Perf improvements in tokenizer

compiler/NubLang/Code/SourceSpan.cs

@@ -2,34 +2,33 @@ namespace NubLang.Code;
 
 public readonly struct SourceSpan : IEquatable<SourceSpan>, IComparable<SourceSpan>
 {
-    public static SourceSpan Zero => new(SourceLocation.Zero, SourceLocation.Zero);
-
     public static SourceSpan Merge(params IEnumerable<SourceSpan> spans)
     {
         var spanArray = spans as SourceSpan[] ?? spans.ToArray();
-
         if (spanArray.Length == 0)
         {
-            return Zero;
+            return new SourceSpan(string.Empty, new SourceLocation(0, 0), new SourceLocation(0, 0));
         }
 
         var minStart = spanArray.Min(s => s.Start);
         var maxEnd = spanArray.Max(s => s.End);
 
-        return new SourceSpan(minStart, maxEnd);
+        return new SourceSpan(spanArray[0].FilePath, minStart, maxEnd);
     }
 
-    public SourceSpan(SourceLocation start, SourceLocation end)
+    public SourceSpan(string filePath, SourceLocation start, SourceLocation end)
     {
         if (start > end)
         {
             throw new ArgumentException("Start location cannot be after end location");
         }
 
+        FilePath = filePath;
         Start = start;
         End = end;
     }
 
+    public string FilePath { get; }
     public SourceLocation Start { get; }
     public SourceLocation End { get; }
 
@@ -37,15 +36,15 @@ public readonly struct SourceSpan : IEquatable<SourceSpan>, IComparable<SourceSp
     {
         if (Start == End)
         {
-            return $"{Start}";
+            return $"{FilePath}:{Start}";
         }
 
         if (Start.Line == End.Line)
         {
-            return Start.Column == End.Column ? $"{Start}" : $"{Start.Line}:{Start.Column}-{End.Column}";
+            return Start.Column == End.Column ? $"{FilePath}:{Start}" : $"{FilePath}:{Start.Line}:{Start.Column}-{End.Column}";
         }
 
-        return $"{Start}-{End}";
+        return $"{FilePath}:{Start}-{End}";
     }
 
     public bool Equals(SourceSpan other) => Start == other.Start && End == other.End;
@@ -54,7 +53,7 @@ public readonly struct SourceSpan : IEquatable<SourceSpan>, IComparable<SourceSp
 
     public static bool operator ==(SourceSpan left, SourceSpan right) => Equals(left, right);
     public static bool operator !=(SourceSpan left, SourceSpan right) => !Equals(left, right);
-    
+
     public static bool operator <(SourceSpan left, SourceSpan right) => left.CompareTo(right) < 0;
     public static bool operator <=(SourceSpan left, SourceSpan right) => left.CompareTo(right) <= 0;
     public static bool operator >(SourceSpan left, SourceSpan right) => left.CompareTo(right) > 0;