Fixed an issue with assignments to dynamic properties with `exactOptionalPropertyTypes`

src/compiler/checker.ts

@@ -32200,7 +32200,10 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
         // accessor, or optional method.
         const assignmentKind = getAssignmentTargetKind(node);
         if (assignmentKind === AssignmentKind.Definite) {
-            return removeMissingType(propType, !!(prop && prop.flags & SymbolFlags.Optional));
+            // since this is used as an assignment target we always want to remove the missing type
+            // usually this is done conditionally based on the `prop.flags`
+            // the prop might not be available here though if the assignment is done to a dynamic property
+            return removeMissingType(propType, /*isOptional*/ true);
         }
         if (
             prop &&

tests/baselines/reference/propertyAssignmentDynamicOptionalProp(exactoptionalpropertytypes=false).symbols

@@ -0,0 +1,56 @@
+//// [tests/cases/compiler/propertyAssignmentDynamicOptionalProp.ts] ////
+
+=== propertyAssignmentDynamicOptionalProp.ts ===
+// https://github.com/microsoft/TypeScript/issues/55526
+
+type Something1 = {
+>Something1 : Symbol(Something1, Decl(propertyAssignmentDynamicOptionalProp.ts, 0, 0))
+
+  a?: string;
+>a : Symbol(a, Decl(propertyAssignmentDynamicOptionalProp.ts, 2, 19))
+
+};
+
+const x1: Something1 = {};
+>x1 : Symbol(x1, Decl(propertyAssignmentDynamicOptionalProp.ts, 6, 5))
+>Something1 : Symbol(Something1, Decl(propertyAssignmentDynamicOptionalProp.ts, 0, 0))
+
+function assignToKey1(key: keyof Something1, value: string | undefined) {
+>assignToKey1 : Symbol(assignToKey1, Decl(propertyAssignmentDynamicOptionalProp.ts, 6, 26))
+>key : Symbol(key, Decl(propertyAssignmentDynamicOptionalProp.ts, 8, 22))
+>Something1 : Symbol(Something1, Decl(propertyAssignmentDynamicOptionalProp.ts, 0, 0))
+>value : Symbol(value, Decl(propertyAssignmentDynamicOptionalProp.ts, 8, 44))
+
+  x1[key] = value;
+>x1 : Symbol(x1, Decl(propertyAssignmentDynamicOptionalProp.ts, 6, 5))
+>key : Symbol(key, Decl(propertyAssignmentDynamicOptionalProp.ts, 8, 22))
+>value : Symbol(value, Decl(propertyAssignmentDynamicOptionalProp.ts, 8, 44))
+}
+
+type Something2 = {
+>Something2 : Symbol(Something2, Decl(propertyAssignmentDynamicOptionalProp.ts, 10, 1))
+
+  a?: string;
+>a : Symbol(a, Decl(propertyAssignmentDynamicOptionalProp.ts, 12, 19))
+
+  b?: string;
+>b : Symbol(b, Decl(propertyAssignmentDynamicOptionalProp.ts, 13, 13))
+
+};
+
+const x2: Something2 = {};
+>x2 : Symbol(x2, Decl(propertyAssignmentDynamicOptionalProp.ts, 17, 5))
+>Something2 : Symbol(Something2, Decl(propertyAssignmentDynamicOptionalProp.ts, 10, 1))
+
+function assignToKey2(key: keyof Something2, value: string | undefined) {
+>assignToKey2 : Symbol(assignToKey2, Decl(propertyAssignmentDynamicOptionalProp.ts, 17, 26))
+>key : Symbol(key, Decl(propertyAssignmentDynamicOptionalProp.ts, 19, 22))
+>Something2 : Symbol(Something2, Decl(propertyAssignmentDynamicOptionalProp.ts, 10, 1))
+>value : Symbol(value, Decl(propertyAssignmentDynamicOptionalProp.ts, 19, 44))
+
+  x2[key] = value;
+>x2 : Symbol(x2, Decl(propertyAssignmentDynamicOptionalProp.ts, 17, 5))
+>key : Symbol(key, Decl(propertyAssignmentDynamicOptionalProp.ts, 19, 22))
+>value : Symbol(value, Decl(propertyAssignmentDynamicOptionalProp.ts, 19, 44))
+}
+

tests/baselines/reference/propertyAssignmentDynamicOptionalProp(exactoptionalpropertytypes=false).types

@@ -0,0 +1,58 @@
+//// [tests/cases/compiler/propertyAssignmentDynamicOptionalProp.ts] ////
+
+=== propertyAssignmentDynamicOptionalProp.ts ===
+// https://github.com/microsoft/TypeScript/issues/55526
+
+type Something1 = {
+>Something1 : { a?: string | undefined; }
+
+  a?: string;
+>a : string | undefined
+
+};
+
+const x1: Something1 = {};
+>x1 : Something1
+>{} : {}
+
+function assignToKey1(key: keyof Something1, value: string | undefined) {
+>assignToKey1 : (key: keyof Something1, value: string | undefined) => void
+>key : "a"
+>value : string | undefined
+
+  x1[key] = value;
+>x1[key] = value : string | undefined
+>x1[key] : string | undefined
+>x1 : Something1
+>key : "a"
+>value : string | undefined
+}
+
+type Something2 = {
+>Something2 : { a?: string | undefined; b?: string | undefined; }
+
+  a?: string;
+>a : string | undefined
+
+  b?: string;
+>b : string | undefined
+
+};
+
+const x2: Something2 = {};
+>x2 : Something2
+>{} : {}
+
+function assignToKey2(key: keyof Something2, value: string | undefined) {
+>assignToKey2 : (key: keyof Something2, value: string | undefined) => void
+>key : keyof Something2
+>value : string | undefined
+
+  x2[key] = value;
+>x2[key] = value : string | undefined
+>x2[key] : string | undefined
+>x2 : Something2
+>key : keyof Something2
+>value : string | undefined
+}
+

tests/baselines/reference/propertyAssignmentDynamicOptionalProp(exactoptionalpropertytypes=true).errors.txt

@@ -0,0 +1,36 @@
+propertyAssignmentDynamicOptionalProp.ts(10,3): error TS2322: Type 'string | undefined' is not assignable to type 'string'.
+  Type 'undefined' is not assignable to type 'string'.
+propertyAssignmentDynamicOptionalProp.ts(21,3): error TS2322: Type 'string | undefined' is not assignable to type 'string'.
+  Type 'undefined' is not assignable to type 'string'.
+
+
+==== propertyAssignmentDynamicOptionalProp.ts (2 errors) ====
+    // https://github.com/microsoft/TypeScript/issues/55526
+    
+    type Something1 = {
+      a?: string;
+    };
+    
+    const x1: Something1 = {};
+    
+    function assignToKey1(key: keyof Something1, value: string | undefined) {
+      x1[key] = value;
+      ~~~~~~~
+!!! error TS2322: Type 'string | undefined' is not assignable to type 'string'.
+!!! error TS2322:   Type 'undefined' is not assignable to type 'string'.
+    }
+    
+    type Something2 = {
+      a?: string;
+      b?: string;
+    };
+    
+    const x2: Something2 = {};
+    
+    function assignToKey2(key: keyof Something2, value: string | undefined) {
+      x2[key] = value;
+      ~~~~~~~
+!!! error TS2322: Type 'string | undefined' is not assignable to type 'string'.
+!!! error TS2322:   Type 'undefined' is not assignable to type 'string'.
+    }
+    

tests/baselines/reference/propertyAssignmentDynamicOptionalProp(exactoptionalpropertytypes=true).symbols

@@ -0,0 +1,56 @@
+//// [tests/cases/compiler/propertyAssignmentDynamicOptionalProp.ts] ////
+
+=== propertyAssignmentDynamicOptionalProp.ts ===
+// https://github.com/microsoft/TypeScript/issues/55526
+
+type Something1 = {
+>Something1 : Symbol(Something1, Decl(propertyAssignmentDynamicOptionalProp.ts, 0, 0))
+
+  a?: string;
+>a : Symbol(a, Decl(propertyAssignmentDynamicOptionalProp.ts, 2, 19))
+
+};
+
+const x1: Something1 = {};
+>x1 : Symbol(x1, Decl(propertyAssignmentDynamicOptionalProp.ts, 6, 5))
+>Something1 : Symbol(Something1, Decl(propertyAssignmentDynamicOptionalProp.ts, 0, 0))
+
+function assignToKey1(key: keyof Something1, value: string | undefined) {
+>assignToKey1 : Symbol(assignToKey1, Decl(propertyAssignmentDynamicOptionalProp.ts, 6, 26))
+>key : Symbol(key, Decl(propertyAssignmentDynamicOptionalProp.ts, 8, 22))
+>Something1 : Symbol(Something1, Decl(propertyAssignmentDynamicOptionalProp.ts, 0, 0))
+>value : Symbol(value, Decl(propertyAssignmentDynamicOptionalProp.ts, 8, 44))
+
+  x1[key] = value;
+>x1 : Symbol(x1, Decl(propertyAssignmentDynamicOptionalProp.ts, 6, 5))
+>key : Symbol(key, Decl(propertyAssignmentDynamicOptionalProp.ts, 8, 22))
+>value : Symbol(value, Decl(propertyAssignmentDynamicOptionalProp.ts, 8, 44))
+}
+
+type Something2 = {
+>Something2 : Symbol(Something2, Decl(propertyAssignmentDynamicOptionalProp.ts, 10, 1))
+
+  a?: string;
+>a : Symbol(a, Decl(propertyAssignmentDynamicOptionalProp.ts, 12, 19))
+
+  b?: string;
+>b : Symbol(b, Decl(propertyAssignmentDynamicOptionalProp.ts, 13, 13))
+
+};
+
+const x2: Something2 = {};
+>x2 : Symbol(x2, Decl(propertyAssignmentDynamicOptionalProp.ts, 17, 5))
+>Something2 : Symbol(Something2, Decl(propertyAssignmentDynamicOptionalProp.ts, 10, 1))
+
+function assignToKey2(key: keyof Something2, value: string | undefined) {
+>assignToKey2 : Symbol(assignToKey2, Decl(propertyAssignmentDynamicOptionalProp.ts, 17, 26))
+>key : Symbol(key, Decl(propertyAssignmentDynamicOptionalProp.ts, 19, 22))
+>Something2 : Symbol(Something2, Decl(propertyAssignmentDynamicOptionalProp.ts, 10, 1))
+>value : Symbol(value, Decl(propertyAssignmentDynamicOptionalProp.ts, 19, 44))
+
+  x2[key] = value;
+>x2 : Symbol(x2, Decl(propertyAssignmentDynamicOptionalProp.ts, 17, 5))
+>key : Symbol(key, Decl(propertyAssignmentDynamicOptionalProp.ts, 19, 22))
+>value : Symbol(value, Decl(propertyAssignmentDynamicOptionalProp.ts, 19, 44))
+}
+

tests/baselines/reference/propertyAssignmentDynamicOptionalProp(exactoptionalpropertytypes=true).types

@@ -0,0 +1,58 @@
+//// [tests/cases/compiler/propertyAssignmentDynamicOptionalProp.ts] ////
+
+=== propertyAssignmentDynamicOptionalProp.ts ===
+// https://github.com/microsoft/TypeScript/issues/55526
+
+type Something1 = {
+>Something1 : { a?: string; }
+
+  a?: string;
+>a : string | undefined
+
+};
+
+const x1: Something1 = {};
+>x1 : Something1
+>{} : {}
+
+function assignToKey1(key: keyof Something1, value: string | undefined) {
+>assignToKey1 : (key: keyof Something1, value: string | undefined) => void
+>key : "a"
+>value : string | undefined
+
+  x1[key] = value;
+>x1[key] = value : string | undefined
+>x1[key] : string
+>x1 : Something1
+>key : "a"
+>value : string | undefined
+}
+
+type Something2 = {
+>Something2 : { a?: string; b?: string; }
+
+  a?: string;
+>a : string | undefined
+
+  b?: string;
+>b : string | undefined
+
+};
+
+const x2: Something2 = {};
+>x2 : Something2
+>{} : {}
+
+function assignToKey2(key: keyof Something2, value: string | undefined) {
+>assignToKey2 : (key: keyof Something2, value: string | undefined) => void
+>key : keyof Something2
+>value : string | undefined
+
+  x2[key] = value;
+>x2[key] = value : string | undefined
+>x2[key] : string
+>x2 : Something2
+>key : keyof Something2
+>value : string | undefined
+}
+

tests/cases/compiler/propertyAssignmentDynamicOptionalProp.ts

@@ -0,0 +1,26 @@
+// @strict: true
+// @exactOptionalPropertyTypes: true, false
+// @noEmit: true
+
+// https://github.com/microsoft/TypeScript/issues/55526
+
+type Something1 = {
+  a?: string;
+};
+
+const x1: Something1 = {};
+
+function assignToKey1(key: keyof Something1, value: string | undefined) {
+  x1[key] = value;
+}
+
+type Something2 = {
+  a?: string;
+  b?: string;
+};
+
+const x2: Something2 = {};
+
+function assignToKey2(key: keyof Something2, value: string | undefined) {
+  x2[key] = value;
+}