Preserve trivia when simplifier removes unnecessary this / Me keywords.

Fixes #50

src/EditorFeatures/Test2/Simplification/TypeNameSimplifierTest.vb

@@ -1426,6 +1426,42 @@ public class C
             Test(input, expected)
         End Sub
 
+        <Fact, Trait(Traits.Feature, Traits.Features.Simplification)>
+        <WorkItem(50, "https://github.com/dotnet/roslyn/issues/50")>
+        Public Sub TestCSRemoveThisPreservesTrivia()
+            Dim input =
+<Workspace>
+    <Project Language="C#" CommonReferences="true">
+        <Document>
+class C1
+{
+    int _field;
+
+    void M()
+    {
+        this /*comment 1*/ . /* comment 2 */ {|SimplifyParent:_field|} /* comment 3 */ = 0;
+    }
+}
+        </Document>
+    </Project>
+</Workspace>
+
+            Dim expected =
+<code>
+class C1
+{
+    int _field;
+
+    void M()
+    {
+         /*comment 1*/  /* comment 2 */ _field /* comment 3 */ = 0;
+    }
+}
+</code>
+
+            Test(input, expected)
+        End Sub
+
         <WorkItem(649385)>
         <Fact, Trait(Traits.Feature, Traits.Features.Simplification)>
         Public Sub CSharpSimplifyToVarCorrect()

src/Workspaces/CSharp/Portable/Extensions/ExpressionSyntaxExtensions.cs

@@ -773,7 +773,9 @@ private static bool TryReduce(
                 }
             }
 
-            replacementNode = memberAccess.Name.WithLeadingTrivia(memberAccess.GetLeadingTrivia()).WithTrailingTrivia(memberAccess.GetTrailingTrivia());
+            replacementNode = memberAccess.Name
+                .WithLeadingTrivia(memberAccess.GetLeadingTriviaForSimplifiedMemberAccess())
+                .WithTrailingTrivia(memberAccess.GetTrailingTrivia());
             issueSpan = memberAccess.Expression.Span;
 
             if (replacementNode == null)
@@ -784,6 +786,24 @@ private static bool TryReduce(
             return memberAccess.CanReplaceWithReducedName(replacementNode, semanticModel, cancellationToken);
         }
 
+        private static SyntaxTriviaList GetLeadingTriviaForSimplifiedMemberAccess(this MemberAccessExpressionSyntax memberAccess)
+        {
+            // We want to include any user-typed trivia that may be present between the 'Expression', 'OperatorToken' and 'Identifier' of the MemberAccessExpression.
+            // However, we don't want to include any elastic trivia that may have been introduced by the expander in these locations. This is to avoid triggering
+            // aggressive formatting. Otherwise, formatter will see this elastic trivia added by the expander and use that as a cue to introduce unnecessary blank lines
+            // etc. around the user's original code.
+            return memberAccess.GetLeadingTrivia()
+                .AddRange(memberAccess.Expression.GetTrailingTrivia().WithoutElasticTrivia())
+                .AddRange(memberAccess.OperatorToken.LeadingTrivia.WithoutElasticTrivia())
+                .AddRange(memberAccess.OperatorToken.TrailingTrivia.WithoutElasticTrivia())
+                .AddRange(memberAccess.Name.GetLeadingTrivia().WithoutElasticTrivia());
+        }
+
+        private static IEnumerable<SyntaxTrivia> WithoutElasticTrivia(this IEnumerable<SyntaxTrivia> list)
+        {
+            return list.Where(t => !t.IsElastic());
+        }
+
         private static bool InsideCrefReference(ExpressionSyntax expr)
         {
             var crefAttribute = expr.FirstAncestorOrSelf<XmlCrefAttributeSyntax>();

src/Workspaces/VisualBasic/Portable/Extensions/ExpressionSyntaxExtensions.vb

@@ -1023,7 +1023,8 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Extensions
                     .WithIdentifier(VisualBasicSimplificationService.TryEscapeIdentifierToken(
                         memberAccess.Name.Identifier,
                         semanticModel)) _
-                            .WithLeadingTrivia(memberAccess.GetLeadingTrivia())
+                    .WithLeadingTrivia(memberAccess.GetLeadingTriviaForSimplifiedMemberAccess()) _
+                    .WithTrailingTrivia(memberAccess.GetTrailingTrivia())
                 issueSpan = memberAccess.Expression.Span
 
                 If memberAccess.CanReplaceWithReducedName(replacementNode, semanticModel, cancellationToken) Then
@@ -1040,6 +1041,24 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Extensions
             Return False
         End Function
 
+        <Extension>
+        Private Function GetLeadingTriviaForSimplifiedMemberAccess(memberAccess As MemberAccessExpressionSyntax) As SyntaxTriviaList
+            ' We want to include any user-typed trivia that may be present between the 'Expression', 'OperatorToken' and 'Identifier' of the MemberAccessExpression.
+            ' However, we don't want to include any elastic trivia that may have been introduced by the expander in these locations. This is to avoid triggering
+            ' aggressive formatting. Otherwise, formatter will see this elastic trivia added by the expander And use that as a cue to introduce unnecessary blank lines
+            ' etc. around the user's original code.
+            Return memberAccess.GetLeadingTrivia().
+                AddRange(memberAccess.Expression.GetTrailingTrivia().WithoutElasticTrivia()).
+                AddRange(memberAccess.OperatorToken.LeadingTrivia.WithoutElasticTrivia()).
+                AddRange(memberAccess.OperatorToken.TrailingTrivia.WithoutElasticTrivia()).
+                AddRange(memberAccess.Name.GetLeadingTrivia().WithoutElasticTrivia())
+        End Function
+
+        <Extension>
+        Private Function WithoutElasticTrivia(list As IEnumerable(Of SyntaxTrivia)) As IEnumerable(Of SyntaxTrivia)
+            Return list.Where(Function(t) Not t.IsElastic())
+        End Function
+
         Private Function InsideCrefReference(expr As ExpressionSyntax) As Boolean
             Dim crefAttribute = expr.FirstAncestorOrSelf(Of XmlCrefAttributeSyntax)()
             Return crefAttribute IsNot Nothing