Re: [Emacs-diffs] trunk r116999: Provide function for asking vc about project root

Re: [Emacs-diffs] trunk r116999: Provide function for asking vc about project root

[Stefan Monnier]

> +        (condition-case err
> +            (vc-call-backend backend 'root default-directory)
> +          (vc-not-supported
> +           (unless (eq (cadr err) 'root)
> +             (signal (car err) (cdr err)))
> +           nil)))))

Why do we need this gymnastics?


        Stefan

Re: [Emacs-diffs] trunk r116999: Provide function for asking vc about project root

[Daniel Colascione]

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On 04/21/2014 07:43 AM, Stefan Monnier wrote:
>> +        (condition-case err
>> +            (vc-call-backend backend 'root default-directory)
>> +          (vc-not-supported
>> +           (unless (eq (cadr err) 'root)
>> +             (signal (car err) (cdr err)))
>> +           nil)))))
> 
> Why do we need this gymnastics?

So that we don't accidentally suppress errors we *don't* expect to get.


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Re: [Emacs-diffs] trunk r116999: Provide function for asking vc about project root

[Stefan Monnier]

>>> +        (condition-case err
>>> +            (vc-call-backend backend 'root default-directory)
>>> +          (vc-not-supported
>>> +           (unless (eq (cadr err) 'root)
>>> +             (signal (car err) (cdr err)))
>>> +           nil)))))
>> Why do we need this gymnastics?
> So that we don't accidentally suppress errors we *don't* expect to get.

No: I see the hypothetical reason, but I was wondering about
a practical reason.  IOW, I think this is overkill.  Note that the cost
is not only in code complexity but catching&re-raising signals also
defeats the backtraces in debug-on-error, which can be a pain.

I even wonder if we should allow `root' to fail.  E.g. RCS/CVS could
just walk up the directories until there's no RCS/CVS subdir.


        Stefan

Re: [Emacs-diffs] trunk r116999: Provide function for asking vc about project root

[Daniel Colascione]

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On 04/21/2014 02:51 PM, Stefan Monnier wrote:
>>>> +        (condition-case err
>>>> +            (vc-call-backend backend 'root default-directory)
>>>> +          (vc-not-supported
>>>> +           (unless (eq (cadr err) 'root)
>>>> +             (signal (car err) (cdr err)))
>>>> +           nil)))))
>>> Why do we need this gymnastics?
>> So that we don't accidentally suppress errors we *don't* expect to get.
> 
> No: I see the hypothetical reason, but I was wondering about
> a practical reason.  IOW, I think this is overkill.  Note that the cost
> is not only in code complexity but catching&re-raising signals also
> defeats the backtraces in debug-on-error, which can be a pain.

We're not catching all errors --- just vc-not-supported --- and it
amounts to an assertion that nothing else went horribly wrong, because
we re-raise only in cases where we'd otherwise swallow the error, and an
error with a truncated stack is at least better than nothing at all.

> I even wonder if we should allow `root' to fail.  E.g. RCS/CVS could
> just walk up the directories until there's no RCS/CVS subdir.

Works for me. Backends could also just have their root functions
explicitly return nil if they can't figure it out.


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Re: [Emacs-diffs] trunk r116999: Provide function for asking vc about project root

[Stefan Monnier]

>> I even wonder if we should allow `root' to fail.  E.g. RCS/CVS could
>> just walk up the directories until there's no RCS/CVS subdir.
> Works for me. Backends could also just have their root functions
> explicitly return nil if they can't figure it out.

Exactly.  So we shouldn't catch errors at all in vc-root-dir.


        Stefan