Add SyntacticEntity, an interface shared by AstNode and Token.

pkg/analyzer/lib/dart/ast/token.dart

Index: pkg/analyzer/lib/dart/ast/token.dart
diff --git a/pkg/analyzer/lib/dart/ast/token.dart b/pkg/analyzer/lib/dart/ast/token.dart
index 687111a2c3a71fd5c2ad2a2864fb87cfe119bb1a..05a146bdcdb66f2118594f8cf1847b348dfb7a51 100644
--- a/pkg/analyzer/lib/dart/ast/token.dart
+++ b/pkg/analyzer/lib/dart/ast/token.dart
@@ -214,21 +214,41 @@ class Keyword {
 }
 
 /**
+ * Interface representing a syntactic entity (either a token or an AST node)
+ * which has a location and extent in the source file.
+ */
+abstract class SyntacticEntity {

[Brian Wilkerson, 2016/09/21 13:21:41]

Seems like this ought to be in a library of it's own.

+  /**
+   * Return the offset from the beginning of the file to the character after the
+   * last character of the syntactic entity.
+   */
+  int get end;
+
+  /**
+   * Return the number of characters in the syntactic entity's source range.
+   */
+  int get length;
+
+  /**
+   * Return the offset from the beginning of the file to the first character in
+   * the syntactic entity.
+   */
+  int get offset;
+}
+
+/**
  * A token that was scanned from the input. Each token knows which tokens
  * precede and follow it, acting as a link in a doubly linked list of tokens.
  *
  * Clients may not extend, implement or mix-in this class.
  */
-abstract class Token {
+abstract class Token implements SyntacticEntity {
   /**
    * Initialize a newly created token to have the given [type] and [offset].
    */
   factory Token(TokenType type, int offset) = SimpleToken;
 
-  /**
-   * Return the offset from the beginning of the file to the character after the
-   * last character of the token.
-   */
+  @override
   int get end;
 
   /**
@@ -254,9 +274,7 @@ abstract class Token {
    */
   Keyword get keyword;
 
-  /**
-   * Return the number of characters in the node's source range.
-   */
+  @override
   int get length;
 
   /**
@@ -269,10 +287,7 @@ abstract class Token {
    */
   Token get next;
 
-  /**
-   * Return the offset from the beginning of the file to the first character in
-   * the token.
-   */
+  @override
   int get offset;
 
   /**