fix missing type parameters

src/services/codefixes/helpers.ts

@@ -376,6 +376,7 @@ namespace ts.codefix {
         let maxArgsSignature = signatures[0];
         let minArgumentCount = signatures[0].minArgumentCount;
         let someSigHasRestParameter = false;
+        let maxTypeArgsSignature = signatures[0];
         for (const sig of signatures) {
             minArgumentCount = Math.min(sig.minArgumentCount, minArgumentCount);
             if (signatureHasRestParameter(sig)) {
@@ -384,6 +385,9 @@ namespace ts.codefix {
             if (sig.parameters.length >= maxArgsSignature.parameters.length && (!signatureHasRestParameter(sig) || signatureHasRestParameter(maxArgsSignature))) {
                 maxArgsSignature = sig;
             }
+            if (sig.typeParameters && (!maxTypeArgsSignature.typeParameters ||  sig.typeParameters.length > maxTypeArgsSignature.typeParameters.length)) {
+                maxTypeArgsSignature = sig;
+            }
         }
         const maxNonRestArgs = maxArgsSignature.parameters.length - (signatureHasRestParameter(maxArgsSignature) ? 1 : 0);
         const maxArgsParameterSymbolNames = maxArgsSignature.parameters.map(symbol => symbol.name);
@@ -402,11 +406,14 @@ namespace ts.codefix {
             parameters.push(restParameter);
         }
 
+        const typeParameters = maxTypeArgsSignature.typeParameters?.map(typeParam =>
+            factory.createTypeParameterDeclaration(typeParam.symbol.getName()));
+
         return createStubbedMethod(
             modifiers,
             name,
             optional,
-            /*typeParameters*/ undefined,
+            typeParameters,
             parameters,
             getReturnTypeFromSignatures(signatures, checker, context, enclosingDeclaration),
             quotePreference,

tests/cases/fourslash/completionsOverridingMethod7.ts

@@ -0,0 +1,56 @@
+/// <reference path="fourslash.ts" />
+
+// @Filename: a.ts
+// @newline: LF
+// Case: generic methods
+////abstract class A {
+////    abstract M<T>(x: number): number;
+////    abstract M<T>(x: string): string;
+////    N<T>(x: string): void {
+////        return;
+////    }
+////}
+////
+////class B extends A {
+////    /*a*/
+////}
+
+
+verify.completions({
+    marker: "a",
+    isNewIdentifierLocation: true,
+    preferences: {
+        includeCompletionsWithInsertText: true,
+        includeCompletionsWithSnippetText: false,
+    },
+    includes: [
+        {
+            name: "M",
+            sortText: completion.SortText.LocationPriority,
+            replacementSpan: {
+                fileName: "",
+                pos: 0,
+                end: 0,
+            },
+            insertText:
+`M<T>(x: number): number;
+M<T>(x: string): string;
+M<T>(x: any): string | number {
+}
+`,
+        },
+        {
+            name: "N",
+            sortText: completion.SortText.LocationPriority,
+            replacementSpan: {
+                fileName: "",
+                pos: 0,
+                end: 0,
+            },
+            insertText:
+`N<T>(x: string): void {
+}
+`,
+        },
+    ],
+});