Properly support indentation within text of XML doc comment on ENTER

src/EditorFeatures/CSharpTest/DocumentationComments/DocumentationCommentTests.cs

@@ -1114,6 +1114,156 @@ void M()
             VerifyPressingEnter(code, expected);
         }
 
+        [WorkItem(2108, "https://github.com/dotnet/roslyn/issues/2108")]
+        [Fact, Trait(Traits.Feature, Traits.Features.DocumentationComments)]
+        public void PressingEnter_Indentation1()
+        {
+            const string code =
+@"class C
+{
+    /// <summary>
+    ///     hello world$$
+    /// </summary>
+    void M()
+    {
+    }
+}";
+
+            const string expected =
+@"class C
+{
+    /// <summary>
+    ///     hello world
+    ///     $$
+    /// </summary>
+    void M()
+    {
+    }
+}";
+
+            VerifyPressingEnter(code, expected);
+        }
+
+        [WorkItem(2108, "https://github.com/dotnet/roslyn/issues/2108")]
+        [Fact, Trait(Traits.Feature, Traits.Features.DocumentationComments)]
+        public void PressingEnter_Indentation2()
+        {
+            const string code =
+@"class C
+{
+    /// <summary>
+    ///     hello $$world
+    /// </summary>
+    void M()
+    {
+    }
+}";
+
+            const string expected =
+@"class C
+{
+    /// <summary>
+    ///     hello 
+    ///     $$world
+    /// </summary>
+    void M()
+    {
+    }
+}";
+
+            VerifyPressingEnter(code, expected);
+        }
+
+        [WorkItem(2108, "https://github.com/dotnet/roslyn/issues/2108")]
+        [Fact, Trait(Traits.Feature, Traits.Features.DocumentationComments)]
+        public void PressingEnter_Indentation3()
+        {
+            const string code =
+@"class C
+{
+    /// <summary>
+    ///     hello$$ world
+    /// </summary>
+    void M()
+    {
+    }
+}";
+
+            const string expected =
+@"class C
+{
+    /// <summary>
+    ///     hello
+    ///     $$world
+    /// </summary>
+    void M()
+    {
+    }
+}";
+
+            VerifyPressingEnter(code, expected);
+        }
+
+        [WorkItem(2108, "https://github.com/dotnet/roslyn/issues/2108")]
+        [Fact, Trait(Traits.Feature, Traits.Features.DocumentationComments)]
+        public void PressingEnter_Indentation4()
+        {
+            const string code =
+@"class C
+{
+    /// <summary>
+    ///     $$hello world
+    /// </summary>
+    void M()
+    {
+    }
+}";
+
+            const string expected =
+@"class C
+{
+    /// <summary>
+    ///     
+    /// $$hello world
+    /// </summary>
+    void M()
+    {
+    }
+}";
+
+            VerifyPressingEnter(code, expected);
+        }
+
+        [WorkItem(2108, "https://github.com/dotnet/roslyn/issues/2108")]
+        [Fact, Trait(Traits.Feature, Traits.Features.DocumentationComments)]
+        public void PressingEnter_Indentation5_UseTabs()
+        {
+            const string code =
+@"class C
+{
+    /// <summary>
+	///     hello world$$
+    /// </summary>
+    void M()
+    {
+    }
+}";
+
+            const string expected =
+@"class C
+{
+    /// <summary>
+	///     hello world
+	///     $$
+    /// </summary>
+    void M()
+    {
+    }
+}";
+
+            VerifyPressingEnter(code, expected, useTabs: true);
+        }
+
         [Fact, Trait(Traits.Feature, Traits.Features.DocumentationComments)]
         public void Command_Class()
         {

src/EditorFeatures/Core/Implementation/DocumentationComments/AbstractDocumentationCommentCommandHandler.cs

@@ -2,6 +2,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Diagnostics;
 using System.Threading;
 using Microsoft.CodeAnalysis.Editor.Commands;
 using Microsoft.CodeAnalysis.Editor.Host;
@@ -657,20 +658,39 @@ private void InsertExteriorTriviaIfNeeded(ITextView view, ITextBuffer subjectBuf
 
         private void InsertExteriorTrivia(ITextView view, ITextBuffer subjectBuffer, TextLine currentLine, TextLine previousLine)
         {
-            var useTabs = subjectBuffer.GetOption(FormattingOptions.UseTabs);
-            var tabSize = subjectBuffer.GetOption(FormattingOptions.TabSize);
-
-            var firstNonWhitespaceColumn = previousLine.GetColumnOfFirstNonWhitespaceCharacterOrEndOfLine(tabSize);
-            var indentText = firstNonWhitespaceColumn.CreateIndentationString(useTabs, tabSize) + ExteriorTriviaText + " ";
+            var insertionText = CreateInsertionTextFromPreviousLine(previousLine, subjectBuffer);
 
             var firstNonWhitespaceOffset = currentLine.GetFirstNonWhitespaceOffset();
             var replaceSpan = firstNonWhitespaceOffset != null
                 ? TextSpan.FromBounds(currentLine.Start, currentLine.Start + firstNonWhitespaceOffset.Value)
                 : currentLine.Span;
 
-            subjectBuffer.Replace(replaceSpan.ToSpan(), indentText);
+            subjectBuffer.Replace(replaceSpan.ToSpan(), insertionText);
+
+            view.TryMoveCaretToAndEnsureVisible(subjectBuffer.CurrentSnapshot.GetPoint(replaceSpan.Start + insertionText.Length));
+        }
+
+        private string CreateInsertionTextFromPreviousLine(TextLine previousLine, ITextBuffer subjectBuffer)
+        {
+            var useTabs = subjectBuffer.GetOption(FormattingOptions.UseTabs);
+            var tabSize = subjectBuffer.GetOption(FormattingOptions.TabSize);
+
+            var previousLineText = previousLine.ToString();
+            var firstNonWhitespaceColumn = previousLineText.GetColumnOfFirstNonWhitespaceCharacterOrEndOfLine(tabSize);
+
+            var trimmedPreviousLine = previousLineText.Trim();
+            Debug.Assert(trimmedPreviousLine.StartsWith(ExteriorTriviaText), "Unexpected: previous line does not begin with doc comment exterior trivia.");
+
+            // skip exterior trivia.
+            trimmedPreviousLine = trimmedPreviousLine.Substring(3);
+
+            var firstNonWhitespaceOffsetInPreviousXmlText = trimmedPreviousLine.GetFirstNonWhitespaceOffset();
+
+            var extraIndent = firstNonWhitespaceOffsetInPreviousXmlText != null
+                ? trimmedPreviousLine.Substring(0, firstNonWhitespaceOffsetInPreviousXmlText.Value)
+                : " ";
 
-            view.TryMoveCaretToAndEnsureVisible(subjectBuffer.CurrentSnapshot.GetPoint(replaceSpan.Start + indentText.Length));
+            return firstNonWhitespaceColumn.CreateIndentationString(useTabs, tabSize) + ExteriorTriviaText + extraIndent;
         }
 
         private bool CurrentLineStartsWithExteriorTrivia(ITextBuffer subjectBuffer, int position)

src/EditorFeatures/VisualBasicTest/DocumentationComments/DocumentationCommentTests.vb

@@ -611,6 +611,131 @@ End Class
             VerifyPressingEnter(code, expected)
         End Sub
 
+        <WorkItem(2108, "https://github.com/dotnet/roslyn/issues/2108")>
+        <Fact, Trait(Traits.Feature, Traits.Features.DocumentationComments)>
+        Public Sub PressingEnter_Indentation1()
+            Const code = "
+Class C
+    ''' <summary>
+    '''     hello world$$
+    ''' </summary>
+    Sub M()
+    End Sub
+End Class
+"
+            Const expected = "
+Class C
+    ''' <summary>
+    '''     hello world
+    '''     $$
+    ''' </summary>
+    Sub M()
+    End Sub
+End Class
+"
+            VerifyPressingEnter(code, expected)
+        End Sub
+
+        <WorkItem(2108, "https://github.com/dotnet/roslyn/issues/2108")>
+        <Fact, Trait(Traits.Feature, Traits.Features.DocumentationComments)>
+        Public Sub PressingEnter_Indentation2()
+            Const code = "
+Class C
+    ''' <summary>
+    '''     hello $$world
+    ''' </summary>
+    Sub M()
+    End Sub
+End Class
+"
+            Const expected = "
+Class C
+    ''' <summary>
+    '''     hello 
+    '''     $$world
+    ''' </summary>
+    Sub M()
+    End Sub
+End Class
+"
+            VerifyPressingEnter(code, expected)
+        End Sub
+
+        <WorkItem(2108, "https://github.com/dotnet/roslyn/issues/2108")>
+        <Fact, Trait(Traits.Feature, Traits.Features.DocumentationComments)>
+        Public Sub PressingEnter_Indentation3()
+            Const code = "
+Class C
+    ''' <summary>
+    '''     hello$$ world
+    ''' </summary>
+    Sub M()
+    End Sub
+End Class
+"
+            Const expected = "
+Class C
+    ''' <summary>
+    '''     hello
+    '''     $$world
+    ''' </summary>
+    Sub M()
+    End Sub
+End Class
+"
+            VerifyPressingEnter(code, expected)
+        End Sub
+
+        <WorkItem(2108, "https://github.com/dotnet/roslyn/issues/2108")>
+        <Fact, Trait(Traits.Feature, Traits.Features.DocumentationComments)>
+        Public Sub PressingEnter_Indentation4()
+            Const code = "
+Class C
+    ''' <summary>
+    '''     $$hello world
+    ''' </summary>
+    Sub M()
+    End Sub
+End Class
+"
+            Const expected = "
+Class C
+    ''' <summary>
+    '''     
+    ''' $$hello world
+    ''' </summary>
+    Sub M()
+    End Sub
+End Class
+"
+            VerifyPressingEnter(code, expected)
+        End Sub
+
+        <WorkItem(2108, "https://github.com/dotnet/roslyn/issues/2108")>
+        <Fact, Trait(Traits.Feature, Traits.Features.DocumentationComments)>
+        Public Sub PressingEnter_Indentation5_UseTabs()
+            Const code = "
+Class C
+    ''' <summary>
+	'''     hello world$$
+    ''' </summary>
+    Sub M()
+    End Sub
+End Class
+"
+            Const expected = "
+Class C
+    ''' <summary>
+	'''     hello world
+	'''     $$
+    ''' </summary>
+    Sub M()
+    End Sub
+End Class
+"
+            VerifyPressingEnter(code, expected, useTabs:=True)
+        End Sub
+
         <Fact, Trait(Traits.Feature, Traits.Features.DocumentationComments)>
         Public Sub Command_Class()
             Const code = "