This helps with some confusion caused in GH-2538, since the output says:
> Running cleanup tasks for 'shell' provisioner...
But that's actually not true. It is running the cleanup tasks iff the
provisioner defined a cleanup task. This commit changes the
provisioner_cleanup middleware to only run cleanup tasks if the subclass
defines a cleanup task.
The reason we can't just check if the provisioner `respond_to?` the
`cleanup` method is because the parent provisioner base class (which
all provisioners inherit from) defines a blank cleanup method. This is
important because it means we never risk calling an unimplemented
cleanup function, and it also helps define the public API for a
provisioner.
Here we implement a naive solution to #5605 which catches the case that
a provided source contains an object which cannot be inspected, because
an object contained within in has an #inspect string that returns a
string that is incompatible with the encoding in
`Encoding.default_external` or a string which cannot be downcast to
7-bit ascii.
The Ruby VM implementation of "#inspect" implements this checking on
these lines of code: http://git.io/vZYNS. A Ruby level override of
this method does not cause this problem. For example:
```ruby
class Foo
def inspect
"😍".encode("UTF-16LE")
end
```
will not cause the problem, because that's a Ruby implementation and the
VM's checks don't occur.
However, if we have an Object which **does** use the VM implementation
of inspect, that contains an object that has an inspect string which
returns non-ascii, we encounter the bug. For example:
```ruby
class Bar
def inspect
"😍".encode("UTF-16LE")
end
end
class Foo
def initialize
@bar = Bar.new
end
end
Foo.new.inspect
```
Will cause the issue.
The solution this patch provides basically catches the encoding error
and inserts a string which attempts to help the user work out which
object was provided without blowing up. Most likely, this was caused
by a user having a weird encoding coming out of one of the sources
passed in, but without a full repro case, it's not clear whether a patch
should be applied to a different object in the system.
Closes#5605.
Use of $stdin, $stdout, and $stderr globals makes testing difficult. By
exposing the IO objects as writable attributes, input/output can be more
easily simulated using StringIO or doubles.
