Exception throwing when required, and fixes for unit tests

Upsilon/Diagnostics.cs

@@ -1,5 +1,6 @@
 using System.Collections.Generic;
 using Upsilon.BaseTypes;
+using Upsilon.Exceptions;
 using Upsilon.Parser;
 using Upsilon.Text;
 
@@ -9,10 +10,12 @@ namespace Upsilon
     {
         public SourceText ScriptString { get; }
         public readonly List<DiagnosticsMessage> Messages = new List<DiagnosticsMessage>();
+        public bool ThrowsOnError { get; }
 
-        public Diagnostics(SourceText scriptString)
+        public Diagnostics(SourceText scriptString, bool throwsOnError)
         {
             ScriptString = scriptString;
+            ThrowsOnError = throwsOnError;
         }
 
         public void Log(DiagnosticLevel level, string message, TextSpan location)
@@ -22,6 +25,12 @@ namespace Upsilon
 
         public void LogError(string message, TextSpan location)
         {
+            if (ThrowsOnError)
+            {
+                var linePos = ScriptString.GetLinePosition(location.Start);
+                var line = ScriptString.GetLine(linePos.Line);
+                throw new ParseException(message, linePos.Line, linePos.Pos, line);
+            }
             Log(DiagnosticLevel.Error, message, location);
         }