Stop showing smart tags for subsequent 'Unnecessary' diagnostics

src/EditorFeatures/CSharpTest/SimplifyInterpolation/SimplifyInterpolationTests.cs

@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+using System.Linq;
 using System.Threading.Tasks;
 using Microsoft.CodeAnalysis.CodeFixes;
 using Microsoft.CodeAnalysis.CSharp.SimplifyInterpolation;
@@ -19,6 +20,30 @@ public partial class SimplifyInterpolationTests : AbstractCSharpDiagnosticProvid
         internal override (DiagnosticAnalyzer, CodeFixProvider) CreateDiagnosticProviderAndFixer(Workspace workspace)
             => (new CSharpSimplifyInterpolationDiagnosticAnalyzer(), new CSharpSimplifyInterpolationCodeFixProvider());
 
+        [Fact]
+        public async Task SubsequentUnnecessarySpansDoNotRepeatTheSmartTag()
+        {
+            var parameters = new TestParameters(retainNonFixableDiagnostics: true, includeDiagnosticsOutsideSelection: true);
+
+            using var workspace = CreateWorkspaceFromOptions(@"class C
+{
+    void M(string someValue)
+    {
+        _ = $""prefix {someValue{|Unnecessary:[||].ToString()|}{|Unnecessary:.PadLeft(|}3{|Unnecessary:)|}} suffix"";
+    }
+}", parameters);
+
+            var diagnostics = await GetDiagnosticsWorkerAsync(workspace, parameters);
+
+            Assert.Equal(
+                new[] {
+                    ("IDE0071", DiagnosticSeverity.Info),
+                    ("IDE0071WithoutSuggestion", DiagnosticSeverity.Hidden),
+                    ("IDE0071WithoutSuggestion", DiagnosticSeverity.Hidden),
+                },
+                diagnostics.Select(d => (d.Descriptor.Id, d.Severity)));
+        }
+
         [Fact]
         public async Task ToStringWithNoParameter()
         {

src/Features/Core/Portable/SimplifyInterpolation/AbstractSimplifyInterpolationDiagnosticAnalyzer.cs

@@ -3,6 +3,7 @@
 // See the LICENSE file in the project root for more information.
 
 using System.Collections.Immutable;
+using System.Linq;
 using Microsoft.CodeAnalysis.CodeStyle;
 using Microsoft.CodeAnalysis.Diagnostics;
 using Microsoft.CodeAnalysis.EmbeddedLanguages.VirtualChars;
@@ -63,18 +64,19 @@ private void AnalyzeInterpolation(OperationAnalysisContext context)
                 return;
             }
 
-            var locations = ImmutableArray.Create(interpolation.Syntax.GetLocation());
+            context.ReportDiagnostic(DiagnosticHelper.Create(
+                UnnecessaryWithSuggestionDescriptor,
+                unnecessaryLocations.First(),
+                option.Notification.Severity,
+                additionalLocations: ImmutableArray.Create(interpolation.Syntax.GetLocation()),
+                properties: null));
 
-            var severity = option.Notification.Severity;
-
-            for (var i = 0; i < unnecessaryLocations.Length; i++)
+            // We start at 1 because the 0th element was used above to make the main diagnostic descriptor.
+            // All the rest are used to just fade out the correct portions of the user's code.
+            for (var i = 1; i < unnecessaryLocations.Length; i++)
             {
-                context.ReportDiagnostic(DiagnosticHelper.Create(
-                    i == 0 ? UnnecessaryWithSuggestionDescriptor : UnnecessaryWithoutSuggestionDescriptor,
-                    unnecessaryLocations[i],
-                    severity,
-                    additionalLocations: locations,
-                    properties: null));
+                context.ReportDiagnostic(Diagnostic.Create(
+                    UnnecessaryWithoutSuggestionDescriptor, unnecessaryLocations[i]));
             }
         }
     }