No longer try to parse a generic type if there's no possible candidat…

…es (#315)

* No longer try to parse a generic type if there's no possible generic definition candidate in the known types.
Fix #314

src/DynamicExpresso.Core/ParserArguments.cs

@@ -5,6 +5,7 @@
 using System.Linq.Expressions;
 using System.Reflection;
 using DynamicExpresso.Exceptions;
+using System.Text.RegularExpressions;
 
 namespace DynamicExpresso
 {
@@ -75,6 +76,15 @@ public bool TryGetKnownType(string name, out Type type)
 			return false;
 		}
 
+		/// <summary>
+		/// Returns true if the known types contain a generic type definition with the given name + any arity (e.g. name`1).
+		/// </summary>
+		internal bool HasKnownGenericTypeDefinition(string name)
+		{
+			var regex = new Regex("^" + name + "`\\d+$");
+			return Settings.KnownTypes.Values.Any(refType => regex.IsMatch(refType.Name) && refType.Type.IsGenericTypeDefinition);
+		}
+
 		public bool TryGetIdentifier(string name, out Expression expression)
 		{
 			Identifier identifier;

src/DynamicExpresso.Core/Parsing/Parser.cs

@@ -1399,9 +1399,14 @@ private bool TryParseKnownType(string name, out Type type)
 		{
 			// if the type is unknown, we need to restart parsing 
 			var originalPos = _token.pos;
-			_arguments.TryGetKnownType(name, out type);
 
-			type = ParseKnownGenericType(name, type);
+			// the name might reference a generic type, with an aliased name (e.g. List<T> = MyList instead of List`1)
+			// it can also reference a generic type for which we don't know the arity yet (and therefore the name doesn't contain the `n suffix)
+			if (_arguments.TryGetKnownType(name, out type) || _arguments.HasKnownGenericTypeDefinition(name))
+			{
+				type = ParseKnownGenericType(name, type);
+			}
+
 			type = ParseTypeModifiers(type);
 
 			if (type == null)

test/DynamicExpresso.UnitTest/GithubIssues.cs

@@ -836,6 +836,18 @@ public void GitHub_Issue_311()
 			// It works if we cast to int
 			Assert.AreEqual("AA", interpreter2.Eval("a.Substring((int)0, (int)2)"));
 		}
+
+		[Test]
+		public void GitHub_Issue_314()
+		{
+			var interpreter = new Interpreter();
+
+			var exception1 = Assert.Throws<UnknownIdentifierException>(() => interpreter.Eval("b < 1"));
+			Assert.AreEqual("b", exception1.Identifier);
+
+			var exception2 = Assert.Throws<UnknownIdentifierException>(() => interpreter.Eval("b > 1"));
+			Assert.AreEqual("b", exception2.Identifier);
+		}
 	}
 
 	internal static class GithubIssuesTestExtensionsMethods