Re: An xmlXPathTypeVal is never equal to XML_NAMESPACE_DECL

Hi Daniel,

On Tue, Sep 25, 2012 at 7:21 PM, Daniel Veillard <[email protected]> wrote:
> On Tue, Sep 25, 2012 at 04:21:34PM +0100, Hans Wennborg wrote:
>> Hi,
>>
>> We're using libxml2 in Chromium, and I just noticed that recent
>> versions of Clang have started warning about the following code:
>>
>> /usr/local/google/work/chrome/src/third_party/libxml/src/xpath.c:12269:13:
>> warning: comparison of constant 18 with expression of type
>> 'xmlXPathTypeVal' is always false
>> [-Wtautological-constant-out-of-range-compare]
>>                         if (type == XML_NAMESPACE_DECL)
>>                             ~~~~ ^  ~~~~~~~~~~~~~~~~~~
>>
>> In the latest version of xpath.c, the code is still there, but on line 12402.
>>
>>
>> Looking at the code, 'type' is a variable of type 'xmlXPathTypeVal',
>> whereas XML_NAMESPACE_DECL is an enumerator in 'xmlElementType'.
>>
>> Clang warns because the 'xmlXPathTypeVal' type is not wide enough to
>> hold the value of XML_NAMESPACE_DECL, and therefore the comparison
>> will never be true.
>>
>> I've tried to figure out what a good fix would be here, but I don't
>> know the code well enough. It would be great if someone could advice
>> on the best way to fix this.
>
>   You need a bit more context, the code fragment is:
>
>                     } else if (cur->type == type) {
>                         if (type == XML_NAMESPACE_DECL)
>                             XP_TEST_HIT_NS
>                         else
>                             XP_TEST_HIT
>                     } else if
>
>  So yes the comparison is done to the wrong type ... but the line
> before we checked that type and cur->type have the same value !
>
> We can change the test to:
>
>                         if (cur->type == XML_NAMESPACE_DECL)
>
> this will silent Clang, but the semantic should be exactly the same
> (as far as I know equality is transitive even in C :-)
> I'm  pushing the change,

New versions of Clang have started warning about this code again,
specifically this:

../../third_party/libxml/src/xpath.c:12420:28:
error: comparison of two values with different enumeration types
('xmlElementType' and 'xmlXPathTypeVal') [-Werror,-Wenum-compare]
                    } else if (cur->type == type) {
                               ~~~~~~~~~ ^  ~~~~

I'm not familiar enough with this code to tell what's going on, but
the comparison does look a little odd.

Just wanted to let you know.

Thanks,
Hans