Merge pull request #24648 from chborl/twoIDsOn157

Port fix for duplicate IDEDiagnosticIDs to 15.7

src/EditorFeatures/Test/Diagnostics/IDEDiagnosticIDUniquenessTest.cs

+using System;
+using System.Collections.Generic;
+using System.Linq;
+using Microsoft.CodeAnalysis.Diagnostics;
+using Roslyn.Test.Utilities;
+using Xunit;
+
+namespace Microsoft.CodeAnalysis.Editor.UnitTests.Diagnostics
+{
+    public class IDEDiagnosticIDUniquenessTest
+    {
+        [Fact, Trait(Traits.Feature, Traits.Features.Diagnostics)]
+        public void UniqueIDEDiagnosticIds()
+        {
+            Type type = typeof(IDEDiagnosticIds);
+            List<string> listOfIDEDiagnosticIds = type.GetFields().Select(x => x.GetValue(null).ToString()).ToList();
+            Assert.Equal(listOfIDEDiagnosticIds.Count, listOfIDEDiagnosticIds.Distinct().Count());
+        }
+    }
+}

src/Features/Core/Portable/Diagnostics/Analyzers/IDEDiagnosticIds.cs

@@ -45,7 +45,6 @@ internal static class IDEDiagnosticIds
         public const string UseExplicitTupleNameDiagnosticId = "IDE0033";
 
         public const string UseDefaultLiteralDiagnosticId = "IDE0034";
-        public const string ValidateFormatStringDiagnosticID = "IDE0035";
 
         public const string RemoveUnreachableCodeDiagnosticId = "IDE0035";
 
@@ -63,6 +62,8 @@ internal static class IDEDiagnosticIds
 
         public const string UseDeconstructionDiagnosticId = "IDE0042";
 
+        public const string ValidateFormatStringDiagnosticID = "IDE0043";
+
         // Analyzer error Ids
         public const string AnalyzerChangedId = "IDE1001";
         public const string AnalyzerDependencyConflictId = "IDE1002";