https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106608
--- Comment #7 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Egor Pugin from comment #1)
> All major compilers (MSVC, GCC, Clang) of all (tried) modern versions (in
> case of GCC — before 12) build this code without problems. Is this a GCC
> regression?
Your links clearly show you're compiling with Clang though, not GCC. The paste
starts with:
[1/135] /usr/lib/ccache/bin/clang++
The code can be reduced to:
template<class T>
struct vector
{
T* ptr;
vector();
vector(const vector&);
~vector() { ++ptr; } // requires T to be complete
};
struct nullopt_t { };
constexpr nullopt_t nullopt{};
template<class T>
struct optional_payload
{
optional_payload() = default;
~optional_payload() { if (engaged) value.~T(); }
union {
unsigned char dummy;
T value;
};
bool engaged = false;
};
template<class T>
struct optional_base
{
optional_base() = default;
~optional_base() = default;
optional_payload<T> payload;
};
template<class T>
struct optional : optional_base<T>
{
constexpr optional(nullopt_t) { }
};
struct ScanInfo;
struct List {
List(optional<vector<ScanInfo>>&& = nullopt);
};
GCC compiles this, but Clang doesn't:
$ clang++ -std=c++17 -c inc.cc
inc.cc:36:13: error: call to implicitly-deleted default constructor of
'optional_base<vector<ScanInfo>>'
constexpr optional(nullopt_t) { }
^
inc.cc:47:39: note: in instantiation of member function
'optional<vector<ScanInfo>>::optional' requested here
List(optional<vector<ScanInfo>>&& = nullopt);
^
inc.cc:28:3: note: explicitly defaulted function was implicitly deleted here
optional_base() = default;
^
inc.cc:30:23: note: default constructor of 'optional_base<vector<ScanInfo>>' is
implicitly deleted because field 'payload' has a deleted default constructor
optional_payload<T> payload;
^
inc.cc:16:3: note: explicitly defaulted function was implicitly deleted here
optional_payload() = default;
^
inc.cc:20:7: note: default constructor of 'optional_payload<vector<ScanInfo>>'
is implicitly deleted because variant field 'value' has a non-trivial default
constructor
T value;
^
1 error generated.
Neither does EDG:
$ edg --c++17 -c inc.cc
"inc.cc", line 36: error: the default constructor of
"optional_base<vector<ScanInfo>>" cannot be referenced -- it is a
deleted function
constexpr optional(nullopt_t) { }
^
detected during instantiation of "optional<T>::optional(nullopt_t)
[with T=vector<ScanInfo>]" at line 42
"inc.cc", line 7: error: expression must be a pointer to a complete object type
~vector() { ++ptr; } // requires T to be complete
^
detected during:
instantiation of "vector<T>::~vector() [with T=ScanInfo]" at line
17
instantiation of "optional_payload<T>::~optional_payload() [with
T=vector<ScanInfo>]" at line 43
2 errors detected in the compilation of "inc.cc".
Nor MSVC:
<source>(7): error C2036: 'ScanInfo *': unknown size
<source>(7): note: while compiling class template member function
'vector<ScanInfo>::~vector(void)'
<source>(44): note: see reference to function template instantiation
'vector<ScanInfo>::~vector(void)' being compiled
<source>(20): note: see reference to class template instantiation
'vector<ScanInfo>' being compiled
<source>(30): note: see reference to class template instantiation
'optional_payload<T>' being compiled
with
[
T=vector<ScanInfo>
]
<source>(35): note: see reference to class template instantiation
'optional_base<T>' being compiled
with
[
T=vector<ScanInfo>
]
<source>(42): note: see reference to class template instantiation
'optional<vector<ScanInfo>>' being compiled
Compiler returned: 2
Maybe the code is ill-formed (no diagnostic required), or maybe G++ is being
too generous to compile it, but I don't think there's a libstdc++ bug here.
