Use simplifier to remove 'this.' usage

Author: jaredpar

src/Microsoft.DotNet.CodeFormatting.Tests/Rules/ExplicitThisRuleTests.cs

@@ -109,6 +109,9 @@ class C1
     void M()
     {
         this. /* comment1 */ _field /* comment 2 */ = 0;
+        // before comment
+        this._field = 42;
+        // after comment
     }
 }
 ";
@@ -120,7 +123,10 @@ class C1
 
     void M()
     {
-         /* comment1 */ _field /* comment 2 */ = 0;
+        _field /* comment 2 */ = 0;
+        // before comment
+        _field = 42;
+        // after comment
     }
 }
 ";

src/Microsoft.DotNet.CodeFormatting/Rules/ExplicitThisRule.cs

@@ -7,6 +7,7 @@
 using Microsoft.CodeAnalysis;
 using Microsoft.CodeAnalysis.CSharp;
 using Microsoft.CodeAnalysis.CSharp.Syntax;
+using Microsoft.CodeAnalysis.Simplification;
 
 namespace Microsoft.DotNet.CodeFormatting.Rules
 {
@@ -17,6 +18,12 @@ private sealed class ExplicitThisRewriter : CSharpSyntaxRewriter
         {
             private readonly SemanticModel _semanticModel;
             private readonly CancellationToken _cancellationToken;
+            private bool _addedAnnotations;
+
+            internal bool AddedAnnotations
+            {
+                get { return _addedAnnotations; }
+            }
 
             internal ExplicitThisRewriter(SemanticModel semanticModel, CancellationToken cancellationToken)
             {
@@ -38,25 +45,14 @@ public override SyntaxNode VisitMemberAccessExpression(MemberAccessExpressionSyn
                         var field = (IFieldSymbol)symbolInfo.Symbol;
                         if (field.DeclaredAccessibility == Accessibility.Private)
                         {
-                            return RemoveQualification(node);
+                            _addedAnnotations = true;
+                            return node.WithAdditionalAnnotations(Simplifier.Annotation);
                         }
                     }
                 }
 
                 return node;
             }
-
-            private static NameSyntax RemoveQualification(MemberAccessExpressionSyntax memberSyntax)
-            {
-                var thisSyntax = memberSyntax.Expression;
-                var nameSyntax = memberSyntax.Name;
-                var triviaList = thisSyntax
-                    .GetLeadingTrivia()
-                    .AddRange(thisSyntax.GetTrailingTrivia())
-                    .AddRange(memberSyntax.OperatorToken.GetAllTrivia())
-                    .AddRange(nameSyntax.GetLeadingTrivia());
-                return nameSyntax.WithLeadingTrivia(triviaList);
-            }
         }
 
         public async Task<Document> ProcessAsync(Document document, CancellationToken cancellationToken)
@@ -70,7 +66,12 @@ public async Task<Document> ProcessAsync(Document document, CancellationToken ca
             var semanticModel = await document.GetSemanticModelAsync(cancellationToken);
             var rewriter = new ExplicitThisRewriter(semanticModel, cancellationToken);
             var newNode = rewriter.Visit(syntaxNode);
-            return document.WithSyntaxRoot(newNode);
+            if (!rewriter.AddedAnnotations)
+            {
+                return document;
+            }
+
+            return await Simplifier.ReduceAsync(document.WithSyntaxRoot(newNode), cancellationToken: cancellationToken);
         }
     }
 }