More accurately record an end position for default parameters in arrows

src/parsing/parser.cc

Index: src/parsing/parser.cc
diff --git a/src/parsing/parser.cc b/src/parsing/parser.cc
index c2d32c0d94ee0ffd6f406b67259fab83c054d87d..d841d66e240bbd8a8bd5acab899a09eae0431028 100644
--- a/src/parsing/parser.cc
+++ b/src/parsing/parser.cc
@@ -3827,16 +3827,9 @@ Handle<FixedArray> CompileTimeValue::GetElements(Handle<FixedArray> value) {
   return Handle<FixedArray>(FixedArray::cast(value->get(kElementsSlot)));
 }
 
-
 void ParserTraits::ParseArrowFunctionFormalParameters(
-    ParserFormalParameters* parameters, Expression* expr,
-    const Scanner::Location& params_loc, bool* ok) {
-  if (parameters->Arity() >= Code::kMaxArguments) {
-    ReportMessageAt(params_loc, MessageTemplate::kMalformedArrowFunParamList);
-    *ok = false;
-    return;
-  }
-
+    ParserFormalParameters* parameters, Expression* expr, int end_pos,
+    bool* ok) {
   // ArrowFunctionFormals ::
   //    Binary(Token::COMMA, NonTailArrowFunctionFormals, Tail)
   //    Tail
@@ -3857,7 +3850,8 @@ void ParserTraits::ParseArrowFunctionFormalParameters(
     DCHECK_EQ(binop->op(), Token::COMMA);
     Expression* left = binop->left();
     Expression* right = binop->right();
-    ParseArrowFunctionFormalParameters(parameters, left, params_loc, ok);
+    int comma_pos = binop->position();
+    ParseArrowFunctionFormalParameters(parameters, left, comma_pos, ok);
     if (!*ok) return;
     // LHS of comma expression should be unparenthesized.
     expr = right;
@@ -3894,11 +3888,7 @@ void ParserTraits::ParseArrowFunctionFormalParameters(
                                      parser_->scope_, parameters->scope);
   }
 
-  // TODO(adamk): params_loc.end_pos is not the correct initializer position,
-  // but it should be conservative enough to trigger hole checks for variables
-  // referenced in the initializer (if any).
-  AddFormalParameter(parameters, expr, initializer, params_loc.end_pos,
-                     is_rest);
+  AddFormalParameter(parameters, expr, initializer, end_pos, is_rest);
 }
 
 
@@ -3927,7 +3917,13 @@ void ParserTraits::ParseArrowFunctionFormalParameterList(
     Scanner::Location* duplicate_loc, bool* ok) {
   if (expr->IsEmptyParentheses()) return;
 
-  ParseArrowFunctionFormalParameters(parameters, expr, params_loc, ok);
+  if (parameters->Arity() >= Code::kMaxArguments) {

[nickie, 2016/04/20 11:01:41]

I'm not sure if exactly Code::kMaxArguments (65535) should be allowed or not. 
If yes, then the ">=" should be a ">" here.  I used the following to test this
and it failed:

    python -c 'print "print(((" + ",".join("a"+str(i) for i in range(2**16-1)) +
")=>42)())"' > foo.js
    out/Release/d8 foo.js

[adamk, 2016/04/20 18:51:45]

Indeed, ">" is the comparison used elsewhere. Will fix as part of this patch,
though I do think it's somewhat academic.

+    ReportMessageAt(params_loc, MessageTemplate::kMalformedArrowFunParamList);
+    *ok = false;
+    return;
+  }
+

[nickie, 2016/04/20 11:01:41]

I believe that putting these five lines here does not do the trick.  Where it
was (line 3832), it was checked on each recursive call of
ParseArrowFunctionFormalParameters.  Now, whether that was good or bad is a
different story.  (Or even, the idea of having a recursive
ParseArrowFunctionFormalParameters that overflows the stack in Debug mode before
reaching kMaxArguments.)  I believe that these five lines should go after the
call to ParseArrowFunctionFormalParameters, before line 3929.

[adamk, 2016/04/20 18:51:45]

Ah, I misunderstood what the Arity() function did. Moved after the call to
ParseArrowFunctionFormalParameters.

+  ParseArrowFunctionFormalParameters(parameters, expr, params_loc.end_pos, ok);
   if (!*ok) return;
 
   Type::ExpressionClassifier classifier(parser_);