Properties on intersections should be readonly only if all declarations are

src/compiler/checker.ts

@@ -11800,7 +11800,7 @@ namespace ts {
             // Flags we want to propagate to the result if they exist in all source symbols
             let optionalFlag = isUnion ? SymbolFlags.None : SymbolFlags.Optional;
             let syntheticFlag = CheckFlags.SyntheticMethod;
-            let checkFlags = 0;
+            let checkFlags = isUnion ? 0 : CheckFlags.Readonly;
             let mergedInstantiations = false;
             for (const current of containingType.types) {
                 const type = getApparentType(current);
@@ -11839,8 +11839,13 @@ namespace ts {
                                 }
                             }
                         }
-                        checkFlags |= (isReadonlySymbol(prop) ? CheckFlags.Readonly : 0) |
-                            (!(modifiers & ModifierFlags.NonPublicAccessibilityModifier) ? CheckFlags.ContainsPublic : 0) |
+                        if (isUnion && isReadonlySymbol(prop)) {
+                            checkFlags |= CheckFlags.Readonly;
+                        }
+                        else if (!isUnion && !isReadonlySymbol(prop)) {
+                            checkFlags &= ~CheckFlags.Readonly;
+                        }
+                        checkFlags |= (!(modifiers & ModifierFlags.NonPublicAccessibilityModifier) ? CheckFlags.ContainsPublic : 0) |
                             (modifiers & ModifierFlags.Protected ? CheckFlags.ContainsProtected : 0) |
                             (modifiers & ModifierFlags.Private ? CheckFlags.ContainsPrivate : 0) |
                             (modifiers & ModifierFlags.Static ? CheckFlags.ContainsStatic : 0);

tests/baselines/reference/intersectionTypeReadonly.errors.txt

@@ -1,11 +1,10 @@
 tests/cases/conformance/types/intersection/intersectionTypeReadonly.ts(17,6): error TS2540: Cannot assign to 'value' because it is a read-only property.
 tests/cases/conformance/types/intersection/intersectionTypeReadonly.ts(19,11): error TS2540: Cannot assign to 'value' because it is a read-only property.
-tests/cases/conformance/types/intersection/intersectionTypeReadonly.ts(21,9): error TS2540: Cannot assign to 'value' because it is a read-only property.
 tests/cases/conformance/types/intersection/intersectionTypeReadonly.ts(23,15): error TS2540: Cannot assign to 'value' because it is a read-only property.
 tests/cases/conformance/types/intersection/intersectionTypeReadonly.ts(25,15): error TS2540: Cannot assign to 'value' because it is a read-only property.
 
 
-==== tests/cases/conformance/types/intersection/intersectionTypeReadonly.ts (5 errors) ====
+==== tests/cases/conformance/types/intersection/intersectionTypeReadonly.ts (4 errors) ====
     interface Base {
         readonly value: number;
     }
@@ -30,9 +29,7 @@ tests/cases/conformance/types/intersection/intersectionTypeReadonly.ts(25,15): e
               ~~~~~
 !!! error TS2540: Cannot assign to 'value' because it is a read-only property.
     let mutable: Base & Mutable;
-    mutable.value = 12; // error, lhs can't be a readonly property
-            ~~~~~
-!!! error TS2540: Cannot assign to 'value' because it is a read-only property.
+    mutable.value = 12;
     let differentType: Base & DifferentType;
     differentType.value = 12; // error, lhs can't be a readonly property
                   ~~~~~

tests/baselines/reference/intersectionTypeReadonly.js

@@ -19,7 +19,7 @@ base.value = 12 // error, lhs can't be a readonly property
 let identical: Base & Identical;
 identical.value = 12; // error, lhs can't be a readonly property
 let mutable: Base & Mutable;
-mutable.value = 12; // error, lhs can't be a readonly property
+mutable.value = 12;
 let differentType: Base & DifferentType;
 differentType.value = 12; // error, lhs can't be a readonly property
 let differentName: Base & DifferentName;
@@ -32,7 +32,7 @@ base.value = 12; // error, lhs can't be a readonly property
 var identical;
 identical.value = 12; // error, lhs can't be a readonly property
 var mutable;
-mutable.value = 12; // error, lhs can't be a readonly property
+mutable.value = 12;
 var differentType;
 differentType.value = 12; // error, lhs can't be a readonly property
 var differentName;

tests/baselines/reference/intersectionTypeReadonly.symbols

@@ -53,7 +53,7 @@ let mutable: Base & Mutable;
 >Base : Symbol(Base, Decl(intersectionTypeReadonly.ts, 0, 0))
 >Mutable : Symbol(Mutable, Decl(intersectionTypeReadonly.ts, 5, 1))
 
-mutable.value = 12; // error, lhs can't be a readonly property
+mutable.value = 12;
 >mutable.value : Symbol(value, Decl(intersectionTypeReadonly.ts, 0, 16), Decl(intersectionTypeReadonly.ts, 6, 19))
 >mutable : Symbol(mutable, Decl(intersectionTypeReadonly.ts, 19, 3))
 >value : Symbol(value, Decl(intersectionTypeReadonly.ts, 0, 16), Decl(intersectionTypeReadonly.ts, 6, 19))

tests/baselines/reference/intersectionTypeReadonly.types

@@ -42,11 +42,11 @@ identical.value = 12; // error, lhs can't be a readonly property
 let mutable: Base & Mutable;
 >mutable : Base & Mutable
 
-mutable.value = 12; // error, lhs can't be a readonly property
+mutable.value = 12;
 >mutable.value = 12 : 12
->mutable.value : any
+>mutable.value : number
 >mutable : Base & Mutable
->value : any
+>value : number
 >12 : 12
 
 let differentType: Base & DifferentType;

tests/baselines/reference/intersectionsAndReadonlyProperties.errors.txt

@@ -0,0 +1,24 @@
+tests/cases/compiler/intersectionsAndReadonlyProperties.ts(17,4): error TS2540: Cannot assign to 'a' because it is a read-only property.
+
+
+==== tests/cases/compiler/intersectionsAndReadonlyProperties.ts (1 errors) ====
+    // readonly and non-readonly
+    type Intersection1 = { readonly a: number } & { a: number };
+    declare let i1: Intersection1;
+
+    i1.a = 2;
+
+    // getter and setter
+    type Intersection2 = { get a(): number } & { set a(v: number) };
+    declare let i2: Intersection2;
+
+    i2.a = 2;
+
+    // assignment to an all read-only property should still be disallowed
+    type IntersectionAllReadonly = { readonly a: number } & { get a(): number };
+    declare let ia: IntersectionAllReadonly;
+
+    ia.a = 2; // Error
+       ~
+!!! error TS2540: Cannot assign to 'a' because it is a read-only property.
+

tests/baselines/reference/intersectionsAndReadonlyProperties.js

@@ -0,0 +1,24 @@
+//// [intersectionsAndReadonlyProperties.ts]
+// readonly and non-readonly
+type Intersection1 = { readonly a: number } & { a: number };
+declare let i1: Intersection1;
+
+i1.a = 2;
+
+// getter and setter
+type Intersection2 = { get a(): number } & { set a(v: number) };
+declare let i2: Intersection2;
+
+i2.a = 2;
+
+// assignment to an all read-only property should still be disallowed
+type IntersectionAllReadonly = { readonly a: number } & { get a(): number };
+declare let ia: IntersectionAllReadonly;
+
+ia.a = 2; // Error
+
+
+//// [intersectionsAndReadonlyProperties.js]
+i1.a = 2;
+i2.a = 2;
+ia.a = 2; // Error

tests/baselines/reference/intersectionsAndReadonlyProperties.symbols

@@ -0,0 +1,47 @@
+=== tests/cases/compiler/intersectionsAndReadonlyProperties.ts ===
+// readonly and non-readonly
+type Intersection1 = { readonly a: number } & { a: number };
+>Intersection1 : Symbol(Intersection1, Decl(intersectionsAndReadonlyProperties.ts, 0, 0))
+>a : Symbol(a, Decl(intersectionsAndReadonlyProperties.ts, 1, 22))
+>a : Symbol(a, Decl(intersectionsAndReadonlyProperties.ts, 1, 47))
+
+declare let i1: Intersection1;
+>i1 : Symbol(i1, Decl(intersectionsAndReadonlyProperties.ts, 2, 11))
+>Intersection1 : Symbol(Intersection1, Decl(intersectionsAndReadonlyProperties.ts, 0, 0))
+
+i1.a = 2;
+>i1.a : Symbol(a, Decl(intersectionsAndReadonlyProperties.ts, 1, 22), Decl(intersectionsAndReadonlyProperties.ts, 1, 47))
+>i1 : Symbol(i1, Decl(intersectionsAndReadonlyProperties.ts, 2, 11))
+>a : Symbol(a, Decl(intersectionsAndReadonlyProperties.ts, 1, 22), Decl(intersectionsAndReadonlyProperties.ts, 1, 47))
+
+// getter and setter
+type Intersection2 = { get a(): number } & { set a(v: number) };
+>Intersection2 : Symbol(Intersection2, Decl(intersectionsAndReadonlyProperties.ts, 4, 9))
+>a : Symbol(a, Decl(intersectionsAndReadonlyProperties.ts, 7, 22))
+>a : Symbol(a, Decl(intersectionsAndReadonlyProperties.ts, 7, 44))
+>v : Symbol(v, Decl(intersectionsAndReadonlyProperties.ts, 7, 51))
+
+declare let i2: Intersection2;
+>i2 : Symbol(i2, Decl(intersectionsAndReadonlyProperties.ts, 8, 11))
+>Intersection2 : Symbol(Intersection2, Decl(intersectionsAndReadonlyProperties.ts, 4, 9))
+
+i2.a = 2;
+>i2.a : Symbol(a, Decl(intersectionsAndReadonlyProperties.ts, 7, 22), Decl(intersectionsAndReadonlyProperties.ts, 7, 44))
+>i2 : Symbol(i2, Decl(intersectionsAndReadonlyProperties.ts, 8, 11))
+>a : Symbol(a, Decl(intersectionsAndReadonlyProperties.ts, 7, 22), Decl(intersectionsAndReadonlyProperties.ts, 7, 44))
+
+// assignment to an all read-only property should still be disallowed
+type IntersectionAllReadonly = { readonly a: number } & { get a(): number };
+>IntersectionAllReadonly : Symbol(IntersectionAllReadonly, Decl(intersectionsAndReadonlyProperties.ts, 10, 9))
+>a : Symbol(a, Decl(intersectionsAndReadonlyProperties.ts, 13, 32))
+>a : Symbol(a, Decl(intersectionsAndReadonlyProperties.ts, 13, 57))
+
+declare let ia: IntersectionAllReadonly;
+>ia : Symbol(ia, Decl(intersectionsAndReadonlyProperties.ts, 14, 11))
+>IntersectionAllReadonly : Symbol(IntersectionAllReadonly, Decl(intersectionsAndReadonlyProperties.ts, 10, 9))
+
+ia.a = 2; // Error
+>ia.a : Symbol(a, Decl(intersectionsAndReadonlyProperties.ts, 13, 32), Decl(intersectionsAndReadonlyProperties.ts, 13, 57))
+>ia : Symbol(ia, Decl(intersectionsAndReadonlyProperties.ts, 14, 11))
+>a : Symbol(a, Decl(intersectionsAndReadonlyProperties.ts, 13, 32), Decl(intersectionsAndReadonlyProperties.ts, 13, 57))
+

tests/baselines/reference/intersectionsAndReadonlyProperties.types

@@ -0,0 +1,50 @@
+=== tests/cases/compiler/intersectionsAndReadonlyProperties.ts ===
+// readonly and non-readonly
+type Intersection1 = { readonly a: number } & { a: number };
+>Intersection1 : Intersection1
+>a : number
+>a : number
+
+declare let i1: Intersection1;
+>i1 : Intersection1
+
+i1.a = 2;
+>i1.a = 2 : 2
+>i1.a : number
+>i1 : Intersection1
+>a : number
+>2 : 2
+
+// getter and setter
+type Intersection2 = { get a(): number } & { set a(v: number) };
+>Intersection2 : Intersection2
+>a : number
+>a : number
+>v : number
+
+declare let i2: Intersection2;
+>i2 : Intersection2
+
+i2.a = 2;
+>i2.a = 2 : 2
+>i2.a : number
+>i2 : Intersection2
+>a : number
+>2 : 2
+
+// assignment to an all read-only property should still be disallowed
+type IntersectionAllReadonly = { readonly a: number } & { get a(): number };
+>IntersectionAllReadonly : IntersectionAllReadonly
+>a : number
+>a : number
+
+declare let ia: IntersectionAllReadonly;
+>ia : IntersectionAllReadonly
+
+ia.a = 2; // Error
+>ia.a = 2 : 2
+>ia.a : any
+>ia : IntersectionAllReadonly
+>a : any
+>2 : 2
+

tests/cases/compiler/intersectionsAndReadonlyProperties.ts

@@ -0,0 +1,17 @@
+// readonly and non-readonly
+type Intersection1 = { readonly a: number } & { a: number };
+declare let i1: Intersection1;
+
+i1.a = 2;
+
+// getter and setter
+type Intersection2 = { get a(): number } & { set a(v: number) };
+declare let i2: Intersection2;
+
+i2.a = 2;
+
+// assignment to an all read-only property should still be disallowed
+type IntersectionAllReadonly = { readonly a: number } & { get a(): number };
+declare let ia: IntersectionAllReadonly;
+
+ia.a = 2; // Error

tests/cases/conformance/types/intersection/intersectionTypeReadonly.ts

@@ -18,7 +18,7 @@ base.value = 12 // error, lhs can't be a readonly property
 let identical: Base & Identical;
 identical.value = 12; // error, lhs can't be a readonly property
 let mutable: Base & Mutable;
-mutable.value = 12; // error, lhs can't be a readonly property
+mutable.value = 12;
 let differentType: Base & DifferentType;
 differentType.value = 12; // error, lhs can't be a readonly property
 let differentName: Base & DifferentName;