.ts, 3, 5))
+>a : Symbol(a, Decl(spreadUnion4.ts, 0, 13))
+>b : Symbol(b, Decl(spreadUnion4.ts, 1, 13))
+

tests/baselines/reference/spreadUnion4.types

@@ -0,0 +1,15 @@
+=== tests/cases/conformance/types/spread/spreadUnion4.ts ===
+declare const a: { x: () => void }
+>a : { x: () => void; }
+>x : () => void
+
+declare const b: { x?: () => void }
+>b : { x?: () => void; }
+>x : () => void
+
+const c = { ...a, ...b };
+>c : { x: () => void; }
+>{ ...a, ...b } : { x: () => void; }
+>a : { x: () => void; }
+>b : { x?: () => void; }
+

tests/cases/conformance/types/spread/spreadUnion4.ts

@@ -0,0 +1,4 @@
+declare const a: { x: () => void }
+declare const b: { x?: () => void }
+
+const c = { ...a, ...b };