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Apr 7, 2023
-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.
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.
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