Unduplicate missing abstract member codefix

src/harness/fourslash.ts

@@ -2150,10 +2150,18 @@ namespace FourSlash {
          * @param fileName Path to file where error should be retrieved from.
          */
         private getCodeFixActions(fileName: string, errorCode?: number): ts.CodeAction[] {
-            const diagnostics: ts.Diagnostic[] = this.getDiagnostics(fileName);
+            const diagnosticsForCodeFix = this.getDiagnostics(fileName).map(diagnostic => {
+                return {
+                    start: diagnostic.start,
+                    length: diagnostic.length,
+                    code: diagnostic.code
+                }
+            });
+            const dedupedDiagnositcs = ts.deduplicate(diagnosticsForCodeFix, ts.equalOwnProperties);
 
             let actions: ts.CodeAction[] = undefined;
-            for (const diagnostic of diagnostics) {
+
+            for (const diagnostic of dedupedDiagnositcs) {
 
                 if (errorCode && errorCode !== diagnostic.code) {
                     continue;

src/services/services.ts

@@ -1688,7 +1688,7 @@ namespace ts {
 
             let allFixes: CodeAction[] = [];
 
-            forEach(errorCodes, error => {
+            forEach(deduplicate(errorCodes), error => {
                 cancellationToken.throwIfCancellationRequested();
 
                 const context = {

tests/cases/fourslash/codeFixClassExtendAbstractProperty.ts

@@ -2,11 +2,15 @@
 
 //// abstract class A {
 ////    abstract x: number;
+////    abstract foo(): number;
 //// }
 ////
 //// class C extends A {[|
 //// |]}
 
 verify.rangeAfterCodeFix(`
-x: number;
+    x: number;
+    foo(): number {
+        throw new Error('Method not implemented.');
+    }
 `);