Improve positioning of the implement interface codefix (#34928)

src/services/codefixes/fixClassIncorrectlyImplementsInterface.ts

@@ -54,6 +54,7 @@ namespace ts.codefix {
         const nonPrivateAndNotExistedInHeritageClauseMembers = implementedTypeSymbols.filter(and(symbolPointsToNonPrivateMember, symbol => !maybeHeritageClauseSymbol.has(symbol.escapedName)));
 
         const classType = checker.getTypeAtLocation(classDeclaration);
+        const constructor = find(classDeclaration.members, m => isConstructorDeclaration(m));
 
         if (!classType.getNumberIndexType()) {
             createMissingIndexSignatureDeclaration(implementedType, IndexKind.Number);
@@ -62,12 +63,22 @@ namespace ts.codefix {
             createMissingIndexSignatureDeclaration(implementedType, IndexKind.String);
         }
 
-        createMissingMemberNodes(classDeclaration, nonPrivateAndNotExistedInHeritageClauseMembers, context, preferences, member => changeTracker.insertNodeAtClassStart(sourceFile, classDeclaration, member));
+        createMissingMemberNodes(classDeclaration, nonPrivateAndNotExistedInHeritageClauseMembers, context, preferences, member => insertInterfaceMemberNode(sourceFile, classDeclaration, member));
 
         function createMissingIndexSignatureDeclaration(type: InterfaceType, kind: IndexKind): void {
             const indexInfoOfKind = checker.getIndexInfoOfType(type, kind);
             if (indexInfoOfKind) {
-                changeTracker.insertNodeAtClassStart(sourceFile, classDeclaration, checker.indexInfoToIndexSignatureDeclaration(indexInfoOfKind, kind, classDeclaration, /*flags*/ undefined, getNoopSymbolTrackerWithResolver(context))!);
+                insertInterfaceMemberNode(sourceFile, classDeclaration, checker.indexInfoToIndexSignatureDeclaration(indexInfoOfKind, kind, classDeclaration, /*flags*/ undefined, getNoopSymbolTrackerWithResolver(context))!);
+            }
+        }
+
+        // Either adds the node at the top of the class, or if there's a constructor right after that
+        function insertInterfaceMemberNode(sourceFile: SourceFile, cls: ClassLikeDeclaration | InterfaceDeclaration, newElement: ClassElement): void {
+            if (constructor) {
+                changeTracker.insertNodeAfter(sourceFile, constructor, newElement);
+            }
+            else {
+                changeTracker.insertNodeAtClassStart(sourceFile, cls, newElement);
             }
         }
     }

tests/cases/fourslash/codeFixClassImplementInterfaceEmptyTypeLiteral.ts

@@ -1,5 +1,6 @@
 /// <reference path='fourslash.ts' />
 
+////
 //// interface I {
 ////     x: {};
 //// }
@@ -8,6 +9,15 @@
 ////    |]constructor() { }
 //// }
 
-verify.rangeAfterCodeFix(`
-x: {};
-`);
+verify.codeFix({
+  description: "Implement interface 'I'",
+  newFileContent:`
+interface I {
+    x: {};
+}
+
+class C implements I {
+   constructor() { }
+    x: {};
+}`,
+});

tests/cases/fourslash/codeFixClassImplementInterfaceSomePropertiesPresent.ts

@@ -1,5 +1,6 @@
 /// <reference path='fourslash.ts' />
 
+////
 //// interface I {
 ////     x: number;
 ////     y: number;
@@ -11,6 +12,20 @@
 ////    y: number;
 //// }
 
-verify.rangeAfterCodeFix(`
-z: number & { __iBrand: any; };
-`);
+
+verify.codeFix({
+  description: "Implement interface 'I'",
+  newFileContent:`
+interface I {
+    x: number;
+    y: number;
+    z: number & { __iBrand: any };
+}
+
+class C implements I {
+   constructor(public x: number) { }
+    z: number & { __iBrand: any; };
+   y: number;
+}`,
+});
+

tests/cases/fourslash/codeFixClassImplementInterface_order.ts

@@ -0,0 +1,28 @@
+/// <reference path='fourslash.ts' />
+
+// #34841
+
+////interface IFoo {
+////  bar(): void;
+////}
+////
+////class Foo implements IFoo {
+////  private x = 1;
+////  constructor() { this.x = 2 }
+////}
+
+verify.codeFix({
+  description: "Implement interface 'IFoo'",
+  index: 0,
+  newFileContent:
+`interface IFoo {
+  bar(): void;
+}
+
+class Foo implements IFoo {
+  private x = 1;
+  constructor() { this.x = 2 }
+    bar(): void {
+        throw new Error("Method not implemented.");
+    }
+}`});