Treat tuple type as a struct if underlying type is error type (#13258)

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

@@ -668,7 +668,7 @@ public override bool IsValueType
         {
             get
             {
-                return _underlyingType.IsValueType;
+                return _underlyingType.IsErrorType() || _underlyingType.IsValueType;
             }
         }
 

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

@@ -17525,20 +17525,6 @@ public struct S
                 );
         }
 
-        [Fact(Skip = "https://github.com/dotnet/roslyn/issues/13088")]
-        public void AssignNullWithMissingValueTuple()
-        {
-            var source = @"
-public struct S
-{
-    (int, int) t = null;
-}
-";
-
-            var comp = CreateCompilationWithMscorlib(source);
-            comp.VerifyDiagnostics(); // crashes
-        }
-
         [Fact]
         public void RetargetTupleErrorType()
         {
@@ -17571,5 +17557,80 @@ public class B
             Assert.False(methodM.ReturnType.IsErrorType());
             Assert.True(methodM.ReturnType.TupleUnderlyingType.IsErrorType());
         }
+
+        [Fact, WorkItem(13088, "https://github.com/dotnet/roslyn/issues/13088")]
+        public void AssignNullWithMissingValueTuple()
+        {
+            var source = @"
+public class S
+{
+    (int, int) t = null;
+}
+";
+
+            var comp = CreateCompilationWithMscorlib(source);
+            comp.VerifyDiagnostics(
+                // (4,5): error CS0518: Predefined type 'System.ValueTuple`2' is not defined or imported
+                //     (int, int) t = null;
+                Diagnostic(ErrorCode.ERR_PredefinedTypeNotFound, "(int, int)").WithArguments("System.ValueTuple`2").WithLocation(4, 5),
+                // (4,20): error CS0037: Cannot convert null to '(int, int)' because it is a non-nullable value type
+                //     (int, int) t = null;
+                Diagnostic(ErrorCode.ERR_ValueCantBeNull, "null").WithArguments("(int, int)").WithLocation(4, 20)
+                );
+        }
+
+        [Fact, WorkItem(11302, "https://github.com/dotnet/roslyn/issues/11302")]
+        public void CrashInVisitCallReceiverOnBadTupleSyntax()
+        {
+            var source1 = @"
+public static class C1
+{
+    public void M1(this int x, (int, int)))
+    {
+        System.Console.WriteLine(""M1"");
+    }
+}
+" + trivial2uple;
+
+            var source2 = @"
+public static class C2
+{
+    public void M1(this int x, (int, int)))
+    {
+        System.Console.WriteLine(""M1"");
+    }
+}
+" + trivial2uple;
+
+            var comp1 = CreateCompilationWithMscorlibAndSystemCore(source1, assemblyName: "comp1",
+                          parseOptions: TestOptions.Regular.WithTuplesFeature());
+            var comp2 = CreateCompilationWithMscorlibAndSystemCore(source2, assemblyName: "comp2",
+                          parseOptions: TestOptions.Regular.WithTuplesFeature());
+
+            var source = @"
+class C3
+{
+    public static void Main()
+    {
+        int x = 0;
+        x.M1((1, 1));
+    }
+}
+";
+
+            var comp = CreateCompilationWithMscorlib(source,
+                        references: new[] { comp1.ToMetadataReference(), comp2.ToMetadataReference() },
+                        parseOptions: TestOptions.Regular.WithTuplesFeature(),
+                        options: TestOptions.DebugExe);
+
+            comp.VerifyDiagnostics(
+                // (7,14): error CS0518: Predefined type 'System.ValueTuple`2' is not defined or imported
+                //         x.M1((1, 1));
+                Diagnostic(ErrorCode.ERR_PredefinedTypeNotFound, "(1, 1)").WithArguments("System.ValueTuple`2").WithLocation(7, 14),
+                // (7,11): error CS0121: The call is ambiguous between the following methods or properties: 'C1.M1(int, (int, int))' and 'C2.M1(int, (int, int))'
+                //         x.M1((1, 1));
+                Diagnostic(ErrorCode.ERR_AmbigCall, "M1").WithArguments("C1.M1(int, (int, int))", "C2.M1(int, (int, int))").WithLocation(7, 11)
+                );
+        }
     }
 }

src/Compilers/CSharp/Test/Semantic/Semantics/DeconstructionTests.cs

@@ -2303,5 +2303,34 @@ static void Main()
                 Diagnostic(ErrorCode.ERR_VariableUsedBeforeDeclaration, "x1").WithArguments("x1").WithLocation(6, 42)
                 );
         }
+
+        [Fact, WorkItem(13081, "https://github.com/dotnet/roslyn/issues/13081")]
+        public void GettingDiagnosticsWhenValueTupleIsMissing()
+        {
+            var source = @"
+class C1
+{
+    static void Test(int arg1, (byte, byte) arg2)
+    {
+        foreach ((int, int) e in new (int, int)[10])
+        {
+        }
+    }
+}
+";
+            var comp = CreateCompilationWithMscorlib(source);
+            comp.VerifyDiagnostics(
+                // (4,32): error CS0518: Predefined type 'System.ValueTuple`2' is not defined or imported
+                //     static void Test(int arg1, (byte, byte) arg2)
+                Diagnostic(ErrorCode.ERR_PredefinedTypeNotFound, "(byte, byte)").WithArguments("System.ValueTuple`2").WithLocation(4, 32),
+                // (6,38): error CS0518: Predefined type 'System.ValueTuple`2' is not defined or imported
+                //         foreach ((int, int) e in new (int, int)[10])
+                Diagnostic(ErrorCode.ERR_PredefinedTypeNotFound, "(int, int)").WithArguments("System.ValueTuple`2").WithLocation(6, 38),
+                // (6,18): error CS0518: Predefined type 'System.ValueTuple`2' is not defined or imported
+                //         foreach ((int, int) e in new (int, int)[10])
+                Diagnostic(ErrorCode.ERR_PredefinedTypeNotFound, "(int, int)").WithArguments("System.ValueTuple`2").WithLocation(6, 18)
+                );
+            // no crash
+        }
     }
 }

src/Compilers/CSharp/Test/Symbol/Symbols/Retargeting/NoPia.cs

@@ -1506,7 +1506,7 @@ public void TestDeconstruction()
 
             var expectedDiagnostics = new[]
             {
-                // (8,12): error CS1768: Type 'ValueTuple<T1, T2>' cannot be embedded because it has a generic argument. Consider setting the 'Embed Interop Types' property to false.
+              // (8,12): error CS1768: Type 'ValueTuple<T1, T2>' cannot be embedded because it has a generic argument. Consider setting the 'Embed Interop Types' property to false.
                 //     public (int, int) TestTuple()
                 Diagnostic(ErrorCode.ERR_GenericsUsedInNoPIAType, "(int, int)").WithArguments("System.ValueTuple<T1, T2>").WithLocation(8, 12),
                 // (4,19): error CS1768: Type 'ValueTuple<T1, T2>' cannot be embedded because it has a generic argument. Consider setting the 'Embed Interop Types' property to false.
@@ -1514,7 +1514,10 @@ public void TestDeconstruction()
                 Diagnostic(ErrorCode.ERR_GenericsUsedInNoPIAType, "ValueTuple<string, string>").WithArguments("System.ValueTuple<T1, T2>").WithLocation(4, 19),
                 // (14,16): error CS1768: Type 'ValueTuple<T1, T2>' cannot be embedded because it has a generic argument. Consider setting the 'Embed Interop Types' property to false.
                 //         return (1, 2);
-                Diagnostic(ErrorCode.ERR_GenericsUsedInNoPIAType, "(1, 2)").WithArguments("System.ValueTuple<T1, T2>").WithLocation(14, 16)
+                Diagnostic(ErrorCode.ERR_GenericsUsedInNoPIAType, "(1, 2)").WithArguments("System.ValueTuple<T1, T2>").WithLocation(14, 16),
+                // (19,9): error CS1768: Type 'ValueTuple<T1, T2>' cannot be embedded because it has a generic argument. Consider setting the 'Embed Interop Types' property to false.
+                //         (x, y) = new C();
+                Diagnostic(ErrorCode.ERR_GenericsUsedInNoPIAType, "(x, y) = new C()").WithArguments("System.ValueTuple<T1, T2>").WithLocation(19, 9)
             };
 
             var comp1 = CreateCompilationWithMscorlib(source, options: TestOptions.ReleaseDll,