As [class.copy.ctor] says, the type of an implicitly declared copy constructor will be either
X::X(const X&) if each potentially constructed subobject of a class type M (or array thereof) has a copy constructor whose first parameter is of type const M& or const volatile M&. Otherwise, the implicitly-declared copy constructor will have the form X::X(X&) Similarly for implicitly-declared copy assignment operator: it will be either X& operator=(const X&) or X& operator=(X&) Previously, the declared type of an explicitly defaulted function had to be the same as if it had been implicitly declared, otherwise the code was ill-formed. But Core Issue 1331 [1] changes this in such a way that it be defined as deleted instead, with two exceptions for an assignment operator with a mismatched return type, and an assignment operator with a parameter type that's not a reference. The change itself seems trivial (unless I'm missing something), so most of my effort went into writing testcases for various scenarios I could think of. We already give errors for cases that are still considered ill-formed. [1] http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0641r2.html Bootstrapped/regtested on x86_64-linux, ok for trunk? 2018-06-12 Marek Polacek <pola...@redhat.com> Core issue 1331 - const mismatch with defaulted copy constructor * class.c (check_bases_and_members): When checking a defaulted function, mark it as deleted rather than giving an error. * g++.dg/cpp0x/defaulted15.C (struct F): Remove dg-error. * g++.dg/cpp0x/defaulted52.C: New test. * g++.dg/cpp0x/defaulted53.C: New test. * g++.dg/cpp0x/defaulted54.C: New test. * g++.dg/cpp0x/defaulted55.C: New test. * g++.dg/cpp0x/defaulted56.C: New test. * g++.dg/cpp0x/defaulted57.C: New test. * g++.dg/cpp0x/defaulted58.C: New test. * g++.dg/cpp0x/defaulted59.C: New test. * g++.dg/cpp0x/defaulted60.C: New test. diff --git gcc/cp/class.c gcc/cp/class.c index fbf39035e18..b6e78c6377d 100644 --- gcc/cp/class.c +++ gcc/cp/class.c @@ -5660,9 +5660,9 @@ check_bases_and_members (tree t) if (fn_const_p && !imp_const_p) /* If the function is defaulted outside the class, we just - give the synthesis error. */ - error ("%q+D declared to take const reference, but implicit " - "declaration would take non-const", fn); + give the synthesis error. Core Issue #1331 says this is + no longer ill-formed, it is defined as deleted instead. */ + DECL_DELETED_FN (fn) = true; } defaulted_late_check (fn); } diff --git gcc/testsuite/g++.dg/cpp0x/defaulted15.C gcc/testsuite/g++.dg/cpp0x/defaulted15.C index fabcc23a150..1e0b3545840 100644 --- gcc/testsuite/g++.dg/cpp0x/defaulted15.C +++ gcc/testsuite/g++.dg/cpp0x/defaulted15.C @@ -48,8 +48,7 @@ struct F struct G: public F { - // Can't be const because F copy ctor isn't. - G(const G&) = default; // { dg-error "const" } + G(const G&) = default; }; struct H diff --git gcc/testsuite/g++.dg/cpp0x/defaulted52.C gcc/testsuite/g++.dg/cpp0x/defaulted52.C index e69de29bb2d..c617230b493 100644 --- gcc/testsuite/g++.dg/cpp0x/defaulted52.C +++ gcc/testsuite/g++.dg/cpp0x/defaulted52.C @@ -0,0 +1,20 @@ +// Core Issue #1331 (const mismatch with defaulted copy constructor) +// { dg-do compile { target c++11 } } + +struct M +{ + M(); + // So that W wouldn't have had "const W&" copy ctor if it were + // implicitly declared. + M(M&); +}; + +template<typename T> struct W +{ + W(); + // This should now compile and be =deleted. + W(const W&) = default; + T t; +}; + +W<M> w; diff --git gcc/testsuite/g++.dg/cpp0x/defaulted53.C gcc/testsuite/g++.dg/cpp0x/defaulted53.C index e69de29bb2d..8147e7e2ad1 100644 --- gcc/testsuite/g++.dg/cpp0x/defaulted53.C +++ gcc/testsuite/g++.dg/cpp0x/defaulted53.C @@ -0,0 +1,35 @@ +// Core Issue #1331 (const mismatch with defaulted copy constructor) +// { dg-do compile { target c++11 } } + +struct M +{ + M& operator=(M&); +}; + +struct R +{ + R& operator=(R&) = default; + M m; +}; + +struct S +{ + S& operator=(const S&) = default; + M m; +}; + +struct T +{ + // If F is an assignment operator, and the return type of T1 + // differs from the return type of T2 the program is ill-formed. + T operator=(T&) = default; // { dg-error "defaulted" } + M m; +}; + +struct U +{ + // If F is an assignment operator, and T1's parameter type is + // not a reference, the program is ill-formed. + U& operator=(U) = default; // { dg-error "defaulted" } + M m; +}; diff --git gcc/testsuite/g++.dg/cpp0x/defaulted54.C gcc/testsuite/g++.dg/cpp0x/defaulted54.C index e69de29bb2d..f8ddc4e47ce 100644 --- gcc/testsuite/g++.dg/cpp0x/defaulted54.C +++ gcc/testsuite/g++.dg/cpp0x/defaulted54.C @@ -0,0 +1,18 @@ +// Core Issue #1331 (const mismatch with defaulted copy constructor) +// { dg-do compile { target c++11 } } + +struct M +{ + M(); + M(M&); +}; + +template<typename T> struct W +{ + W(); + W(const W&) = default; // { dg-error "binding" } + T t; +}; + +W<M> w; +W<M> w2 = w; // { dg-error "use of deleted function" } diff --git gcc/testsuite/g++.dg/cpp0x/defaulted55.C gcc/testsuite/g++.dg/cpp0x/defaulted55.C index e69de29bb2d..04cfc172000 100644 --- gcc/testsuite/g++.dg/cpp0x/defaulted55.C +++ gcc/testsuite/g++.dg/cpp0x/defaulted55.C @@ -0,0 +1,19 @@ +// Core Issue #1331 (const mismatch with defaulted copy constructor) +// { dg-do compile { target c++11 } } + +struct M +{ + M(); + M(M&); +}; + +template<typename T> struct W +{ + W(); + W(W&) = default; + // T1 and T2 may have differing ref-qualifiers (copy assign op). + constexpr W& operator=(const W&) && = default; // { dg-error "defaulted" "" { target c++11_down } } + T t; +}; + +W<M> w; diff --git gcc/testsuite/g++.dg/cpp0x/defaulted56.C gcc/testsuite/g++.dg/cpp0x/defaulted56.C index e69de29bb2d..e7ce12c5566 100644 --- gcc/testsuite/g++.dg/cpp0x/defaulted56.C +++ gcc/testsuite/g++.dg/cpp0x/defaulted56.C @@ -0,0 +1,25 @@ +// Core Issue #1331 (const mismatch with defaulted copy constructor) +// { dg-do compile { target c++11 } } + +// If T2 (what would be the implicit declaration) has a parameter of +// type const C&, the corresponding parameter of T1 may be of type C&. + +struct S +{ + constexpr S(S &) = default; +}; + +struct T +{ + constexpr T(volatile T &) = default; // { dg-error "defaulted" } +}; + +struct U +{ + constexpr U(const volatile U &) = default; // { dg-error "defaulted" } +}; + +struct V +{ + constexpr V(const V &) = default; +}; diff --git gcc/testsuite/g++.dg/cpp0x/defaulted57.C gcc/testsuite/g++.dg/cpp0x/defaulted57.C index e69de29bb2d..37fb7dd6e1d 100644 --- gcc/testsuite/g++.dg/cpp0x/defaulted57.C +++ gcc/testsuite/g++.dg/cpp0x/defaulted57.C @@ -0,0 +1,25 @@ +// Core Issue #1331 (const mismatch with defaulted copy constructor) +// { dg-do compile { target c++11 } } + +// If T2 (what would be the implicit declaration) has a parameter of +// type const C&, the corresponding parameter of T1 may be of type C&. + +struct S +{ + S& operator=(S &) = default; +}; + +struct T +{ + T& operator=(volatile T &) = default; // { dg-error "defaulted" } +}; + +struct U +{ + U& operator=(const volatile U &) = default; // { dg-error "defaulted" } +}; + +struct V +{ + V& operator=(const V &) = default; +}; diff --git gcc/testsuite/g++.dg/cpp0x/defaulted58.C gcc/testsuite/g++.dg/cpp0x/defaulted58.C index e69de29bb2d..920a4ad0c6d 100644 --- gcc/testsuite/g++.dg/cpp0x/defaulted58.C +++ gcc/testsuite/g++.dg/cpp0x/defaulted58.C @@ -0,0 +1,22 @@ +// Core Issue #1331 (const mismatch with defaulted copy constructor) +// { dg-do compile { target c++11 } } + +struct M +{ + M() = default; + M& operator=(M&); +}; + +template<typename T> struct W +{ + W() = default; + W& operator=(const W&) = default; // { dg-error "binding" } + T t; +}; + +int +main () +{ + W<M> w1, w2; + w1 = w2; // { dg-error "use of deleted function" } +} diff --git gcc/testsuite/g++.dg/cpp0x/defaulted59.C gcc/testsuite/g++.dg/cpp0x/defaulted59.C index e69de29bb2d..4f871d7f5b1 100644 --- gcc/testsuite/g++.dg/cpp0x/defaulted59.C +++ gcc/testsuite/g++.dg/cpp0x/defaulted59.C @@ -0,0 +1,12 @@ +// Core Issue #1331 (const mismatch with defaulted copy constructor) +// { dg-do compile { target c++11 } } + +struct M +{ + M(M&) = default; +}; + +struct W : public M +{ + W(const W&) = default; +}; diff --git gcc/testsuite/g++.dg/cpp0x/defaulted60.C gcc/testsuite/g++.dg/cpp0x/defaulted60.C index e69de29bb2d..ad025236cce 100644 --- gcc/testsuite/g++.dg/cpp0x/defaulted60.C +++ gcc/testsuite/g++.dg/cpp0x/defaulted60.C @@ -0,0 +1,18 @@ +// Core Issue #1331 (const mismatch with defaulted copy constructor) +// { dg-do compile { target c++11 } } + +struct M +{ + M(M&); +}; + +struct W +{ + W(); + W(const W&); + M m; +}; + +// Not first declaration. +W::W(const W&) = default; // { dg-error "binding" } +W w;
