Include code fix after prologue

Fixes #15515

Author: sheetalkamat

src/services/textChanges.ts

@@ -1005,9 +1005,26 @@ namespace ts.textChanges {
         }
     }
 
-    function getInsertionPositionAtSourceFileTop({ text }: SourceFile): number {
-        const shebang = getShebang(text);
+    function getInsertionPositionAtSourceFileTop(sourceFile: SourceFile): number {
+        let lastPrologue: PrologueDirective | undefined;
+        for (const node of sourceFile.statements) {
+            if (isPrologueDirective(node)) {
+                lastPrologue = node;
+            }
+            else {
+                break;
+            }
+        }
+
         let position = 0;
+        const text = sourceFile.text;
+        if (lastPrologue) {
+            position = lastPrologue.end;
+            advancePastLineBreak();
+            return position;
+        }
+
+        const shebang = getShebang(text);
         if (shebang !== undefined) {
             position = shebang.length;
             advancePastLineBreak();

tests/cases/fourslash/importNameCodeFixWithPrologue.ts

@@ -0,0 +1,45 @@
+/// <reference path='fourslash.ts' />
+
+// @Filename: /a.ts
+////"use strict";
+////export class A { }
+
+// @Filename: /b.ts
+////"use strict";
+////export class B extends A { }
+
+// @Filename: /c.ts
+/////*---------------------------------------------------------------------------------------------
+//// *  Copyright (c) Microsoft Corporation. All rights reserved.
+//// *  Licensed under the MIT License. See License.txt in the project root for license information.
+//// *--------------------------------------------------------------------------------------------*/
+////"use strict";
+////export class B extends A { }
+
+goTo.file("/b.ts");
+verify.codeFixAll({
+    fixId: "fixMissingImport",
+    fixAllDescription: "Add all missing imports",
+    newFileContent:
+`"use strict";
+
+import { A } from "./a";
+
+export class B extends A { }`,
+});
+
+goTo.file("/c.ts");
+verify.codeFixAll({
+    fixId: "fixMissingImport",
+    fixAllDescription: "Add all missing imports",
+    newFileContent:
+`/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the MIT License. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+"use strict";
+
+import { A } from "./a";
+
+export class B extends A { }`,
+});