[EnC] Make it a rude edit to change the value of a constant field

src/EditorFeatures/CSharpTest/EditAndContinue/ActiveStatementTests.cs

@@ -1804,7 +1804,7 @@ class C
             var active = GetActiveStatements(src1, src2);
 
             edits.VerifyRudeDiagnostics(active,
-                Diagnostic(RudeEditKind.ModifiersUpdate, "const int a = 1", "field"));
+                Diagnostic(RudeEditKind.ModifiersUpdate, "const int a = 1", "const field"));
         }
 
         [Fact]
@@ -1854,7 +1854,7 @@ class C
             var active = GetActiveStatements(src1, src2);
 
             edits.VerifyRudeDiagnostics(active,
-                Diagnostic(RudeEditKind.ModifiersUpdate, "const int a = 1, b = 2", "field"));
+                Diagnostic(RudeEditKind.ModifiersUpdate, "const int a = 1, b = 2", "const field"));
         }
 
         [Fact]

src/EditorFeatures/CSharpTest/EditAndContinue/RudeEditTopLevelTests.cs

@@ -5777,6 +5777,49 @@ class SampleCollection<T>
                 Diagnostic(RudeEditKind.Delete, "public T this[int i]", "indexer setter"));
         }
 
+        [WorkItem(1120407)]
+        [Fact]
+        public void ConstField_Update()
+        {
+            var src1 = "class C { const int x = 0; }";
+            var src2 = "class C { const int x = 1; }";
+
+            var edits = GetTopEdits(src1, src2);
+
+            edits.VerifyEdits("Update [x = 0]@20 -> [x = 1]@20");
+
+            edits.VerifyRudeDiagnostics(
+                Diagnostic(RudeEditKind.Update, "x = 1", "const field"));
+        }
+
+        [Fact]
+        public void ConstField_Delete()
+        {
+            var src1 = "class C { const int x = 0; }";
+            var src2 = "class C { int x = 0; }";
+
+            var edits = GetTopEdits(src1, src2);
+
+            edits.VerifyEdits("Update [const int x = 0;]@10 -> [int x = 0;]@10");
+
+            edits.VerifyRudeDiagnostics(
+                Diagnostic(RudeEditKind.ModifiersUpdate, "int x = 0", "field"));
+        }
+
+        [Fact]
+        public void ConstField_Add()
+        {
+            var src1 = "class C { int x = 0; }";
+            var src2 = "class C { const int x = 0; }";
+
+            var edits = GetTopEdits(src1, src2);
+
+            edits.VerifyEdits("Update [int x = 0;]@10 -> [const int x = 0;]@10");
+
+            edits.VerifyRudeDiagnostics(
+                Diagnostic(RudeEditKind.ModifiersUpdate, "const int x = 0", "const field"));
+        }
+
         #endregion
 
         #region Events

src/EditorFeatures/VisualBasicTest/EditAndContinue/ActiveStatementTests.vb

@@ -1893,7 +1893,7 @@ End Class
             Dim active = GetActiveStatements(src1, src2)
 
             edits.VerifyRudeDiagnostics(active,
-                Diagnostic(RudeEditKind.ModifiersUpdate, "Private Const a As Integer = 1", "field"))
+                Diagnostic(RudeEditKind.ModifiersUpdate, "Private Const a As Integer = 1", "const field"))
         End Sub
 
         <Fact>
@@ -1938,7 +1938,7 @@ End Class
             Dim active = GetActiveStatements(src1, src2)
 
             edits.VerifyRudeDiagnostics(active,
-                Diagnostic(RudeEditKind.ModifiersUpdate, "Private Const a As Integer = 1, b As Integer = 2", "field"))
+                Diagnostic(RudeEditKind.ModifiersUpdate, "Private Const a As Integer = 1, b As Integer = 2", "const field"))
         End Sub
 
         <Fact>

src/EditorFeatures/VisualBasicTest/EditAndContinue/RudeEditTopLevelTests.vb

@@ -4698,6 +4698,37 @@ End Class
 
             edits.VerifyRudeDiagnostics()
         End Sub
+
+        <Fact>
+        Public Sub ConstField_Update()
+            Dim src1 = "Class C : Const x = 0 : End Class"
+            Dim src2 = "Class C : Const x = 1 : End Class"
+            Dim edits = GetTopEdits(src1, src2)
+
+            edits.VerifyRudeDiagnostics(
+                Diagnostic(RudeEditKind.Update, "x = 1", "const field"))
+        End Sub
+
+        <Fact>
+        Public Sub ConstField_Delete()
+            Dim src1 = "Class C : Const x = 0 : End Class"
+            Dim src2 = "Class C : Dim x = 0 : End Class"
+            Dim edits = GetTopEdits(src1, src2)
+
+            edits.VerifyRudeDiagnostics(
+                Diagnostic(RudeEditKind.ModifiersUpdate, "Dim x = 0", "field"))
+        End Sub
+
+        <Fact>
+        Public Sub ConstField_Add()
+            Dim src1 = "Class C : Dim x = 0 : End Class"
+            Dim src2 = "Class C : Const x = 0 : End Class"
+            Dim edits = GetTopEdits(src1, src2)
+
+            edits.VerifyRudeDiagnostics(
+                Diagnostic(RudeEditKind.ModifiersUpdate, "Const x = 0", "const field"))
+        End Sub
+
 #End Region
 
 #Region "Events"

src/Features/CSharp/EditAndContinue/CSharpEditAndContinueAnalyzer.cs

@@ -1250,7 +1250,8 @@ internal static string GetTopLevelDisplayNameImpl(SyntaxNode node, EditKind edit
                     return "delegate";
 
                 case SyntaxKind.FieldDeclaration:
-                    return "field";
+                    var declaration = (FieldDeclarationSyntax)node;
+                    return declaration.Modifiers.Any(SyntaxKind.ConstKeyword) ? "const field" : "field";
 
                 case SyntaxKind.EventFieldDeclaration:
                     return "event field";
@@ -2108,6 +2109,14 @@ private void ClassifyUpdate(VariableDeclaratorSyntax oldNode, VariableDeclarator
                     return;
                 }
 
+                // Check if a constant field is updated:
+                var fieldDeclaration = oldNode.Parent.Parent as FieldDeclarationSyntax;
+                if (fieldDeclaration != null && fieldDeclaration.Modifiers.Any(SyntaxKind.ConstKeyword))
+                {
+                    ReportError(RudeEditKind.Update);
+                    return;
+                }
+
                 // TODO (#749): handle lambdas in initializers & constructors
                 ClassifyDeclarationBodyRudeUpdates(newNode, allowLambdas: false);
             }

src/Features/VisualBasic/EditAndContinue/VisualBasicEditAndContinueAnalyzer.vb

@@ -1341,7 +1341,8 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.EditAndContinue
 
                 Case SyntaxKind.FieldDeclaration
                     Dim declaration = DirectCast(node, FieldDeclarationSyntax)
-                    Return If(declaration.Modifiers.Any(SyntaxKind.WithEventsKeyword), "WithEvents field", "field")
+                    Return If(declaration.Modifiers.Any(SyntaxKind.WithEventsKeyword), "WithEvents field",
+                           If(declaration.Modifiers.Any(SyntaxKind.ConstKeyword), "const field", "field"))
 
                 Case SyntaxKind.VariableDeclarator,
                      SyntaxKind.ModifiedIdentifier
@@ -2269,10 +2270,17 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.EditAndContinue
                     Return
                 End If
 
-                ClassifyTypeAndInitializerUpdates(oldNode.Initializer,
+                If ClassifyTypeAndInitializerUpdates(oldNode.Initializer,
                                                   oldNode.AsClause,
                                                   newNode.Initializer,
-                                                  newNode.AsClause)
+                                                  newNode.AsClause) Then
+                    ' Check if a constant field is updated:
+                    Dim fieldDeclaration = TryCast(oldNode.Parent, FieldDeclarationSyntax)
+                    If fieldDeclaration IsNot Nothing AndAlso fieldDeclaration.Modifiers.Any(SyntaxKind.ConstKeyword) Then
+                        ReportError(RudeEditKind.Update)
+                        Return
+                    End If
+                End If
             End Sub
 
             Private Sub ClassifyUpdate(oldNode As PropertyStatementSyntax, newNode As PropertyStatementSyntax)