From @Juerd

  use v6;

  my $foo;

  my $promise = Promise.new;
  $promise.then​: {
  note 41;
  $foo.does-not-exist; # hangs? thread dies? no error message!
  note 42; # never reached!
  };

  $promise.keep; # no difference with break

  sleep 60;

From @timo

Try with this slightly different code to see that it's not about "calling to methods inside promises", just about an exception in a Promise that nobody is interested in (no await, no .then, ...) are silently nommed​:

  use v6;

  my $foo;

  my $promise = Promise.new;

  $promise.keep; # no difference with break

  # note i added an "await" here.
  await $promise.then​: {
  note 41;
  $foo.does-not-exist; # hangs? thread dies? no error message!
  note 42; # never reached!
  };

  sleep 5;

The RT System itself - Status changed from 'new' to 'open'

From @zoffixznet

On Wed, 02 Dec 2015 13​:52​:24 -0800, timo wrote​:

just about an exception in a
Promise that nobody is interested in (no await, no .then, ...) are
silently nommed​:

This version has a `.then` but doesn't explode. Is it meant to then?

  use v6;
  my $foo;
  my $promise = Promise.new;
  $promise.keep; # no difference with break

  # note i added an "await" here.
  $promise.then({
  note 41;
  $foo.does-not-exist; # hangs? thread dies? no error message!
  note 42; # never reached!
  }).then​: { say "hi" };

  sleep 5;

And this one explodes, but there's no location shown for where the error occurs​:

  use v6;
  my $foo;
  my $promise = Promise.new;
  $promise.keep; # no difference with break

  # note i added an "await" here.
  await $promise.then({
  note 41;
  $foo.does-not-exist; # hangs? thread dies? no error message!
  note 42; # never reached!
  });

  sleep 5;

  # zoffix@​VirtualBox​:~/CPANPRC/rakudo$ ./perl6 test.p6 41
  # ===SORRY!===
  # No such method 'does-not-exist' for invocant of type 'Any'
  # zoffix@​VirtualBox​:~/CPANPRC/rakudo$

This is Rakudo version 2016.11-220-g29b228c built on MoarVM version 2016.11-41-gd2139b5