Properly handle byte-order mark column offsets at the beginnings of files.

Author: kddnewton

CHANGELOG.md

@@ -61,6 +61,7 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/) a
 - Force using braces if the block is within a `Binary` within the predicate of a loop or conditional.
 - Make sure `StringLiteral` and `StringEmbExpr` know that they can be extended by heredocs.
 - Ensure `Int` nodes with preceding unary `+` get formatted properly.
+- Properly handle byte-order mark column offsets at the beginnings of files.
 
 ### Removed
 

lib/syntax_tree.rb

@@ -48,8 +48,11 @@ def initialize(start, line)
       end
     end
 
+    # Technically it's possible for the column index to be a negative value if
+    # there's a BOM at the beginning of the file, which is the reason we need to
+    # compare it to 0 here.
     def [](byteindex)
-      @indices[byteindex]
+      @indices[byteindex < 0 ? 0 : byteindex]
     end
   end