Synthetic signature uses existing parameter names

src/services/codefixes/fixClassDoesntImplementInheritedAbstractMember.ts

@@ -20,7 +20,7 @@ namespace ts.codefix {
 
                 const insertion = getMissingMembersInsertion(classDecl, abstractAndNonPrivateExtendsSymbols, checker, context.newLineCharacter);
 
-                if (insertion) {
+                if (insertion.length) {
                     return [{
                         description: getLocaleSpecificMessage(Diagnostics.Implement_inherited_abstract_class),
                         changes: [{

src/services/codefixes/helpers.ts

@@ -93,6 +93,7 @@ namespace ts.codefix {
         newSignatureDeclaration.name = signatures[0].getDeclaration().name;
 
         let maxNonRestArgs = -1;
+        let maxArgsIndex = 0;
         let minArgumentCount = signatures[0].minArgumentCount;
         let hasRestParameter = false;
         for (let i = 0; i < signatures.length; i++) {
@@ -102,8 +103,10 @@ namespace ts.codefix {
             const nonRestLength = sig.parameters.length - (sig.hasRestParameter ? 1 : 0);
             if (nonRestLength > maxNonRestArgs) {
                 maxNonRestArgs = nonRestLength;
+                maxArgsIndex = i;
             }
         }
+        const maxArgsParameterSymbolNames = signatures[maxArgsIndex].getParameters().map(symbol => symbol.getName());
 
         const anyTypeNode: TypeNode = createNode(SyntaxKind.AnyKeyword) as TypeNode;
         const optionalToken = createToken(SyntaxKind.QuestionToken);
@@ -130,7 +133,7 @@ namespace ts.codefix {
 
         function createParameterDeclaration(index: number, minArgCount: number, typeNode: TypeNode, enclosingSignatureDeclaration: SignatureDeclaration): ParameterDeclaration {
             const newParameter = createNode(SyntaxKind.Parameter) as ParameterDeclaration;
-            newParameter.symbol = checker.createSymbol(SymbolFlags.FunctionScopedVariable, "arg" + index);
+            newParameter.symbol = checker.createSymbol(SymbolFlags.FunctionScopedVariable, maxArgsParameterSymbolNames[index] || "rest");
             newParameter.symbol.valueDeclaration = newParameter;
             newParameter.symbol.declarations = [newParameter];
             newParameter.type = typeNode;

tests/cases/fourslash/codeFixClassExtendsAbstractMethod.ts

@@ -12,7 +12,7 @@ verify.rangeAfterCodeFix(`
     f(a: number, b: string): boolean;
     f(a: string, b: number): Function;
     f(a: string): Function;
-    f(arg0: any, arg1?: any) {
+    f(a: any, b?: any) {
         throw new Error('Method not implemented.');
     }
 `);

tests/cases/fourslash/codeFixUnImplementedInterfaceComputedPropertyNameWellKnownSymbols.ts

@@ -44,7 +44,7 @@ verify.rangeAfterCodeFix(`
     [Symbol.toPrimitive](hint: "number"): number;
     [Symbol.toPrimitive](hint: "default"): number;
     [Symbol.toPrimitive](hint: "string"): string;
-    [Symbol.toPrimitive](arg0: any) {
+    [Symbol.toPrimitive](hint: any) {
         throw new Error('Method not implemented.');
     }
     [Symbol.toStringTag]: string;

tests/cases/fourslash/codeFixUnImplementedInterfaceMultipleSignatures.ts

@@ -12,7 +12,7 @@ verify.rangeAfterCodeFix(`
     method(a: number, b: string): boolean;
     method(a: string, b: number): Function;
     method(a: string): Function;
-    method(arg0: any, arg1?: any) {
+    method(a: any, b?: any) {
         throw new Error('Method not implemented.');
     }
 `);

tests/cases/fourslash/codeFixUnImplementedInterfaceMultipleSignaturesRest1.ts

@@ -12,7 +12,7 @@ verify.rangeAfterCodeFix(`
     method(a: number, ...b: string[]): boolean;
     method(a: string, ...b: number[]): Function;
     method(a: string): Function;
-    method(arg0: any, ...arg1?: any[]) {
+    method(a: any, ...b?: any[]) {
         throw new Error('Method not implemented.');
     }
 `);

tests/cases/fourslash/codeFixUnImplementedInterfaceMultipleSignaturesRest2.ts

@@ -12,7 +12,7 @@ verify.rangeAfterCodeFix(`
     method(a: number, ...b: string[]): boolean;
     method(a: string, b: number): Function;
     method(a: string): Function;
-    method(arg0: any, arg1?: any, ...arg2?: any[]) {
+    method(a: any, b?: any, ...rest?: any[]) {
         throw new Error('Method not implemented.');
     }
 `);