On 3/1/23 17:33, Marek Polacek wrote:
On Wed, Mar 01, 2023 at 04:44:12PM -0500, Jason Merrill wrote:
On 3/1/23 16:40, Marek Polacek wrote:
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>.
I'd expect the
/* Stop if we run into an explicitly specialized class template. */
code in most_general_template to avoid that problem.
Ah, I had no idea it does that. The unconditional most_general_template
works fine for the new test, but some of the existing tests then fail.
Reduced:
template <class Z> struct S2; // #1
template <class T> class S2<const T>; // #2
extern class S2<const int> s2ci; // #3
extern struct S2<const int> s2ci; // { dg-warning "\\\[-Wmismatched-tags" }
where the unconditional most_general_template changes spec from
"class S2<const T>" to "struct S2<Z>" (both of which are in class2loc).
So it regresses the diagnostic, complaining that #3 should have "struct"
since #1 has "struct". I think we want to keep the current diagnostic,
saying that the last line should have "class" since the specialization
in line #2 has "class".
Makes sense, the patch is OK.
Jason
