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c++: ICE with -Wmismatched-tags and member template [PR106259]

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-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.
This commit is contained in:
Marek Polacek 2023-03-01 14:28:46 -05:00
parent da19e37ced
commit 71afd06284
2 changed files with 47 additions and 6 deletions
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30
gcc/cp/parser.cc
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@ -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));
cdlguide = class2loc.get (spec);
}
/* Now we really should have found something. */
gcc_assert (cdlguide != NULL);
}
else
{
/* Skip declarations that consistently use the same class-key. */
if (def_class_key != none_type)
return;
}
/* Skip declarations that consistently use the same class-key. */
else if (def_class_key != none_type)
return;
/* Set if a definition for the class has been seen. */
const bool def_p = cdlguide->def_p ();

23
gcc/testsuite/g++.dg/warn/Wmismatched-tags-11.C Normal file
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@ -0,0 +1,23 @@
// PR c++/106259
// { dg-do compile }
// { dg-options "-Wmismatched-tags" }
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" }
struct A<int>::W<int> w2;
class A<char>::W<int> w3;
class A<int>::W<int> w4; // { dg-warning "mismatched" }
}