microsoft · GokhanKabar · Mar 14, 2026
diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
@@ -20135,7 +20135,11 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
                     const isSetonlyAccessor = prop.flags & SymbolFlags.SetAccessor && !(prop.flags & SymbolFlags.GetAccessor);
                     const flags = SymbolFlags.Property | SymbolFlags.Optional;
                     const result = createSymbol(flags, prop.escapedName, getIsLateCheckFlag(prop) | (readonly ? CheckFlags.Readonly : 0));
-                    result.links.type = isSetonlyAccessor ? undefinedType : addOptionality(getTypeOfSymbol(prop), /*isProperty*/ true);
+                    let propType = isSetonlyAccessor ? undefinedType : getTypeOfSymbol(prop);
+                    if (exactOptionalPropertyTypes && !isSetonlyAccessor && !(prop.flags & SymbolFlags.Optional) && containsMissingType(propType)) {
+                        propType = getUnionType([removeMissingOrUndefinedType(propType), undefinedType]);
+                    }
+                    result.links.type = isSetonlyAccessor ? undefinedType : addOptionality(propType, /*isProperty*/ true);
                     result.declarations = prop.declarations;
                     result.links.nameType = getSymbolLinks(prop).nameType;
                     result.links.syntheticOrigin = prop;

diff --git a/tests/baselines/reference/exactOptionalPropertyTypes_spreadTernary.errors.txt b/tests/baselines/reference/exactOptionalPropertyTypes_spreadTernary.errors.txt
@@ -0,0 +1,80 @@
+exactOptionalPropertyTypes_spreadTernary.ts(13,1): error TS2375: Type '{ parentId: string | undefined; }' is not assignable to type 'Foo' with 'exactOptionalPropertyTypes: true'. Consider adding 'undefined' to the types of the target's properties.
+  Types of property 'parentId' are incompatible.
+    Type 'string | undefined' is not assignable to type 'string'.
+      Type 'undefined' is not assignable to type 'string'.
+exactOptionalPropertyTypes_spreadTernary.ts(16,1): error TS2375: Type '{ parentId?: string | undefined; }' is not assignable to type 'Foo' with 'exactOptionalPropertyTypes: true'. Consider adding 'undefined' to the types of the target's properties.
+  Types of property 'parentId' are incompatible.
+    Type 'string | undefined' is not assignable to type 'string'.
+      Type 'undefined' is not assignable to type 'string'.
+exactOptionalPropertyTypes_spreadTernary.ts(20,1): error TS2375: Type '{ parentId?: string | undefined; }' is not assignable to type 'Foo' with 'exactOptionalPropertyTypes: true'. Consider adding 'undefined' to the types of the target's properties.
+  Types of property 'parentId' are incompatible.
+    Type 'string | undefined' is not assignable to type 'string'.
+      Type 'undefined' is not assignable to type 'string'.
+exactOptionalPropertyTypes_spreadTernary.ts(24,1): error TS2375: Type '{ parentId?: string | undefined; }' is not assignable to type 'Foo' with 'exactOptionalPropertyTypes: true'. Consider adding 'undefined' to the types of the target's properties.
+  Types of property 'parentId' are incompatible.
+    Type 'string | undefined' is not assignable to type 'string'.
+      Type 'undefined' is not assignable to type 'string'.
+
+
+==== exactOptionalPropertyTypes_spreadTernary.ts (4 errors) ====
+    // Repro from https://github.com/microsoft/TypeScript/issues/63240
+    // exactOptionalPropertyTypes should flag optional-property values spread via ternary
+
+    type Foo = {
+        parentId?: string;
+    };
+
+    declare const requestBody: Foo;
+    declare const cond: boolean;
+    let target: Foo;
+
+    // Direct assignment — correctly flagged
+    target = { parentId: requestBody.parentId }; // Error
+    ~~~~~~
+!!! error TS2375: Type '{ parentId: string | undefined; }' is not assignable to type 'Foo' with 'exactOptionalPropertyTypes: true'. Consider adding 'undefined' to the types of the target's properties.
+!!! error TS2375:   Types of property 'parentId' are incompatible.
+!!! error TS2375:     Type 'string | undefined' is not assignable to type 'string'.
+!!! error TS2375:       Type 'undefined' is not assignable to type 'string'.
+
+    // Spread + ternary with optional property access — must also be flagged
+    target = { ...(cond ? { parentId: requestBody.parentId } : {}) }; // Error
+    ~~~~~~
+!!! error TS2375: Type '{ parentId?: string | undefined; }' is not assignable to type 'Foo' with 'exactOptionalPropertyTypes: true'. Consider adding 'undefined' to the types of the target's properties.
+!!! error TS2375:   Types of property 'parentId' are incompatible.
+!!! error TS2375:     Type 'string | undefined' is not assignable to type 'string'.
+!!! error TS2375:       Type 'undefined' is not assignable to type 'string'.
+
+    // Destructured optional property — must also be flagged
+    const { parentId } = requestBody;
+    target = { ...(cond ? { parentId } : {}) }; // Error
+    ~~~~~~
+!!! error TS2375: Type '{ parentId?: string | undefined; }' is not assignable to type 'Foo' with 'exactOptionalPropertyTypes: true'. Consider adding 'undefined' to the types of the target's properties.
+!!! error TS2375:   Types of property 'parentId' are incompatible.
+!!! error TS2375:     Type 'string | undefined' is not assignable to type 'string'.
+!!! error TS2375:       Type 'undefined' is not assignable to type 'string'.
+
+    // Explicit `string | undefined` value — must be flagged (was already working)
+    const parentId2 = '' as string | undefined;
+    target = { ...(cond ? { parentId: parentId2 } : {}) }; // Error
+    ~~~~~~
+!!! error TS2375: Type '{ parentId?: string | undefined; }' is not assignable to type 'Foo' with 'exactOptionalPropertyTypes: true'. Consider adding 'undefined' to the types of the target's properties.
+!!! error TS2375:   Types of property 'parentId' are incompatible.
+!!! error TS2375:     Type 'string | undefined' is not assignable to type 'string'.
+!!! error TS2375:       Type 'undefined' is not assignable to type 'string'.
+
+    // ------------------------------------------------------------------
+    // Valid cases — must NOT produce errors
+    // ------------------------------------------------------------------
+
+    // Spreading the whole Foo object is fine (its optional properties are already correctly typed)
+    target = { ...(cond ? requestBody : {}) }; // OK
+
+    // A required string value is fine
+    const parentId3 = 'hello';
+    target = { ...(cond ? { parentId: parentId3 } : {}) }; // OK
+
+    // Spreading an object where the property is narrowed to string
+    if (cond && requestBody.parentId !== undefined) {
+        target = { ...(cond ? { parentId: requestBody.parentId } : {}) }; // OK — narrowed to string
+    }
+
diff --git a/tests/baselines/reference/exactOptionalPropertyTypes_spreadTernary.js b/tests/baselines/reference/exactOptionalPropertyTypes_spreadTernary.js
@@ -0,0 +1,69 @@
+//// [tests/cases/compiler/exactOptionalPropertyTypes_spreadTernary.ts] ////
+
+//// [exactOptionalPropertyTypes_spreadTernary.ts]
+type Foo = {
+    parentId?: string;
+};
+
+declare const requestBody: Foo;
+declare const cond: boolean;
+let target: Foo;
+
+// Direct assignment — correctly flagged
+target = { parentId: requestBody.parentId }; // Error
+
+// Spread + ternary with optional property access — must also be flagged
+target = { ...(cond ? { parentId: requestBody.parentId } : {}) }; // Error
+
+// Destructured optional property — must also be flagged
+const { parentId } = requestBody;
+target = { ...(cond ? { parentId } : {}) }; // Error
+
+// Explicit `string | undefined` value — must be flagged (was already working)
+const parentId2 = '' as string | undefined;
+target = { ...(cond ? { parentId: parentId2 } : {}) }; // Error
+
+// ------------------------------------------------------------------
+// Valid cases — must NOT produce errors
+// ------------------------------------------------------------------
+
+// Spreading the whole Foo object is fine (its optional properties are already correctly typed)
+target = { ...(cond ? requestBody : {}) }; // OK
+
+// A required string value is fine
+const parentId3 = 'hello';
+target = { ...(cond ? { parentId: parentId3 } : {}) }; // OK
+
+// Spreading an object where the property is narrowed to string
+if (cond && requestBody.parentId !== undefined) {
+    target = { ...(cond ? { parentId: requestBody.parentId } : {}) }; // OK — narrowed to string
+}
+
+
+//// [exactOptionalPropertyTypes_spreadTernary.js]
+"use strict";
+// Repro from https://github.com/microsoft/TypeScript/issues/63240
+// exactOptionalPropertyTypes should flag optional-property values spread via ternary
+let target;
+// Direct assignment — correctly flagged
+target = { parentId: requestBody.parentId }; // Error
+// Spread + ternary with optional property access — must also be flagged
+target = Object.assign({}, (cond ? { parentId: requestBody.parentId } : {})); // Error
+// Destructured optional property — must also be flagged
+const { parentId } = requestBody;
+target = Object.assign({}, (cond ? { parentId } : {})); // Error
+// Explicit `string | undefined` value — must be flagged (was already working)
+const parentId2 = '';
+target = Object.assign({}, (cond ? { parentId: parentId2 } : {})); // Error
+// ------------------------------------------------------------------
+// Valid cases — must NOT produce errors
+// ------------------------------------------------------------------
+// Spreading the whole Foo object is fine (its optional properties are already correctly typed)
+target = Object.assign({}, (cond ? requestBody : {})); // OK
+// A required string value is fine
+const parentId3 = 'hello';
+target = Object.assign({}, (cond ? { parentId: parentId3 } : {})); // OK
+// Spreading an object where the property is narrowed to string
+if (cond && requestBody.parentId !== undefined) {
+    target = Object.assign({}, (cond ? { parentId: requestBody.parentId } : {})); // OK — narrowed to string
+}
diff --git a/tests/baselines/reference/exactOptionalPropertyTypes_spreadTernary.symbols b/tests/baselines/reference/exactOptionalPropertyTypes_spreadTernary.symbols
@@ -0,0 +1,99 @@
+//// [tests/cases/compiler/exactOptionalPropertyTypes_spreadTernary.ts] ////
+
+=== exactOptionalPropertyTypes_spreadTernary.ts ===
+// Repro from https://github.com/microsoft/TypeScript/issues/63240
+// exactOptionalPropertyTypes should flag optional-property values spread via ternary
+
+type Foo = {
+>Foo : Symbol(Foo, Decl(exactOptionalPropertyTypes_spreadTernary.ts, 0, 0))
+
+    parentId?: string;
+>parentId : Symbol(parentId, Decl(exactOptionalPropertyTypes_spreadTernary.ts, 3, 12))
+
+};
+
+declare const requestBody: Foo;
+>requestBody : Symbol(requestBody, Decl(exactOptionalPropertyTypes_spreadTernary.ts, 7, 13))
+>Foo : Symbol(Foo, Decl(exactOptionalPropertyTypes_spreadTernary.ts, 0, 0))
+
+declare const cond: boolean;
+>cond : Symbol(cond, Decl(exactOptionalPropertyTypes_spreadTernary.ts, 8, 13))
+
+let target: Foo;
+>target : Symbol(target, Decl(exactOptionalPropertyTypes_spreadTernary.ts, 9, 3))
+>Foo : Symbol(Foo, Decl(exactOptionalPropertyTypes_spreadTernary.ts, 0, 0))
+
+// Direct assignment — correctly flagged
+target = { parentId: requestBody.parentId }; // Error
+>target : Symbol(target, Decl(exactOptionalPropertyTypes_spreadTernary.ts, 9, 3))
+>parentId : Symbol(parentId, Decl(exactOptionalPropertyTypes_spreadTernary.ts, 12, 10))
+>requestBody.parentId : Symbol(parentId, Decl(exactOptionalPropertyTypes_spreadTernary.ts, 3, 12))
+>requestBody : Symbol(requestBody, Decl(exactOptionalPropertyTypes_spreadTernary.ts, 7, 13))
+>parentId : Symbol(parentId, Decl(exactOptionalPropertyTypes_spreadTernary.ts, 3, 12))
+
+// Spread + ternary with optional property access — must also be flagged
+target = { ...(cond ? { parentId: requestBody.parentId } : {}) }; // Error
+>target : Symbol(target, Decl(exactOptionalPropertyTypes_spreadTernary.ts, 9, 3))
+>cond : Symbol(cond, Decl(exactOptionalPropertyTypes_spreadTernary.ts, 8, 13))
+>parentId : Symbol(parentId, Decl(exactOptionalPropertyTypes_spreadTernary.ts, 15, 23))
+>requestBody.parentId : Symbol(parentId, Decl(exactOptionalPropertyTypes_spreadTernary.ts, 3, 12))
+>requestBody : Symbol(requestBody, Decl(exactOptionalPropertyTypes_spreadTernary.ts, 7, 13))
+>parentId : Symbol(parentId, Decl(exactOptionalPropertyTypes_spreadTernary.ts, 3, 12))
+
+// Destructured optional property — must also be flagged
+const { parentId } = requestBody;
+>parentId : Symbol(parentId, Decl(exactOptionalPropertyTypes_spreadTernary.ts, 18, 7))
+>requestBody : Symbol(requestBody, Decl(exactOptionalPropertyTypes_spreadTernary.ts, 7, 13))
+
+target = { ...(cond ? { parentId } : {}) }; // Error
+>target : Symbol(target, Decl(exactOptionalPropertyTypes_spreadTernary.ts, 9, 3))
+>cond : Symbol(cond, Decl(exactOptionalPropertyTypes_spreadTernary.ts, 8, 13))
+>parentId : Symbol(parentId, Decl(exactOptionalPropertyTypes_spreadTernary.ts, 19, 23))
+
+// Explicit `string | undefined` value — must be flagged (was already working)
+const parentId2 = '' as string | undefined;
+>parentId2 : Symbol(parentId2, Decl(exactOptionalPropertyTypes_spreadTernary.ts, 22, 5))
+
+target = { ...(cond ? { parentId: parentId2 } : {}) }; // Error
+>target : Symbol(target, Decl(exactOptionalPropertyTypes_spreadTernary.ts, 9, 3))
+>cond : Symbol(cond, Decl(exactOptionalPropertyTypes_spreadTernary.ts, 8, 13))
+>parentId : Symbol(parentId, Decl(exactOptionalPropertyTypes_spreadTernary.ts, 23, 23))
+>parentId2 : Symbol(parentId2, Decl(exactOptionalPropertyTypes_spreadTernary.ts, 22, 5))
+
+// ------------------------------------------------------------------
+// Valid cases — must NOT produce errors
+// ------------------------------------------------------------------
+
+// Spreading the whole Foo object is fine (its optional properties are already correctly typed)
+target = { ...(cond ? requestBody : {}) }; // OK
+>target : Symbol(target, Decl(exactOptionalPropertyTypes_spreadTernary.ts, 9, 3))
+>cond : Symbol(cond, Decl(exactOptionalPropertyTypes_spreadTernary.ts, 8, 13))
+>requestBody : Symbol(requestBody, Decl(exactOptionalPropertyTypes_spreadTernary.ts, 7, 13))
+
+// A required string value is fine
+const parentId3 = 'hello';
+>parentId3 : Symbol(parentId3, Decl(exactOptionalPropertyTypes_spreadTernary.ts, 33, 5))
+
+target = { ...(cond ? { parentId: parentId3 } : {}) }; // OK
+>target : Symbol(target, Decl(exactOptionalPropertyTypes_spreadTernary.ts, 9, 3))
+>cond : Symbol(cond, Decl(exactOptionalPropertyTypes_spreadTernary.ts, 8, 13))
+>parentId : Symbol(parentId, Decl(exactOptionalPropertyTypes_spreadTernary.ts, 34, 23))
+>parentId3 : Symbol(parentId3, Decl(exactOptionalPropertyTypes_spreadTernary.ts, 33, 5))
+
+// Spreading an object where the property is narrowed to string
+if (cond && requestBody.parentId !== undefined) {
+>cond : Symbol(cond, Decl(exactOptionalPropertyTypes_spreadTernary.ts, 8, 13))
+>requestBody.parentId : Symbol(parentId, Decl(exactOptionalPropertyTypes_spreadTernary.ts, 3, 12))
+>requestBody : Symbol(requestBody, Decl(exactOptionalPropertyTypes_spreadTernary.ts, 7, 13))
+>parentId : Symbol(parentId, Decl(exactOptionalPropertyTypes_spreadTernary.ts, 3, 12))
+>undefined : Symbol(undefined)
+
+    target = { ...(cond ? { parentId: requestBody.parentId } : {}) }; // OK — narrowed to string
+>target : Symbol(target, Decl(exactOptionalPropertyTypes_spreadTernary.ts, 9, 3))
+>cond : Symbol(cond, Decl(exactOptionalPropertyTypes_spreadTernary.ts, 8, 13))
+>parentId : Symbol(parentId, Decl(exactOptionalPropertyTypes_spreadTernary.ts, 38, 27))
+>requestBody.parentId : Symbol(parentId, Decl(exactOptionalPropertyTypes_spreadTernary.ts, 3, 12))
+>requestBody : Symbol(requestBody, Decl(exactOptionalPropertyTypes_spreadTernary.ts, 7, 13))
+>parentId : Symbol(parentId, Decl(exactOptionalPropertyTypes_spreadTernary.ts, 3, 12))
+}
+