exist-development

[Exist-development] Pushing error message xquery line numbers into type comparisons

[Adam R. <ad...@ex...>]

I had a problem with a type data conversion, in this case with
effectiveBooleanValue being called on AbstractDateTimeValue.

I could not find the cause of the error, and so I 'hacked' the code to
push the calling expression into the type comparisson, so that I could
then extract the line and column numbers of the calling XQuery to
annotate the XPathException that was thrown.

This is just a simple example, see the attached diff, but I am
wondering if there is value in, expanding on this concept and pushing
xquery line context information into the datatype system for better
errors.

A cleaner approach might be to change the exceptions thrown by the
types, then catch them in the expression, add the expression
information and then throw them as XPathExceptions?

The following xquery -

if(current-dateTime())then
()
else()

Will cause the error I was seeing, with my patch applied you will also
get the line number of where the error in the XQuery occurred.

Thoughts please :-)


-- 
Adam Retter

eXist Developer
{ United Kingdom }
ad...@ex...
irc://irc.freenode.net/existdb

Re: [Exist-development] Pushing error message xquery line numbers into type comparisons

[Wolfgang M. <wol...@ex...>]

> This is just a simple example, see the attached diff, but I am
> wondering if there is value in, expanding on this concept and pushing
> xquery line context information into the datatype system for better
> errors.

It somehow doesn't feel right to add caller information to the
returned data values. Our approach so far has been to catch the thrown
exception on a higher level and add the line information there. See
class FunctionCall for an example. I think this concept could be
extended, though we won't be able to cover all cases where a type
error could occur.
But for your example, the if expression could certainly catch and
rethrow the exception.

Wolfgang

Re: [Exist-development] Pushing error message xquery line numbers into type comparisons

[Adam R. <ad...@ex...>]

On 17 March 2010 21:07, Wolfgang Meier <wol...@ex...> wrote:
>> This is just a simple example, see the attached diff, but I am
>> wondering if there is value in, expanding on this concept and pushing
>> xquery line context information into the datatype system for better
>> errors.
>
> It somehow doesn't feel right to add caller information to the
> returned data values. Our approach so far has been to catch the thrown
> exception on a higher level and add the line information there. See
> class FunctionCall for an example. I think this concept could be
> extended, though we won't be able to cover all cases where a type
> error could occur.
> But for your example, the if expression could certainly catch and
> rethrow the exception.

Okay cool :-)

I actually simplified, in my case the invoking expression was OpOr.

I agree that maybe it doesnt make sense to send in the Expression to
the Type, which is what lead me to thinking about changing the
Exception thrown by Types from XPathExpression (which I think we over
use too much) to something new like XMLDataTypeException, this should
then immediately highlight where this Exception is being thrown, we
can then write wrapper try/catch in the culprit Expressions that catch
that Exception, and throw an XPathException with the line and column
number of the Expression added in.

Hows that sound?


> Wolfgang
>



-- 
Adam Retter

eXist Developer
{ United Kingdom }
ad...@ex...
irc://irc.freenode.net/existdb