[mcs] Constrain expression bodied accessors to C# 7 (#9547)

* [mcs] Expression body for accessors are a C# 7 feature

* [mcs] Add tests for constraining expression accessors to C# 7

3 files changed, 43 insertions, 0 deletions

diff --git a/mcs/errors/cs1644-64.cs b/mcs/errors/cs1644-64.cs
new file mode 100644
index 00000000000..88917a0a5d5
--- /dev/null
+++ b/mcs/errors/cs1644-64.cs
@@ -0,0 +1,13 @@
+// CS1644: Feature `expression body property accessor' cannot be used because it is not part of the C# 6.0 language specification 
+// Line: 11
+// Compiler options: -langversion:6
+
+using System;
+
+class C
+{
+	public int Integer
+	{
+		get => 0;
+	}
+}
\ No newline at end of file
diff --git a/mcs/errors/cs1644-65.cs b/mcs/errors/cs1644-65.cs
new file mode 100644
index 00000000000..dea648b7846
--- /dev/null
+++ b/mcs/errors/cs1644-65.cs
@@ -0,0 +1,13 @@
+// CS1644: Feature `expression body property accessor' cannot be used because it is not part of the C# 6.0 language specification 
+// Line: 11
+// Compiler options: -langversion:6
+
+using System;
+
+class C
+{
+	public int this[int i]
+	{
+		get => i;
+	}
+}
\ No newline at end of file
diff --git a/mcs/errors/cs1644-66.cs b/mcs/errors/cs1644-66.cs
new file mode 100644
index 00000000000..3f393b50d30
--- /dev/null
+++ b/mcs/errors/cs1644-66.cs
@@ -0,0 +1,17 @@
+// CS1644: Feature `expression body event accessor' cannot be used because it is not part of the C# 6.0 language specification 
+// Line: 11
+// Compiler options: -langversion:6
+
+using System;
+
+class C
+{
+	public event EventHandler Event
+	{
+		add => Ignore ();
+	}
+
+	static void Ignore ()
+	{
+	}
+}
\ No newline at end of file