Improve isValidSpreadType check

src/compiler/checker.ts

@@ -20857,7 +20857,7 @@ namespace ts {
         // flags for the string, number, boolean, "", 0, false, void, undefined, or null types respectively. Returns
         // no flags for all other types (including non-falsy literal types).
         function getFalsyFlags(type: Type): TypeFlags {
-            return type.flags & TypeFlags.Union ? getFalsyFlagsOfTypes((type as UnionType).types) :
+            return type.flags & TypeFlags.UnionOrIntersection ? getFalsyFlagsOfTypes((type as UnionType).types) :
                 type.flags & TypeFlags.StringLiteral ? (type as StringLiteralType).value === "" ? TypeFlags.StringLiteral : 0 :
                 type.flags & TypeFlags.NumberLiteral ? (type as NumberLiteralType).value === 0 ? TypeFlags.NumberLiteral : 0 :
                 type.flags & TypeFlags.BigIntLiteral ? isZeroBigInt(type as BigIntLiteralType) ? TypeFlags.BigIntLiteral : 0 :
@@ -27265,15 +27265,9 @@ namespace ts {
         }
 
         function isValidSpreadType(type: Type): boolean {
-            if (type.flags & TypeFlags.Instantiable) {
-                const constraint = getBaseConstraintOfType(type);
-                if (constraint !== undefined) {
-                    return isValidSpreadType(constraint);
-                }
-            }
-            return !!(type.flags & (TypeFlags.Any | TypeFlags.NonPrimitive | TypeFlags.Object | TypeFlags.InstantiableNonPrimitive) ||
-                getFalsyFlags(type) & TypeFlags.DefinitelyFalsy && isValidSpreadType(removeDefinitelyFalsyTypes(type)) ||
-                type.flags & TypeFlags.UnionOrIntersection && every((type as UnionOrIntersectionType).types, isValidSpreadType));
+            const t = removeDefinitelyFalsyTypes(mapType(type, getBaseConstraintOrType));
+            return !!(t.flags & (TypeFlags.Any | TypeFlags.NonPrimitive | TypeFlags.Object | TypeFlags.InstantiableNonPrimitive) ||
+                t.flags & TypeFlags.UnionOrIntersection && every((t as UnionOrIntersectionType).types, isValidSpreadType));
         }
 
         function checkJsxSelfClosingElementDeferred(node: JsxSelfClosingElement) {

tests/baselines/reference/spreadObjectOrFalsy.errors.txt

@@ -0,0 +1,42 @@
+tests/cases/conformance/types/spread/spreadObjectOrFalsy.ts(2,14): error TS2698: Spread types may only be created from object types.
+tests/cases/conformance/types/spread/spreadObjectOrFalsy.ts(10,14): error TS2698: Spread types may only be created from object types.
+
+
+==== tests/cases/conformance/types/spread/spreadObjectOrFalsy.ts (2 errors) ====
+    function f1<T>(a: T & undefined) {
+        return { ...a };  // Error
+                 ~~~~
+!!! error TS2698: Spread types may only be created from object types.
+    }
+
+    function f2<T>(a: T | T & undefined) {
+        return { ...a };
+    }
+
+    function f3<T extends undefined>(a: T) {
+        return { ...a };  // Error
+                 ~~~~
+!!! error TS2698: Spread types may only be created from object types.
+    }
+
+    function f4<T extends undefined>(a: object | T) {
+        return { ...a };
+    }
+
+    function f5<S, T extends undefined>(a: S | T) {
+        return { ...a };
+    }
+
+    function f6<T extends object | undefined>(a: T) {
+        return { ...a };
+    }
+
+    // Repro from #46976
+
+    function g1<T extends {}, A extends { z: (T | undefined) & T }>(a: A) {
+        const { z } = a;
+        return {
+            ...z
+        };
+    }
+

tests/baselines/reference/spreadObjectOrFalsy.js

@@ -0,0 +1,83 @@
+//// [spreadObjectOrFalsy.ts]
+function f1<T>(a: T & undefined) {
+    return { ...a };  // Error
+}
+
+function f2<T>(a: T | T & undefined) {
+    return { ...a };
+}
+
+function f3<T extends undefined>(a: T) {
+    return { ...a };  // Error
+}
+
+function f4<T extends undefined>(a: object | T) {
+    return { ...a };
+}
+
+function f5<S, T extends undefined>(a: S | T) {
+    return { ...a };
+}
+
+function f6<T extends object | undefined>(a: T) {
+    return { ...a };
+}
+
+// Repro from #46976
+
+function g1<T extends {}, A extends { z: (T | undefined) & T }>(a: A) {
+    const { z } = a;
+    return {
+        ...z
+    };
+}
+
+
+//// [spreadObjectOrFalsy.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);
+};
+function f1(a) {
+    return __assign({}, a); // Error
+}
+function f2(a) {
+    return __assign({}, a);
+}
+function f3(a) {
+    return __assign({}, a); // Error
+}
+function f4(a) {
+    return __assign({}, a);
+}
+function f5(a) {
+    return __assign({}, a);
+}
+function f6(a) {
+    return __assign({}, a);
+}
+// Repro from #46976
+function g1(a) {
+    var z = a.z;
+    return __assign({}, z);
+}
+
+
+//// [spreadObjectOrFalsy.d.ts]
+declare function f1<T>(a: T & undefined): any;
+declare function f2<T>(a: T | T & undefined): T | (T & undefined);
+declare function f3<T extends undefined>(a: T): any;
+declare function f4<T extends undefined>(a: object | T): {};
+declare function f5<S, T extends undefined>(a: S | T): S | T;
+declare function f6<T extends object | undefined>(a: T): T;
+declare function g1<T extends {}, A extends {
+    z: (T | undefined) & T;
+}>(a: A): (T | undefined) & T;

tests/baselines/reference/spreadObjectOrFalsy.symbols

@@ -0,0 +1,87 @@
+=== tests/cases/conformance/types/spread/spreadObjectOrFalsy.ts ===
+function f1<T>(a: T & undefined) {
+>f1 : Symbol(f1, Decl(spreadObjectOrFalsy.ts, 0, 0))
+>T : Symbol(T, Decl(spreadObjectOrFalsy.ts, 0, 12))
+>a : Symbol(a, Decl(spreadObjectOrFalsy.ts, 0, 15))
+>T : Symbol(T, Decl(spreadObjectOrFalsy.ts, 0, 12))
+
+    return { ...a };  // Error
+>a : Symbol(a, Decl(spreadObjectOrFalsy.ts, 0, 15))
+}
+
+function f2<T>(a: T | T & undefined) {
+>f2 : Symbol(f2, Decl(spreadObjectOrFalsy.ts, 2, 1))
+>T : Symbol(T, Decl(spreadObjectOrFalsy.ts, 4, 12))
+>a : Symbol(a, Decl(spreadObjectOrFalsy.ts, 4, 15))
+>T : Symbol(T, Decl(spreadObjectOrFalsy.ts, 4, 12))
+>T : Symbol(T, Decl(spreadObjectOrFalsy.ts, 4, 12))
+
+    return { ...a };
+>a : Symbol(a, Decl(spreadObjectOrFalsy.ts, 4, 15))
+}
+
+function f3<T extends undefined>(a: T) {
+>f3 : Symbol(f3, Decl(spreadObjectOrFalsy.ts, 6, 1))
+>T : Symbol(T, Decl(spreadObjectOrFalsy.ts, 8, 12))
+>a : Symbol(a, Decl(spreadObjectOrFalsy.ts, 8, 33))
+>T : Symbol(T, Decl(spreadObjectOrFalsy.ts, 8, 12))
+
+    return { ...a };  // Error
+>a : Symbol(a, Decl(spreadObjectOrFalsy.ts, 8, 33))
+}
+
+function f4<T extends undefined>(a: object | T) {
+>f4 : Symbol(f4, Decl(spreadObjectOrFalsy.ts, 10, 1))
+>T : Symbol(T, Decl(spreadObjectOrFalsy.ts, 12, 12))
+>a : Symbol(a, Decl(spreadObjectOrFalsy.ts, 12, 33))
+>T : Symbol(T, Decl(spreadObjectOrFalsy.ts, 12, 12))
+
+    return { ...a };
+>a : Symbol(a, Decl(spreadObjectOrFalsy.ts, 12, 33))
+}
+
+function f5<S, T extends undefined>(a: S | T) {
+>f5 : Symbol(f5, Decl(spreadObjectOrFalsy.ts, 14, 1))
+>S : Symbol(S, Decl(spreadObjectOrFalsy.ts, 16, 12))
+>T : Symbol(T, Decl(spreadObjectOrFalsy.ts, 16, 14))
+>a : Symbol(a, Decl(spreadObjectOrFalsy.ts, 16, 36))
+>S : Symbol(S, Decl(spreadObjectOrFalsy.ts, 16, 12))
+>T : Symbol(T, Decl(spreadObjectOrFalsy.ts, 16, 14))
+
+    return { ...a };
+>a : Symbol(a, Decl(spreadObjectOrFalsy.ts, 16, 36))
+}
+
+function f6<T extends object | undefined>(a: T) {
+>f6 : Symbol(f6, Decl(spreadObjectOrFalsy.ts, 18, 1))
+>T : Symbol(T, Decl(spreadObjectOrFalsy.ts, 20, 12))
+>a : Symbol(a, Decl(spreadObjectOrFalsy.ts, 20, 42))
+>T : Symbol(T, Decl(spreadObjectOrFalsy.ts, 20, 12))
+
+    return { ...a };
+>a : Symbol(a, Decl(spreadObjectOrFalsy.ts, 20, 42))
+}
+
+// Repro from #46976
+
+function g1<T extends {}, A extends { z: (T | undefined) & T }>(a: A) {
+>g1 : Symbol(g1, Decl(spreadObjectOrFalsy.ts, 22, 1))
+>T : Symbol(T, Decl(spreadObjectOrFalsy.ts, 26, 12))
+>A : Symbol(A, Decl(spreadObjectOrFalsy.ts, 26, 25))
+>z : Symbol(z, Decl(spreadObjectOrFalsy.ts, 26, 37))
+>T : Symbol(T, Decl(spreadObjectOrFalsy.ts, 26, 12))
+>T : Symbol(T, Decl(spreadObjectOrFalsy.ts, 26, 12))
+>a : Symbol(a, Decl(spreadObjectOrFalsy.ts, 26, 64))
+>A : Symbol(A, Decl(spreadObjectOrFalsy.ts, 26, 25))
+
+    const { z } = a;
+>z : Symbol(z, Decl(spreadObjectOrFalsy.ts, 27, 11))
+>a : Symbol(a, Decl(spreadObjectOrFalsy.ts, 26, 64))
+
+    return {
+        ...z
+>z : Symbol(z, Decl(spreadObjectOrFalsy.ts, 27, 11))
+
+    };
+}
+

tests/baselines/reference/spreadObjectOrFalsy.types

@@ -0,0 +1,75 @@
+=== tests/cases/conformance/types/spread/spreadObjectOrFalsy.ts ===
+function f1<T>(a: T & undefined) {
+>f1 : <T>(a: T & undefined) => any
+>a : T & undefined
+
+    return { ...a };  // Error
+>{ ...a } : any
+>a : T & undefined
+}
+
+function f2<T>(a: T | T & undefined) {
+>f2 : <T>(a: T | (T & undefined)) => T | (T & undefined)
+>a : T | (T & undefined)
+
+    return { ...a };
+>{ ...a } : T | (T & undefined)
+>a : T | (T & undefined)
+}
+
+function f3<T extends undefined>(a: T) {
+>f3 : <T extends undefined>(a: T) => any
+>a : T
+
+    return { ...a };  // Error
+>{ ...a } : any
+>a : T
+}
+
+function f4<T extends undefined>(a: object | T) {
+>f4 : <T extends undefined>(a: object | T) => {}
+>a : object | T
+
+    return { ...a };
+>{ ...a } : {}
+>a : object | T
+}
+
+function f5<S, T extends undefined>(a: S | T) {
+>f5 : <S, T extends undefined>(a: S | T) => S | T
+>a : S | T
+
+    return { ...a };
+>{ ...a } : S | T
+>a : S | T
+}
+
+function f6<T extends object | undefined>(a: T) {
+>f6 : <T extends object | undefined>(a: T) => T
+>a : T
+
+    return { ...a };
+>{ ...a } : T
+>a : T
+}
+
+// Repro from #46976
+
+function g1<T extends {}, A extends { z: (T | undefined) & T }>(a: A) {
+>g1 : <T extends {}, A extends { z: (T | undefined) & T; }>(a: A) => (T | undefined) & T
+>z : (T | undefined) & T
+>a : A
+
+    const { z } = a;
+>z : (T | undefined) & T
+>a : A
+
+    return {
+>{        ...z    } : (T | undefined) & T
+
+        ...z
+>z : (T | undefined) & T
+
+    };
+}
+

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

@@ -0,0 +1,35 @@
+// @strict: true
+// @declaration: true
+
+function f1<T>(a: T & undefined) {
+    return { ...a };  // Error
+}
+
+function f2<T>(a: T | T & undefined) {
+    return { ...a };
+}
+
+function f3<T extends undefined>(a: T) {
+    return { ...a };  // Error
+}
+
+function f4<T extends undefined>(a: object | T) {
+    return { ...a };
+}
+
+function f5<S, T extends undefined>(a: S | T) {
+    return { ...a };
+}
+
+function f6<T extends object | undefined>(a: T) {
+    return { ...a };
+}
+
+// Repro from #46976
+
+function g1<T extends {}, A extends { z: (T | undefined) & T }>(a: A) {
+    const { z } = a;
+    return {
+        ...z
+    };
+}