For tuple types, NamedTypeSymbol.GetFieldsToEmit API should return symbols for...

For tuple types, NamedTypeSymbol.GetFieldsToEmit API should return symbols for tuple underlying fields. (#43552)

Fixes #43524.
Related to #43549.

Also, ensure nested type is generated for a fixed size buffer declared within a tuple type.

Related to #43621.

src/Compilers/CSharp/Portable/Compiler/MethodCompiler.cs

@@ -541,7 +541,8 @@ private void CompileNamedType(NamedTypeSymbol containingType)
 
                     case SymbolKind.Field:
                         {
-                            FieldSymbol fieldSymbol = member as FieldSymbol;
+                            var field = (FieldSymbol)member;
+                            var fieldSymbol = (field.TupleUnderlyingField ?? field) as SourceMemberFieldSymbol;
                             if ((object)fieldSymbol != null)
                             {
                                 if (fieldSymbol.IsConst)

src/Compilers/CSharp/Portable/Emitter/Model/NamedTypeSymbolAdapter.cs

@@ -407,6 +407,7 @@ IEnumerable<Cci.IFieldDefinition> Cci.ITypeDefinition.GetFields(EmitContext cont
 
             foreach (var f in GetFieldsToEmit())
             {
+                Debug.Assert((object)(f.TupleUnderlyingField ?? f) == f);
                 if (isStruct || f.ShouldInclude(context))
                 {
                     yield return f;

src/Compilers/CSharp/Portable/Emitter/Model/PEModuleBuilder.cs

@@ -271,19 +271,26 @@ internal sealed override IEnumerable<Cci.INestedTypeDefinition> GetSynthesizedNe
                                         break;
 
                                     case SymbolKind.Property:
+                                        AddSymbolLocation(result, member);
+                                        break;
                                     case SymbolKind.Field:
                                         // NOTE: Dev11 does not add synthesized backing fields for properties,
                                         //       but adds backing fields for events, Roslyn adds both
-                                        AddSymbolLocation(result, member);
+                                        {
+                                            var field = (FieldSymbol)member;
+                                            AddSymbolLocation(result, field.TupleUnderlyingField ?? field);
+                                        }
                                         break;
 
                                     case SymbolKind.Event:
                                         AddSymbolLocation(result, member);
                                         //  event backing fields do not show up in GetMembers
-                                        FieldSymbol field = ((EventSymbol)member).AssociatedField;
-                                        if ((object)field != null)
                                         {
-                                            AddSymbolLocation(result, field);
+                                            FieldSymbol field = ((EventSymbol)member).AssociatedField;
+                                            if ((object)field != null)
+                                            {
+                                                AddSymbolLocation(result, field.TupleUnderlyingField ?? field);
+                                            }
                                         }
                                         break;
 
@@ -1003,7 +1010,7 @@ internal static Cci.IGenericParameterReference Translate(TypeParameterSymbol par
             bool needDeclaration = false)
         {
             Debug.Assert(fieldSymbol.IsDefinitionOrDistinct());
-            Debug.Assert(!fieldSymbol.IsVirtualTupleField, "virtual tuple fields should be rewritten to underlying by now");
+            Debug.Assert(!fieldSymbol.IsVirtualTupleField && (object)(fieldSymbol.TupleUnderlyingField ?? fieldSymbol) == fieldSymbol, "tuple fields should be rewritten to underlying by now");
 
             if (!fieldSymbol.IsDefinition)
             {

src/Compilers/CSharp/Portable/Symbols/Metadata/PE/PENamedTypeSymbol.cs

@@ -878,7 +878,7 @@ internal override IEnumerable<FieldSymbol> GetFieldsToEmit()
             else
             {
                 // If there are any non-event fields, they are at the very beginning.
-                IEnumerable<FieldSymbol> nonEventFields = GetMembers<FieldSymbol>(this.GetMembers(), SymbolKind.Field, offset: 0);
+                IEnumerable<FieldSymbol> nonEventFields = GetMembers<FieldSymbol>(this.GetMembers(), SymbolKind.Field, offset: 0).Select(f => f.TupleUnderlyingField ?? f);
 
                 // Event backing fields are not part of the set returned by GetMembers. Let's add them manually.
                 ArrayBuilder<FieldSymbol> eventFields = null;
@@ -889,6 +889,9 @@ internal override IEnumerable<FieldSymbol> GetFieldsToEmit()
                     if ((object)associatedField != null)
                     {
                         Debug.Assert((object)associatedField.AssociatedSymbol != null);
+
+                        associatedField = associatedField.TupleUnderlyingField ?? associatedField;
+
                         Debug.Assert(!nonEventFields.Contains(associatedField));
 
                         if (eventFields == null)

src/Compilers/CSharp/Portable/Symbols/Source/SourceMemberContainerSymbol.cs

@@ -1279,13 +1279,14 @@ internal override IEnumerable<FieldSymbol> GetFieldsToEmit()
                 switch (m.Kind)
                 {
                     case SymbolKind.Field:
-                        yield return (FieldSymbol)m;
+                        var field = (FieldSymbol)m;
+                        yield return field.TupleUnderlyingField ?? field;
                         break;
                     case SymbolKind.Event:
                         FieldSymbol associatedField = ((EventSymbol)m).AssociatedField;
                         if ((object)associatedField != null)
                         {
-                            yield return associatedField;
+                            yield return associatedField.TupleUnderlyingField ?? associatedField;
                         }
                         break;
                 }

src/Compilers/CSharp/Test/Emit/CodeGen/CodeGenTupleTest.cs

@@ -26462,6 +26462,7 @@ void verifyTupleTypeWithErrorUnderlyingType(CSharpCompilation compilation, bool
         [Fact]
         [WorkItem(41207, "https://github.com/dotnet/roslyn/issues/41207")]
         [WorkItem(1056281, "https://dev.azure.com/devdiv/DevDiv/_workitems/edit/1056281")]
+        [WorkItem(43549, "https://github.com/dotnet/roslyn/issues/43549")]
         public void CustomFields_01()
         {
             var source0 = @"
@@ -26508,25 +26509,44 @@ public static void Main()
 }
 ";
 
-            var comp1 = CreateCompilation(source0 + source1, targetFramework: TargetFramework.Mscorlib46, options: TestOptions.DebugExe);
+            var comp1 = CreateCompilation(source0 + source1, targetFramework: TargetFramework.Mscorlib40, options: TestOptions.DebugExe);
             CompileAndVerify(comp1, expectedOutput: "123");
+            verifyField(comp1);
 
             var comp1Ref = new[] { comp1.ToMetadataReference() };
             var comp1ImageRef = new[] { comp1.EmitToImageReference() };
 
-            var comp4 = CreateCompilation(source0 + source2, targetFramework: TargetFramework.Mscorlib46, options: TestOptions.DebugExe);
+            var comp4 = CreateCompilation(source0 + source2, targetFramework: TargetFramework.Mscorlib40, options: TestOptions.DebugExe);
             CompileAndVerify(comp4, expectedOutput: "123");
 
-            var comp5 = CreateCompilation(source2, targetFramework: TargetFramework.Mscorlib46, options: TestOptions.DebugExe, references: comp1Ref);
+            var comp5 = CreateCompilation(source2, targetFramework: TargetFramework.Mscorlib40, options: TestOptions.DebugExe, references: comp1Ref);
             CompileAndVerify(comp5, expectedOutput: "123");
+            verifyField(comp5);
 
-            var comp6 = CreateCompilation(source2, targetFramework: TargetFramework.Mscorlib46, options: TestOptions.DebugExe, references: comp1ImageRef);
+            var comp6 = CreateCompilation(source2, targetFramework: TargetFramework.Mscorlib40, options: TestOptions.DebugExe, references: comp1ImageRef);
             CompileAndVerify(comp6, expectedOutput: "123");
+            verifyField(comp6);
+
+            // Uncomment after https://github.com/dotnet/roslyn/issues/43549 is fixed.
+            //var comp7 = CreateCompilation(source2, targetFramework: TargetFramework.Mscorlib46, options: TestOptions.DebugExe, references: comp1Ref);
+            //CompileAndVerify(comp7, expectedOutput: "123");
+            //verifyField(comp7);
+
+            void verifyField(CSharpCompilation comp)
+            {
+                var field = comp.GetMember<FieldSymbol>("System.ValueTuple.F1");
+                Assert.NotNull(field.TupleUnderlyingField);
+                Assert.NotSame(field, field.TupleUnderlyingField);
+                var toEmit = field.ContainingType.GetFieldsToEmit().Where(f => f.Name == "F1").Single();
+                Assert.Same(toEmit, toEmit.TupleUnderlyingField);
+                Assert.Same(field.TupleUnderlyingField, toEmit);
+            }
         }
 
         [Fact]
         [WorkItem(41207, "https://github.com/dotnet/roslyn/issues/41207")]
         [WorkItem(1056281, "https://dev.azure.com/devdiv/DevDiv/_workitems/edit/1056281")]
+        [WorkItem(43549, "https://github.com/dotnet/roslyn/issues/43549")]
         public void CustomFields_02()
         {
             var source0 = @"
@@ -26574,20 +26594,224 @@ public static void Main()
 }
 ";
 
-            var comp1 = CreateCompilation(source0 + source1, targetFramework: TargetFramework.Mscorlib46, options: TestOptions.DebugExe);
+            var comp1 = CreateCompilation(source0 + source1, targetFramework: TargetFramework.Mscorlib40, options: TestOptions.DebugExe);
             CompileAndVerify(comp1, expectedOutput: "123");
+            verifyField(comp1);
 
             var comp1Ref = new[] { comp1.ToMetadataReference() };
             var comp1ImageRef = new[] { comp1.EmitToImageReference() };
 
-            var comp4 = CreateCompilation(source0 + source2, targetFramework: TargetFramework.Mscorlib46, options: TestOptions.DebugExe);
+            var comp4 = CreateCompilation(source0 + source2, targetFramework: TargetFramework.Mscorlib40, options: TestOptions.DebugExe);
             CompileAndVerify(comp4, expectedOutput: "123");
 
-            var comp5 = CreateCompilation(source2, targetFramework: TargetFramework.Mscorlib46, options: TestOptions.DebugExe, references: comp1Ref);
+            var comp5 = CreateCompilation(source2, targetFramework: TargetFramework.Mscorlib40, options: TestOptions.DebugExe, references: comp1Ref);
             CompileAndVerify(comp5, expectedOutput: "123");
+            verifyField(comp5);
 
-            var comp6 = CreateCompilation(source2, targetFramework: TargetFramework.Mscorlib46, options: TestOptions.DebugExe, references: comp1ImageRef);
+            var comp6 = CreateCompilation(source2, targetFramework: TargetFramework.Mscorlib40, options: TestOptions.DebugExe, references: comp1ImageRef);
             CompileAndVerify(comp6, expectedOutput: "123");
+            verifyField(comp6);
+
+            // Uncomment after https://github.com/dotnet/roslyn/issues/43549 is fixed.
+            //var comp7 = CreateCompilation(source2, targetFramework: TargetFramework.Mscorlib46, options: TestOptions.DebugExe, references: comp1Ref);
+            //CompileAndVerify(comp7, expectedOutput: "123");
+            //verifyField(comp7);
+
+            void verifyField(CSharpCompilation comp)
+            {
+                var field = comp.GetMember<FieldSymbol>("System.ValueTuple.F1");
+                Assert.NotNull(field.TupleUnderlyingField);
+                Assert.NotSame(field, field.TupleUnderlyingField);
+                var toEmit = field.ContainingType.GetFieldsToEmit().Where(f => f.Name == "F1").Single();
+                Assert.Same(toEmit, toEmit.TupleUnderlyingField);
+                Assert.Same(field.TupleUnderlyingField, toEmit);
+            }
+        }
+
+        [Fact]
+        [WorkItem(43524, "https://github.com/dotnet/roslyn/issues/43524")]
+        [WorkItem(1095184, "https://devdiv.visualstudio.com/DevDiv/_workitems/edit/1095184")]
+        [WorkItem(43549, "https://github.com/dotnet/roslyn/issues/43549")]
+        public void CustomFields_03()
+        {
+            var source0 = @"
+namespace System
+{
+    public struct ValueTuple
+    {
+        public static readonly int F1 = 4;
+
+        public static int CombineHashCodes(int h1, int h2)
+        {
+            return F1 + h1 + h2;
+        }
+    }
+}
+";
+
+            var source1 = @"
+class Program
+{
+    static void Main()
+    {
+        System.Console.WriteLine(System.ValueTuple.CombineHashCodes(2, 3));
+    }
+}
+";
+
+            var source2 = @"
+class Program
+{
+    public static void Main()
+    {
+        System.Console.WriteLine(System.ValueTuple.F1 + 2 + 3);
+    }
+}
+";
+
+            var comp1 = CreateCompilation(source0 + source1, targetFramework: TargetFramework.Mscorlib40, options: TestOptions.DebugExe);
+            CompileAndVerify(comp1, expectedOutput: "9");
+            verifyField(comp1);
+
+            var comp1Ref = new[] { comp1.ToMetadataReference() };
+            var comp1ImageRef = new[] { comp1.EmitToImageReference() };
+
+            var comp4 = CreateCompilation(source0 + source2, targetFramework: TargetFramework.Mscorlib40, options: TestOptions.DebugExe);
+            CompileAndVerify(comp4, expectedOutput: "9");
+
+            var comp5 = CreateCompilation(source2, targetFramework: TargetFramework.Mscorlib40, options: TestOptions.DebugExe, references: comp1Ref);
+            CompileAndVerify(comp5, expectedOutput: "9");
+            verifyField(comp5);
+
+            var comp6 = CreateCompilation(source2, targetFramework: TargetFramework.Mscorlib40, options: TestOptions.DebugExe, references: comp1ImageRef);
+            CompileAndVerify(comp6, expectedOutput: "9");
+            verifyField(comp6);
+
+            // Uncomment after https://github.com/dotnet/roslyn/issues/43549 is fixed.
+            //var comp7 = CreateCompilation(source2, targetFramework: TargetFramework.Mscorlib46, options: TestOptions.DebugExe, references: comp1Ref);
+            //CompileAndVerify(comp7, expectedOutput: "9");
+            //verifyField(comp7);
+
+            void verifyField(CSharpCompilation comp)
+            {
+                var field = comp.GetMember<FieldSymbol>("System.ValueTuple.F1");
+                Assert.NotNull(field.TupleUnderlyingField);
+                Assert.NotSame(field, field.TupleUnderlyingField);
+                var toEmit = field.ContainingType.GetFieldsToEmit().Single();
+                Assert.Same(toEmit, toEmit.TupleUnderlyingField);
+                Assert.Same(field.TupleUnderlyingField, toEmit);
+            }
+        }
+
+        [Fact]
+        [WorkItem(43524, "https://github.com/dotnet/roslyn/issues/43524")]
+        [WorkItem(1095184, "https://devdiv.visualstudio.com/DevDiv/_workitems/edit/1095184")]
+        [WorkItem(43549, "https://github.com/dotnet/roslyn/issues/43549")]
+        public void CustomFields_04()
+        {
+            var source0 = @"
+namespace System
+{
+    public struct ValueTuple
+    {
+        public int F1;
+
+        public int CombineHashCodes(int h1, int h2)
+        {
+            return F1 + h1 + h2;
+        }
+    }
+}
+";
+
+            var source1 = @"
+class Program
+{
+    static void Main()
+    {
+        System.ValueTuple tuple = default;
+        tuple.F1 = 4;
+        System.Console.WriteLine(tuple.CombineHashCodes(2, 3));
+    }
+}
+";
+
+            var source2 = @"
+class Program
+{
+    public static void Main()
+    {
+        System.ValueTuple tuple = default;
+        tuple.F1 = 4;
+        System.Console.WriteLine(tuple.F1 + 2 + 3);
+    }
+}
+";
+
+            var comp1 = CreateCompilation(source0 + source1, targetFramework: TargetFramework.Mscorlib40, options: TestOptions.DebugExe);
+            CompileAndVerify(comp1, expectedOutput: "9");
+            verifyField(comp1);
+
+            var comp1Ref = new[] { comp1.ToMetadataReference() };
+            var comp1ImageRef = new[] { comp1.EmitToImageReference() };
+
+            var comp4 = CreateCompilation(source0 + source2, targetFramework: TargetFramework.Mscorlib40, options: TestOptions.DebugExe);
+            CompileAndVerify(comp4, expectedOutput: "9");
+
+            var comp5 = CreateCompilation(source2, targetFramework: TargetFramework.Mscorlib40, options: TestOptions.DebugExe, references: comp1Ref);
+            CompileAndVerify(comp5, expectedOutput: "9");
+            verifyField(comp5);
+
+            var comp6 = CreateCompilation(source2, targetFramework: TargetFramework.Mscorlib40, options: TestOptions.DebugExe, references: comp1ImageRef);
+            CompileAndVerify(comp6, expectedOutput: "9");
+            verifyField(comp6);
+
+            // Uncomment after https://github.com/dotnet/roslyn/issues/43549 is fixed.
+            //var comp7 = CreateCompilation(source2, targetFramework: TargetFramework.Mscorlib46, options: TestOptions.DebugExe, references: comp1Ref);
+            //CompileAndVerify(comp7, expectedOutput: "9");
+            //verifyField(comp7);
+
+            void verifyField(CSharpCompilation comp)
+            {
+                var field = comp.GetMember<FieldSymbol>("System.ValueTuple.F1");
+                Assert.NotNull(field.TupleUnderlyingField);
+                Assert.NotSame(field, field.TupleUnderlyingField);
+                var toEmit = field.ContainingType.GetFieldsToEmit().Single();
+                Assert.Same(toEmit, toEmit.TupleUnderlyingField);
+                Assert.Same(field.TupleUnderlyingField, toEmit);
+            }
+        }
+
+        [Fact(Skip = "https://github.com/dotnet/roslyn/issues/43621")]
+        [WorkItem(43621, "https://github.com/dotnet/roslyn/issues/43621")]
+        public void CustomFields_05()
+        {
+            var source0 = @"
+using System;
+
+namespace System
+{
+    public class C
+    {
+        public unsafe static void Main()
+        {
+            var s = new ValueTuple();
+            int* p = s.MessageType;
+            s.MessageType[0] = 12;
+            p[1] = p[0];
+            Console.WriteLine(s.MessageType[1]);
+        }
+    }
+
+    public unsafe struct ValueTuple
+    {
+        public fixed int MessageType[50];
+    }
+}
+";
+
+            var comp1 = CreateCompilation(source0, options: TestOptions.DebugExe.WithAllowUnsafe(true));
+            CompileAndVerify(comp1, expectedOutput: "12");
         }
 
         [Fact]

src/Compilers/VisualBasic/Test/Emit/CodeGen/CodeGenTuples.vb

@@ -22872,20 +22872,34 @@ class Program
 End Class
 "
 
-            Dim comp1 = CreateCompilation(source0 + source1, targetFramework:=TargetFramework.Mscorlib46, options:=TestOptions.DebugExe)
+            Dim verifyField = Sub(comp As VisualBasicCompilation)
+                                  Dim field = comp.GetMember(Of FieldSymbol)("System.ValueTuple.F1")
+                                  Assert.Null(field.TupleUnderlyingField)
+                                  Dim toEmit = field.ContainingType.GetFieldsToEmit().Where(Function(f) f.Name = "F1").Single()
+                                  Assert.Same(field, toEmit)
+                              End Sub
+
+            Dim comp1 = CreateCompilation(source0 + source1, targetFramework:=TargetFramework.Mscorlib40, options:=TestOptions.DebugExe)
             CompileAndVerify(comp1, expectedOutput:="123")
+            verifyField(comp1)
 
             Dim comp1Ref = {comp1.ToMetadataReference()}
             Dim comp1ImageRef = {comp1.EmitToImageReference()}
 
-            Dim comp4 = CreateCompilation(source0 + source2, targetFramework:=TargetFramework.Mscorlib46, options:=TestOptions.DebugExe)
+            Dim comp4 = CreateCompilation(source0 + source2, targetFramework:=TargetFramework.Mscorlib40, options:=TestOptions.DebugExe)
             CompileAndVerify(comp4, expectedOutput:="123")
 
-            Dim comp5 = CreateCompilation(source2, targetFramework:=TargetFramework.Mscorlib46, options:=TestOptions.DebugExe, references:=comp1Ref)
+            Dim comp5 = CreateCompilation(source2, targetFramework:=TargetFramework.Mscorlib40, options:=TestOptions.DebugExe, references:=comp1Ref)
             CompileAndVerify(comp5, expectedOutput:="123")
+            verifyField(comp5)
 
-            Dim comp6 = CreateCompilation(source2, targetFramework:=TargetFramework.Mscorlib46, options:=TestOptions.DebugExe, references:=comp1ImageRef)
+            Dim comp6 = CreateCompilation(source2, targetFramework:=TargetFramework.Mscorlib40, options:=TestOptions.DebugExe, references:=comp1ImageRef)
             CompileAndVerify(comp6, expectedOutput:="123")
+            verifyField(comp6)
+
+            Dim comp7 = CreateCompilation(source2, targetFramework:=TargetFramework.Mscorlib46, options:=TestOptions.DebugExe, references:=comp1Ref)
+            CompileAndVerify(comp7, expectedOutput:="123")
+            verifyField(comp7)
         End Sub
 
         <Fact>
@@ -22928,20 +22942,162 @@ class Program
 End Class
 "
 
-            Dim comp1 = CreateCompilation(source0 + source1, targetFramework:=TargetFramework.Mscorlib46, options:=TestOptions.DebugExe)
+            Dim verifyField = Sub(comp As VisualBasicCompilation)
+                                  Dim field = comp.GetMember(Of FieldSymbol)("System.ValueTuple.F1")
+                                  Assert.Null(field.TupleUnderlyingField)
+                                  Dim toEmit = field.ContainingType.GetFieldsToEmit().Where(Function(f) f.Name = "F1").Single()
+                                  Assert.Same(field, toEmit)
+                              End Sub
+
+            Dim comp1 = CreateCompilation(source0 + source1, targetFramework:=TargetFramework.Mscorlib40, options:=TestOptions.DebugExe)
             CompileAndVerify(comp1, expectedOutput:="123")
+            verifyField(comp1)
 
             Dim comp1Ref = {comp1.ToMetadataReference()}
             Dim comp1ImageRef = {comp1.EmitToImageReference()}
 
-            Dim comp4 = CreateCompilation(source0 + source2, targetFramework:=TargetFramework.Mscorlib46, options:=TestOptions.DebugExe)
+            Dim comp4 = CreateCompilation(source0 + source2, targetFramework:=TargetFramework.Mscorlib40, options:=TestOptions.DebugExe)
             CompileAndVerify(comp4, expectedOutput:="123")
 
-            Dim comp5 = CreateCompilation(source2, targetFramework:=TargetFramework.Mscorlib46, options:=TestOptions.DebugExe, references:=comp1Ref)
+            Dim comp5 = CreateCompilation(source2, targetFramework:=TargetFramework.Mscorlib40, options:=TestOptions.DebugExe, references:=comp1Ref)
             CompileAndVerify(comp5, expectedOutput:="123")
+            verifyField(comp5)
 
-            Dim comp6 = CreateCompilation(source2, targetFramework:=TargetFramework.Mscorlib46, options:=TestOptions.DebugExe, references:=comp1ImageRef)
+            Dim comp6 = CreateCompilation(source2, targetFramework:=TargetFramework.Mscorlib40, options:=TestOptions.DebugExe, references:=comp1ImageRef)
             CompileAndVerify(comp6, expectedOutput:="123")
+            verifyField(comp6)
+
+            Dim comp7 = CreateCompilation(source2, targetFramework:=TargetFramework.Mscorlib46, options:=TestOptions.DebugExe, references:=comp1Ref)
+            CompileAndVerify(comp7, expectedOutput:="123")
+            verifyField(comp7)
+        End Sub
+
+        <Fact>
+        <WorkItem(43524, "https://github.com/dotnet/roslyn/issues/43524")>
+        <WorkItem(1095184, "https://devdiv.visualstudio.com/DevDiv/_workitems/edit/1095184")>
+        Public Sub CustomFields_03()
+            Dim source0 = "
+namespace System
+    public structure ValueTuple
+        public shared readonly F1 As Integer = 4
+
+        public Shared Function CombineHashCodes(h1 As Integer, h2 As Integer) As Integer
+            return F1 + h1 + h2
+        End Function
+    End Structure
+End Namespace
+"
+
+            Dim source1 = "
+class Program
+    shared sub Main()
+        System.Console.WriteLine(System.ValueTuple.CombineHashCodes(2, 3))
+    End Sub
+End Class
+"
+
+            Dim source2 = "
+class Program
+    public shared Sub Main()
+        System.Console.WriteLine(System.ValueTuple.F1 + 2 + 3)
+    End Sub
+End Class
+"
+
+            Dim verifyField = Sub(comp As VisualBasicCompilation)
+                                  Dim field = comp.GetMember(Of FieldSymbol)("System.ValueTuple.F1")
+                                  Assert.Null(field.TupleUnderlyingField)
+                                  Dim toEmit = field.ContainingType.GetFieldsToEmit().Single()
+                                  Assert.Same(field, toEmit)
+                              End Sub
+
+            Dim comp1 = CreateCompilation(source0 + source1, targetFramework:=TargetFramework.Mscorlib40, options:=TestOptions.DebugExe)
+            CompileAndVerify(comp1, expectedOutput:="9")
+            verifyField(comp1)
+
+            Dim comp1Ref = {comp1.ToMetadataReference()}
+            Dim comp1ImageRef = {comp1.EmitToImageReference()}
+
+            Dim comp4 = CreateCompilation(source0 + source2, targetFramework:=TargetFramework.Mscorlib40, options:=TestOptions.DebugExe)
+            CompileAndVerify(comp4, expectedOutput:="9")
+
+            Dim comp5 = CreateCompilation(source2, targetFramework:=TargetFramework.Mscorlib40, options:=TestOptions.DebugExe, references:=comp1Ref)
+            CompileAndVerify(comp5, expectedOutput:="9")
+            verifyField(comp5)
+
+            Dim comp6 = CreateCompilation(source2, targetFramework:=TargetFramework.Mscorlib40, options:=TestOptions.DebugExe, references:=comp1ImageRef)
+            CompileAndVerify(comp6, expectedOutput:="9")
+            verifyField(comp6)
+
+            Dim comp7 = CreateCompilation(source2, targetFramework:=TargetFramework.Mscorlib46, options:=TestOptions.DebugExe, references:=comp1Ref)
+            CompileAndVerify(comp7, expectedOutput:="9")
+            verifyField(comp7)
+        End Sub
+
+        <Fact>
+        <WorkItem(43524, "https://github.com/dotnet/roslyn/issues/43524")>
+        <WorkItem(1095184, "https://devdiv.visualstudio.com/DevDiv/_workitems/edit/1095184")>
+        Public Sub CustomFields_04()
+            Dim source0 = "
+namespace System
+    public structure ValueTuple
+        public F1 as Integer
+
+        public Function CombineHashCodes(h1 as Integer, h2 as Integer)  as Integer
+            return F1 + h1 + h2
+        End Function
+    End Structure
+End Namespace
+"
+
+            Dim source1 = "
+class Program
+    shared sub Main()
+        Dim tuple as System.ValueTuple = Nothing
+        tuple.F1 = 4
+        System.Console.WriteLine(tuple.CombineHashCodes(2, 3))
+    End Sub
+End Class
+"
+
+            Dim source2 = "
+class Program
+    public shared Sub Main()
+        Dim tuple as System.ValueTuple = Nothing
+        tuple.F1 = 4
+        System.Console.WriteLine(tuple.F1 + 2 + 3)
+    End Sub
+End Class
+"
+
+            Dim verifyField = Sub(comp As VisualBasicCompilation)
+                                  Dim field = comp.GetMember(Of FieldSymbol)("System.ValueTuple.F1")
+                                  Assert.Null(field.TupleUnderlyingField)
+                                  Dim toEmit = field.ContainingType.GetFieldsToEmit().Single()
+                                  Assert.Same(field, toEmit)
+                              End Sub
+
+            Dim comp1 = CreateCompilation(source0 + source1, targetFramework:=TargetFramework.Mscorlib40, options:=TestOptions.DebugExe)
+            CompileAndVerify(comp1, expectedOutput:="9")
+            verifyField(comp1)
+
+            Dim comp1Ref = {comp1.ToMetadataReference()}
+            Dim comp1ImageRef = {comp1.EmitToImageReference()}
+
+            Dim comp4 = CreateCompilation(source0 + source2, targetFramework:=TargetFramework.Mscorlib40, options:=TestOptions.DebugExe)
+            CompileAndVerify(comp4, expectedOutput:="9")
+
+            Dim comp5 = CreateCompilation(source2, targetFramework:=TargetFramework.Mscorlib40, options:=TestOptions.DebugExe, references:=comp1Ref)
+            CompileAndVerify(comp5, expectedOutput:="9")
+            verifyField(comp5)
+
+            Dim comp6 = CreateCompilation(source2, targetFramework:=TargetFramework.Mscorlib40, options:=TestOptions.DebugExe, references:=comp1ImageRef)
+            CompileAndVerify(comp6, expectedOutput:="9")
+            verifyField(comp6)
+
+            Dim comp7 = CreateCompilation(source2, targetFramework:=TargetFramework.Mscorlib46, options:=TestOptions.DebugExe, references:=comp1Ref)
+            CompileAndVerify(comp7, expectedOutput:="9")
+            verifyField(comp7)
         End Sub
 
         <Fact>