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Revert "[SemaCXX] Implement CWG2137 (list-initialization from objects of the same type) (#77768)"
This reverts commit 9247013. Causes compilation errors on valid code, see #77768 (comment).
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7 files changed

+33
-210
lines changed

7 files changed

+33
-210
lines changed

‎clang/lib/Sema/SemaInit.cpp

Lines changed: 10 additions & 30 deletions
Original file line numberDiff line numberDiff line change
@@ -4200,7 +4200,7 @@ static OverloadingResult ResolveConstructorOverload(
42004200
/// \param IsListInit Is this list-initialization?
42014201
/// \param IsInitListCopy Is this non-list-initialization resulting from a
42024202
/// list-initialization from {x} where x is the same
4203-
/// aggregate type as the entity?
4203+
/// type as the entity?
42044204
static void TryConstructorInitialization(Sema &S,
42054205
const InitializedEntity &Entity,
42064206
const InitializationKind &Kind,
@@ -4230,14 +4230,6 @@ static void TryConstructorInitialization(Sema &S,
42304230
Entity.getKind() !=
42314231
InitializedEntity::EK_LambdaToBlockConversionBlockElement);
42324232

4233-
bool CopyElisionPossible = false;
4234-
auto ElideConstructor = [&] {
4235-
// Convert qualifications if necessary.
4236-
Sequence.AddQualificationConversionStep(DestType, VK_PRValue);
4237-
if (ILE)
4238-
Sequence.RewrapReferenceInitList(DestType, ILE);
4239-
};
4240-
42414233
// C++17 [dcl.init]p17:
42424234
// - If the initializer expression is a prvalue and the cv-unqualified
42434235
// version of the source type is the same class as the class of the
@@ -4250,17 +4242,11 @@ static void TryConstructorInitialization(Sema &S,
42504242
if (S.getLangOpts().CPlusPlus17 && !RequireActualConstructor &&
42514243
UnwrappedArgs.size() == 1 && UnwrappedArgs[0]->isPRValue() &&
42524244
S.Context.hasSameUnqualifiedType(UnwrappedArgs[0]->getType(), DestType)) {
4253-
if (ILE && !DestType->isAggregateType()) {
4254-
// CWG2311: T{ prvalue_of_type_T } is not eligible for copy elision
4255-
// Make this an elision if this won't call an initializer-list
4256-
// constructor. (Always on an aggregate type or check constructors first.)
4257-
assert(!IsInitListCopy &&
4258-
"IsInitListCopy only possible with aggregate types");
4259-
CopyElisionPossible = true;
4260-
} else {
4261-
ElideConstructor();
4262-
return;
4263-
}
4245+
// Convert qualifications if necessary.
4246+
Sequence.AddQualificationConversionStep(DestType, VK_PRValue);
4247+
if (ILE)
4248+
Sequence.RewrapReferenceInitList(DestType, ILE);
4249+
return;
42644250
}
42654251

42664252
const RecordType *DestRecordType = DestType->getAs<RecordType>();
@@ -4305,12 +4291,6 @@ static void TryConstructorInitialization(Sema &S,
43054291
S, Kind.getLocation(), Args, CandidateSet, DestType, Ctors, Best,
43064292
CopyInitialization, AllowExplicit,
43074293
/*OnlyListConstructors=*/true, IsListInit, RequireActualConstructor);
4308-
4309-
if (CopyElisionPossible && Result == OR_No_Viable_Function) {
4310-
// No initializer list candidate
4311-
ElideConstructor();
4312-
return;
4313-
}
43144294
}
43154295

43164296
// C++11 [over.match.list]p1:
@@ -4592,9 +4572,9 @@ static void TryListInitialization(Sema &S,
45924572
return;
45934573
}
45944574

4595-
// C++11 [dcl.init.list]p3, per DR1467 and DR2137:
4596-
// - If T is an aggregate class and the initializer list has a single element
4597-
// of type cv U, where U is T or a class derived from T, the object is
4575+
// C++11 [dcl.init.list]p3, per DR1467:
4576+
// - If T is a class type and the initializer list has a single element of
4577+
// type cv U, where U is T or a class derived from T, the object is
45984578
// initialized from that element (by copy-initialization for
45994579
// copy-list-initialization, or by direct-initialization for
46004580
// direct-list-initialization).
@@ -4605,7 +4585,7 @@ static void TryListInitialization(Sema &S,
46054585
// - Otherwise, if T is an aggregate, [...] (continue below).
46064586
if (S.getLangOpts().CPlusPlus11 && InitList->getNumInits() == 1 &&
46074587
!IsDesignatedInit) {
4608-
if (DestType->isRecordType() && DestType->isAggregateType()) {
4588+
if (DestType->isRecordType()) {
46094589
QualType InitType = InitList->getInit(0)->getType();
46104590
if (S.Context.hasSameUnqualifiedType(InitType, DestType) ||
46114591
S.IsDerivedFrom(InitList->getBeginLoc(), InitType, DestType)) {

‎clang/lib/Sema/SemaOverload.cpp

Lines changed: 10 additions & 28 deletions
Original file line numberDiff line numberDiff line change
@@ -1568,37 +1568,19 @@ TryUserDefinedConversion(Sema &S, Expr *From, QualType ToType,
15681568
// called for those cases.
15691569
if (CXXConstructorDecl *Constructor
15701570
= dyn_cast<CXXConstructorDecl>(ICS.UserDefined.ConversionFunction)) {
1571-
QualType FromType;
1572-
SourceLocation FromLoc;
1573-
// C++11 [over.ics.list]p6, per DR2137:
1574-
// C++17 [over.ics.list]p6:
1575-
// If C is not an initializer-list constructor and the initializer list
1576-
// has a single element of type cv U, where U is X or a class derived
1577-
// from X, the implicit conversion sequence has Exact Match rank if U is
1578-
// X, or Conversion rank if U is derived from X.
1579-
if (const auto *InitList = dyn_cast<InitListExpr>(From);
1580-
InitList && InitList->getNumInits() == 1 &&
1581-
!S.isInitListConstructor(Constructor)) {
1582-
const Expr *SingleInit = InitList->getInit(0);
1583-
FromType = SingleInit->getType();
1584-
FromLoc = SingleInit->getBeginLoc();
1585-
} else {
1586-
FromType = From->getType();
1587-
FromLoc = From->getBeginLoc();
1588-
}
1589-
QualType FromCanon =
1590-
S.Context.getCanonicalType(FromType.getUnqualifiedType());
1571+
QualType FromCanon
1572+
= S.Context.getCanonicalType(From->getType().getUnqualifiedType());
15911573
QualType ToCanon
15921574
= S.Context.getCanonicalType(ToType).getUnqualifiedType();
15931575
if (Constructor->isCopyConstructor() &&
15941576
(FromCanon == ToCanon ||
1595-
S.IsDerivedFrom(FromLoc, FromCanon, ToCanon))) {
1577+
S.IsDerivedFrom(From->getBeginLoc(), FromCanon, ToCanon))) {
15961578
// Turn this into a "standard" conversion sequence, so that it
15971579
// gets ranked with standard conversion sequences.
15981580
DeclAccessPair Found = ICS.UserDefined.FoundConversionFunction;
15991581
ICS.setStandard();
16001582
ICS.Standard.setAsIdentityConversion();
1601-
ICS.Standard.setFromType(FromType);
1583+
ICS.Standard.setFromType(From->getType());
16021584
ICS.Standard.setAllToTypes(ToType);
16031585
ICS.Standard.CopyConstructor = Constructor;
16041586
ICS.Standard.FoundCopyConstructor = Found;
@@ -5324,18 +5306,18 @@ TryListConversion(Sema &S, InitListExpr *From, QualType ToType,
53245306
IsDesignatedInit)
53255307
return Result;
53265308

5327-
// Per DR1467 and DR2137:
5328-
// If the parameter type is an aggregate class X and the initializer list
5329-
// has a single element of type cv U, where U is X or a class derived from
5330-
// X, the implicit conversion sequence is the one required to convert the
5331-
// element to the parameter type.
5309+
// Per DR1467:
5310+
// If the parameter type is a class X and the initializer list has a single
5311+
// element of type cv U, where U is X or a class derived from X, the
5312+
// implicit conversion sequence is the one required to convert the element
5313+
// to the parameter type.
53325314
//
53335315
// Otherwise, if the parameter type is a character array [... ]
53345316
// and the initializer list has a single element that is an
53355317
// appropriately-typed string literal (8.5.2 [dcl.init.string]), the
53365318
// implicit conversion sequence is the identity conversion.
53375319
if (From->getNumInits() == 1 && !IsDesignatedInit) {
5338-
if (ToType->isRecordType() && ToType->isAggregateType()) {
5320+
if (ToType->isRecordType()) {
53395321
QualType InitType = From->getInit(0)->getType();
53405322
if (S.Context.hasSameUnqualifiedType(InitType, ToType) ||
53415323
S.IsDerivedFrom(From->getBeginLoc(), InitType, ToType))

‎clang/test/CXX/drs/dr14xx.cpp

Lines changed: 10 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -488,6 +488,16 @@ namespace dr1467 { // dr1467: 3.7 c++11
488488
}
489489
} // nonaggregate
490490

491+
namespace SelfInitIsNotListInit {
492+
struct S {
493+
S();
494+
explicit S(S &);
495+
S(const S &);
496+
};
497+
S s1;
498+
S s2 = {s1}; // ok, not list-initialization so we pick the non-explicit constructor
499+
}
500+
491501
struct NestedInit { int a, b, c; };
492502
NestedInit ni[1] = {{NestedInit{1, 2, 3}}};
493503

‎clang/test/CXX/drs/dr21xx.cpp

Lines changed: 0 additions & 45 deletions
Original file line numberDiff line numberDiff line change
@@ -11,16 +11,6 @@
1111
// cxx98-error@-1 {{variadic macros are a C99 feature}}
1212
#endif
1313

14-
namespace std {
15-
__extension__ typedef __SIZE_TYPE__ size_t;
16-
17-
template<typename E> struct initializer_list {
18-
const E *p; size_t n;
19-
initializer_list(const E *p, size_t n);
20-
initializer_list();
21-
};
22-
}
23-
2414
namespace dr2100 { // dr2100: 12
2515
template<const int *P, bool = true> struct X {};
2616
template<typename T> struct A {
@@ -142,41 +132,6 @@ namespace dr2126 { // dr2126: 12
142132
#endif
143133
}
144134

145-
namespace dr2137 { // dr2137: 18
146-
#if __cplusplus >= 201103L
147-
struct Q {
148-
Q();
149-
Q(Q&&);
150-
Q(std::initializer_list<Q>) = delete; // #dr2137-Qcons
151-
};
152-
153-
Q x = Q { Q() };
154-
// since-cxx11-error@-1 {{call to deleted constructor of 'Q'}}
155-
// since-cxx11-note@#dr2137-Qcons {{'Q' has been explicitly marked deleted here}}
156-
157-
int f(Q); // #dr2137-f
158-
int y = f({ Q() });
159-
// since-cxx11-error@-1 {{call to deleted constructor of 'Q'}}
160-
// since-cxx11-note@#dr2137-Qcons {{'Q' has been explicitly marked deleted here}}
161-
// since-cxx11-note@#dr2137-f {{passing argument to parameter here}}
162-
163-
struct U {
164-
U();
165-
U(const U&);
166-
};
167-
168-
struct Derived : U {
169-
Derived();
170-
Derived(const Derived&);
171-
} d;
172-
173-
int g(Derived);
174-
int g(U(&&)[1]) = delete;
175-
176-
int z = g({ d });
177-
#endif
178-
}
179-
180135
namespace dr2140 { // dr2140: 9
181136
#if __cplusplus >= 201103L
182137
union U { int a; decltype(nullptr) b; };

‎clang/test/CXX/drs/dr23xx.cpp

Lines changed: 0 additions & 85 deletions
Original file line numberDiff line numberDiff line change
@@ -6,16 +6,6 @@
66
// RUN: %clang_cc1 -std=c++23 %s -verify=expected,since-cxx11,since-cxx14,since-cxx17,since-cxx20 -fexceptions -fcxx-exceptions -pedantic-errors 2>&1 | FileCheck %s
77
// RUN: %clang_cc1 -std=c++2c %s -verify=expected,since-cxx11,since-cxx14,since-cxx17,since-cxx20 -fexceptions -fcxx-exceptions -pedantic-errors 2>&1 | FileCheck %s
88

9-
namespace std {
10-
__extension__ typedef __SIZE_TYPE__ size_t;
11-
12-
template<typename E> struct initializer_list {
13-
const E *p; size_t n;
14-
initializer_list(const E *p, size_t n);
15-
initializer_list();
16-
};
17-
}
18-
199
#if __cplusplus >= 201103L
2010
namespace dr2303 { // dr2303: 12
2111
template <typename... T>
@@ -57,81 +47,6 @@ void g() {
5747
} //namespace dr2303
5848
#endif
5949

60-
namespace dr2311 { // dr2311: 18 open
61-
#if __cplusplus >= 201707L
62-
template<typename T>
63-
void test() {
64-
// Ensure none of these try to call a move constructor.
65-
T a = T{T(0)};
66-
T b{T(0)};
67-
auto c{T(0)};
68-
T d = {T(0)};
69-
auto e = {T(0)};
70-
#if __cplusplus >= 202302L
71-
auto f = auto{T(0)};
72-
#endif
73-
void(*fn)(T);
74-
fn({T(0)});
75-
}
76-
77-
struct NonMovable {
78-
NonMovable(int);
79-
NonMovable(NonMovable&&) = delete;
80-
};
81-
struct NonMovableNonApplicableIList {
82-
NonMovableNonApplicableIList(int);
83-
NonMovableNonApplicableIList(NonMovableNonApplicableIList&&) = delete;
84-
NonMovableNonApplicableIList(std::initializer_list<int>);
85-
};
86-
struct ExplicitMovable {
87-
ExplicitMovable(int);
88-
explicit ExplicitMovable(ExplicitMovable&&);
89-
};
90-
struct ExplicitNonMovable {
91-
ExplicitNonMovable(int);
92-
explicit ExplicitNonMovable(ExplicitNonMovable&&) = delete;
93-
};
94-
struct ExplicitNonMovableNonApplicableIList {
95-
ExplicitNonMovableNonApplicableIList(int);
96-
explicit ExplicitNonMovableNonApplicableIList(ExplicitNonMovableNonApplicableIList&&) = delete;
97-
ExplicitNonMovableNonApplicableIList(std::initializer_list<int>);
98-
};
99-
struct CopyOnly {
100-
CopyOnly(int);
101-
CopyOnly(const CopyOnly&);
102-
CopyOnly(CopyOnly&&) = delete;
103-
};
104-
struct ExplicitCopyOnly {
105-
ExplicitCopyOnly(int);
106-
explicit ExplicitCopyOnly(const ExplicitCopyOnly&);
107-
explicit ExplicitCopyOnly(ExplicitCopyOnly&&) = delete;
108-
};
109-
110-
template void test<NonMovable>();
111-
template void test<NonMovableNonApplicableIList>();
112-
template void test<ExplicitMovable>();
113-
template void test<ExplicitNonMovable>();
114-
template void test<ExplicitNonMovableNonApplicableIList>();
115-
template void test<CopyOnly>();
116-
template void test<ExplicitCopyOnly>();
117-
118-
struct any {
119-
template<typename T>
120-
any(T&&);
121-
};
122-
123-
template<typename T>
124-
struct X {
125-
X();
126-
X(T) = delete; // #dr2311-X
127-
};
128-
129-
X<std::initializer_list<any>> x{ X<std::initializer_list<any>>() };
130-
// since-cxx17-error@-1 {{call to deleted constructor of 'X<std::initializer_list<any>>'}}
131-
// since-cxx17-note@#dr2311-X {{'X' has been explicitly marked deleted here}}
132-
#endif
133-
}
134-
13550
// dr2331: na
13651
// dr2335 is in dr2335.cxx
13752

‎clang/www/cxx_dr_status.html

Lines changed: 2 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -12630,7 +12630,7 @@ <h2 id="cxxdr">C++ defect report implementation status</h2>
1263012630
<td><a href="https://cplusplus.github.io/CWG/issues/2137.html">2137</a></td>
1263112631
<td>CD4</td>
1263212632
<td>List-initialization from object of same type</td>
12633-
<td class="unreleased" align="center">Clang 18</td>
12633+
<td class="unknown" align="center">Unknown</td>
1263412634
</tr>
1263512635
<tr id="2138">
1263612636
<td><a href="https://cplusplus.github.io/CWG/issues/2138.html">2138</a></td>
@@ -13674,7 +13674,7 @@ <h2 id="cxxdr">C++ defect report implementation status</h2>
1367413674
<td><a href="https://cplusplus.github.io/CWG/issues/2311.html">2311</a></td>
1367513675
<td>open</td>
1367613676
<td>Missed case for guaranteed copy elision</td>
13677-
<td class="unreleased" align="center">Clang 18</td>
13677+
<td align="center">Not resolved</td>
1367813678
</tr>
1367913679
<tr id="2312">
1368013680
<td><a href="https://cplusplus.github.io/CWG/issues/2312.html">2312</a></td>

‎libcxx/test/std/utilities/utility/pairs/pairs.pair/ctor.pair_U_V_move.pass.cpp

Lines changed: 1 addition & 20 deletions
Original file line numberDiff line numberDiff line change
@@ -121,26 +121,7 @@ int main(int, char**)
121121
test_pair_rv<CopyOnly, CopyOnly&>();
122122
test_pair_rv<CopyOnly, CopyOnly&&>();
123123

124-
/* For ExplicitTypes::CopyOnly, two of the viable candidates for initializing from a non-const xvalue are:
125-
* pair(const pair&); // (defaulted copy constructor)
126-
* template<class U1, class U2> explicit pair(const pair<U1, U2>&&); [U1 = ExplicitTypes::CopyOnly, U2 = int]
127-
* This results in diverging behavior for test_convertible which uses copy-list-initialization
128-
* Prior to CWG2137, this would have selected the first (non-explicit) ctor as explicit ctors would not be considered
129-
* Afterwards, it should select the second since it is a better match, and then failed because it is explicit
130-
*
131-
* This may change with future defect reports, and some compilers only have partial support for CWG2137,
132-
* so use std::is_convertible directly to avoid a copy-list-initialization
133-
*/
134-
{
135-
using P1 = std::pair<ExplicitTypes::CopyOnly, int>;
136-
using P2 = std::pair<int, ExplicitTypes::CopyOnly>;
137-
using UP1 = std::pair<ExplicitTypes::CopyOnly, int>&&;
138-
using UP2 = std::pair<int, ExplicitTypes::CopyOnly>&&;
139-
static_assert(std::is_constructible<P1, UP1>::value, "");
140-
static_assert(std::is_convertible<P1, UP1>::value, "");
141-
static_assert(std::is_constructible<P2, UP2>::value, "");
142-
static_assert(std::is_convertible<P2, UP2>::value, "");
143-
}
124+
test_pair_rv<ExplicitTypes::CopyOnly, ExplicitTypes::CopyOnly>();
144125
test_pair_rv<ExplicitTypes::CopyOnly, ExplicitTypes::CopyOnly&, true, false>();
145126
test_pair_rv<ExplicitTypes::CopyOnly, ExplicitTypes::CopyOnly&&, true, false>();
146127

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