Remove duplicated code from comma-separated Expression parsing

src/messages.h

 // Copyright 2006-2008 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.
 
 // The infrastructure used for (localized) message reporting in V8.
 //
 // Note: there's a big unresolved issue about ownership of the data
 // structures used by this framework.
 
 #ifndef V8_MESSAGES_H_
@@ skipping 436 matching lines @@
   T(MalformedArrowFunParamList, "Malformed arrow function parameter list")     \
   T(MalformedRegExp, "Invalid regular expression: /%/: %")                     \
   T(MalformedRegExpFlags, "Invalid regular expression flags")                  \
   T(ModuleExportUndefined, "Export '%' is not defined in module")              \
   T(MultipleDefaultsInSwitch,                                                  \
     "More than one default clause in switch statement")                        \
   T(NewlineAfterThrow, "Illegal newline after throw")                          \
   T(NoCatchOrFinally, "Missing catch or finally after try")                    \
   T(NotIsvar, "builtin %%IS_VAR: not a variable")                              \
   T(ParamAfterRest, "Rest parameter must be last formal parameter")            \
-  T(InvalidRestParameter,                                                      \
-    "Rest parameter must be an identifier or destructuring pattern")           \

[adamk, 2016/08/26 20:13:03]

I don't think there's much lost for users in losing this message. We didn't emit
it in non-arrow functions anyway.

[Dan Ehrenberg, 2016/08/26 22:48:53]

This doesn't make me all that happy. The old message was better. Could we extend
the better message to the non-arrow function case?

[nickie, 2016/08/29 08:42:59]

In principle I would agree with Dan.  But this error is only reported very
rarely and even in those cases, the message is misleading.  All the following
wrong arrow functions produce different error messages (unexpected something or
other):

d8> f = (...42) => 42;
d8> f = (x, ...42) => 42;
d8> f = (...[42]) => 42;
d8> f = (x, ...[42]) => 42;
d8> f = (...[x+1]) => 42;
d8> f = (a, ...[x+1]) => 42;

I'm not saying that these error messages are good, only that Adam's change does
not affect these cases.

Only things like this produce InvalidRestParameter:

d8> f = (...x = []) => 42;
(d8):1: SyntaxError: Rest parameter must be an identifier or destructuring
pattern
f = (...x = []) => 42;
     ^^^^^^^^^
SyntaxError: Rest parameter must be an identifier or destructuring pattern

As I see it, the rest parameter is "x" and it is indeed an identifier.  The
problem is that it carries an initializer and that is forbidden.  I think the
error message is not good anyway.

   T(PushPastSafeLength,                                                        \
     "Pushing % elements on an array-like of length % "                         \
     "is disallowed, as the total surpasses 2**53-1")                           \
   T(ElementAfterRest, "Rest element must be last element in array")            \
   T(BadSetterRestParameter,                                                    \
     "Setter function argument must not be a rest parameter")                   \
   T(ParamDupe, "Duplicate parameter name not allowed in this context")         \
   T(ParenthesisInArgString, "Function arg string contains parenthesis")        \
   T(RuntimeWrongNumArgs, "Runtime function given wrong number of arguments")   \
   T(SingleFunctionLiteral, "Single function literal required")                 \
@@ skipping 113 matching lines @@
   static Handle<String> GetMessage(Isolate* isolate, Handle<Object> data);
   static std::unique_ptr<char[]> GetLocalizedMessage(Isolate* isolate,
                                                      Handle<Object> data);
 };
 
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_MESSAGES_H_