Fix 367: generate proper expression for null-coalescing operators on nullable types (#369)

Author: metoule

src/DynamicExpresso.Core/Parsing/Parser.cs

@@ -249,7 +249,16 @@ private Expression ParseConditional()
 			{
 				NextToken();
 				var exprRight = ParseExpressionSegment();
-				expr = GenerateConditional(GenerateEqual(expr, ParserConstants.NullLiteralExpression), exprRight, expr, errorPos);
+				if (TypeUtils.IsNullableType(expr.Type))
+				{
+					// expr.HasValue ? expr.Value : exprRight
+					expr = GenerateConditional(GenerateGetNullableHasValue(expr), GenerateGetNullableValue(expr), exprRight, errorPos);
+				}
+				else
+				{
+					// expr == null ? exprRight : expr
+					expr = GenerateConditional(GenerateEqual(expr, ParserConstants.NullLiteralExpression), exprRight, expr, errorPos);
+				}
 			}
 			else if (_token.id == TokenId.Question)
 			{
@@ -734,6 +743,16 @@ private Expression ParsePrimary()
 			return expr;
 		}
 
+		/// <summary>
+		/// Generate a call to the HasValue property of the Nullable type */
+		/// </summary>
+		private Expression GenerateGetNullableHasValue(Expression expr)
+		{
+			if (!TypeUtils.IsNullableType(expr.Type))
+				return expr;
+			return GeneratePropertyOrFieldExpression(expr.Type, expr, _token.pos, "HasValue");
+		}
+
 		/// <summary>
 		/// Generate a call to the Value property of the Nullable type */
 		/// </summary>

test/DynamicExpresso.UnitTest/GithubIssues.cs

@@ -891,6 +891,16 @@ public void GitHub_Issue_354()
 
 			Assert.That(interpreter.Eval<Guid>("b.ReturnsGuid()"), Is.EqualTo(Guid.Empty));
 		}
+
+		[Test]
+		public void GitHub_Issue_367()
+		{
+			var interpreter = new DynamicExpresso.Interpreter();
+			interpreter.SetVariable("MyValue", null, typeof(int?));
+
+			var result = interpreter.Eval<int>("MyValue ?? 10");
+			Assert.That(result, Is.EqualTo(10));
+		}
 	}
 
 	internal static class GithubIssuesTestExtensionsMethods