Restore merging code.

src/Features/CSharp/Portable/RemoveUnnecessaryImports/CSharpRemoveUnnecessaryImportsDiagnosticAnalyzer.cs

 // Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
+using System;
 using System.Collections.Generic;
+using System.Collections.Immutable;
 using System.Linq;
 using System.Threading;
 using Microsoft.CodeAnalysis.CSharp.RemoveUnnecessaryImports;
@@ -21,9 +23,13 @@ internal sealed class CSharpRemoveUnnecessaryImportsDiagnosticAnalyzer :
             new LocalizableResourceString(nameof(CSharpFeaturesResources.Using_directive_is_unnecessary), CSharpFeaturesResources.ResourceManager, typeof(CSharpFeaturesResources));
 
         protected override LocalizableString GetTitleAndMessageFormatForClassificationIdDescriptor()
-        {
-            return s_TitleAndMessageFormat;
-        }
+            => s_TitleAndMessageFormat;
+
+        // C# has no need to do any merging of using statements.  Only VB needs to
+        // merge import clauses to an import statement if it all the import clauses
+        // are unnecessary.
+        protected override ImmutableArray<SyntaxNode> MergeImports(ImmutableArray<SyntaxNode> unnecessaryImports)
+            => unnecessaryImports;
 
         protected override IEnumerable<TextSpan> GetFixableDiagnosticSpans(
             IEnumerable<SyntaxNode> nodes, SyntaxTree tree, CancellationToken cancellationToken)

src/Features/Core/Portable/RemoveUnnecessaryImports/AbstractRemoveUnnecessaryImportsDiagnosticAnalyzer.cs

@@ -50,6 +50,7 @@ private DiagnosticDescriptor GetClassificationIdDescriptor()
         }
 
         public override ImmutableArray<DiagnosticDescriptor> SupportedDiagnostics => ImmutableArray.Create(s_fixableIdDescriptor, GetClassificationIdDescriptor());
+
         public bool OpenFileOnly(Workspace workspace) => true;
 
         public override void Initialize(AnalysisContext context)
@@ -70,6 +71,8 @@ private void AnalyzeSemanticModel(SemanticModelAnalysisContext context)
             var unnecessaryImports = service.GetUnnecessaryImports(context.SemanticModel, root, cancellationToken);
             if (unnecessaryImports.Any())
             {
+                unnecessaryImports = MergeImports(unnecessaryImports);
+
                 Func<SyntaxNode, SyntaxToken> getLastTokenFunc = GetLastTokenDelegateForContiguousSpans();
                 var contiguousSpans = unnecessaryImports.GetContiguousSpans(getLastTokenFunc);
                 var diagnostics =
@@ -83,6 +86,8 @@ private void AnalyzeSemanticModel(SemanticModelAnalysisContext context)
             }
         }
 
+        protected abstract ImmutableArray<SyntaxNode> MergeImports(ImmutableArray<SyntaxNode> unnecessaryImports);
+
         protected virtual Func<SyntaxNode, SyntaxToken> GetLastTokenDelegateForContiguousSpans()
         {
             return null;

src/Features/VisualBasic/Portable/RemoveUnnecessaryImports/VisualBasicRemoveUnnecessaryImportsDiagnosticAnalyzer.vb

@@ -5,7 +5,7 @@ Imports System.Threading
 Imports Microsoft.CodeAnalysis.Diagnostics
 Imports Microsoft.CodeAnalysis.RemoveUnnecessaryImports
 Imports Microsoft.CodeAnalysis.Text
-Imports Microsoft.CodeAnalysis.VisualBasic.RemoveUnnecessaryImports
+Imports Microsoft.CodeAnalysis.VisualBasic.Syntax
 
 Namespace Microsoft.CodeAnalysis.VisualBasic.RemoveUnnecessaryImports
 
@@ -20,6 +20,24 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.RemoveUnnecessaryImports
             Return s_TitleAndMessageFormat
         End Function
 
+        Protected Overrides Function MergeImports(unnecessaryImports As ImmutableArray(Of SyntaxNode)) As ImmutableArray(Of SyntaxNode)
+            Dim result = ArrayBuilder(Of SyntaxNode).GetInstance()
+            Dim importsClauses = unnecessaryImports.CastArray(Of ImportsClauseSyntax)
+
+            For Each clause In importsClauses
+                If Not result.Contains(clause.Parent) Then
+                    Dim statement = DirectCast(clause.Parent, ImportsStatementSyntax)
+                    If statement.ImportsClauses.All(AddressOf importsClauses.Contains) Then
+                        result.Add(statement)
+                    Else
+                        result.Add(clause)
+                    End If
+                End If
+            Next
+
+            Return result.ToImmutableAndFree()
+        End Function
+
         Protected Overrides Function GetFixableDiagnosticSpans(
                 nodes As IEnumerable(Of SyntaxNode), tree As SyntaxTree, cancellationToken As CancellationToken) As IEnumerable(Of TextSpan)
             ' Create one fixable diagnostic that contains the entire Imports list.