Please don't use toString when printing NoSuchMethodException

[peter-ahe-google]

It would be nice if the VM would tell me the class name, not the result of calling toString when throwing a NoSuchMethodException.

Otherwise, things like this is hard to debug:

class Fisk {
  toString() => "1";
}

class Hest {
  toString() { throw "hest"; }
}

main() {
  try {
    1 + new Fisk();
  } catch (var e) {
    print(e);
  }
  1 + new Hest();
}

Right now the VM says:

NoSuchMethodException - receiver: '1' function name: 'addFromInteger' arguments: [1]]
Unhandled exception:
<Received exception while converting exception to string>
 0. Function: 'Object.noSuchMethod' url: 'bootstrap' line:315 col:3
 1. Function: 'IntegerImplementation.+' url: 'bootstrap_impl' line:1463 col:32
 2. Function: '::.main' url: '/Users/ahe/Dart/all/dart.googlecode.com/dart/frog/fisk.dart' line:15 col:5

These examples are silly, but very similar issues are making it hard to debug problems in Frog/Leg.

[peter-ahe-google]

This is also confusing:

class Fisk {
  toString() => "";
}

main() {
  new Object().toString(new Fisk());
}

NoSuchMethodException - receiver: 'Instance of 'Object'' function name: 'toString' arguments: []]
 0. Function: 'Object.noSuchMethod' url: 'bootstrap' line:315 col:3
 1. Function: '::.main' url: '/Users/ahe/Dart/all/dart.googlecode.com/dart/frog/fisk.dart' line:6 col:24

[iposva-google]

To understand better what Peter means with his second example from comment 1:

main() {
  new Object().toString(1);
}

produces

Unhandled exception:
NoSuchMethodException - receiver: 'Instance of 'Object'' function name: 'toString' arguments: [1]]
 0. Function: 'Object.noSuchMethod' url: 'bootstrap' line:350 col:3
 1. Function: '::.main' url: 'Issue546.dart' line:2 col:24

Note that the parameter is printed here. Maybe we should also print the class name of the parameter or the position of the parameter, such as:
NoSuchMethodException - receiver: 'Instance of 'Object'' function name: 'toString' arguments: [1: "1"]]

I assume this will be revised when we address the general problems of NoSuchMethod handling.

[iposva-google]

Issue #420 has been merged into this issue.

[iposva-google]

Set owner to @sgmitrovic.
Added Accepted label.

[sethladd]

Is this still valid?

[peter-ahe-google]

I think this bug is still valid. The error message is slightly different (as in much better):

NoSuchMethodException : method not found: 'addFromInteger'
Receiver: 1
Arguments: [1]
Unhandled exception:
<Received error while converting exception to string>
 0. Function: 'Object.noSuchMethod' url: 'bootstrap' line:717 col:3
 1. Function: 'IntegerImplementation.+' url: 'bootstrap_impl' line:1428 col:32
 2. Function: '::main' url: 'file:///Users/ahe/Dart/all/dart/fisk.dart' line:15 col:5

The information I would like to have in the first part is the classes of the receiver and arguments, for example:

NoSuchMethodException : method not found: 'addFromInteger'
Receiver: int(1)
Arguments: [1]

Also, if toString is broken, it hides the original exception:

Unhandled exception:
<Received error while converting exception to string>
 0. Function: 'Object.noSuchMethod' url: 'bootstrap' line:717 col:3
 1. Function: 'IntegerImplementation.+' url: 'bootstrap_impl' line:1428 col:32
 2. Function: '::main' url: 'file:///Users/ahe/Dart/all/dart/fisk.dart' line:15 col:5

In addition, there is no stack trace for the broken toString method.

Here is one possible solution to this problem:

Add a private helper method to Object:

String _toExceptionString() {
  String classname = /* native call */;
  String result;
  try {
    result = '$classname("${toString}()")';
  } finally {
    if (result === null) {
      result = '<Error when calling $classname.toString.>';
    }
    // Ignore any exceptions.
    return result;
  }
}

Override this method in String, int, and double implementations. For example, in Smi:

String _toExceptionString() => 'int(${toString()})';

[ghost]

Added this to the M2 milestone.

[ghost]

Is this still valid, I think this has been fixed by library team.

[peter-ahe-google]

I fixed this in r12533.

---

Set owner to @peter-ahe-google.
Added Fixed label.