Fix Error.prototype.toString to be ES5 conform.

test/mjsunit/cyclic-error-to-string.js

Index: test/mjsunit/cyclic-error-to-string.js
diff --git a/test/mjsunit/cyclic-error-to-string.js b/test/mjsunit/cyclic-error-to-string.js
index 2502b5340fd87ca4601160027f4435c6f443b452..7c43fc580e8378f00cfe22ba80f3948c726f8b21 100644
--- a/test/mjsunit/cyclic-error-to-string.js
+++ b/test/mjsunit/cyclic-error-to-string.js
@@ -36,11 +36,11 @@ e.name = e;
 e.message = e;
 e.stack = e;
 e.arguments = e;

[Lasse Reichstein, 2011/10/26 07:40:24]

Why .stack and .arguments? They don't seem to affect (and should not be expected
to affect) the toString function.
It would be better if they actually contained string values that should not
occur in the result. I.e. change them to:
  e.stack = "Does not occur in output";
  e.arguments = "Does not occur in output";
  e.type = "Does not occur in output";
(adding .type just to be sure).

[Michael Starzinger, 2011/10/26 09:30:20]

Done.

-assertEquals(': ', e + '');
+assertEquals('', e + '');

[Lasse Reichstein, 2011/10/26 07:40:24]

Seems a little odd that we can get ": " when neither name nor message is the
empty string. I can see that we need to do something, but I'd prefer putting
something else than the empty string in place of recurring objects in the
toString call graph. E.g. "#<error>". But we match Safari, so let's keep it for
now.

[Michael Starzinger, 2011/10/26 09:30:20]

I agree, having a more sensible string representation for the cyclic case would
be good. But since it is not specified how to treat cycles, I think staying in
sync with Firefox (and probably Safari once they fix the ES5 issue here) is a
good thing.

 
 e = new Error();
 e.name = [ e ];
 e.message = [ e ];
 e.stack = [ e ];
 e.arguments = [ e ];
-assertEquals(': ', e + '');
+assertEquals('', e + '');

[Lasse Reichstein, 2011/10/26 07:40:24]

Add a test to check the sequence of visible operations of toString, e.g.,

var seq;
function testSeq(name, message) {
 var e = {
   get name() { 
     seq.push(1); 
     return (name === undefined) ? name : {
         toString: function() { seq.push(2); return name; }; 
     };
   }, 
   get message() {
     seq.push(3);
     return message === undefined ? message : {
       toString: function() { seq.push(4); return message; }
     };
   }
 };
 return Error.prototype.toString.call(e);
}

seq = [];
assertEquals("Error", testSeq(undefined, undefined));
assertEquals([1,3], seq);
seq = [];
assertEquals("e1", testSeq("e1", undefined));
assertEquals([1,2,3], seq);

seq = [];
assertEquals("e2", testSeq(undefined, "e2"));
assertEquals([1,3,4], seq);

seq = [];
assertEquals("e1: e2", testSeq("e1", "e2"));
assertEquals([1,2,3,4], seq);

(not tested).

[Michael Starzinger, 2011/10/26 09:30:20]

Done (added with slight modifications).