Fixes object literal and block ambiguity

- Follows the requirements in 12.4 - Additions to the grammar test suite. - Repairs older grammar tests and adds a test-grammar to the Makefile. - All the examples from the WAT talk should now work as expected (well, according to spec. They're not really what I'd call expected ;)
ndreynolds · Feb 15, 2013 · 197a6ee · 197a6ee
1 parent f88c754
commit 197a6ee
Show file tree

Hide file tree

Showing 11 changed files with 115 additions and 31 deletions.
diff --git a/Makefile b/Makefile
@@ -108,6 +108,9 @@ test-sm:
 test-rhino:
 	node test/runner.js --exec rhino --timeout 10000 --args "-f test/harness.js -f [test]"
 
+test-grammar:
+	mocha test/grammar
+
 archive:
 	git archive --format=tar.gz --prefix="flathead-$(VERSION)/" \
 		--output="flathead-$(VERSION).tar.gz" master .
diff --git a/src/grammar.y b/src/grammar.y
@@ -209,6 +209,7 @@
 %type<node> LeftHSExpression
 %type<node> LeftHSExpressionNoFn
 %type<node> Literal
+%type<node> LiteralNoObj
 %type<node> LogicalANDExpression
 %type<node> LogicalANDExpressionNoIn
 %type<node> LogicalANDExpressionNoFn
@@ -228,6 +229,7 @@
 %type<node> PostfixExpression
 %type<node> PostfixExpressionNoFn
 %type<node> PrimaryExpression
+%type<node> PrimaryExpressionNoObj
 %type<node> Program
 %type<node> PropertyAssignment
 %type<node> PropertyName
@@ -264,11 +266,17 @@
  * declaration and a named function expression. Expression statements cannot
  * begin with the 'function' keyword (Ecma-252 12.4). These productions
  * prevent that.
+ * 
+ * 'NoObj' rides the 'NoFn' train, forking at 'MemberExpressionNoFn' to ensure
+ * that 'PrimaryExpression' cannot be an object literal. Like the function
+ * declaration and expression, object literals must be disambiguated from
+ * blocks, and therefore may not be used to start an expression statement
+ * (Ecma-252 12.4).
  */
 
 %%
 
-Program                  : SourceElements                                    
+Program                  : SourceElements
                              { root = $1; }
                          ;
 
@@ -314,7 +322,9 @@ Statement                : Block
                              { $$ = $1; }
                          ; 
 
-Block                    : '{' StatementList '}'                             
+Block                    : '{' '}'
+                             { $$ = NEW_BLOCK(NULL); }
+                         | '{' StatementList '}'                             
                              { $$ = NEW_BLOCK($2); }
                          ;
 
@@ -501,6 +511,18 @@ Literal                  : NullLiteral
                              { $$ = $1; }
                          ;
 
+LiteralNoObj             : NullLiteral                        
+                             { $$ = $1; }
+                         | BooleanLiteral                   
+                             { $$ = $1; }
+                         | NumericLiteral                   
+                             { $$ = $1; }
+                         | StringLiteral                    
+                             { $$ = $1; }
+                         | RegularExpressionLiteral
+                             { $$ = $1; }
+                         ;
+
 ArrayLiteral             : '[' ']'                            
                              { $$ = NEW_ARR(NULL); }
                          | '[' Elision ']'                  
@@ -630,6 +652,18 @@ PrimaryExpression        : THIS
                              { $$ = $2; }
                          ;
 
+PrimaryExpressionNoObj   : THIS
+                             { $$ = NEW_THIS(); }
+                         | Identifier
+                             { $$ = $1; }
+                         | LiteralNoObj
+                             { $$ = $1; }
+                         | ArrayLiteral
+                             { $$ = $1; }
+                         | '(' Expression ')'  
+                             { $$ = $2; }
+                         ;
+
 ConditionalExpression    : LogicalORExpression                                  
                              { $$ = $1; }
                          | LogicalORExpression '?' AssignmentExpression ':' AssignmentExpression
@@ -1056,7 +1090,7 @@ MemberExpression         : PrimaryExpression
                              { $$ = NEW_NEW(NEW_MEMBER($3, $2, false)); }
                          ;
 
-MemberExpressionNoFn     : PrimaryExpression
+MemberExpressionNoFn     : PrimaryExpressionNoObj
                              { $$ = $1; }
                          | MemberExpressionNoFn '[' Expression ']'
                              { $$ = NEW_MEMBER($3, $1, 42); }

diff --git a/test/grammar/expressions.js b/test/grammar/expressions.js
@@ -7,29 +7,56 @@ describe('Expressions', function() {
   describe('Arithmetic', function() {
 
     it('should handle 2+2', function(done) {
-      withParseTree("2+2;", function(tree) {
-        assert.equal(tree, fixture("expression1"));
+      withParseTree('2+2;', function(tree) {
+        assert.equal(tree, fixture('expression1'));
         done();
       });
     });
 
     it('should handle 6%(12-2*7)*3+9/1', function(done) {
-      withParseTree("6%(12-2*7)*3+9/1;", function(tree) {
-        assert.equal(tree, fixture("expression2"));
+      withParseTree('6%(12-2*7)*3+9/1;', function(tree) {
+        assert.equal(tree, fixture('expression2'));
         done();
       });
     });
 
     it('should give * precedence over /', function(done) {
-      withParseTree("1*2/3;", function(tree) {
-        assert.equal(tree, fixture("expression3"));
+      withParseTree('1*2/3;', function(tree) {
+        assert.equal(tree, fixture('expression3'));
         done();
       });
-    })
+    });
 
     it('should give + precedence over -', function(done) {
-      withParseTree("1+2-3;", function(tree) {
-        assert.equal(tree, fixture("expression4"));
+      withParseTree('1+2-3;', function(tree) {
+        assert.equal(tree, fixture('expression4'));
+        done();
+      });
+    });
+  });
+
+  describe('12.4 Ambiguities', function() {
+
+    it('should properly distinguish object literals from blocks', function(done) {
+      // block and unary + operator on an object literal
+      withParseTree('{}+{};', function(tree) {
+        assert.equal(tree, fixture('block-object1'));
+        done();
+      });
+    });
+
+    it('should properly distinguish object literals from blocks (2)', function(done) {
+      // block and unary + operator on an array literal
+      withParseTree('{}+[];', function(tree) {
+        assert.equal(tree, fixture('block-object2'));
+        done();
+      });
+    });
+
+    it('should properly distinguish object literals from blocks (3)', function(done) {
+      // binary + operator on array literal and object literal
+      withParseTree('[]+{};', function(tree) {
+        assert.equal(tree, fixture('block-object3'));
         done();
       });
     });

diff --git a/test/grammar/fixtures/block-object1 b/test/grammar/fixtures/block-object1
@@ -0,0 +1,7 @@
+source list
+  expression statement
+    expression (unary prefix)
+      +
+      object
+  source list
+    block
diff --git a/test/grammar/fixtures/block-object2 b/test/grammar/fixtures/block-object2
@@ -0,0 +1,7 @@
+source list
+  expression statement
+    expression (unary prefix)
+      +
+      array literal
+  source list
+    block
diff --git a/test/grammar/fixtures/block-object3 b/test/grammar/fixtures/block-object3
@@ -0,0 +1,6 @@
+source list
+  expression statement
+    expression (binary)
+      +
+      array literal
+      object
diff --git a/test/grammar/fixtures/expression1 b/test/grammar/fixtures/expression1
@@ -1,6 +1,6 @@
-statement list
+source list
   expression statement
-    expression
+    expression (binary)
       +
       number (2.000000)
       number (2.000000)
diff --git a/test/grammar/fixtures/expression2 b/test/grammar/fixtures/expression2
@@ -1,21 +1,21 @@
-statement list
+source list
   expression statement
-    expression
+    expression (binary)
       +
-      expression
+      expression (binary)
         *
-        expression
+        expression (binary)
           %
           number (6.000000)
-          expression
+          expression (binary)
             -
             number (12.000000)
-            expression
+            expression (binary)
               *
               number (2.000000)
               number (7.000000)
         number (3.000000)
-      expression
+      expression (binary)
         /
         number (9.000000)
         number (1.000000)
diff --git a/test/grammar/fixtures/expression3 b/test/grammar/fixtures/expression3
@@ -1,8 +1,8 @@
-statement list
+source list
   expression statement
-    expression
+    expression (binary)
       /
-      expression
+      expression (binary)
         *
         number (1.000000)
         number (2.000000)

diff --git a/test/grammar/fixtures/expression4 b/test/grammar/fixtures/expression4
@@ -1,8 +1,8 @@
-statement list
+source list
   expression statement
-    expression
+    expression (binary)
       -
-      expression
+      expression (binary)
         +
         number (1.000000)
         number (2.000000)

diff --git a/test/grammar/utils.js b/test/grammar/utils.js
@@ -4,18 +4,18 @@
 
 var exec = require('child_process').exec,
     fs = require('fs'),
-    cmd = __dirname + '/../../bin/fh',
+    cmd = __dirname + '/../../bin/flat',
     fixtures = __dirname + '/fixtures/';
 
 exports.withParseTree = function(evalString, cb) {
   var parseTree;
-  var child = exec(cmd + ' -p', function(err, stdout, stderr) {
+  var child = exec(cmd + ' -n', function(err, stdout, stderr) {
     cb(stdout);
   });
   child.stdin.write(evalString);
   child.stdin.end();
-}
+};
 
 exports.fixture = function(name) {
   return fs.readFileSync(fixtures + name, 'utf8');
-}
+};