Error when writing to readonly tuple in rest element range

src/compiler/checker.ts

@@ -10101,6 +10101,7 @@ namespace ts {
                             error(indexNode, Diagnostics.Property_0_does_not_exist_on_type_1, unescapeLeadingUnderscores(propName), typeToString(objectType));
                         }
                     }
+                    errorIfWritingToReadonlyIndex(getIndexInfoOfType(objectType, IndexKind.Number));
                     return mapType(objectType, t => getRestTypeOfTupleType(<TupleTypeReference>t) || undefinedType);
                 }
             }
@@ -10122,13 +10123,7 @@ namespace ts {
                         error(indexNode, Diagnostics.Type_0_cannot_be_used_as_an_index_type, typeToString(indexType));
                         return indexInfo.type;
                     }
-                    if (indexInfo.isReadonly && accessExpression && (isAssignmentTarget(accessExpression) || isDeleteTarget(accessExpression))) {
-                        if (accessExpression) {
-                            error(accessExpression, Diagnostics.Index_signature_in_type_0_only_permits_reading, typeToString(objectType));
-                            return indexInfo.type;
-                        }
-                        return undefined;
-                    }
+                    errorIfWritingToReadonlyIndex(indexInfo);
                     return indexInfo.type;
                 }
                 if (indexType.flags & TypeFlags.Never) {
@@ -10188,6 +10183,12 @@ namespace ts {
                 return indexType;
             }
             return undefined;
+
+            function errorIfWritingToReadonlyIndex(indexInfo: IndexInfo | undefined): void {
+                if (indexInfo && indexInfo.isReadonly && accessExpression && (isAssignmentTarget(accessExpression) || isDeleteTarget(accessExpression))) {
+                    error(accessExpression, Diagnostics.Index_signature_in_type_0_only_permits_reading, typeToString(objectType));
+                }
+            }
         }
 
         function getIndexNodeForAccessExpression(accessNode: ElementAccessExpression | IndexedAccessTypeNode | PropertyName | BindingName | SyntheticExpression) {

tests/baselines/reference/readonlyArraysAndTuples.errors.txt

@@ -9,9 +9,16 @@ tests/cases/conformance/types/tuple/readonlyArraysAndTuples.ts(22,5): error TS27
 tests/cases/conformance/types/tuple/readonlyArraysAndTuples.ts(23,5): error TS4104: The type 'readonly [string, string]' is 'readonly' and cannot be assigned to the mutable type '[string, string]'.
 tests/cases/conformance/types/tuple/readonlyArraysAndTuples.ts(24,5): error TS2739: Type 'string[]' is missing the following properties from type 'readonly [string, string]': 0, 1
 tests/cases/conformance/types/tuple/readonlyArraysAndTuples.ts(25,5): error TS2739: Type 'readonly string[]' is missing the following properties from type 'readonly [string, string]': 0, 1
+tests/cases/conformance/types/tuple/readonlyArraysAndTuples.ts(30,3): error TS2540: Cannot assign to '0' because it is a read-only property.
+tests/cases/conformance/types/tuple/readonlyArraysAndTuples.ts(31,3): error TS2540: Cannot assign to '1' because it is a read-only property.
+tests/cases/conformance/types/tuple/readonlyArraysAndTuples.ts(32,1): error TS2542: Index signature in type 'readonly [number, number, ...number[]]' only permits reading.
+tests/cases/conformance/types/tuple/readonlyArraysAndTuples.ts(33,8): error TS2542: Index signature in type 'readonly [number, number, ...number[]]' only permits reading.
+tests/cases/conformance/types/tuple/readonlyArraysAndTuples.ts(34,1): error TS2542: Index signature in type 'readonly [number, number, ...number[]]' only permits reading.
+tests/cases/conformance/types/tuple/readonlyArraysAndTuples.ts(35,1): error TS2542: Index signature in type 'readonly [number, number, ...number[]]' only permits reading.
+tests/cases/conformance/types/tuple/readonlyArraysAndTuples.ts(36,8): error TS2542: Index signature in type 'readonly [number, number, ...number[]]' only permits reading.
 
 
-==== tests/cases/conformance/types/tuple/readonlyArraysAndTuples.ts (11 errors) ====
+==== tests/cases/conformance/types/tuple/readonlyArraysAndTuples.ts (18 errors) ====
     type T10 = string[];
     type T11 = Array<string>;
     type T12 = readonly string[];
@@ -61,4 +68,27 @@ tests/cases/conformance/types/tuple/readonlyArraysAndTuples.ts(25,5): error TS27
 !!! error TS2739: Type 'readonly string[]' is missing the following properties from type 'readonly [string, string]': 0, 1
         rt = mt;
     }
+    
+    declare var v: readonly[number, number, ...number[]];
+    v[0] = 1;        // Error
+      ~
+!!! error TS2540: Cannot assign to '0' because it is a read-only property.
+    v[1] = 1;        // Error
+      ~
+!!! error TS2540: Cannot assign to '1' because it is a read-only property.
+    v[2] = 1;        // Error
+    ~~~~
+!!! error TS2542: Index signature in type 'readonly [number, number, ...number[]]' only permits reading.
+    delete v[2];     // Error
+           ~~~~
+!!! error TS2542: Index signature in type 'readonly [number, number, ...number[]]' only permits reading.
+    v[0 + 1] = 1;    // Error
+    ~~~~~~~~
+!!! error TS2542: Index signature in type 'readonly [number, number, ...number[]]' only permits reading.
+    v[0 + 2] = 1;    // Error
+    ~~~~~~~~
+!!! error TS2542: Index signature in type 'readonly [number, number, ...number[]]' only permits reading.
+    delete v[0 + 1]; // Error
+           ~~~~~~~~
+!!! error TS2542: Index signature in type 'readonly [number, number, ...number[]]' only permits reading.
     

tests/baselines/reference/readonlyArraysAndTuples.js

@@ -26,6 +26,15 @@ function f1(ma: string[], ra: readonly string[], mt: [string, string], rt: reado
     rt = ra;  // Error
     rt = mt;
 }
+
+declare var v: readonly[number, number, ...number[]];
+v[0] = 1;        // Error
+v[1] = 1;        // Error
+v[2] = 1;        // Error
+delete v[2];     // Error
+v[0 + 1] = 1;    // Error
+v[0 + 2] = 1;    // Error
+delete v[0 + 1]; // Error
 
 
 //// [readonlyArraysAndTuples.js]
@@ -44,6 +53,13 @@ function f1(ma, ra, mt, rt) {
     rt = ra; // Error
     rt = mt;
 }
+v[0] = 1; // Error
+v[1] = 1; // Error
+v[2] = 1; // Error
+delete v[2]; // Error
+v[0 + 1] = 1; // Error
+v[0 + 2] = 1; // Error
+delete v[0 + 1]; // Error
 
 
 //// [readonlyArraysAndTuples.d.ts]
@@ -58,3 +74,4 @@ declare type T31<T> = readonly T;
 declare type T32 = readonly readonly string[];
 declare type T33 = readonly Array<string>;
 declare function f1(ma: string[], ra: readonly string[], mt: [string, string], rt: readonly [string, string]): void;
+declare var v: readonly [number, number, ...number[]];

tests/baselines/reference/readonlyArraysAndTuples.symbols

@@ -90,3 +90,29 @@ function f1(ma: string[], ra: readonly string[], mt: [string, string], rt: reado
 >mt : Symbol(mt, Decl(readonlyArraysAndTuples.ts, 13, 48))
 }
 
+declare var v: readonly[number, number, ...number[]];
+>v : Symbol(v, Decl(readonlyArraysAndTuples.ts, 28, 11))
+
+v[0] = 1;        // Error
+>v : Symbol(v, Decl(readonlyArraysAndTuples.ts, 28, 11))
+>0 : Symbol(0)
+
+v[1] = 1;        // Error
+>v : Symbol(v, Decl(readonlyArraysAndTuples.ts, 28, 11))
+>1 : Symbol(1)
+
+v[2] = 1;        // Error
+>v : Symbol(v, Decl(readonlyArraysAndTuples.ts, 28, 11))
+
+delete v[2];     // Error
+>v : Symbol(v, Decl(readonlyArraysAndTuples.ts, 28, 11))
+
+v[0 + 1] = 1;    // Error
+>v : Symbol(v, Decl(readonlyArraysAndTuples.ts, 28, 11))
+
+v[0 + 2] = 1;    // Error
+>v : Symbol(v, Decl(readonlyArraysAndTuples.ts, 28, 11))
+
+delete v[0 + 1]; // Error
+>v : Symbol(v, Decl(readonlyArraysAndTuples.ts, 28, 11))
+

tests/baselines/reference/readonlyArraysAndTuples.types

@@ -97,3 +97,59 @@ function f1(ma: string[], ra: readonly string[], mt: [string, string], rt: reado
 >mt : [string, string]
 }
 
+declare var v: readonly[number, number, ...number[]];
+>v : readonly [number, number, ...number[]]
+
+v[0] = 1;        // Error
+>v[0] = 1 : 1
+>v[0] : any
+>v : readonly [number, number, ...number[]]
+>0 : 0
+>1 : 1
+
+v[1] = 1;        // Error
+>v[1] = 1 : 1
+>v[1] : any
+>v : readonly [number, number, ...number[]]
+>1 : 1
+>1 : 1
+
+v[2] = 1;        // Error
+>v[2] = 1 : 1
+>v[2] : number
+>v : readonly [number, number, ...number[]]
+>2 : 2
+>1 : 1
+
+delete v[2];     // Error
+>delete v[2] : boolean
+>v[2] : number
+>v : readonly [number, number, ...number[]]
+>2 : 2
+
+v[0 + 1] = 1;    // Error
+>v[0 + 1] = 1 : 1
+>v[0 + 1] : number
+>v : readonly [number, number, ...number[]]
+>0 + 1 : number
+>0 : 0
+>1 : 1
+>1 : 1
+
+v[0 + 2] = 1;    // Error
+>v[0 + 2] = 1 : 1
+>v[0 + 2] : number
+>v : readonly [number, number, ...number[]]
+>0 + 2 : number
+>0 : 0
+>2 : 2
+>1 : 1
+
+delete v[0 + 1]; // Error
+>delete v[0 + 1] : boolean
+>v[0 + 1] : number
+>v : readonly [number, number, ...number[]]
+>0 + 1 : number
+>0 : 0
+>1 : 1
+

tests/cases/conformance/types/tuple/readonlyArraysAndTuples.ts

@@ -30,8 +30,10 @@ function f1(ma: string[], ra: readonly string[], mt: [string, string], rt: reado
 }
 
 declare var v: readonly[number, number, ...number[]];
-v[0] = 1; // Error
-v[1] = 1; // Error
-v[2] = 1; // Error
-v[0 + 1] = 1; // Error
-v[0 + 2] = 1; // Error
+v[0] = 1;        // Error
+v[1] = 1;        // Error
+v[2] = 1;        // Error
+delete v[2];     // Error
+v[0 + 1] = 1;    // Error
+v[0 + 2] = 1;    // Error
+delete v[0 + 1]; // Error