Unify, simplify and fixup assignment errors

- Show the same type of error message for compound assignment as for `=`
  assignment when the LHS is invalid.
- Show the same type of error message when trying to assign to a CoffeeScript
  keyword as when trying to assign to a JavaScript keyword.
- Now longer treat `&& =` as `&&=`. The same goes for `and=`, `||=` and `or=`.
- Unify the error message to: `<optional type> '<value>' can't be assigned`.

lib/coffee-script/lexer.js

@@ -1,7 +1,8 @@
 // Generated by CoffeeScript 1.10.0
 (function() {
-  var BOM, BOOL, CALLABLE, CODE, COFFEE_ALIASES, COFFEE_ALIAS_MAP, COFFEE_KEYWORDS, COMMENT, COMPARE, COMPOUND_ASSIGN, HERECOMMENT_ILLEGAL, HEREDOC_DOUBLE, HEREDOC_INDENT, HEREDOC_SINGLE, HEREGEX, HEREGEX_OMIT, IDENTIFIER, INDENTABLE_CLOSERS, INDEXABLE, INVALID_ESCAPE, INVERSES, JSTOKEN, JS_FORBIDDEN, JS_KEYWORDS, LEADING_BLANK_LINE, LINE_BREAK, LINE_CONTINUER, LOGIC, Lexer, MATH, MULTI_DENT, NOT_REGEX, NUMBER, OPERATOR, POSSIBLY_DIVISION, REGEX, REGEX_FLAGS, REGEX_ILLEGAL, RELATION, RESERVED, Rewriter, SHIFT, SIMPLE_STRING_OMIT, STRICT_PROSCRIBED, STRING_DOUBLE, STRING_OMIT, STRING_SINGLE, STRING_START, TRAILING_BLANK_LINE, TRAILING_SPACES, UNARY, UNARY_MATH, VALID_FLAGS, WHITESPACE, compact, count, invertLiterate, key, locationDataToString, ref, ref1, repeat, starts, throwSyntaxError,
+  var BOM, BOOL, CALLABLE, CODE, COFFEE_ALIASES, COFFEE_ALIAS_MAP, COFFEE_KEYWORDS, COMMENT, COMPARE, COMPOUND_ASSIGN, HERECOMMENT_ILLEGAL, HEREDOC_DOUBLE, HEREDOC_INDENT, HEREDOC_SINGLE, HEREGEX, HEREGEX_OMIT, IDENTIFIER, INDENTABLE_CLOSERS, INDEXABLE, INVALID_ESCAPE, INVERSES, JSTOKEN, JS_FORBIDDEN, JS_KEYWORDS, LEADING_BLANK_LINE, LINE_BREAK, LINE_CONTINUER, LOGIC, Lexer, MATH, MULTI_DENT, NOT_REGEX, NUMBER, OPERATOR, POSSIBLY_DIVISION, REGEX, REGEX_FLAGS, REGEX_ILLEGAL, RELATION, RESERVED, Rewriter, SHIFT, SIMPLE_STRING_OMIT, STRICT_PROSCRIBED, STRING_DOUBLE, STRING_OMIT, STRING_SINGLE, STRING_START, TRAILING_BLANK_LINE, TRAILING_SPACES, UNARY, UNARY_MATH, VALID_FLAGS, WHITESPACE, compact, count, invertLiterate, isUnassignable, key, locationDataToString, ref, ref1, repeat, starts, throwSyntaxError,
-    indexOf = [].indexOf || function(item) { for (var i = 0, l = this.length; i < l; i++) { if (i in this && this[i] === item) return i; } return -1; };
+    indexOf = [].indexOf || function(item) { for (var i = 0, l = this.length; i < l; i++) { if (i in this && this[i] === item) return i; } return -1; },
+    slice = [].slice;
 
   ref = require('./rewriter'), Rewriter = ref.Rewriter, INVERSES = ref.INVERSES;
 
@@ -495,7 +496,7 @@
     };
 
     Lexer.prototype.literalToken = function() {
-      var match, prev, ref2, ref3, ref4, ref5, ref6, tag, token, value;
+      var match, message, origin, prev, ref2, ref3, ref4, ref5, ref6, skipToken, tag, token, value;
       if (match = OPERATOR.exec(this.chunk)) {
         value = match[0];
         if (CODE.test(value)) {
@@ -506,16 +507,22 @@
       }
       tag = value;
       ref2 = this.tokens, prev = ref2[ref2.length - 1];
-      if (value === '=' && prev) {
+      if (prev && indexOf.call(['='].concat(slice.call(COMPOUND_ASSIGN)), value) >= 0) {
-        if (prev.variable && (ref3 = prev[1], indexOf.call(JS_FORBIDDEN, ref3) >= 0)) {
+        skipToken = false;
-          if (prev.origin) {
+        if (value === '=' && ((ref3 = prev[1]) === '||' || ref3 === '&&') && !prev.spaced) {
-            prev = prev.origin;
-          }
-          this.error("reserved word '" + prev[1] + "' can't be assigned", prev[2]);
-        }
-        if ((ref4 = prev[1]) === '||' || ref4 === '&&') {
           prev[0] = 'COMPOUND_ASSIGN';
           prev[1] += '=';
+          prev = this.tokens[this.tokens.length - 2];
+          skipToken = true;
+        }
+        if (prev && prev.variable) {
+          origin = (ref4 = prev.origin) != null ? ref4 : prev;
+          message = isUnassignable(prev[1], origin[1]);
+          if (message) {
+            this.error(message, origin[2]);
+          }
+        }
+        if (skipToken) {
           return value.length;
         }
       }
@@ -886,6 +893,24 @@
 
   })();
 
+  isUnassignable = function(name, displayName) {
+    if (displayName == null) {
+      displayName = name;
+    }
+    switch (false) {
+      case indexOf.call(slice.call(JS_KEYWORDS).concat(slice.call(COFFEE_KEYWORDS)), name) < 0:
+        return "keyword '" + displayName + "' can't be assigned";
+      case indexOf.call(STRICT_PROSCRIBED, name) < 0:
+        return "'" + displayName + "' can't be assigned";
+      case indexOf.call(RESERVED, name) < 0:
+        return "reserved word '" + displayName + "' can't be assigned";
+      default:
+        return false;
+    }
+  };
+
+  exports.isUnassignable = isUnassignable;
+
   JS_KEYWORDS = ['true', 'false', 'null', 'this', 'new', 'delete', 'typeof', 'in', 'instanceof', 'return', 'throw', 'break', 'continue', 'debugger', 'yield', 'if', 'else', 'switch', 'for', 'while', 'do', 'try', 'catch', 'finally', 'class', 'extends', 'super'];
 
   COFFEE_KEYWORDS = ['undefined', 'then', 'unless', 'until', 'loop', 'of', 'by', 'when'];
@@ -915,15 +940,11 @@
 
   RESERVED = ['case', 'default', 'function', 'var', 'void', 'with', 'const', 'let', 'enum', 'export', 'import', 'native', 'implements', 'interface', 'package', 'private', 'protected', 'public', 'static'];
 
-  STRICT_PROSCRIBED = ['arguments', 'eval', 'yield*'];
+  STRICT_PROSCRIBED = ['arguments', 'eval'];
 
   JS_FORBIDDEN = JS_KEYWORDS.concat(RESERVED).concat(STRICT_PROSCRIBED);
 
-  exports.RESERVED = RESERVED.concat(JS_KEYWORDS).concat(COFFEE_KEYWORDS).concat(STRICT_PROSCRIBED);
+  exports.JS_FORBIDDEN = JS_KEYWORDS.concat(RESERVED).concat(STRICT_PROSCRIBED);
-
-  exports.STRICT_PROSCRIBED = STRICT_PROSCRIBED;
-
-  exports.JS_FORBIDDEN = JS_FORBIDDEN;
 
   BOM = 65279;
 

lib/coffee-script/nodes.js

@@ -1,6 +1,6 @@
 // Generated by CoffeeScript 1.10.0
 (function() {
-  var Access, Arr, Assign, Base, Block, BooleanLiteral, Call, Class, Code, CodeFragment, Comment, Existence, Expansion, Extends, For, IdentifierLiteral, If, In, Index, InfinityLiteral, JS_FORBIDDEN, LEVEL_ACCESS, LEVEL_COND, LEVEL_LIST, LEVEL_OP, LEVEL_PAREN, LEVEL_TOP, Literal, NEGATE, NO, NullLiteral, NumberLiteral, Obj, Op, Param, Parens, PassthroughLiteral, RESERVED, Range, RegexLiteral, RegexWithInterpolations, Return, SIMPLENUM, STRICT_PROSCRIBED, Scope, Slice, Splat, StatementLiteral, StringLiteral, StringWithInterpolations, SuperCall, Switch, TAB, THIS, ThisLiteral, Throw, Try, UTILITIES, UndefinedLiteral, Value, While, YES, YieldReturn, addLocationDataFn, compact, del, ends, extend, flatten, fragmentsToText, isComplexOrAssignable, isLiteralArguments, isLiteralThis, locationDataToString, merge, multident, ref1, ref2, some, starts, throwSyntaxError, unfoldSoak, utility,
+  var Access, Arr, Assign, Base, Block, BooleanLiteral, Call, Class, Code, CodeFragment, Comment, Existence, Expansion, Extends, For, IdentifierLiteral, If, In, Index, InfinityLiteral, JS_FORBIDDEN, LEVEL_ACCESS, LEVEL_COND, LEVEL_LIST, LEVEL_OP, LEVEL_PAREN, LEVEL_TOP, Literal, NEGATE, NO, NullLiteral, NumberLiteral, Obj, Op, Param, Parens, PassthroughLiteral, Range, RegexLiteral, RegexWithInterpolations, Return, SIMPLENUM, Scope, Slice, Splat, StatementLiteral, StringLiteral, StringWithInterpolations, SuperCall, Switch, TAB, THIS, ThisLiteral, Throw, Try, UTILITIES, UndefinedLiteral, Value, While, YES, YieldReturn, addLocationDataFn, compact, del, ends, extend, flatten, fragmentsToText, isComplexOrAssignable, isLiteralArguments, isLiteralThis, isUnassignable, locationDataToString, merge, multident, ref1, ref2, some, starts, throwSyntaxError, unfoldSoak, utility,
     extend1 = function(child, parent) { for (var key in parent) { if (hasProp.call(parent, key)) child[key] = parent[key]; } function ctor() { this.constructor = child; } ctor.prototype = parent.prototype; child.prototype = new ctor(); child.__super__ = parent.prototype; return child; },
     hasProp = {}.hasOwnProperty,
     indexOf = [].indexOf || function(item) { for (var i = 0, l = this.length; i < l; i++) { if (i in this && this[i] === item) return i; } return -1; },
@@ -10,7 +10,7 @@
 
   Scope = require('./scope').Scope;
 
-  ref1 = require('./lexer'), RESERVED = ref1.RESERVED, STRICT_PROSCRIBED = ref1.STRICT_PROSCRIBED, JS_FORBIDDEN = ref1.JS_FORBIDDEN;
+  ref1 = require('./lexer'), isUnassignable = ref1.isUnassignable, JS_FORBIDDEN = ref1.JS_FORBIDDEN;
 
   ref2 = require('./helpers'), compact = ref2.compact, flatten = ref2.flatten, extend = ref2.extend, merge = ref2.merge, del = ref2.del, starts = ref2.starts, ends = ref2.ends, some = ref2.some, addLocationDataFn = ref2.addLocationDataFn, locationDataToString = ref2.locationDataToString, throwSyntaxError = ref2.throwSyntaxError;
 
@@ -608,10 +608,7 @@
       return IdentifierLiteral.__super__.constructor.apply(this, arguments);
     }
 
-    IdentifierLiteral.prototype.isAssignable = function() {
+    IdentifierLiteral.prototype.isAssignable = YES;
-      var ref3;
-      return ref3 = this.value, indexOf.call(RESERVED, ref3) < 0;
-    };
 
     return IdentifierLiteral;
 
@@ -1580,7 +1577,7 @@
     Class.prototype.defaultClassVariableName = '_Class';
 
     Class.prototype.determineName = function() {
-      var name, node, ref3, tail;
+      var message, name, node, ref3, tail;
       if (!this.variable) {
         return this.defaultClassVariableName;
       }
@@ -1590,6 +1587,12 @@
         return this.defaultClassVariableName;
       }
       name = node.value;
+      if (!tail) {
+        message = isUnassignable(name);
+        if (message) {
+          this.variable.error(message);
+        }
+      }
       if (indexOf.call(JS_FORBIDDEN, name) >= 0) {
         return "_" + name;
       } else {
@@ -1762,7 +1765,6 @@
     extend1(Assign, superClass1);
 
     function Assign(variable1, value1, context, options) {
-      var forbidden, name, ref3;
       this.variable = variable1;
       this.value = value1;
       this.context = context;
@@ -1770,10 +1772,6 @@
         options = {};
       }
       this.param = options.param, this.subpattern = options.subpattern, this.operatorToken = options.operatorToken;
-      forbidden = (ref3 = (name = this.variable.unwrapAll().value), indexOf.call(STRICT_PROSCRIBED, ref3) >= 0);
-      if (forbidden && this.context !== 'object') {
-        this.variable.error("variable name may not be \"" + name + "\"");
-      }
     }
 
     Assign.prototype.children = ['variable', 'value'];
@@ -1823,7 +1821,7 @@
       if (!this.context) {
         varBase = this.variable.unwrapAll();
         if (!varBase.isAssignable()) {
-          this.variable.error("\"" + (this.variable.compile(o)) + "\" cannot be assigned");
+          this.variable.error("'" + (this.variable.compile(o)) + "' can't be assigned");
         }
         if (!(typeof varBase.hasProperties === "function" ? varBase.hasProperties() : void 0)) {
           if (this.param) {
@@ -1854,7 +1852,7 @@
     };
 
     Assign.prototype.compilePatternMatch = function(o) {
-      var acc, assigns, code, defaultValue, expandedIdx, fragments, i, idx, isObject, ivar, j, len1, name, obj, objects, olen, ref, ref3, ref4, ref5, ref6, ref7, rest, top, val, value, vvar, vvarText;
+      var acc, assigns, code, defaultValue, expandedIdx, fragments, i, idx, isObject, ivar, j, len1, message, name, obj, objects, olen, ref, ref3, ref4, ref5, ref6, rest, top, val, value, vvar, vvarText;
       top = o.level === LEVEL_TOP;
       value = this.value;
       objects = this.variable.base.objects;
@@ -1889,8 +1887,9 @@
         acc = idx.unwrap() instanceof IdentifierLiteral;
         value = new Value(value);
         value.properties.push(new (acc ? Access : Index)(idx));
-        if (ref5 = obj.unwrap().value, indexOf.call(RESERVED, ref5) >= 0) {
+        message = isUnassignable(obj.unwrap().value);
-          obj.error("assignment to a reserved word: " + (obj.compile(o)));
+        if (message) {
+          obj.error(message);
         }
         if (defaultValue) {
           value = new Op('?', value, defaultValue);
@@ -1945,7 +1944,7 @@
           }
           defaultValue = null;
           if (obj instanceof Assign && obj.context === 'object') {
-            ref6 = obj, (ref7 = ref6.variable, idx = ref7.base), obj = ref6.value;
+            ref5 = obj, (ref6 = ref5.variable, idx = ref6.base), obj = ref5.value;
             if (obj instanceof Assign) {
               defaultValue = obj.value;
               obj = obj.variable;
@@ -1964,8 +1963,11 @@
             val = new Op('?', val, defaultValue);
           }
         }
-        if ((name != null) && indexOf.call(RESERVED, name) >= 0) {
+        if (name != null) {
-          obj.error("assignment to a reserved word: " + (obj.compile(o)));
+          message = isUnassignable(name);
+          if (message) {
+            obj.error(message);
+          }
         }
         assigns.push(new Assign(obj, val, null, {
           param: this.param,
@@ -2223,12 +2225,13 @@
     extend1(Param, superClass1);
 
     function Param(name1, value1, splat) {
-      var name, ref3, token;
+      var message, token;
       this.name = name1;
       this.value = value1;
       this.splat = splat;
-      if (ref3 = (name = this.name.unwrapAll().value), indexOf.call(STRICT_PROSCRIBED, ref3) >= 0) {
+      message = isUnassignable(this.name.unwrapAll().value);
-        this.name.error("parameter name \"" + name + "\" is not allowed");
+      if (message) {
+        this.name.error(message);
       }
       if (this.name instanceof Obj && this.name.generated) {
         token = this.name.objects[0].operatorToken;
@@ -2611,7 +2614,7 @@
     };
 
     Op.prototype.compileNode = function(o) {
-      var answer, isChain, lhs, ref3, ref4, rhs;
+      var answer, isChain, lhs, message, ref3, rhs;
       isChain = this.isChainable() && this.first.isChainable();
       if (!isChain) {
         this.first.front = this.front;
@@ -2619,8 +2622,11 @@
       if (this.operator === 'delete' && o.scope.check(this.first.unwrapAll().value)) {
         this.error('delete operand may not be argument or var');
       }
-      if (((ref3 = this.operator) === '--' || ref3 === '++') && (ref4 = this.first.unwrapAll().value, indexOf.call(STRICT_PROSCRIBED, ref4) >= 0)) {
+      if ((ref3 = this.operator) === '--' || ref3 === '++') {
-        this.error("cannot increment/decrement \"" + (this.first.unwrapAll().value) + "\"");
+        message = isUnassignable(this.first.unwrapAll().value);
+        if (message) {
+          this.first.error(message);
+        }
       }
       if (this.isYield()) {
         return this.compileYield(o);
@@ -2858,12 +2864,12 @@
     };
 
     Try.prototype.compileNode = function(o) {
-      var catchPart, ensurePart, generatedErrorVariableName, placeholder, tryPart;
+      var catchPart, ensurePart, generatedErrorVariableName, message, placeholder, tryPart;
       o.indent += TAB;
       tryPart = this.attempt.compileToFragments(o, LEVEL_TOP);
       catchPart = this.recovery ? (generatedErrorVariableName = o.scope.freeVariable('error', {
         reserve: false
-      }), placeholder = new IdentifierLiteral(generatedErrorVariableName), this.errorVariable ? this.recovery.unshift(new Assign(this.errorVariable, placeholder)) : void 0, [].concat(this.makeCode(" catch ("), placeholder.compileToFragments(o), this.makeCode(") {\n"), this.recovery.compileToFragments(o, LEVEL_TOP), this.makeCode("\n" + this.tab + "}"))) : !(this.ensure || this.recovery) ? (generatedErrorVariableName = o.scope.freeVariable('error', {
+      }), placeholder = new IdentifierLiteral(generatedErrorVariableName), this.errorVariable ? (message = isUnassignable(this.errorVariable.unwrapAll().value), message ? this.errorVariable.error(message) : void 0, this.recovery.unshift(new Assign(this.errorVariable, placeholder))) : void 0, [].concat(this.makeCode(" catch ("), placeholder.compileToFragments(o), this.makeCode(") {\n"), this.recovery.compileToFragments(o, LEVEL_TOP), this.makeCode("\n" + this.tab + "}"))) : !(this.ensure || this.recovery) ? (generatedErrorVariableName = o.scope.freeVariable('error', {
         reserve: false
       }), [this.makeCode(" catch (" + generatedErrorVariableName + ") {}")]) : [];
       ensurePart = this.ensure ? [].concat(this.makeCode(" finally {\n"), this.ensure.compileToFragments(o, LEVEL_TOP), this.makeCode("\n" + this.tab + "}")) : [];

src/lexer.coffee

@@ -411,14 +411,20 @@ exports.Lexer = class Lexer
       value = @chunk.charAt 0
     tag  = value
     [..., prev] = @tokens
-    if value is '=' and prev
+
-      if prev.variable and prev[1] in JS_FORBIDDEN
+    if prev and value in ['=', COMPOUND_ASSIGN...]
-        prev = prev.origin if prev.origin
+      skipToken = false
-        @error "reserved word '#{prev[1]}' can't be assigned", prev[2]
+      if value is '=' and prev[1] in ['||', '&&'] and not prev.spaced
-      if prev[1] in ['||', '&&']
         prev[0] = 'COMPOUND_ASSIGN'
         prev[1] += '='
-        return value.length
+        prev = @tokens[@tokens.length - 2]
+        skipToken = true
+      if prev and prev.variable
+        origin = prev.origin ? prev
+        message = isUnassignable prev[1], origin[1]
+        @error message, origin[2] if message
+      return value.length if skipToken
+
     if value is ';'
       @seenFor = no
       tag = 'TERMINATOR'
@@ -744,6 +750,21 @@ exports.Lexer = class Lexer
         {first_line, first_column, last_column: first_column + (options.length ? 1) - 1}
     throwSyntaxError message, location
 
+# Helper functions
+# ----------------
+
+isUnassignable = (name, displayName = name) -> switch
+  when name in [JS_KEYWORDS..., COFFEE_KEYWORDS...]
+    "keyword '#{displayName}' can't be assigned"
+  when name in STRICT_PROSCRIBED
+    "'#{displayName}' can't be assigned"
+  when name in RESERVED
+    "reserved word '#{displayName}' can't be assigned"
+  else
+    false
+
+exports.isUnassignable = isUnassignable
+
 # Constants
 # ---------
 
@@ -782,15 +803,12 @@ RESERVED = [
   'protected', 'public', 'static'
 ]
 
-STRICT_PROSCRIBED = ['arguments', 'eval', 'yield*']
+STRICT_PROSCRIBED = ['arguments', 'eval']
 
 # The superset of both JavaScript keywords and reserved words, none of which may
 # be used as identifiers or properties.
 JS_FORBIDDEN = JS_KEYWORDS.concat(RESERVED).concat(STRICT_PROSCRIBED)
-
+exports.JS_FORBIDDEN = JS_KEYWORDS.concat(RESERVED).concat(STRICT_PROSCRIBED)
-exports.RESERVED = RESERVED.concat(JS_KEYWORDS).concat(COFFEE_KEYWORDS).concat(STRICT_PROSCRIBED)
-exports.STRICT_PROSCRIBED = STRICT_PROSCRIBED
-exports.JS_FORBIDDEN = JS_FORBIDDEN
 
 # The character code of the nasty Microsoft madness otherwise known as the BOM.
 BOM = 65279

src/nodes.coffee

@@ -6,7 +6,7 @@
 Error.stackTraceLimit = Infinity
 
 {Scope} = require './scope'
-{RESERVED, STRICT_PROSCRIBED, JS_FORBIDDEN} = require './lexer'
+{isUnassignable, JS_FORBIDDEN} = require './lexer'
 
 # Import the helpers we plan to use.
 {compact, flatten, extend, merge, del, starts, ends, some,
@@ -411,7 +411,7 @@ exports.RegexLiteral = class RegexLiteral extends Literal
 exports.PassthroughLiteral = class PassthroughLiteral extends Literal
 
 exports.IdentifierLiteral = class IdentifierLiteral extends Literal
-  isAssignable: -> @value not in RESERVED
+  isAssignable: YES
 
 exports.StatementLiteral = class StatementLiteral extends Literal
   isStatement: YES
@@ -1081,6 +1081,9 @@ exports.Class = class Class extends Base
       @variable.base
     return @defaultClassVariableName unless node instanceof IdentifierLiteral
     name = node.value
+    unless tail
+      message = isUnassignable name
+      @variable.error message if message
     if name in JS_FORBIDDEN then "_#{name}" else name
 
   # For all `this`-references and bound functions in the class definition,
@@ -1215,9 +1218,6 @@ exports.Class = class Class extends Base
 exports.Assign = class Assign extends Base
   constructor: (@variable, @value, @context, options = {}) ->
     {@param, @subpattern, @operatorToken} = options
-    forbidden = (name = @variable.unwrapAll().value) in STRICT_PROSCRIBED
-    if forbidden and @context isnt 'object'
-      @variable.error "variable name may not be \"#{name}\""
 
   children: ['variable', 'value']
 
@@ -1254,7 +1254,7 @@ exports.Assign = class Assign extends Base
     unless @context
       varBase = @variable.unwrapAll()
       unless varBase.isAssignable()
-        @variable.error "\"#{@variable.compile o}\" cannot be assigned"
+        @variable.error "'#{@variable.compile o}' can't be assigned"
       unless varBase.hasProperties?()
         if @param
           o.scope.add varBase.value, 'var'
@@ -1309,8 +1309,8 @@ exports.Assign = class Assign extends Base
       acc   = idx.unwrap() instanceof IdentifierLiteral
       value = new Value value
       value.properties.push new (if acc then Access else Index) idx
-      if obj.unwrap().value in RESERVED
+      message = isUnassignable obj.unwrap().value
-        obj.error "assignment to a reserved word: #{obj.compile o}"
+      obj.error message if message
       value = new Op '?', value, defaultValue if defaultValue
       return new Assign(obj, value, null, param: @param).compileToFragments o, LEVEL_TOP
     vvar     = value.compileToFragments o, LEVEL_LIST
@@ -1369,8 +1369,9 @@ exports.Assign = class Assign extends Base
         acc = idx.unwrap() instanceof IdentifierLiteral
         val = new Value new Literal(vvarText), [new (if acc then Access else Index) idx]
         val = new Op '?', val, defaultValue if defaultValue
-      if name? and name in RESERVED
+      if name?
-        obj.error "assignment to a reserved word: #{obj.compile o}"
+        message = isUnassignable name
+        obj.error message if message
       assigns.push new Assign(obj, val, null, param: @param, subpattern: yes).compileToFragments o, LEVEL_LIST
     assigns.push vvar unless top or @subpattern
     fragments = @joinFragmentArrays assigns, ', '
@@ -1527,8 +1528,8 @@ exports.Code = class Code extends Base
 # as well as be a splat, gathering up a group of parameters into an array.
 exports.Param = class Param extends Base
   constructor: (@name, @value, @splat) ->
-    if (name = @name.unwrapAll().value) in STRICT_PROSCRIBED
+    message = isUnassignable @name.unwrapAll().value
-      @name.error "parameter name \"#{name}\" is not allowed"
+    @name.error message if message
     if @name instanceof Obj and @name.generated
       token = @name.objects[0].operatorToken
       token.error "unexpected #{token.value}"
@@ -1817,8 +1818,9 @@ exports.Op = class Op extends Base
     @first.front = @front unless isChain
     if @operator is 'delete' and o.scope.check(@first.unwrapAll().value)
       @error 'delete operand may not be argument or var'
-    if @operator in ['--', '++'] and @first.unwrapAll().value in STRICT_PROSCRIBED
+    if @operator in ['--', '++']
-      @error "cannot increment/decrement \"#{@first.unwrapAll().value}\""
+      message = isUnassignable @first.unwrapAll().value
+      @first.error message if message
     return @compileYield     o if @isYield()
     return @compileUnary     o if @isUnary()
     return @compileChain     o if isChain
@@ -1969,7 +1971,10 @@ exports.Try = class Try extends Base
     catchPart = if @recovery
       generatedErrorVariableName = o.scope.freeVariable 'error', reserve: no
       placeholder = new IdentifierLiteral generatedErrorVariableName
-      @recovery.unshift new Assign @errorVariable, placeholder if @errorVariable
+      if @errorVariable
+        message = isUnassignable @errorVariable.unwrapAll().value
+        @errorVariable.error message if message
+        @recovery.unshift new Assign @errorVariable, placeholder
       [].concat @makeCode(" catch ("), placeholder.compileToFragments(o), @makeCode(") {\n"),
         @recovery.compileToFragments(o, LEVEL_TOP), @makeCode("\n#{@tab}}")
     else unless @ensure or @recovery

test/error_messages.coffee

@@ -36,7 +36,7 @@ test "compiler error formatting", ->
     evil = (foo, eval, bar) ->
   ''',
   '''
-    [stdin]:1:14: error: parameter name "eval" is not allowed
+    [stdin]:1:14: error: 'eval' can't be assigned
     evil = (foo, eval, bar) ->
                  ^^^^
   '''
@@ -656,22 +656,88 @@ test "reserved words", ->
     case
     ^^^^
   '''
+  assertErrorFormat '''
+    case = 1
+  ''', '''
+    [stdin]:1:1: error: reserved word 'case'
+    case = 1
+    ^^^^
+  '''
   assertErrorFormat '''
     for = 1
   ''', '''
-    [stdin]:1:1: error: reserved word 'for' can't be assigned
+    [stdin]:1:1: error: keyword 'for' can't be assigned
     for = 1
     ^^^
   '''
+  assertErrorFormat '''
+    unless = 1
+  ''', '''
+    [stdin]:1:1: error: keyword 'unless' can't be assigned
+    unless = 1
+    ^^^^^^
+  '''
+  assertErrorFormat '''
+    for += 1
+  ''', '''
+    [stdin]:1:1: error: keyword 'for' can't be assigned
+    for += 1
+    ^^^
+  '''
+  assertErrorFormat '''
+    for &&= 1
+  ''', '''
+    [stdin]:1:1: error: keyword 'for' can't be assigned
+    for &&= 1
+    ^^^
+  '''
+  # Make sure token look-behind doesn't go out of range.
+  assertErrorFormat '''
+    &&= 1
+  ''', '''
+    [stdin]:1:1: error: unexpected &&=
+    &&= 1
+    ^^^
+  '''
   # #2306: Show unaliased name in error messages.
   assertErrorFormat '''
     on = 1
   ''', '''
-    [stdin]:1:1: error: reserved word 'on' can't be assigned
+    [stdin]:1:1: error: keyword 'on' can't be assigned
     on = 1
     ^^
   '''
 
+test "strict mode errors", ->
+  assertErrorFormat '''
+    eval = 1
+  ''', '''
+    [stdin]:1:1: error: 'eval' can't be assigned
+    eval = 1
+    ^^^^
+  '''
+  assertErrorFormat '''
+    class eval
+  ''', '''
+    [stdin]:1:7: error: 'eval' can't be assigned
+    class eval
+          ^^^^
+  '''
+  assertErrorFormat '''
+    arguments++
+  ''', '''
+    [stdin]:1:1: error: 'arguments' can't be assigned
+    arguments++
+    ^^^^^^^^^
+  '''
+  assertErrorFormat '''
+    --arguments
+  ''', '''
+    [stdin]:1:3: error: 'arguments' can't be assigned
+    --arguments
+      ^^^^^^^^^
+  '''
+
 test "invalid numbers", ->
   assertErrorFormat '''
     0X0
@@ -832,35 +898,35 @@ test "#4130: unassignable in destructured param", ->
     }) ->
       console.log "Oh hello!"
   ''', '''
-    [stdin]:2:12: error: assignment to a reserved word: null
+    [stdin]:2:12: error: keyword 'null' can't be assigned
       @param : null
                ^^^^
   '''
   assertErrorFormat '''
     ({a: null}) ->
   ''', '''
-    [stdin]:1:6: error: assignment to a reserved word: null
+    [stdin]:1:6: error: keyword 'null' can't be assigned
     ({a: null}) ->
          ^^^^
   '''
   assertErrorFormat '''
     ({a: 1}) ->
   ''', '''
-    [stdin]:1:6: error: "1" cannot be assigned
+    [stdin]:1:6: error: '1' can't be assigned
     ({a: 1}) ->
          ^
   '''
   assertErrorFormat '''
     ({1}) ->
   ''', '''
-    [stdin]:1:3: error: "1" cannot be assigned
+    [stdin]:1:3: error: '1' can't be assigned
     ({1}) ->
       ^
   '''
   assertErrorFormat '''
     ({a: true = 1}) ->
   ''', '''
-    [stdin]:1:6: error: reserved word 'true' can't be assigned
+    [stdin]:1:6: error: keyword 'true' can't be assigned
     ({a: true = 1}) ->
          ^^^^
   '''
@@ -889,3 +955,37 @@ test "#4097: `yield return` as an expression", ->
     -> (yield return)
         ^^^^^^^^^^^^
   '''
+
+test "`&&=` and `||=` with a space in-between", ->
+  assertErrorFormat '''
+    a = 0
+    a && = 1
+  ''', '''
+    [stdin]:2:6: error: unexpected =
+    a && = 1
+         ^
+  '''
+  assertErrorFormat '''
+    a = 0
+    a and = 1
+  ''', '''
+    [stdin]:2:7: error: unexpected =
+    a and = 1
+          ^
+  '''
+  assertErrorFormat '''
+    a = 0
+    a || = 1
+  ''', '''
+    [stdin]:2:6: error: unexpected =
+    a || = 1
+         ^
+  '''
+  assertErrorFormat '''
+    a = 0
+    a or = 1
+  ''', '''
+    [stdin]:2:6: error: unexpected =
+    a or = 1
+         ^
+  '''