fix malformed nodes

Author: Arthur Ozga

src/compiler/checker.ts

@@ -2752,7 +2752,7 @@ namespace ts {
 
             function indexInfoToIndexSignatureDeclarationHelper(indexInfo: IndexInfo, kind: IndexKind, context: NodeBuilderContext): IndexSignatureDeclaration {
                 const indexerTypeNode = createKeywordTypeNode(kind === IndexKind.String ? SyntaxKind.StringKeyword : SyntaxKind.NumberKeyword);
-                const name = getNameFromIndexInfo(indexInfo);
+                const name = getNameFromIndexInfo(indexInfo) || "x";
 
                 const indexingParameter = createParameter(
                     /*decorators*/ undefined,
@@ -2830,8 +2830,8 @@ namespace ts {
                     initializer = parameterDeclaration.initializer;
                 }
                 const parameterNode = createParameter(
-                    parameterDeclaration.decorators,
-                    parameterDeclaration.modifiers,
+                    /*decorators*/ undefined,
+                    cloneNodeArray(parameterDeclaration.modifiers),
                     (parameterDeclaration ? isRestParameter(parameterDeclaration) : isTransientSymbol(parameterSymbol) && parameterSymbol.isRestParameter) ?
                         createToken(SyntaxKind.DotDotDotToken) :
                         undefined,

src/compiler/factory.ts

@@ -89,6 +89,10 @@ namespace ts {
         return nodeIsSynthesized(clone) ? clone : getSynthesizedClone(clone);
     }
 
+    export function cloneNodeArray<T extends Node>(nodeArray: NodeArray<T>) {
+        return nodeArray && nodeArray.map(getDeepSynthesizedClone);
+    }
+
     // Literals
 
     export function createLiteral(value: string): StringLiteral;

src/compiler/utilities.ts

@@ -466,7 +466,7 @@ namespace ts {
         return getFullWidth(name) === 0 ? "(Missing)" : getTextOfNode(name);
     }
 
-    export function getNameFromIndexInfo(info: IndexInfo) {
+    export function getNameFromIndexInfo(info: IndexInfo): string | undefined {
         return info.declaration ? declarationNameToString(info.declaration.parameters[0].name) : undefined;
     }