From b05dad9f314b48f86516f9833d40c3ef6f1e9a7d Mon Sep 17 00:00:00 2001
From: Marek Safar <marek.safar@gmail.com>
Date: Fri, 29 Dec 2017 23:38:40 +0100
Subject: [PATCH] readonly struct this can be reassigned within ctor

---
 mcs/mcs/expression.cs         |  2 +-
 mcs/tests/test-readonly-03.cs | 16 ++++++++++++++++
 mcs/tests/ver-il-net_4_x.xml  | 13 +++++++++++++
 3 files changed, 30 insertions(+), 1 deletion(-)
 create mode 100644 mcs/tests/test-readonly-03.cs

diff --git a/mcs/mcs/expression.cs b/mcs/mcs/expression.cs
index 51f268737c0..183be4d8cb3 100644
--- a/mcs/mcs/expression.cs
+++ b/mcs/mcs/expression.cs
@@ -9059,7 +9059,7 @@ namespace Mono.CSharp
 			if (eclass == ExprClass.Unresolved)
 				ResolveBase (ec);
 
-			if (type.IsClass || type.IsReadOnly) {
+			if (type.IsClass || (type.IsReadOnly && !ec.HasSet (ResolveContext.Options.ConstructorScope))) {
 				if (right_side == EmptyExpression.UnaryAddress)
 					ec.Report.Error (459, loc, "Cannot take the address of `this' because it is read-only");
 				else if (right_side == EmptyExpression.OutAccess)
diff --git a/mcs/tests/test-readonly-03.cs b/mcs/tests/test-readonly-03.cs
new file mode 100644
index 00000000000..14cb958b41a
--- /dev/null
+++ b/mcs/tests/test-readonly-03.cs
@@ -0,0 +1,16 @@
+// Compiler options: -langversion:latest
+using System;
+
+readonly struct S
+{
+	static S shared = new S ();
+
+	public S (int arg)
+	{
+		this = shared;
+	}
+
+	public static void Main ()
+	{
+	}
+}
\ No newline at end of file
diff --git a/mcs/tests/ver-il-net_4_x.xml b/mcs/tests/ver-il-net_4_x.xml
index 4e488c37bc4..c8010844ece 100644
--- a/mcs/tests/ver-il-net_4_x.xml
+++ b/mcs/tests/ver-il-net_4_x.xml
@@ -72889,6 +72889,19 @@
       </method>
     </type>
   </test>
+  <test name="test-readonly-03.cs">
+    <type name="S">
+      <method name="Void Main()" attrs="150">
+        <size>2</size>
+      </method>
+      <method name="Void .ctor(Int32)" attrs="6278">
+        <size>13</size>
+      </method>
+      <method name="Void .cctor()" attrs="6289">
+        <size>15</size>
+      </method>
+    </type>
+  </test>
   <test name="test-ref-01.cs">
     <type name="X">
       <method name="Void Main()" attrs="150">
-- 
2.11.4.GIT