reporting node rendering errors using reference to node’s token

Sources/Node.swift

@@ -3,18 +3,38 @@ import Foundation
 public protocol NodeType {
   /// Render the node in the given context
   func render(_ context:Context) throws -> String
+  
+  /// Reference to this node's token
+  var token: Token? { get }
 }
 
 
 /// Render the collection of nodes in the given context
 public func renderNodes(_ nodes:[NodeType], _ context:Context) throws -> String {
-  return try nodes.map { try $0.render(context) }.joined(separator: "")
+  return try nodes.map({
+    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
+      } else {
+        throw error
+      }
+    }
+  }).joined(separator: "")
 }
 
 public class SimpleNode : NodeType {
   public let handler:(Context) throws -> String
+  public let token: Token?
 
-  public init(handler: @escaping (Context) throws -> String) {
+  public init(token: Token, handler: @escaping (Context) throws -> String) {
+    self.token = token
     self.handler = handler
   }
 
@@ -26,9 +46,11 @@ public class SimpleNode : NodeType {
 
 public class TextNode : NodeType {
   public let text:String
+  public let token: Token?
 
   public init(text:String) {
     self.text = text
+    self.token = nil
   }
 
   public func render(_ context:Context) throws -> String {
@@ -44,13 +66,16 @@ public protocol Resolvable {
 
 public class VariableNode : NodeType {
   public let variable: Resolvable
+  public var token: Token?
 
-  public init(variable: Resolvable) {
+  public init(variable: Resolvable, token: Token? = nil) {
     self.variable = variable
+    self.token = token
   }
 
-  public init(variable: String) {
+  public init(variable: String, token: Token? = nil) {
     self.variable = Variable(variable)
+    self.token = token
   }
 
   public func render(_ context: Context) throws -> String {