[cfe-dev] Bug 18275 - Incorrect const qualifier behavior in definition.

Richard Smith richard at metafoo.co.uk
Wed Feb 19 13:00:56 PST 2014

On Wed, Feb 19, 2014 at 12:52 PM, suyog sarda <sardask01 at gmail.com> wrote:

> Thanks Richard for the review. Even i felt that cv qualifier checking and
> setting is not suitable (though the standard 13.1/3 is specifically related
> to CV qualifiers). Earlier i was checking CV qualifiers and setting type,
> which obviously failed for function templates. And i agree to your point
> that if the parameter is not dependent then set the type as in instantiated
> function.
> In that case, do we still need to check if the parameters are CV qualified
> alongwith checking if parameter is dependent? I am attaching a patch where
> we do not check if the parameters are CV qualified but only checks if it is
> not dependent and then set the type. This patch works for the test case in
> the bug with no regression. Also, if we are not checking CV qualifiers and
> just checking only dependent type then is it feasible to put comment
> regarding standard 13.1/3? How should comment look if above patch is fine.

The approach in the patch looks OK.  I don't think referencing 13.1/3 is
worthwhile: it's reasonable to expect that anyone reading the Clang source
knows that parameter declarations in function redeclarations can differ in
top-level cv-qualifiers. What's worth pointing out here is (1) that we need
the type to match the pattern we're instantiating, and (2) that we don't
need to do this for dependent types because those shouldn't differ in
cv-qualifiers (with a FIXME that we currently allow dependent types with
different cv-qualifeirs to be treated as redeclarations).

> Also, i am pasting test case from the bug itself. Please let me know which
> file to put it in. I cannot think of a negative test case for this bug.
> Your help is greatly appreciated.
> Test case :
> *struct B
> {
>     void f(const int);
> };
> void B::f(int x)
> {
>     x = 0;
> }
> void f()
> {
>     B b;
>     b.f(0);
> }*
> This testcase doesn't look right: you need to use a template to trigger
the issue.

> On Wed, Feb 19, 2014 at 12:26 AM, Richard Smith <metafoo at gmail.com> wrote:
>> This patch needs testcases.
>> Also, the way in which you're updating the type of the parameter doesn't
>> look correct -- there's no reason to think that the qualifiers will be
>> local.
>> We discussed cases like this at the WG21 meeting in Issaquah last week,
>> and decided that cv-stripping should *not* be applied to dependent
>> parameter types when determining whether two function templates are
>> redeclarations. Therefore:
>>   template<typename T> void f(T);
>>   template<typename T> void f(const T);
>> ... are not redeclarations (because, for instance, they have different
>> parameter types when T = int[]).
>> That makes this problem easier to fix: if the parameter type within
>> PatternDecl is not dependent, set the type of the parameter in the
>> instantiated function to that type. Otherwise, leave it alone, since we
>> already know it will match.
>> On Tue Feb 18 2014 at 6:02:55 AM, suyog sarda <sardask01 at gmail.com>
>> wrote:
>>> Gentle Ping !! Please help in reviewing the patch for bug 18275.
>>> --
>>> With regards,
>>> Suyog Sarda
> --
> With regards,
> Suyog Sarda
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