Re: [xml] An xmlXPathTypeVal is never equal to XML_NAMESPACE_DECL

[Daniel Veillard <veillard redhat com>]

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,

Daniel

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