Fixes Issue #603 -- a longstanding precedence issue involving prefix vs postfix if and unless, involving using the entire single-line if statment as an expression.

lib/grammar.js

@@ -516,20 +516,20 @@
       })
     ],
     If: [
-      o("IfBlock"), o("Statement IF Expression", function() {
+      o("IfBlock"), o("Statement POST_IF Expression", function() {
         return new IfNode($3, Expressions.wrap([$1]), {
           statement: true
         });
-      }), o("Expression IF Expression", function() {
+      }), o("Expression POST_IF Expression", function() {
         return new IfNode($3, Expressions.wrap([$1]), {
           statement: true
         });
-      }), o("Statement UNLESS Expression", function() {
+      }), o("Statement POST_UNLESS Expression", function() {
         return new IfNode($3, Expressions.wrap([$1]), {
           statement: true,
           invert: true
         });
-      }), o("Expression UNLESS Expression", function() {
+      }), o("Expression POST_UNLESS Expression", function() {
         return new IfNode($3, Expressions.wrap([$1]), {
           statement: true,
           invert: true
@@ -644,7 +644,7 @@
       })
     ]
   };
-  operators = [["left", '?'], ["nonassoc", 'UMINUS', 'UPLUS', '!', '!!', '~', '++', '--'], ["left", '*', '/', '%'], ["left", '+', '-'], ["left", '<<', '>>', '>>>'], ["left", '<=', '<', '>', '>='], ["right", 'DELETE', 'INSTANCEOF', 'TYPEOF'], ["left", '==', '!='], ["left", '&', '|', '^'], ["left", '&&', '||', 'OP?'], ["right", '-=', '+=', '/=', '*=', '%=', '||=', '&&=', '?=', '<<=', '>>=', '>>>=', '&=', '^=', '|='], ["left", '.'], ["right", 'INDENT'], ["left", 'OUTDENT'], ["right", 'WHEN', 'LEADING_WHEN', 'IN', 'OF', 'BY', 'THROW'], ["right", 'FOR', 'WHILE', 'UNTIL', 'LOOP', 'NEW', 'SUPER', 'CLASS'], ["left", 'EXTENDS'], ["right", '=', ':', 'RETURN'], ["right", '->', '=>', 'UNLESS', 'IF', 'ELSE']];
+  operators = [["left", '?'], ["nonassoc", 'UMINUS', 'UPLUS', '!', '!!', '~', '++', '--'], ["left", '*', '/', '%'], ["left", '+', '-'], ["left", '<<', '>>', '>>>'], ["left", '<=', '<', '>', '>='], ["right", 'DELETE', 'INSTANCEOF', 'TYPEOF'], ["left", '==', '!='], ["left", '&', '|', '^'], ["left", '&&', '||', 'OP?'], ["right", '-=', '+=', '/=', '*=', '%=', '||=', '&&=', '?=', '<<=', '>>=', '>>>=', '&=', '^=', '|='], ["left", '.'], ["right", 'INDENT'], ["left", 'OUTDENT'], ["right", 'WHEN', 'LEADING_WHEN', 'IN', 'OF', 'BY', 'THROW'], ["right", 'IF', 'UNLESS', 'ELSE', 'FOR', 'WHILE', 'UNTIL', 'LOOP', 'NEW', 'SUPER', 'CLASS'], ["left", 'EXTENDS'], ["right", '=', ':', 'RETURN'], ["right", '->', '=>', 'UNLESS', 'POST_IF', 'POST_UNLESS']];
   tokens = [];
   _a = grammar;
   for (name in _a) {

lib/rewriter.js

@@ -21,6 +21,7 @@
       this.closeOpenIndexes();
       this.addImplicitIndentation();
       this.addImplicitBraces();
+      this.tagPostfixConditionals();
       this.addImplicitParentheses();
       this.ensureBalance(BALANCED_PAIRS);
       this.rewriteClosingParens();
@@ -231,6 +232,26 @@
         return 1;
       });
     };
+    Rewriter.prototype.tagPostfixConditionals = function() {
+      return this.scanTokens(function(token, i) {
+        var _c, action, condition, original;
+        if (('IF' === (_c = token[0]) || 'UNLESS' === _c)) {
+          original = token;
+          condition = function(token, i) {
+            var _c;
+            return ('TERMINATOR' === (_c = token[0]) || 'INDENT' === _c);
+          };
+          action = function(token, i) {
+            if (token[0] !== 'INDENT') {
+              return (original[0] = 'POST_' + original[0]);
+            }
+          };
+          this.detectEnd(i + 1, condition, action);
+          return 1;
+        }
+        return 1;
+      });
+    };
     Rewriter.prototype.ensureBalance = function(pairs) {
       var _c, _d, key, levels, line, open, openLine, unclosed, value;
       levels = {};
@@ -354,9 +375,9 @@
   })();
   EXPRESSION_CLOSE = ['CATCH', 'WHEN', 'ELSE', 'FINALLY'].concat(EXPRESSION_END);
   IMPLICIT_FUNC = ['IDENTIFIER', 'SUPER', ')', 'CALL_END', ']', 'INDEX_END', '@'];
-  IMPLICIT_CALL = ['IDENTIFIER', 'NUMBER', 'STRING', 'JS', 'REGEX', 'NEW', 'PARAM_START', 'CLASS', 'TRY', 'DELETE', 'TYPEOF', 'SWITCH', 'THIS', 'NULL', 'TRUE', 'FALSE', 'YES', 'NO', 'ON', 'OFF', '!', '!!', '@', '->', '=>', '[', '(', '{'];
+  IMPLICIT_CALL = ['IDENTIFIER', 'NUMBER', 'STRING', 'JS', 'REGEX', 'NEW', 'PARAM_START', 'CLASS', 'IF', 'UNLESS', 'TRY', 'DELETE', 'TYPEOF', 'SWITCH', 'THIS', 'NULL', 'TRUE', 'FALSE', 'YES', 'NO', 'ON', 'OFF', '!', '!!', '@', '->', '=>', '[', '(', '{'];
   IMPLICIT_BLOCK = ['->', '=>', '{', '[', ','];
-  IMPLICIT_END = ['IF', 'UNLESS', 'FOR', 'WHILE', 'UNTIL', 'LOOP', 'TERMINATOR', 'INDENT'];
+  IMPLICIT_END = ['POST_IF', 'POST_UNLESS', 'FOR', 'WHILE', 'UNTIL', 'LOOP', 'TERMINATOR', 'INDENT'];
   SINGLE_LINERS = ['ELSE', "->", "=>", 'TRY', 'FINALLY', 'THEN'];
   SINGLE_CLOSERS = ['TERMINATOR', 'CATCH', 'FINALLY', 'ELSE', 'OUTDENT', 'LEADING_WHEN'];
 })();

src/grammar.coffee

@@ -507,10 +507,10 @@ grammar =
   # *if* and *unless*.
   If: [
     o "IfBlock"
-    o "Statement IF Expression",                -> new IfNode $3, Expressions.wrap([$1]), statement: true
+    o "Statement POST_IF Expression",           -> new IfNode $3, Expressions.wrap([$1]), statement: true
-    o "Expression IF Expression",               -> new IfNode $3, Expressions.wrap([$1]), statement: true
+    o "Expression POST_IF Expression",          -> new IfNode $3, Expressions.wrap([$1]), statement: true
-    o "Statement UNLESS Expression",            -> new IfNode $3, Expressions.wrap([$1]), statement: true, invert: true
+    o "Statement POST_UNLESS Expression",       -> new IfNode $3, Expressions.wrap([$1]), statement: true, invert: true
-    o "Expression UNLESS Expression",           -> new IfNode $3, Expressions.wrap([$1]), statement: true, invert: true
+    o "Expression POST_UNLESS Expression",      -> new IfNode $3, Expressions.wrap([$1]), statement: true, invert: true
   ]
 
   # Arithmetic and logical operators, working on one or more operands.
@@ -609,10 +609,10 @@ operators = [
   ["right",     'INDENT']
   ["left",      'OUTDENT']
   ["right",     'WHEN', 'LEADING_WHEN', 'IN', 'OF', 'BY', 'THROW']
-  ["right",     'FOR', 'WHILE', 'UNTIL', 'LOOP', 'NEW', 'SUPER', 'CLASS']
+  ["right",     'IF', 'UNLESS', 'ELSE', 'FOR', 'WHILE', 'UNTIL', 'LOOP', 'NEW', 'SUPER', 'CLASS']
   ["left",      'EXTENDS']
   ["right",     '=', ':', 'RETURN']
-  ["right",     '->', '=>', 'UNLESS', 'IF', 'ELSE']
+  ["right",     '->', '=>', 'UNLESS', 'POST_IF', 'POST_UNLESS']
 ]
 
 # Wrapping Up

src/rewriter.coffee

@@ -36,6 +36,7 @@ exports.Rewriter = class Rewriter
     @closeOpenIndexes()
     @addImplicitIndentation()
     @addImplicitBraces()
+    @tagPostfixConditionals()
     @addImplicitParentheses()
     @ensureBalance BALANCED_PAIRS
     @rewriteClosingParens()
@@ -196,6 +197,20 @@ exports.Rewriter = class Rewriter
         return 2
       return 1
 
+  # Tag postfix conditionals as such, so that we can parse them with a
+  # different precedence.
+  tagPostfixConditionals: ->
+    @scanTokens (token, i) ->
+      if token[0] in ['IF', 'UNLESS']
+        original  = token
+        condition = (token, i) ->
+          token[0] in ['TERMINATOR', 'INDENT']
+        action    = (token, i) ->
+          original[0] = 'POST_' + original[0] if token[0] isnt 'INDENT'
+        @detectEnd i + 1, condition, action
+        return 1
+      return 1
+
   # Ensure that all listed pairs of tokens are correctly balanced throughout
   # the course of the token stream.
   ensureBalance: (pairs) ->
@@ -301,7 +316,7 @@ IMPLICIT_FUNC    = ['IDENTIFIER', 'SUPER', ')', 'CALL_END', ']', 'INDEX_END', '@
 # If preceded by an `IMPLICIT_FUNC`, indicates a function invocation.
 IMPLICIT_CALL    = [
   'IDENTIFIER', 'NUMBER', 'STRING', 'JS', 'REGEX', 'NEW', 'PARAM_START', 'CLASS',
-  'TRY', 'DELETE', 'TYPEOF', 'SWITCH', 'THIS', 'NULL',
+  'IF', 'UNLESS', 'TRY', 'DELETE', 'TYPEOF', 'SWITCH', 'THIS', 'NULL',
   'TRUE', 'FALSE', 'YES', 'NO', 'ON', 'OFF',
   '!', '!!', '@', '->', '=>', '[', '(', '{'
 ]
@@ -310,7 +325,7 @@ IMPLICIT_CALL    = [
 IMPLICIT_BLOCK   = ['->', '=>', '{', '[', ',']
 
 # Tokens that always mark the end of an implicit call for single-liners.
-IMPLICIT_END     = ['IF', 'UNLESS', 'FOR', 'WHILE', 'UNTIL', 'LOOP', 'TERMINATOR', 'INDENT']
+IMPLICIT_END     = ['POST_IF', 'POST_UNLESS', 'FOR', 'WHILE', 'UNTIL', 'LOOP', 'TERMINATOR', 'INDENT']
 
 # Single-line flavors of block expressions that have unclosed endings.
 # The grammar can't disambiguate them, so we insert the implicit indentation.

test/test_if.coffee

@@ -64,10 +64,20 @@ ok result is undefined
 
 # Return an if with no else.
 func = ->
-  return (if false then callback())
+  return if false then callback()
 
 ok func() is null
 
+func = ->
+  return unless false then 100 else -100
+
+ok func() is 100
+
+ident = (x) -> x
+result = ident if false then 300 else 100
+
+ok result is 100
+
 
 # If-to-ternary with instanceof requires parentheses (no comment).
 if {} instanceof Object