EnC: Allow reordering members (#75257)

src/Features/CSharp/Portable/EditAndContinue/CSharpEditAndContinueAnalyzer.cs

@@ -1166,22 +1166,18 @@ newContainingMemberOrType is IPropertySymbol newPropertySymbol &&
             case EditKind.Reorder:
                 Contract.ThrowIfNull(oldNode);
 
+                // When global statements are reordered, we issue an update edit for the synthesized main method, which is what
+                // oldSymbol and newSymbol will point to.
                 if (IsGlobalStatement(oldNode))
                 {
-                    // When global statements are reordered, we issue an update edit for the synthesized main method, which is what
-                    // oldSymbol and newSymbol will point to
                     result.Add((oldSymbol, newSymbol, EditKind.Update));
                     return;
                 }
 
-                // Otherwise, we don't do any semantic checks for reordering
-                // and we don't need to report them to the compiler either.
-                // Consider: Currently symbol ordering changes are not reflected in metadata (Reflection will report original order).
+                // Reordering of data members is only allowed if the layout of the type doesn't change.
+                // Reordering of other members is a no-op, although the new order won't be reflected in metadata (Reflection will report original order).
+                result.Add((oldSymbol, newSymbol, EditKind.Reorder));
 
-                // Consider: Reordering of fields is not allowed since it changes the layout of the type.
-                // This ordering should however not matter unless the type has explicit layout so we might want to allow it.
-                // We do not check changes to the order if they occur across multiple documents (the containing type is partial).
-                Debug.Assert(!IsDeclarationWithInitializer(oldNode!) && !IsDeclarationWithInitializer(newNode!));
                 return;
 
             case EditKind.Update:
@@ -2391,14 +2387,6 @@ private void ClassifyReorder(SyntaxNode newNode)
 
             switch (newNode.Kind())
             {
-                case SyntaxKind.PropertyDeclaration:
-                case SyntaxKind.FieldDeclaration:
-                case SyntaxKind.EventFieldDeclaration:
-                case SyntaxKind.VariableDeclarator:
-                    // Maybe we could allow changing order of field declarations unless the containing type layout is sequential.
-                    ReportError(RudeEditKind.Move);
-                    return;
-
                 case SyntaxKind.EnumMemberDeclaration:
                     // To allow this change we would need to check that values of all fields of the enum 
                     // are preserved, or make sure we can update all method bodies that accessed those that changed.

src/Features/CSharpTest/EditAndContinue/ActiveStatementTests.cs

@@ -3126,7 +3126,6 @@ public C() {}
         var active = GetActiveStatements(src1, src2);
 
         edits.VerifySemanticDiagnostics(active,
-            Diagnostic(RudeEditKind.Move, "int c", GetResource("field")),
             Diagnostic(RudeEditKind.DeleteActiveStatement, "class C", GetResource("field", "C.a")),
             Diagnostic(RudeEditKind.Delete, "class C", GetResource("field", "a")));
     }

src/Features/CSharpTest/EditAndContinue/LineEditTests.cs

@@ -69,12 +69,12 @@ public void Method_Reorder1()
         var src1 = @"
 class C
 {
-    static void Goo()
+    static void G()
     {
         Console.ReadLine(1);
     }
 
-    static void Bar()
+    static void F()
     {
         Console.ReadLine(2);
     }
@@ -83,76 +83,83 @@ static void Bar()
         var src2 = @"
 class C
 {
-    static void Bar()
+    static void F()
     {
         Console.ReadLine(2);
     }
 
-    static void Goo()
+    static void G()
     {
         Console.ReadLine(1);
     }
 }";
         var edits = GetTopEdits(src1, src2);
+
+        // Consider: we could detect that the body of the method hasn't changed and avoid creating an update.
         edits.VerifyLineEdits(
             new[]
             {
                 new SourceLineUpdate(4, 9),
                 new SourceLineUpdate(7, 7),
                 new SourceLineUpdate(9, 4)
-            });
+            },
+            semanticEdits: [SemanticEdit(SemanticEditKind.Update, c => c.GetMember("C.F"))]);
     }
 
     [Fact]
     public void Method_Reorder2()
     {
         var src1 = @"
-class Program
+class C
 {
     static void Main()
     {
-        Goo();
-        Bar();
+        F();
+        G();
     }
 
-    static int Goo()
+    static int G()
     {
         return 1;
     }
 
-    static int Bar()
+    static int F()
     {
         return 2;
     }
 }";
         var src2 = @"
-class Program
+class C
 {
-    static int Goo()
+    static int F()
     {
         return 1;
     }
 
     static void Main()
     {
-        Goo();
-        Bar();
+        F();
+        G();
     }
 
-    static int Bar()
+    static int G()
     {
         return 2;
     }
 }";
         var edits = GetTopEdits(src1, src2);
+
+        // Consider: we could detect that the body of the method hasn't changed and create line edits instead of an update.
         edits.VerifyLineEdits(
             new[]
             {
                 new SourceLineUpdate(4, 9),
-                new SourceLineUpdate(8, 8),
-                new SourceLineUpdate(10, 4),
-                new SourceLineUpdate(13, 13),
-            });
+            },
+            semanticEdits:
+            [
+                SemanticEdit(SemanticEditKind.Update, c => c.GetMember("C.F")),
+                SemanticEdit(SemanticEditKind.Update, c => c.GetMember("C.G"))
+            ]);
     }
 
     [Fact]
@@ -758,13 +765,19 @@ public C(int a)
     }
 }";
         var edits = GetTopEdits(src1, src2);
+
+        // Consider: we could detect that the body of the method hasn't changed and avoid creating an update.
         edits.VerifyLineEdits(
             new[]
             {
                 new SourceLineUpdate(3, 7),
                 new SourceLineUpdate(6, 6),
                 new SourceLineUpdate(7, 3)
-            });
+            },
+            semanticEdits:
+            [
+                SemanticEdit(SemanticEditKind.Update, c => c.GetMember<INamedTypeSymbol>("C").Constructors.Single(c => c.Parameters is [{ Type.SpecialType: SpecialType.System_Boolean }]), preserveLocalVariables: true)
+            ]);
     }
 
     [Fact]
@@ -1357,13 +1370,13 @@ class C
         var src2 = @"
 class C
 {
-    static int Bar = 2;
-    static int Goo = 1;
+    static int Bar = 1;
+    static int Goo = 2;
 }";
         var edits = GetTopEdits(src1, src2);
         edits.VerifyLineEdits(
             Array.Empty<SequencePointUpdates>(),
-            diagnostics: [Diagnostic(RudeEditKind.Move, "static int Bar = 2", FeaturesResources.field)]);
+            semanticEdits: [SemanticEdit(SemanticEditKind.Update, c => c.GetMember<INamedTypeSymbol>("C").StaticConstructors.Single(), preserveLocalVariables: true)]);
     }
 
     [Fact]