Merge pull request #19770 from Microsoft/remove-readonly-from-spread-index-sigs

Remove readonly from index signatures of a spread

src/compiler/checker.ts

@@ -8000,11 +8000,16 @@ namespace ts {
                 }
             }
 
-            const spread = createAnonymousType(undefined, members, emptyArray, emptyArray, stringIndexInfo, numberIndexInfo);
+            const spread = createAnonymousType(
+                symbol,
+                members,
+                emptyArray,
+                emptyArray,
+                getNonReadonlyIndexSignature(stringIndexInfo),
+                getNonReadonlyIndexSignature(numberIndexInfo));
             spread.flags |= propagatedFlags;
             spread.flags |= TypeFlags.FreshLiteral | TypeFlags.ContainsObjectLiteral;
             (spread as ObjectType).objectFlags |= (ObjectFlags.ObjectLiteral | ObjectFlags.ContainsSpread);
-            spread.symbol = symbol;
             return spread;
         }
 
@@ -8020,6 +8025,13 @@ namespace ts {
             return result;
         }
 
+        function getNonReadonlyIndexSignature(index: IndexInfo) {
+            if (index && index.isReadonly) {
+                return createIndexInfo(index.type, /*isReadonly*/ false, index.declaration);
+            }
+            return index;
+        }
+
         function isClassMethod(prop: Symbol) {
             return prop.flags & SymbolFlags.Method && find(prop.declarations, decl => isClassLike(decl.parent));
         }

tests/baselines/reference/objectSpreadIndexSignature.errors.txt

@@ -16,4 +16,8 @@ tests/cases/conformance/types/spread/objectSpreadIndexSignature.ts(6,1): error T
     
     declare const b: boolean;
     indexed3 = { ...b ? indexed3 : undefined };
+    
+    declare var roindex: { readonly [x:string]: number };
+    var writable = { ...roindex };
+    writable.a = 0;  // should be ok.
     

tests/baselines/reference/objectSpreadIndexSignature.js

@@ -11,6 +11,10 @@ ii[1001];
 
 declare const b: boolean;
 indexed3 = { ...b ? indexed3 : undefined };
+
+declare var roindex: { readonly [x:string]: number };
+var writable = { ...roindex };
+writable.a = 0;  // should be ok.
 
 
 //// [objectSpreadIndexSignature.js]
@@ -30,3 +34,5 @@ var ii = __assign({}, indexed1, indexed2);
 // both have indexer, so i[1001]: number | boolean
 ii[1001];
 indexed3 = __assign({}, b ? indexed3 : undefined);
+var writable = __assign({}, roindex);
+writable.a = 0; // should be ok.

tests/baselines/reference/objectSpreadIndexSignature.symbols

@@ -40,3 +40,14 @@ indexed3 = { ...b ? indexed3 : undefined };
 >indexed3 : Symbol(indexed3, Decl(objectSpreadIndexSignature.ts, 2, 11))
 >undefined : Symbol(undefined)
 
+declare var roindex: { readonly [x:string]: number };
+>roindex : Symbol(roindex, Decl(objectSpreadIndexSignature.ts, 13, 11))
+>x : Symbol(x, Decl(objectSpreadIndexSignature.ts, 13, 33))
+
+var writable = { ...roindex };
+>writable : Symbol(writable, Decl(objectSpreadIndexSignature.ts, 14, 3))
+>roindex : Symbol(roindex, Decl(objectSpreadIndexSignature.ts, 13, 11))
+
+writable.a = 0;  // should be ok.
+>writable : Symbol(writable, Decl(objectSpreadIndexSignature.ts, 14, 3))
+

tests/baselines/reference/objectSpreadIndexSignature.types

@@ -50,3 +50,19 @@ indexed3 = { ...b ? indexed3 : undefined };
 >indexed3 : { [n: string]: number; }
 >undefined : undefined
 
+declare var roindex: { readonly [x:string]: number };
+>roindex : { readonly [x: string]: number; }
+>x : string
+
+var writable = { ...roindex };
+>writable : { [x: string]: number; }
+>{ ...roindex } : { [x: string]: number; }
+>roindex : { readonly [x: string]: number; }
+
+writable.a = 0;  // should be ok.
+>writable.a = 0 : 0
+>writable.a : number
+>writable : { [x: string]: number; }
+>a : number
+>0 : 0
+

tests/cases/conformance/types/spread/objectSpreadIndexSignature.ts

@@ -11,3 +11,7 @@ ii[1001];
 
 declare const b: boolean;
 indexed3 = { ...b ? indexed3 : undefined };
+
+declare var roindex: { readonly [x:string]: number };
+var writable = { ...roindex };
+writable.a = 0;  // should be ok.