Implement experimental exponentiation operator via desugaring

src/preparser.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_PREPARSER_H
 #define V8_PREPARSER_H
 
 #include "src/v8.h"
 
 #include "src/bailout-reason.h"
@@ skipping 99 matching lines @@
   }
   bool allow_harmony_templates() const { return scanner()->HarmonyTemplates(); }
   bool allow_harmony_sloppy() const { return allow_harmony_sloppy_; }
   bool allow_harmony_unicode() const { return scanner()->HarmonyUnicode(); }
   bool allow_harmony_computed_property_names() const {
     return allow_harmony_computed_property_names_;
   }
   bool allow_harmony_rest_params() const {
     return allow_harmony_rest_params_;
   }
-
+  bool allow_harmony_exponentiation() const {
+    return scanner()->HarmonyExponentiation();
+  }
   bool allow_strong_mode() const { return allow_strong_mode_; }
 
   // Setters that determine whether certain syntactical constructs are
   // allowed to be parsed by this instance of the parser.
   void set_allow_lazy(bool allow) { allow_lazy_ = allow; }
   void set_allow_natives(bool allow) { allow_natives_ = allow; }
   void set_allow_harmony_arrow_functions(bool allow) {
     allow_harmony_arrow_functions_ = allow;
   }
   void set_allow_harmony_modules(bool allow) {
@@ skipping 19 matching lines @@
   }
   void set_allow_harmony_unicode(bool allow) {
     scanner()->SetHarmonyUnicode(allow);
   }
   void set_allow_harmony_computed_property_names(bool allow) {
     allow_harmony_computed_property_names_ = allow;
   }
   void set_allow_harmony_rest_params(bool allow) {
     allow_harmony_rest_params_ = allow;
   }
+  void set_allow_harmony_exponentiation(bool allow) {
+    scanner()->SetHarmonyExponentiation(allow);
+  }
   void set_allow_strong_mode(bool allow) { allow_strong_mode_ = allow; }
 
  protected:
   enum AllowEvalOrArgumentsAsIdentifier {
     kAllowEvalOrArguments,
     kDontAllowEvalOrArguments
   };
 
   enum Mode {
     PARSE_LAZILY,
@@ skipping 995 matching lines @@
   PreParserExpression NewCall(PreParserExpression expression,
                               PreParserExpressionList arguments,
                               int pos) {
     return PreParserExpression::Call();
   }
   PreParserExpression NewCallNew(PreParserExpression expression,
                                  PreParserExpressionList arguments,
                                  int pos) {
     return PreParserExpression::Default();
   }
+  PreParserExpression NewCallRuntime(const AstRawString* name,
+                                     const Runtime::Function* func,
+                                     PreParserExpressionList arguments,
+                                     int pos) {
+    return PreParserExpression::Call();
+  }
   PreParserStatement NewReturnStatement(PreParserExpression expression,
                                         int pos) {
     return PreParserStatement::Default();
   }
   PreParserExpression NewFunctionLiteral(
       PreParserIdentifier name, AstValueFactory* ast_value_factory,
       Scope* scope, PreParserStatementList body, int materialized_literal_count,
       int expected_property_count, int handler_count, int parameter_count,
       FunctionLiteral::ParameterFlag has_duplicate_parameters,
       FunctionLiteral::FunctionType function_type,
@@ skipping 1148 matching lines @@
   ExpressionT expression =
       this->ParseConditionalExpression(accept_IN, CHECK_OK);
 
   if (allow_harmony_arrow_functions() && peek() == Token::ARROW) {
     checkpoint.Restore();
     expression = this->ParseArrowFunctionLiteral(lhs_location.beg_pos,
                                                  expression, CHECK_OK);
     return expression;
   }
 
+  bool desugar_exponentiation = false;
   if (!Token::IsAssignmentOp(peek())) {
     if (fni_ != NULL) fni_->Leave();
     // Parsed conditional expression only (no assignment).
     return expression;
   }
 
   expression = this->CheckAndRewriteReferenceExpression(
       expression, lhs_location, "invalid_lhs_in_assignment", CHECK_OK);
   expression = this->MarkExpressionAsAssigned(expression);
 
   Token::Value op = Next();  // Get assignment operator.
+  if (op == Token::ASSIGN_EXP) {
+    // TODO(caitp): Desugaring in the parser makes it observable that lhs is
+    // retrieved twice. Fixed by moving implementation to compiler rather than
+    // desugaring, or by allocating a temporary variable.
+    op = Token::ASSIGN;
+    desugar_exponentiation = true;
+  }
+
   int pos = position();
   ExpressionT right = this->ParseAssignmentExpression(accept_IN, CHECK_OK);
 
   // TODO(1231235): We try to estimate the set of properties set by
   // constructors. We define a new property whenever there is an
   // assignment to a property of 'this'. We should probably only add
   // properties if we haven't seen them before. Otherwise we'll
   // probably overestimate the number of properties.
   if (op == Token::ASSIGN && this->IsThisProperty(expression)) {
     function_state_->AddProperty();
   }
 
   this->CheckAssigningFunctionLiteralToProperty(expression, right);
 
   if (fni_ != NULL) {
     // Check if the right hand side is a call to avoid inferring a
     // name if we're dealing with "a = function(){...}();"-like
     // expression.
     if ((op == Token::INIT_VAR
          || op == Token::INIT_CONST_LEGACY
          || op == Token::ASSIGN)
         && (!right->IsCall() && !right->IsCallNew())) {
       fni_->Infer();
     } else {
       fni_->RemoveLastFunction();
     }
     fni_->Leave();
   }
 
+  if (desugar_exponentiation) {
+    // Desugar to runtime call
+    typename Traits::Type::ExpressionList args =
+        this->NewExpressionList(2, zone_);
+    args->Add(expression, zone_);
+    args->Add(right, zone_);
+    right = factory()->NewCallRuntime(
+        ast_value_factory()->math_pow_string(), NULL, args, pos);
+  }
+
   return factory()->NewAssignment(op, expression, right, pos);
 }
 
 template <class Traits>
 typename ParserBase<Traits>::ExpressionT
 ParserBase<Traits>::ParseYieldExpression(bool* ok) {
   // YieldExpression ::
   //   'yield' ([no line terminator] '*'? AssignmentExpression)?
   int pos = peek_position();
   Expect(Token::YIELD, CHECK_OK);
@@ skipping 65 matching lines @@
 typename ParserBase<Traits>::ExpressionT
 ParserBase<Traits>::ParseBinaryExpression(int prec, bool accept_IN, bool* ok) {
   DCHECK(prec >= 4);
   ExpressionT x = this->ParseUnaryExpression(CHECK_OK);
   for (int prec1 = Precedence(peek(), accept_IN); prec1 >= prec; prec1--) {
     // prec1 >= 4
     while (Precedence(peek(), accept_IN) == prec1) {
       Token::Value op = Next();
       Scanner::Location op_location = scanner()->location();
       int pos = position();
-      ExpressionT y = ParseBinaryExpression(prec1 + 1, accept_IN, CHECK_OK);
+      ExpressionT y = Traits::EmptyExpression();
+
+      if (op != Token::EXP) {
+        //  Left-to-right associativity
+        y = ParseBinaryExpression(prec1 + 1, accept_IN, CHECK_OK);
+      } else {
+        // Right-to-left associativity
+        y = ParseBinaryExpression(prec1, accept_IN, CHECK_OK);
+      }
 
       if (this->ShortcutNumericLiteralBinaryExpression(&x, y, op, pos,
                                                        factory())) {
         continue;
       }
 
       // For now we distinguish between comparisons and other binary
       // operations.  (We could combine the two and get rid of this
       // code and AST node eventually.)
       if (Token::IsCompareOp(op)) {
@@ skipping 630 matching lines @@
       *ok = false;
       return;
     }
     has_seen_constructor_ = true;
     return;
   }
 }
 } }  // v8::internal
 
 #endif  // V8_PREPARSER_H