From: Marek Safar <marek.safar@gmail.com>
Date: Wed, 4 Jun 2014 09:24:34 +0000 (+0200)
Subject: [mcs] null coalescing operator cannot reduce constants
X-Git-Url: http://wien.tomnetworks.com/gitweb/?a=commitdiff_plain;h=92e321f26f21b690d3fb965f6e0e70584f643711;p=mono.git

[mcs] null coalescing operator cannot reduce constants
---

diff --git a/mcs/errors/cs0133-6.cs b/mcs/errors/cs0133-6.cs
new file mode 100644
index 00000000000..a523169cdbd
--- /dev/null
+++ b/mcs/errors/cs0133-6.cs
@@ -0,0 +1,10 @@
+// CS0133: The expression being assigned to `o' must be constant
+// Line: 8
+
+class X
+{
+	void Foo ()
+	{
+		const object o = "" ?? null;
+	}
+}
\ No newline at end of file
diff --git a/mcs/errors/cs0133-7.cs b/mcs/errors/cs0133-7.cs
new file mode 100644
index 00000000000..10d82d9fe5e
--- /dev/null
+++ b/mcs/errors/cs0133-7.cs
@@ -0,0 +1,10 @@
+// CS0133: The expression being assigned to `o' must be constant
+// Line: 8
+
+class X
+{
+	void Foo ()
+	{
+		const object o = null ?? "";
+	}
+}
\ No newline at end of file
diff --git a/mcs/mcs/nullable.cs b/mcs/mcs/nullable.cs
index 5f1822d0070..a0ace60b4e7 100644
--- a/mcs/mcs/nullable.cs
+++ b/mcs/mcs/nullable.cs
@@ -1158,26 +1158,25 @@ namespace Mono.CSharp.Nullable
 					//
 					Constant lc = left as Constant;
 					if (lc != null && !lc.IsDefaultValue)
-						return ReducedExpression.Create (lc, this);
+						return ReducedExpression.Create (lc, this, false);
 
 					//
 					// Reduce (left ?? null) to left OR (null-constant ?? right) to right
 					//
-					if (right.IsNull || lc != null)
-						return ReducedExpression.Create (lc != null ? right : left, this);
+					if (right.IsNull || lc != null) {
+						//
+						// Special case null ?? null
+						//
+						if (right.IsNull && ltype == right.Type)
+							return null;
+
+						return ReducedExpression.Create (lc != null ? right : left, this, false);
+					}
 
 					right = Convert.ImplicitConversion (ec, right, ltype, loc);
 					type = ltype;
 					return this;
 				}
-
-				//
-				// Special case null ?? null
-				//
-				if (ltype == right.Type) {
-					type = ltype;
-					return this;
-				}
 			} else {
 				return null;
 			}
@@ -1190,7 +1189,7 @@ namespace Mono.CSharp.Nullable
 			// Reduce (null ?? right) to right
 			//
 			if (left.IsNull)
-				return ReducedExpression.Create (right, this).Resolve (ec);
+				return ReducedExpression.Create (right, this, false).Resolve (ec);
 
 			left = Convert.ImplicitConversion (ec, unwrap ?? left, rtype, loc);
 			type = rtype;