From d4a180c413db7090e70527b00af348608e61b24d Mon Sep 17 00:00:00 2001
From: Jeremy Ashkenas <jashkenas@gmail.com>
Date: Thu, 18 Feb 2010 20:09:41 -0500
Subject: [PATCH] carefully categorizing JS keywords from JS reserved words
 from Coffee keywords, so that we can throw syntax errors at compile time if
 JS keywords are getting assigned to.

---
 lib/lexer.js     | 18 +++++++++++++++---
 src/lexer.coffee | 33 ++++++++++++++++++++++++---------
 2 files changed, 39 insertions(+), 12 deletions(-)

diff --git a/lib/lexer.js b/lib/lexer.js
index 2262216f..87fb6e00 100644
--- a/lib/lexer.js
+++ b/lib/lexer.js
@@ -1,5 +1,5 @@
 (function(){
-  var ACCESSORS, ASSIGNMENT, BEFORE_WHEN, CALLABLE, CODE, COMMENT, COMMENT_CLEANER, HEREDOC, HEREDOC_INDENT, IDENTIFIER, JS, JS_CLEANER, KEYWORDS, LAST_DENT, LAST_DENTS, MULTILINER, MULTI_DENT, NOT_REGEX, NO_NEWLINE, NUMBER, OPERATOR, REGEX, RESERVED, Rewriter, STRING, STRING_NEWLINES, WHITESPACE, lex;
+  var ACCESSORS, ASSIGNMENT, BEFORE_WHEN, CALLABLE, CODE, COFFEE_KEYWORDS, COMMENT, COMMENT_CLEANER, HEREDOC, HEREDOC_INDENT, IDENTIFIER, JS, JS_CLEANER, JS_FORBIDDEN, JS_KEYWORDS, KEYWORDS, LAST_DENT, LAST_DENTS, MULTILINER, MULTI_DENT, NOT_REGEX, NO_NEWLINE, NUMBER, OPERATOR, REGEX, RESERVED, Rewriter, STRING, STRING_NEWLINES, WHITESPACE, lex;
   if ((typeof process !== "undefined" && process !== null)) {
     Rewriter = require('./rewriter').Rewriter;
   } else {
@@ -11,11 +11,17 @@
   // pushing some extra smarts into the Lexer.
   exports.Lexer = (lex = function lex() {  });
   // Constants ============================================================
+  // Keywords that CoffeScript shares in common with JS.
+  JS_KEYWORDS = ["if", "else", "true", "false", "new", "return", "try", "catch", "finally", "throw", "break", "continue", "for", "in", "while", "delete", "instanceof", "typeof", "switch", "super", "extends"];
+  // CoffeeScript-only keywords -- which we're more relaxed about allowing.
+  COFFEE_KEYWORDS = ["then", "unless", "yes", "no", "on", "off", "and", "or", "is", "isnt", "not", "of", "by", "where", "when"];
   // The list of keywords passed verbatim to the parser.
-  KEYWORDS = ["if", "else", "then", "unless", "true", "false", "yes", "no", "on", "off", "and", "or", "is", "isnt", "not", "new", "return", "try", "catch", "finally", "throw", "break", "continue", "for", "in", "of", "by", "where", "while", "delete", "instanceof", "typeof", "switch", "when", "super", "extends"];
+  KEYWORDS = JS_KEYWORDS.concat(COFFEE_KEYWORDS);
   // The list of keywords that are reserved by JavaScript, but not used, and aren't
   // used by CoffeeScript. Using these will throw an error at compile time.
   RESERVED = ["case", "default", "do", "function", "var", "void", "with", "class", "const", "let", "debugger", "enum", "export", "import", "native"];
+  // JavaScript keywords and reserved words together, excluding CoffeeScript ones.
+  JS_FORBIDDEN = JS_KEYWORDS.concat(RESERVED);
   // Token matching regexes. (keep the IDENTIFIER regex in sync with AssignNode.)
   IDENTIFIER = /^([a-zA-Z$_](\w|\$)*)/;
   NUMBER = /^(\b((0(x|X)[0-9a-fA-F]+)|([0-9]+(\.[0-9]+)?(e[+\-]?[0-9]+)?)))\b/i;
@@ -286,7 +292,13 @@
       this.tag_parameters();
     }
     value = value || this.chunk.substr(0, 1);
-    tag = value.match(ASSIGNMENT) ? 'ASSIGN' : value;
+    tag = value;
+    if (value.match(ASSIGNMENT)) {
+      tag = 'ASSIGN';
+      if (JS_FORBIDDEN.indexOf(this.value()) >= 0) {
+        throw new Error('SyntaxError: Reserved word "' + this.value() + '" on line ' + this.line + ' can\'t be assigned');
+      }
+    }
     if (value === ';') {
       tag = 'TERMINATOR';
     }
diff --git a/src/lexer.coffee b/src/lexer.coffee
index ab45c4cb..ef80a8d5 100644
--- a/src/lexer.coffee
+++ b/src/lexer.coffee
@@ -11,20 +11,29 @@ exports.Lexer: lex: ->
 
 # Constants ============================================================
 
-# The list of keywords passed verbatim to the parser.
-KEYWORDS: [
-  "if", "else", "then", "unless",
-  "true", "false", "yes", "no", "on", "off",
-  "and", "or", "is", "isnt", "not",
+# Keywords that CoffeScript shares in common with JS.
+JS_KEYWORDS: [
+  "if", "else",
+  "true", "false",
   "new", "return",
   "try", "catch", "finally", "throw",
   "break", "continue",
-  "for", "in", "of", "by", "where", "while",
+  "for", "in", "while",
   "delete", "instanceof", "typeof",
-  "switch", "when",
-  "super", "extends"
+  "switch", "super", "extends"
 ]
 
+# CoffeeScript-only keywords -- which we're more relaxed about allowing.
+COFFEE_KEYWORDS: [
+  "then", "unless",
+  "yes", "no", "on", "off",
+  "and", "or", "is", "isnt", "not",
+  "of", "by", "where", "when"
+]
+
+# The list of keywords passed verbatim to the parser.
+KEYWORDS: JS_KEYWORDS.concat COFFEE_KEYWORDS
+
 # The list of keywords that are reserved by JavaScript, but not used, and aren't
 # used by CoffeeScript. Using these will throw an error at compile time.
 RESERVED: [
@@ -32,6 +41,9 @@ RESERVED: [
   "const", "let", "debugger", "enum", "export", "import", "native"
 ]
 
+# JavaScript keywords and reserved words together, excluding CoffeeScript ones.
+JS_FORBIDDEN: JS_KEYWORDS.concat RESERVED
+
 # Token matching regexes. (keep the IDENTIFIER regex in sync with AssignNode.)
 IDENTIFIER : /^([a-zA-Z$_](\w|\$)*)/
 NUMBER     : /^(\b((0(x|X)[0-9a-fA-F]+)|([0-9]+(\.[0-9]+)?(e[+\-]?[0-9]+)?)))\b/i
@@ -233,7 +245,10 @@ lex::literal_token: ->
   value: match and match[1]
   @tag_parameters() if value and value.match(CODE)
   value ||= @chunk.substr(0, 1)
-  tag: if value.match(ASSIGNMENT) then 'ASSIGN' else value
+  tag: value
+  if value.match(ASSIGNMENT)
+    tag: 'ASSIGN'
+    throw new Error('SyntaxError: Reserved word "' + @value() + '" on line ' + @line + ' can\'t be assigned') if JS_FORBIDDEN.indexOf(@value()) >= 0
   tag: 'TERMINATOR' if value == ';'
 
   prev: @tokens[@tokens.length - 1]