Simple access of actual tuple fields.

src/Compilers/CSharp/Portable/Binder/Semantics/AccessCheck.cs

@@ -224,6 +224,11 @@ private static bool IsNamedTypeAccessible(NamedTypeSymbol type, Symbol within, r
 
             failedThroughTypeCheck = false;
 
+            // for tuples consider the underlying type as a true container for visibility puroposes.
+            containingType = 
+                (containingType as TupleTypeSymbol)?.UnderlyingTupleType ?? 
+                containingType;
+
             // easy case - members of containing type are accessible.
             if ((object)containingType == (object)within)
             {

src/Compilers/CSharp/Portable/Lowering/LocalRewriter/LocalRewriter_Field.cs

@@ -12,7 +12,11 @@ public override BoundNode VisitFieldAccess(BoundFieldAccess node)
         {
             BoundExpression rewrittenReceiver = VisitExpression(node.ReceiverOpt);
 
-            return MakeFieldAccess(node.Syntax, rewrittenReceiver, node.FieldSymbol, node.ConstantValue, node.ResultKind, node.Type, node);
+            // field access of a tuple actually accesses the underlying field.
+            FieldSymbol field = (node.FieldSymbol as TupleFieldSymbol)?.UnderlyingTypleFieldSymbol ??
+                                node.FieldSymbol;
+
+            return MakeFieldAccess(node.Syntax, rewrittenReceiver, field, node.ConstantValue, node.ResultKind, node.Type, node);
         }
 
         private static BoundExpression MakeFieldAccess(

src/Compilers/CSharp/Portable/Symbols/TupleTypeSymbol.cs

@@ -560,10 +560,26 @@ internal sealed class TupleFieldSymbol : FieldSymbol
         /// </summary>
         public TupleFieldSymbol(string name, TupleTypeSymbol containingTuple, TypeSymbol type, FieldSymbol underlyingFieldOpt)
         {
-            this._name = name;
-            this._containingTuple = containingTuple;
-            this._type = type;
-            this._underlyingFieldOpt = underlyingFieldOpt;
+            _name = name;
+            _containingTuple = containingTuple;
+            _type = type;
+            _underlyingFieldOpt = underlyingFieldOpt;
+        }
+
+        public FieldSymbol UnderlyingTypleFieldSymbol
+        {
+            get
+            {
+                return _underlyingFieldOpt;
+            }
+        }
+
+        public override string Name
+        {
+            get
+            {
+                return _name;
+            }
         }
 
         public override Symbol AssociatedSymbol

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

@@ -162,6 +162,152 @@ .maxstack  3
 ");
         }
 
+        [Fact]
+        public void TupleUnderlyingItemAccess01()
+        {
+            var source = @"
+class C
+{
+    static void Main()
+    {
+        var x = (a: 1, b: 2);
+        System.Console.WriteLine(x.Item2.ToString());
+        x.Item1 = 40;
+        System.Console.WriteLine(x.Item1 + x.Item2);
+    }
+}
+" + trivial2uple;
+
+            var comp = CompileAndVerify(source, expectedOutput: @"2
+42");
+            comp.VerifyDiagnostics();
+            comp.VerifyIL("C.Main", @"
+{
+  // Code size       54 (0x36)
+  .maxstack  3
+  .locals init (System.Runtime.CompilerServices.ValueTuple<int, int> V_0) //x
+  IL_0000:  ldloca.s   V_0
+  IL_0002:  ldc.i4.1
+  IL_0003:  ldc.i4.2
+  IL_0004:  call       ""System.Runtime.CompilerServices.ValueTuple<int, int>..ctor(int, int)""
+  IL_0009:  ldloca.s   V_0
+  IL_000b:  ldflda     ""int System.Runtime.CompilerServices.ValueTuple<int, int>.Item2""
+  IL_0010:  call       ""string int.ToString()""
+  IL_0015:  call       ""void System.Console.WriteLine(string)""
+  IL_001a:  ldloca.s   V_0
+  IL_001c:  ldc.i4.s   40
+  IL_001e:  stfld      ""int System.Runtime.CompilerServices.ValueTuple<int, int>.Item1""
+  IL_0023:  ldloc.0
+  IL_0024:  ldfld      ""int System.Runtime.CompilerServices.ValueTuple<int, int>.Item1""
+  IL_0029:  ldloc.0
+  IL_002a:  ldfld      ""int System.Runtime.CompilerServices.ValueTuple<int, int>.Item2""
+  IL_002f:  add
+  IL_0030:  call       ""void System.Console.WriteLine(int)""
+  IL_0035:  ret
+}
+");
+        }
+
+        [Fact]
+        public void TupleItemAccess()
+        {
+            var source = @"
+class C
+{
+    static void Main()
+    {
+        var x = (a: 1, b: 2);
+        System.Console.WriteLine(x.b.ToString());
+        x.a = 40;
+        System.Console.WriteLine(x.a + x.b);
+    }
+}
+" + trivial2uple;
+
+            var comp = CompileAndVerify(source, expectedOutput: @"2
+42");
+            comp.VerifyDiagnostics();
+            comp.VerifyIL("C.Main", @"
+{
+  // Code size       54 (0x36)
+  .maxstack  3
+  .locals init (System.Runtime.CompilerServices.ValueTuple<int, int> V_0) //x
+  IL_0000:  ldloca.s   V_0
+  IL_0002:  ldc.i4.1
+  IL_0003:  ldc.i4.2
+  IL_0004:  call       ""System.Runtime.CompilerServices.ValueTuple<int, int>..ctor(int, int)""
+  IL_0009:  ldloca.s   V_0
+  IL_000b:  ldflda     ""int System.Runtime.CompilerServices.ValueTuple<int, int>.Item2""
+  IL_0010:  call       ""string int.ToString()""
+  IL_0015:  call       ""void System.Console.WriteLine(string)""
+  IL_001a:  ldloca.s   V_0
+  IL_001c:  ldc.i4.s   40
+  IL_001e:  stfld      ""int System.Runtime.CompilerServices.ValueTuple<int, int>.Item1""
+  IL_0023:  ldloc.0
+  IL_0024:  ldfld      ""int System.Runtime.CompilerServices.ValueTuple<int, int>.Item1""
+  IL_0029:  ldloc.0
+  IL_002a:  ldfld      ""int System.Runtime.CompilerServices.ValueTuple<int, int>.Item2""
+  IL_002f:  add
+  IL_0030:  call       ""void System.Console.WriteLine(int)""
+  IL_0035:  ret
+}
+");
+        }
+
+        [Fact]
+        public void TupleItemAccess01()
+        {
+            var source = @"
+class C
+{
+    static void Main()
+    {
+        var x = (a: 1, b: (c: 2, d: 3));
+        System.Console.WriteLine(x.b.c.ToString());
+        x.b.d = 39;
+        System.Console.WriteLine(x.a + x.b.c + x.b.d);
+    }
+}
+" + trivial2uple;
+
+            var comp = CompileAndVerify(source, expectedOutput: @"2
+42");
+            comp.VerifyDiagnostics();
+            comp.VerifyIL("C.Main", @"
+{
+  // Code size       87 (0x57)
+  .maxstack  4
+  .locals init (System.Runtime.CompilerServices.ValueTuple<int, > V_0) //x
+  IL_0000:  ldloca.s   V_0
+  IL_0002:  ldc.i4.1
+  IL_0003:  ldc.i4.2
+  IL_0004:  ldc.i4.3
+  IL_0005:  newobj     ""System.Runtime.CompilerServices.ValueTuple<int, int>..ctor(int, int)""
+  IL_000a:  call       ""System.Runtime.CompilerServices.ValueTuple<int, >..ctor(int, )""
+  IL_000f:  ldloca.s   V_0
+  IL_0011:  ldflda     "" System.Runtime.CompilerServices.ValueTuple<int, >.Item2""
+  IL_0016:  ldflda     ""int System.Runtime.CompilerServices.ValueTuple<int, int>.Item1""
+  IL_001b:  call       ""string int.ToString()""
+  IL_0020:  call       ""void System.Console.WriteLine(string)""
+  IL_0025:  ldloca.s   V_0
+  IL_0027:  ldflda     "" System.Runtime.CompilerServices.ValueTuple<int, >.Item2""
+  IL_002c:  ldc.i4.s   39
+  IL_002e:  stfld      ""int System.Runtime.CompilerServices.ValueTuple<int, int>.Item2""
+  IL_0033:  ldloc.0
+  IL_0034:  ldfld      ""int System.Runtime.CompilerServices.ValueTuple<int, >.Item1""
+  IL_0039:  ldloc.0
+  IL_003a:  ldfld      "" System.Runtime.CompilerServices.ValueTuple<int, >.Item2""
+  IL_003f:  ldfld      ""int System.Runtime.CompilerServices.ValueTuple<int, int>.Item1""
+  IL_0044:  add
+  IL_0045:  ldloc.0
+  IL_0046:  ldfld      "" System.Runtime.CompilerServices.ValueTuple<int, >.Item2""
+  IL_004b:  ldfld      ""int System.Runtime.CompilerServices.ValueTuple<int, int>.Item2""
+  IL_0050:  add
+  IL_0051:  call       ""void System.Console.WriteLine(int)""
+  IL_0056:  ret
+}
+");
+        }
 
     }
 }