Fwd: New checker "jc.IsNil"

[Tim Penhey]

On 24/11/14 14:02, Tim Penhey wrote:
> On 19/11/14 01:16, roger peppe wrote:
>> On 18 November 2014 04:22, Tim Penhey <tim.penhey at canonical.com> wrote:
>>> 'ello 'ackers,
>>>
>>> This is something that I have been meaning to add for quite some time.
>>>
>>> We have been recording stack traces with the juju/errors library, but
>>> until now, they have been of limited use.
>>>
>>> One of the key places I have wanted to see the stack trace for a while
>>> is when running tests, and I have a function that returns an error, I'd
>>> normally have:
>>>
>>>   c.Assert(err, gc.IsNil)
>>>
>>> to make sure the error is nil.  Now I have added a checker into the
>>> juju/testing/checkers that is error aware.
>>>
>>> If you now use jc.IsNil instead of gc.IsNil, and the value is an error,
>>> and the error has a stack trace, it will get printed out.
>>>
>>> Very handy.
>>>
>>> The dependencies of master have the versions you need to use it now.
>>>
>>> Cheers,
>>> Tim
>>
>> One thing that I've been meaning to do for a while is
>> change all occurrences of c.Assert(err, gc.IsNil) to
>> c.Assert(err, gc.Equals, nil), because technically the former is
>> wrong, as it could be a typed nil but still erroneously
>> pass the test.
> 
> Interesting.  I've modified my checker to reject typed nils, and am
> currently running it over the entire codebase. A few intermittent
> failures the first time through, and a place I missed. Currently running
> the second time through.

Actually I thought it was going this, but when I wrote a test to
confirm, I found that there isn't really a way to check in the checker
the difference between a typed-nil and a nil pointer to a type..

Since the value is passed into the checker as an "interface{}", if it
was a *foo and nil, the interface records those types.  If it was a
typed nil in an interface, it ends up looking like a *foo that is nil.

IFAICT we have four options:

 * gc.Assert(err, gc.Equals, nil)
 * write an explicit nil checker that *ONLY* passes for '== nil'
 * write an explicit error nil checker
 * do nothing, continue using jc.IsNil and code reviews

I'm probably, -1, -1, +0, and +1 respectively on the above options.

Curious about others.

Tim