unified setting higlighting range for errors

Sources/Errors.swift

@@ -32,18 +32,15 @@ public struct TemplateSyntaxError : Error, Equatable, CustomStringConvertible {
   }
   
   static func description(reason: String, lexeme: Lexeme?, template: Template?) -> String {
-    if let template = template, let range = lexeme?.range {
-      let templateName = template.name.map({ "\($0):" }) ?? ""
-      let tokenContent = template.templateString.substring(with: range)
-      let line = template.templateString.rangeLine(range)
-      let highlight = "\(String(Array(repeating: " ", count: line.offset)))^\(String(Array(repeating: "~", count: max(tokenContent.length - 1, 0))))"
-      
-      return "\(templateName)\(line.number):\(line.offset): error: \(reason)\n"
-        + "\(line.content)\n"
-        + "\(highlight)\n"
-    } else {
-      return reason
-    }
+    guard let template = template, let lexeme = lexeme else { return reason }
+    let templateName = template.name.map({ "\($0):" }) ?? ""
+    let range = template.templateString.range(of: lexeme.contents, range: lexeme.range) ?? lexeme.range
+    let line = template.templateString.rangeLine(range)
+    let highlight = "\(String(Array(repeating: " ", count: line.offset)))^\(String(Array(repeating: "~", count: max(lexeme.contents.length - 1, 0))))"
+
+    return "\(templateName)\(line.number):\(line.offset): error: \(reason)\n"
+      + "\(line.content)\n"
+      + "\(highlight)\n"
   }
 
   init(reason: String, lexeme: Lexeme? = nil, template: Template? = nil, parentError: Error? = nil) {

Sources/Lexer.swift

@@ -77,6 +77,7 @@ struct Lexer {
 }
 
 protocol Lexeme {
+  var contents: String { get }
   var range: Range<String.Index> { get }
 }
 

Sources/Node.swift

@@ -15,13 +15,9 @@ public func renderNodes(_ nodes:[NodeType], _ context:Context) throws -> String
     do {
       return try $0.render(context)
     } catch {
-      if var syntaxError = error as? TemplateSyntaxError, syntaxError.lexeme == nil, let token = $0.token {
-        if let contentsRange = context.environment.template?.templateString.range(of: token.contents, range: token.range) {
-          syntaxError.lexeme = Token.block(value: token.contents, at: contentsRange)
-        } else {
-          syntaxError.lexeme = token
-        }
-        throw syntaxError
+      if var error = error as? TemplateSyntaxError {
+        error.lexeme = error.lexeme ?? $0.token
+        throw error
       } else {
         throw error
       }