Always create optional properties when spreading objects conditionally

src/compiler/checker.ts

@@ -14393,23 +14393,17 @@ namespace ts {
             return isEmptyObjectType(type) || !!(type.flags & (TypeFlags.Null | TypeFlags.Undefined | TypeFlags.BooleanLike | TypeFlags.NumberLike | TypeFlags.BigIntLike | TypeFlags.StringLike | TypeFlags.EnumLike | TypeFlags.NonPrimitive | TypeFlags.Index));
         }
 
-        function isSinglePropertyAnonymousObjectType(type: Type) {
-            return !!(type.flags & TypeFlags.Object) &&
-                !!(getObjectFlags(type) & ObjectFlags.Anonymous) &&
-                (length(getPropertiesOfType(type)) === 1 || every(getPropertiesOfType(type), p => !!(p.flags & SymbolFlags.Optional)));
-        }
-
         function tryMergeUnionOfObjectTypeAndEmptyObject(type: UnionType, readonly: boolean): Type | undefined {
             if (type.types.length === 2) {
                 const firstType = type.types[0];
                 const secondType = type.types[1];
                 if (every(type.types, isEmptyObjectTypeOrSpreadsIntoEmptyObject)) {
                     return isEmptyObjectType(firstType) ? firstType : isEmptyObjectType(secondType) ? secondType : emptyObjectType;
                 }
-                if (isEmptyObjectTypeOrSpreadsIntoEmptyObject(firstType) && isSinglePropertyAnonymousObjectType(secondType)) {
+                if (isEmptyObjectTypeOrSpreadsIntoEmptyObject(firstType)) {
                     return getAnonymousPartialType(secondType);
                 }
-                if (isEmptyObjectTypeOrSpreadsIntoEmptyObject(secondType) && isSinglePropertyAnonymousObjectType(firstType)) {
+                if (isEmptyObjectTypeOrSpreadsIntoEmptyObject(secondType)) {
                     return getAnonymousPartialType(firstType);
                 }
             }

tests/baselines/reference/objectSpreadRepeatedComplexity.js

@@ -0,0 +1,160 @@
+//// [objectSpreadRepeatedComplexity.ts]
+function f(cnd: Record<number, boolean>){
+    // Type is a union of 2^(n-1) members, where n is the number of spread objects
+    return {
+        // Without this one, it collapses to {} ?
+        ...(cnd[1] &&
+            cnd[2] && {
+            prop0: 0,
+        }),
+
+        // With one prop each, it collapses to a single object (#34853?)
+        ...(cnd[3] && {
+            prop3a: 1,
+            prop3b: 1,
+        }),
+        ...(cnd[4] && {
+            prop4a: 1,
+            prop4b: 1,
+        }),
+        ...(cnd[5] && {
+            prop5a: 1,
+            prop5b: 1,
+        }),
+        ...(cnd[6] && {
+            prop6a: 1,
+            prop6b: 1,
+        }),
+        ...(cnd[7] && {
+            prop7a: 1,
+            prop7b: 1,
+        }),
+        ...(cnd[8] && {
+            prop8a: 1,
+            prop8b: 1,
+        }),
+        ...(cnd[9] && {
+            prop9a: 1,
+            prop9b: 1,
+        }),
+        ...(cnd[10] && {
+            prop10a: 1,
+            prop10b: 1,
+        }),
+        ...(cnd[11] && {
+            prop11a: 1,
+            prop11b: 1,
+        }),
+        ...(cnd[12] && {
+            prop12a: 1,
+            prop12b: 1,
+        }),
+        ...(cnd[13] && {
+            prop13a: 1,
+            prop13b: 1,
+        }),
+        ...(cnd[14] && {
+            prop14a: 1,
+            prop14b: 1,
+        }),
+        ...(cnd[15] && {
+            prop15a: 1,
+            prop15b: 1,
+        }),
+        ...(cnd[16] && {
+            prop16a: 1,
+            prop16b: 1,
+        }),
+        ...(cnd[17] && {
+            prop17a: 1,
+            prop17b: 1,
+        }),
+        ...(cnd[18] && {
+            prop18a: 1,
+            prop18b: 1,
+        }),
+        ...(cnd[19] && {
+            prop19a: 1,
+            prop19b: 1,
+        }),
+        ...(cnd[20] && {
+            prop20a: 1,
+            prop20b: 1,
+        }),
+    };
+}
+
+//// [objectSpreadRepeatedComplexity.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 f(cnd) {
+    // Type is a union of 2^(n-1) members, where n is the number of spread objects
+    return __assign(__assign(__assign(__assign(__assign(__assign(__assign(__assign(__assign(__assign(__assign(__assign(__assign(__assign(__assign(__assign(__assign(__assign(__assign({}, (cnd[1] &&
+        cnd[2] && {
+        prop0: 0
+    })), (cnd[3] && {
+        prop3a: 1,
+        prop3b: 1
+    })), (cnd[4] && {
+        prop4a: 1,
+        prop4b: 1
+    })), (cnd[5] && {
+        prop5a: 1,
+        prop5b: 1
+    })), (cnd[6] && {
+        prop6a: 1,
+        prop6b: 1
+    })), (cnd[7] && {
+        prop7a: 1,
+        prop7b: 1
+    })), (cnd[8] && {
+        prop8a: 1,
+        prop8b: 1
+    })), (cnd[9] && {
+        prop9a: 1,
+        prop9b: 1
+    })), (cnd[10] && {
+        prop10a: 1,
+        prop10b: 1
+    })), (cnd[11] && {
+        prop11a: 1,
+        prop11b: 1
+    })), (cnd[12] && {
+        prop12a: 1,
+        prop12b: 1
+    })), (cnd[13] && {
+        prop13a: 1,
+        prop13b: 1
+    })), (cnd[14] && {
+        prop14a: 1,
+        prop14b: 1
+    })), (cnd[15] && {
+        prop15a: 1,
+        prop15b: 1
+    })), (cnd[16] && {
+        prop16a: 1,
+        prop16b: 1
+    })), (cnd[17] && {
+        prop17a: 1,
+        prop17b: 1
+    })), (cnd[18] && {
+        prop18a: 1,
+        prop18b: 1
+    })), (cnd[19] && {
+        prop19a: 1,
+        prop19b: 1
+    })), (cnd[20] && {
+        prop20a: 1,
+        prop20b: 1
+    }));
+}

tests/baselines/reference/objectSpreadRepeatedComplexity.symbols

@@ -0,0 +1,203 @@
+=== tests/cases/compiler/objectSpreadRepeatedComplexity.ts ===
+function f(cnd: Record<number, boolean>){
+>f : Symbol(f, Decl(objectSpreadRepeatedComplexity.ts, 0, 0))
+>cnd : Symbol(cnd, Decl(objectSpreadRepeatedComplexity.ts, 0, 11))
+>Record : Symbol(Record, Decl(lib.es5.d.ts, --, --))
+
+    // Type is a union of 2^(n-1) members, where n is the number of spread objects
+    return {
+        // Without this one, it collapses to {} ?
+        ...(cnd[1] &&
+>cnd : Symbol(cnd, Decl(objectSpreadRepeatedComplexity.ts, 0, 11))
+
+            cnd[2] && {
+>cnd : Symbol(cnd, Decl(objectSpreadRepeatedComplexity.ts, 0, 11))
+
+            prop0: 0,
+>prop0 : Symbol(prop0, Decl(objectSpreadRepeatedComplexity.ts, 5, 23))
+
+        }),
+
+        // With one prop each, it collapses to a single object (#34853?)
+        ...(cnd[3] && {
+>cnd : Symbol(cnd, Decl(objectSpreadRepeatedComplexity.ts, 0, 11))
+
+            prop3a: 1,
+>prop3a : Symbol(prop3a, Decl(objectSpreadRepeatedComplexity.ts, 10, 23))
+
+            prop3b: 1,
+>prop3b : Symbol(prop3b, Decl(objectSpreadRepeatedComplexity.ts, 11, 22))
+
+        }),
+        ...(cnd[4] && {
+>cnd : Symbol(cnd, Decl(objectSpreadRepeatedComplexity.ts, 0, 11))
+
+            prop4a: 1,
+>prop4a : Symbol(prop4a, Decl(objectSpreadRepeatedComplexity.ts, 14, 23))
+
+            prop4b: 1,
+>prop4b : Symbol(prop4b, Decl(objectSpreadRepeatedComplexity.ts, 15, 22))
+
+        }),
+        ...(cnd[5] && {
+>cnd : Symbol(cnd, Decl(objectSpreadRepeatedComplexity.ts, 0, 11))
+
+            prop5a: 1,
+>prop5a : Symbol(prop5a, Decl(objectSpreadRepeatedComplexity.ts, 18, 23))
+
+            prop5b: 1,
+>prop5b : Symbol(prop5b, Decl(objectSpreadRepeatedComplexity.ts, 19, 22))
+
+        }),
+        ...(cnd[6] && {
+>cnd : Symbol(cnd, Decl(objectSpreadRepeatedComplexity.ts, 0, 11))
+
+            prop6a: 1,
+>prop6a : Symbol(prop6a, Decl(objectSpreadRepeatedComplexity.ts, 22, 23))
+
+            prop6b: 1,
+>prop6b : Symbol(prop6b, Decl(objectSpreadRepeatedComplexity.ts, 23, 22))
+
+        }),
+        ...(cnd[7] && {
+>cnd : Symbol(cnd, Decl(objectSpreadRepeatedComplexity.ts, 0, 11))
+
+            prop7a: 1,
+>prop7a : Symbol(prop7a, Decl(objectSpreadRepeatedComplexity.ts, 26, 23))
+
+            prop7b: 1,
+>prop7b : Symbol(prop7b, Decl(objectSpreadRepeatedComplexity.ts, 27, 22))
+
+        }),
+        ...(cnd[8] && {
+>cnd : Symbol(cnd, Decl(objectSpreadRepeatedComplexity.ts, 0, 11))
+
+            prop8a: 1,
+>prop8a : Symbol(prop8a, Decl(objectSpreadRepeatedComplexity.ts, 30, 23))
+
+            prop8b: 1,
+>prop8b : Symbol(prop8b, Decl(objectSpreadRepeatedComplexity.ts, 31, 22))
+
+        }),
+        ...(cnd[9] && {
+>cnd : Symbol(cnd, Decl(objectSpreadRepeatedComplexity.ts, 0, 11))
+
+            prop9a: 1,
+>prop9a : Symbol(prop9a, Decl(objectSpreadRepeatedComplexity.ts, 34, 23))
+
+            prop9b: 1,
+>prop9b : Symbol(prop9b, Decl(objectSpreadRepeatedComplexity.ts, 35, 22))
+
+        }),
+        ...(cnd[10] && {
+>cnd : Symbol(cnd, Decl(objectSpreadRepeatedComplexity.ts, 0, 11))
+
+            prop10a: 1,
+>prop10a : Symbol(prop10a, Decl(objectSpreadRepeatedComplexity.ts, 38, 24))
+
+            prop10b: 1,
+>prop10b : Symbol(prop10b, Decl(objectSpreadRepeatedComplexity.ts, 39, 23))
+
+        }),
+        ...(cnd[11] && {
+>cnd : Symbol(cnd, Decl(objectSpreadRepeatedComplexity.ts, 0, 11))
+
+            prop11a: 1,
+>prop11a : Symbol(prop11a, Decl(objectSpreadRepeatedComplexity.ts, 42, 24))
+
+            prop11b: 1,
+>prop11b : Symbol(prop11b, Decl(objectSpreadRepeatedComplexity.ts, 43, 23))
+
+        }),
+        ...(cnd[12] && {
+>cnd : Symbol(cnd, Decl(objectSpreadRepeatedComplexity.ts, 0, 11))
+
+            prop12a: 1,
+>prop12a : Symbol(prop12a, Decl(objectSpreadRepeatedComplexity.ts, 46, 24))
+
+            prop12b: 1,
+>prop12b : Symbol(prop12b, Decl(objectSpreadRepeatedComplexity.ts, 47, 23))
+
+        }),
+        ...(cnd[13] && {
+>cnd : Symbol(cnd, Decl(objectSpreadRepeatedComplexity.ts, 0, 11))
+
+            prop13a: 1,
+>prop13a : Symbol(prop13a, Decl(objectSpreadRepeatedComplexity.ts, 50, 24))
+
+            prop13b: 1,
+>prop13b : Symbol(prop13b, Decl(objectSpreadRepeatedComplexity.ts, 51, 23))
+
+        }),
+        ...(cnd[14] && {
+>cnd : Symbol(cnd, Decl(objectSpreadRepeatedComplexity.ts, 0, 11))
+
+            prop14a: 1,
+>prop14a : Symbol(prop14a, Decl(objectSpreadRepeatedComplexity.ts, 54, 24))
+
+            prop14b: 1,
+>prop14b : Symbol(prop14b, Decl(objectSpreadRepeatedComplexity.ts, 55, 23))
+
+        }),
+        ...(cnd[15] && {
+>cnd : Symbol(cnd, Decl(objectSpreadRepeatedComplexity.ts, 0, 11))
+
+            prop15a: 1,
+>prop15a : Symbol(prop15a, Decl(objectSpreadRepeatedComplexity.ts, 58, 24))
+
+            prop15b: 1,
+>prop15b : Symbol(prop15b, Decl(objectSpreadRepeatedComplexity.ts, 59, 23))
+
+        }),
+        ...(cnd[16] && {
+>cnd : Symbol(cnd, Decl(objectSpreadRepeatedComplexity.ts, 0, 11))
+
+            prop16a: 1,
+>prop16a : Symbol(prop16a, Decl(objectSpreadRepeatedComplexity.ts, 62, 24))
+
+            prop16b: 1,
+>prop16b : Symbol(prop16b, Decl(objectSpreadRepeatedComplexity.ts, 63, 23))
+
+        }),
+        ...(cnd[17] && {
+>cnd : Symbol(cnd, Decl(objectSpreadRepeatedComplexity.ts, 0, 11))
+
+            prop17a: 1,
+>prop17a : Symbol(prop17a, Decl(objectSpreadRepeatedComplexity.ts, 66, 24))
+
+            prop17b: 1,
+>prop17b : Symbol(prop17b, Decl(objectSpreadRepeatedComplexity.ts, 67, 23))
+
+        }),
+        ...(cnd[18] && {
+>cnd : Symbol(cnd, Decl(objectSpreadRepeatedComplexity.ts, 0, 11))
+
+            prop18a: 1,
+>prop18a : Symbol(prop18a, Decl(objectSpreadRepeatedComplexity.ts, 70, 24))
+
+            prop18b: 1,
+>prop18b : Symbol(prop18b, Decl(objectSpreadRepeatedComplexity.ts, 71, 23))
+
+        }),
+        ...(cnd[19] && {
+>cnd : Symbol(cnd, Decl(objectSpreadRepeatedComplexity.ts, 0, 11))
+
+            prop19a: 1,
+>prop19a : Symbol(prop19a, Decl(objectSpreadRepeatedComplexity.ts, 74, 24))
+
+            prop19b: 1,
+>prop19b : Symbol(prop19b, Decl(objectSpreadRepeatedComplexity.ts, 75, 23))
+
+        }),
+        ...(cnd[20] && {
+>cnd : Symbol(cnd, Decl(objectSpreadRepeatedComplexity.ts, 0, 11))
+
+            prop20a: 1,
+>prop20a : Symbol(prop20a, Decl(objectSpreadRepeatedComplexity.ts, 78, 24))
+
+            prop20b: 1,
+>prop20b : Symbol(prop20b, Decl(objectSpreadRepeatedComplexity.ts, 79, 23))
+
+        }),
+    };
+}