On Tue, 2010-08-10 at 15:04 +0300, Daniel Shahaf wrote:
> (I intended to commit that to trunk)
>
> Julian Foad wrote on Tue, Aug 10, 2010 at 12:17:24 +0100:
> > On Mon, 2010-08-09, danie...@apache.org wrote:
> > >
> > > +/** Return TRUE if @a err's chain contains the error code @a apr_err.
> > > + *
> > > + * @since New in 1.7.
> > > + */
> > > +svn_boolean_t
> > > +svn_error_has_cause(svn_error_t *err, apr_status_t apr_err);
> >
> > This looks like it could be a useful API.
> >
>
> I'll need it to dig beneath ra_svn's wrapping of server-generated errors by
> another error code.
>
> > I would expect to be able to call such a function on a NULL error
> > pointer, and the result should be FALSE since "no error" doesn't have
> > any cause that can be expressed in an apr_status_t.
>
> Ahem, doesn't (apr_status_t)APR_SUCCESS mean "no error"?
Yes but it's not really "a cause of the error".
> >
> > > +svn_boolean_t
> > > +svn_error_has_cause(svn_error_t *err, apr_status_t apr_err)
> > > +{
> > > + svn_error_t *child;
> > > +
> > > + if (! err && ! apr_err)
> > > + /* The API doesn't specify the behaviour when ERR is NULL. */
> > > + return TRUE;
> >
> > What's this block for?
>
> To make svn_error_has_cause(SVN_NO_ERROR, apr_err) return TRUE if and only
> if apr_err == APR_SUCCESS.
>
> > The behaviour I mentioned above would fall out
> > from just removing this block. It looks like this is so that you can
> > write svn_error_has_cause(err, APR_SUCCESS) and get TRUE if ERR is NULL
> > or contains APR_SUCCESS anywhere in its chain, but is that really
> > useful?
> >
>
> I didn't consider the option that APR_SUCCESS could occur as part of the
> chain. Good point.
>
> > - Julian
> >
>
> I can see several options:
>
> * forbid passing SVN_NO_ERROR
> * return FALSE on SVN_NO_ERROR
> * reture (apr_err == APR_SUCCESS ? TRUE : FALSE) on SVN_NO_ERROR
>
> Right now, the API does the first and the code the third.
>
>
> I suppose the question is (1) whether we expect the caller to test for
> SVN_NO_ERROR before calling this function, and (2) whether we expect people to
> pass APR_SUCCESS to this function. Personally my answers (while writing
> this) were: (1) yes (2) no.
Generally we have found that with error testing it's convenient to be
able to write "err = foo(); do_something_with(err);" without having to
check "err" is non-null first. I agree with (2) - I don't think it
makes much sense to pass APR_SUCCESS to this function.
- Julian
> >
> > > + for (child = err; child; child = child->child)
> > > + if (child->apr_err == apr_err)
> > > + return TRUE;
> > > +
> > > + return FALSE;
> > > +}
> >
> >
> >
