On Wed, Mar 01, 2023 at 04:30:16PM -0500, Jason Merrill wrote:
> On 3/1/23 15:33, Marek Polacek wrote:
> > -Wmismatched-tags warns about the (harmless) struct/class mismatch.
> > For, e.g.,
> >
> > template<typename T> struct A { };
> > class A<int> a;
> >
> > it works by adding A<T> to the class2loc hash table while parsing the
> > class-head and then, while parsing the elaborate type-specifier, we
> > add A<int>. At the end of c_parse_file we go through the table and
> > warn about the class-key mismatches. In this PR we crash though; we
> > have
> >
> > template<typename T> struct A {
> > template<typename U> struct W { };
> > };
> > struct A<int>::W<int> w; // #1
> >
> > where while parsing A and #1 we've stashed
> > A<T>
> > A<T>::W<U>
> > A<int>::W<int>
> > into class2loc. Then in class_decl_loc_t::diag_mismatched_tags TYPE
> > is A<int>::W<int>, and specialization_of gets us A<int>::W<U>, which
> > is not in class2loc, so we crash on gcc_assert (cdlguide). But it's
> > OK not to have found A<int>::W<U>, we should just look one "level" up,
> > that is, A<T>::W<U>.
> >
> > It's important to handle class specializations, so e.g.
> >
> > template<>
> > struct A<char> {
> > template<typename U>
> > class W { };
> > };
> >
> > where W's class-key is different than in the primary template above,
> > so we should warn depending on whether we're looking into A<char>
> > or into a different instantiation.
> >
> > Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
> >
> > PR c++/106259
> >
> > gcc/cp/ChangeLog:
> >
> > * parser.cc (class_decl_loc_t::diag_mismatched_tags): If the first
> > lookup of SPEC didn't find anything, try to look for
> > most_general_template.
> >
> > gcc/testsuite/ChangeLog:
> >
> > * g++.dg/warn/Wmismatched-tags-11.C: New test.
> > ---
> > gcc/cp/parser.cc | 30 +++++++++++++++----
> > .../g++.dg/warn/Wmismatched-tags-11.C | 23 ++++++++++++++
> > 2 files changed, 47 insertions(+), 6 deletions(-)
> > create mode 100644 gcc/testsuite/g++.dg/warn/Wmismatched-tags-11.C
> >
> > diff --git a/gcc/cp/parser.cc b/gcc/cp/parser.cc
> > index 1a124f5395e..b528ee7b1d9 100644
> > --- a/gcc/cp/parser.cc
> > +++ b/gcc/cp/parser.cc
> > @@ -34473,14 +34473,32 @@ class_decl_loc_t::diag_mismatched_tags (tree
> > type_decl)
> > be (and inevitably is) at index zero. */
> > tree spec = specialization_of (type);
> > cdlguide = class2loc.get (spec);
> > + /* It's possible that we didn't find SPEC. Consider:
> > +
> > + template<typename T> struct A {
> > + template<typename U> struct W { };
> > + };
> > + struct A<int>::W<int> w; // #1
> > +
> > + where while parsing A and #1 we've stashed
> > + A<T>
> > + A<T>::W<U>
> > + A<int>::W<int>
> > + into CLASS2LOC. If TYPE is A<int>::W<int>, specialization_of
> > + will yield A<int>::W<U> which may be in CLASS2LOC if we had
> > + an A<int> class specialization, but otherwise won't be in it.
> > + So try to look up A<T>::W<U>. */
> > + if (!cdlguide)
> > + {
> > + spec = DECL_TEMPLATE_RESULT (most_general_template (spec));
>
> Would it make sense to only look at most_general_template, not A<int>::W<U>
> at all?
I think that would break with class specialization, as in...
> > +template<typename T> struct A {
> > + template<typename U>
> > + struct W { };
> > +};
> > +
> > +template<>
> > +struct A<char> {
> > + template<typename U>
> > + class W { };
> > +};
> > +
> > +void
> > +g ()
> > +{
> > + struct A<char>::W<int> w1; // { dg-warning "mismatched" }
...this, where we should first look into A<char>, and only if not
found, go to A<T>.
class2loc will be filled with A<char>::W<U>, added while parsing
the specialization.
> > + struct A<int>::W<int> w2;
> > + class A<char>::W<int> w3;
> > + class A<int>::W<int> w4; // { dg-warning "mismatched" }
> > +}
> >
> > base-commit: 096f034a8f5df41f610e62c1592fb90a3f551cd5
>
Marek
