c++: explicit ctor and list-initialization [PR109159]

  When I implemented explicit(bool) in r9-3735, I added this code to
add_template_candidate_real:
+  /* Now the explicit specifier might have been deduced; check if this
+     declaration is explicit.  If it is and we're ignoring non-converting
+     constructors, don't add this function to the set of candidates.  */
+  if ((flags & LOOKUP_ONLYCONVERTING) && DECL_NONCONVERTING_P (fn))
+    return NULL;
but as this test demonstrates, that's incorrect when we're initializing
from a {}: for list-initialization we consider explicit constructors and
complain if one is chosen.

Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk/12?

	PR c++/109159

gcc/cp/ChangeLog:

	* call.cc (add_template_candidate_real): Add explicit decls to the
	set of candidates when the initializer is a braced-init-list.

libstdc++-v3/ChangeLog:

	* testsuite/20_util/pair/cons/explicit_construct.cc: Adjust dg-error.
	* testsuite/20_util/tuple/cons/explicit_construct.cc: Likewise.
	* testsuite/23_containers/span/explicit.cc: Likewise.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp0x/explicit16.C: New test.
---
 gcc/cp/call.cc                                |  4 +-
 gcc/testsuite/g++.dg/cpp0x/explicit16.C       | 18 ++++++
 .../20_util/pair/cons/explicit_construct.cc   | 10 ++--
 .../20_util/tuple/cons/explicit_construct.cc  | 58 +++++++++----------
 .../testsuite/23_containers/span/explicit.cc  |  4 +-
 5 files changed, 57 insertions(+), 37 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/cpp0x/explicit16.C


base-commit: fbd50e867e6a782c7b56c9727bf7e1e74dae4b94
  

On 3/20/23 11:55, Marek Polacek wrote:
> When I implemented explicit(bool) in r9-3735, I added this code to
> add_template_candidate_real:
> +  /* Now the explicit specifier might have been deduced; check if this
> +     declaration is explicit.  If it is and we're ignoring non-converting
> +     constructors, don't add this function to the set of candidates.  */
> +  if ((flags & LOOKUP_ONLYCONVERTING) && DECL_NONCONVERTING_P (fn))
> +    return NULL;
> but as this test demonstrates, that's incorrect when we're initializing
> from a {}: for list-initialization we consider explicit constructors and
> complain if one is chosen.
> 
> Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk/12?

OK.

> 	PR c++/109159
> 
> gcc/cp/ChangeLog:
> 
> 	* call.cc (add_template_candidate_real): Add explicit decls to the
> 	set of candidates when the initializer is a braced-init-list.
> 
> libstdc++-v3/ChangeLog:
> 
> 	* testsuite/20_util/pair/cons/explicit_construct.cc: Adjust dg-error.
> 	* testsuite/20_util/tuple/cons/explicit_construct.cc: Likewise.
> 	* testsuite/23_containers/span/explicit.cc: Likewise.
> 
> gcc/testsuite/ChangeLog:
> 
> 	* g++.dg/cpp0x/explicit16.C: New test.
> ---
>   gcc/cp/call.cc                                |  4 +-
>   gcc/testsuite/g++.dg/cpp0x/explicit16.C       | 18 ++++++
>   .../20_util/pair/cons/explicit_construct.cc   | 10 ++--
>   .../20_util/tuple/cons/explicit_construct.cc  | 58 +++++++++----------
>   .../testsuite/23_containers/span/explicit.cc  |  4 +-
>   5 files changed, 57 insertions(+), 37 deletions(-)
>   create mode 100644 gcc/testsuite/g++.dg/cpp0x/explicit16.C
> 
> diff --git a/gcc/cp/call.cc b/gcc/cp/call.cc
> index c01e7b82457..c52a09b9be2 100644
> --- a/gcc/cp/call.cc
> +++ b/gcc/cp/call.cc
> @@ -3612,7 +3612,9 @@ add_template_candidate_real (struct z_candidate **candidates, tree tmpl,
>     /* Now the explicit specifier might have been deduced; check if this
>        declaration is explicit.  If it is and we're ignoring non-converting
>        constructors, don't add this function to the set of candidates.  */
> -  if ((flags & LOOKUP_ONLYCONVERTING) && DECL_NONCONVERTING_P (fn))
> +  if (((flags & (LOOKUP_ONLYCONVERTING|LOOKUP_LIST_INIT_CTOR))
> +       == LOOKUP_ONLYCONVERTING)
> +      && DECL_NONCONVERTING_P (fn))
>       return NULL;
>   
>     if (DECL_CONSTRUCTOR_P (fn) && nargs == 2)
> diff --git a/gcc/testsuite/g++.dg/cpp0x/explicit16.C b/gcc/testsuite/g++.dg/cpp0x/explicit16.C
> new file mode 100644
> index 00000000000..bb5a823aee6
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp0x/explicit16.C
> @@ -0,0 +1,18 @@
> +// PR c++/109159
> +// { dg-do compile { target c++11 } }
> +
> +struct A {
> +  A(float) {}
> +  template<class U>
> +  explicit A(U) {}
> +};
> +
> +void f(A t)
> +{
> +  t = {1}; // { dg-error "explicit constructor" }
> +  t = 1;
> +  A a1{1};
> +  A a2 = {1}; // { dg-error "explicit constructor" }
> +  A a3 = 1;
> +  A a4(1);
> +}
> diff --git a/libstdc++-v3/testsuite/20_util/pair/cons/explicit_construct.cc b/libstdc++-v3/testsuite/20_util/pair/cons/explicit_construct.cc
> index e875f0cbcd2..d550e9c604b 100644
> --- a/libstdc++-v3/testsuite/20_util/pair/cons/explicit_construct.cc
> +++ b/libstdc++-v3/testsuite/20_util/pair/cons/explicit_construct.cc
> @@ -37,7 +37,7 @@ struct ExplicitDefaultDefault
>   
>   std::pair<int, int> f1() {return {1,2};}
>   
> -std::pair<Explicit, Explicit> f2() {return {1,2};} // { dg-error "could not convert" }
> +std::pair<Explicit, Explicit> f2() {return {1,2};} // { dg-error "explicit constructor" }
>   
>   std::pair<long, long> f3() {return std::pair<int, int>{1,2};}
>   
> @@ -52,7 +52,7 @@ std::pair<int, int> v0{1,2};
>   
>   std::pair<Explicit, Explicit> v1{1,2};
>   
> -std::pair<Explicit, Explicit> v2 = {1,2}; // { dg-error "could not convert" }
> +std::pair<Explicit, Explicit> v2 = {1,2}; // { dg-error "explicit constructor" }
>   
>   std::pair<Explicit, Explicit> v3{std::pair<int,int>{1,2}};
>   
> @@ -99,7 +99,7 @@ void test_arg_passing()
>   {
>     f6(v0); // { dg-error "could not convert" }
>     f6(v1);
> -  f6({1,2}); // { dg-error "could not convert" }
> +  f6({1,2}); // { dg-error "explicit constructor" }
>     f6(std::pair<Explicit, Explicit>{});
>     f6(std::pair<int, int>{}); // { dg-error "could not convert" }
>     f7(v0);
> @@ -130,6 +130,6 @@ std::pair<int*, ExplicitMoveOnly> v14{nullptr, MoveOnly{}};
>   std::pair<ExplicitMoveOnly, int*> v15{MoveOnly{}, nullptr};
>   
>   std::pair<int*, ExplicitMoveOnly> v16 =
> -  {nullptr, MoveOnly{}}; // { dg-error "could not convert" }
> +  {nullptr, MoveOnly{}}; // { dg-error "explicit constructor" }
>   std::pair<ExplicitMoveOnly, int*> v17 =
> -  {MoveOnly{}, nullptr}; // { dg-error "could not convert" }
> +  {MoveOnly{}, nullptr}; // { dg-error "explicit constructor" }
> diff --git a/libstdc++-v3/testsuite/20_util/tuple/cons/explicit_construct.cc b/libstdc++-v3/testsuite/20_util/tuple/cons/explicit_construct.cc
> index 820ddef30b4..3352dd15f7d 100644
> --- a/libstdc++-v3/testsuite/20_util/tuple/cons/explicit_construct.cc
> +++ b/libstdc++-v3/testsuite/20_util/tuple/cons/explicit_construct.cc
> @@ -45,11 +45,11 @@ std::tuple<int, int> f1b() {return {1,2};}
>   std::tuple<int, int, int> f1c() {return {1,2,3};}
>   
>   std::tuple<Explicit> f2_a()
> -{return {1};} // { dg-error "could not convert" }
> +{return {1};} // { dg-error "explicit constructor" }
>   std::tuple<Explicit, Explicit> f2_b()
> -{return {1,2};} // { dg-error "could not convert" }
> +{return {1,2};} // { dg-error "explicit constructor" }
>   std::tuple<Explicit, Explicit, Explicit> f2_c()
> -{return {1,2,3};} // { dg-error "could not convert" }
> +{return {1,2,3};} // { dg-error "explicit constructor" }
>   
>   std::tuple<long> f3_a() {return std::tuple<int>{1};}
>   std::tuple<long, long> f3_b() {return std::tuple<int, int>{1,2};}
> @@ -73,22 +73,22 @@ std::tuple<long, long> f5_b() {return {1,2};}
>   std::tuple<long, long, long> f5_c() {return {1,2,3};}
>   
>   std::tuple<ExplicitDefault> f6_a()
> -{return {};} // { dg-error "could not convert" }
> +{return {};} // { dg-error "explicit constructor" }
>   std::tuple<ExplicitDefault, ExplicitDefault> f6_b()
> -{return {};} // { dg-error "could not convert" }
> +{return {};} // { dg-error "explicit constructor" }
>   std::tuple<ExplicitDefault, ExplicitDefault, ExplicitDefault> f6_c()
> -{return {};} // { dg-error "could not convert" }
> +{return {};} // { dg-error "explicit constructor" }
>   std::tuple<ExplicitDefault, int> f6_d()
> -{return {};} // { dg-error "could not convert" }
> +{return {};} // { dg-error "explicit constructor" }
>   
>   std::tuple<ExplicitDefaultDefault> f7_a()
> -{return {};} // { dg-error "could not convert" }
> +{return {};} // { dg-error "explicit constructor" }
>   std::tuple<ExplicitDefaultDefault, ExplicitDefaultDefault> f7_b()
> -{return {};} // { dg-error "could not convert" }
> +{return {};} // { dg-error "explicit constructor" }
>   std::tuple<ExplicitDefaultDefault,
>              ExplicitDefaultDefault,
>              ExplicitDefaultDefault> f7_c()
> -{return {};} // { dg-error "could not convert" }
> +{return {};} // { dg-error "explicit constructor" }
>   
>   std::tuple<int, int> fp1() {return std::pair<int, int>{1,2}; }
>   std::tuple<long, long> fp2() {return std::pair<int, int>{1,2}; }
> @@ -103,9 +103,9 @@ std::tuple<Explicit> v1_a{1};
>   std::tuple<Explicit, Explicit> v1_b{1,2};
>   std::tuple<Explicit, Explicit, Explicit> v1_c{1,2,3};
>   
> -std::tuple<Explicit> v2_a = {1}; // { dg-error "could not convert" }
> -std::tuple<Explicit, Explicit> v2_b = {1,2}; // { dg-error "could not convert" }
> -std::tuple<Explicit, Explicit, Explicit> v2_c = {1,2,3}; // { dg-error "could not convert" }
> +std::tuple<Explicit> v2_a = {1}; // { dg-error "explicit constructor" }
> +std::tuple<Explicit, Explicit> v2_b = {1,2}; // { dg-error "explicit constructor" }
> +std::tuple<Explicit, Explicit, Explicit> v2_c = {1,2,3}; // { dg-error "explicit constructor" }
>   
>   std::tuple<Explicit> v3_a{std::tuple<int>{1}};
>   std::tuple<Explicit, Explicit> v3_b{std::tuple<int,int>{1,2}};
> @@ -196,11 +196,11 @@ std::tuple<long, long, long>
>     v31_c{std::allocator_arg, std::allocator<int>{}, 1,2,3};
>   
>   std::tuple<Explicit> v32_a
> -  = {std::allocator_arg, std::allocator<int>{ }, 1}; // { dg-error "could not convert" }
> +  = {std::allocator_arg, std::allocator<int>{ }, 1}; // { dg-error "explicit constructor" }
>   std::tuple<Explicit, Explicit> v32_b
> -  = {std::allocator_arg, std::allocator<int>{}, 1, 2}; // { dg-error "could not convert" }
> +  = {std::allocator_arg, std::allocator<int>{}, 1, 2}; // { dg-error "explicit constructor" }
>   std::tuple<Explicit, Explicit, Explicit> v32_c
> -  = {std::allocator_arg, std::allocator<int>{}, 1,2,3}; // { dg-error "could not convert" }
> +  = {std::allocator_arg, std::allocator<int>{}, 1,2,3}; // { dg-error "explicit constructor" }
>   
>   std::tuple<int, int> v33{std::allocator_arg, std::allocator<int>{},
>     std::pair<int, int>{1, 2}};
> @@ -218,7 +218,7 @@ std::tuple<long, long> v37 = {std::allocator_arg, std::allocator<int>{},
>     std::pair<int, int>{1, 2}};
>   
>   std::tuple<Explicit, Explicit> v38
> -= {std::allocator_arg, std::allocator<int>{}, std::pair<int, int>{1, 2}}; // { dg-error "could not convert" }
> += {std::allocator_arg, std::allocator<int>{}, std::pair<int, int>{1, 2}}; // { dg-error "explicit constructor" }
>   
>   std::tuple<int, int> v39{std::allocator_arg, std::allocator<int>{}, v20};
>   
> @@ -232,18 +232,18 @@ std::tuple<int, int> v42 = {std::allocator_arg, std::allocator<int>{}, v20};
>   std::tuple<long, long> v43 = {std::allocator_arg, std::allocator<int>{}, v20};
>   
>   std::tuple<Explicit, Explicit> v44
> -= {std::allocator_arg, std::allocator<int>{ }, v20}; // { dg-error "could not convert" }
> += {std::allocator_arg, std::allocator<int>{ }, v20}; // { dg-error "explicit constructor" }
>   std::tuple<ExplicitDefault> v45_a{};
>   std::tuple<ExplicitDefault, int> v45_b{};
>   
> -std::tuple<ExplicitDefault> v46_a = {}; // { dg-error "could not convert" }
> -std::tuple<ExplicitDefault, int> v46_b = {}; // { dg-error "could not convert" }
> +std::tuple<ExplicitDefault> v46_a = {}; // { dg-error "explicit constructor" }
> +std::tuple<ExplicitDefault, int> v46_b = {}; // { dg-error "explicit constructor" }
>   
>   std::tuple<ExplicitDefaultDefault> v47_a{};
>   std::tuple<ExplicitDefaultDefault, int> v47_b{};
>   
> -std::tuple<ExplicitDefaultDefault> v48_a = {}; // { dg-error "could not convert" }
> -std::tuple<ExplicitDefaultDefault, int> v48_b = { }; // { dg-error "could not convert" }
> +std::tuple<ExplicitDefaultDefault> v48_a = {}; // { dg-error "explicit constructor" }
> +std::tuple<ExplicitDefaultDefault, int> v48_b = { }; // { dg-error "explicit constructor" }
>   
>   
>   struct DeletedCopy
> @@ -295,9 +295,9 @@ void test_arg_passing()
>     f8_b(v1_b);
>     f8_c(v1_c);
>   
> -  f8_a({1}); // { dg-error "could not convert" }
> -  f8_b({1,2}); // { dg-error "could not convert" }
> -  f8_c({1,2,3}); // { dg-error "could not convert" }
> +  f8_a({1}); // { dg-error "explicit constructor" }
> +  f8_b({1,2}); // { dg-error "explicit constructor" }
> +  f8_c({1,2,3}); // { dg-error "explicit constructor" }
>   
>     f8_a(std::tuple<Explicit>{});
>     f8_b(std::tuple<Explicit, Explicit>{});
> @@ -330,10 +330,10 @@ void test_arg_passing()
>     f9_b(std::tuple<long, long>{});
>     f9_c(std::tuple<long, long, long>{});
>   
> -  f10_a({}); // { dg-error "could not convert" }
> -  f10_b({}); // { dg-error "could not convert" }
> -  f11_a({}); // { dg-error "could not convert" }
> -  f11_b({}); // { dg-error "could not convert" }
> +  f10_a({}); // { dg-error "explicit constructor" }
> +  f10_b({}); // { dg-error "explicit constructor" }
> +  f11_a({}); // { dg-error "explicit constructor" }
> +  f11_b({}); // { dg-error "explicit constructor" }
>   
>     f10_a(std::tuple<ExplicitDefault>{});
>     f10_b(std::tuple<ExplicitDefault, int>{});
> diff --git a/libstdc++-v3/testsuite/23_containers/span/explicit.cc b/libstdc++-v3/testsuite/23_containers/span/explicit.cc
> index 580d69e4f09..b0a1311f02c 100644
> --- a/libstdc++-v3/testsuite/23_containers/span/explicit.cc
> +++ b/libstdc++-v3/testsuite/23_containers/span/explicit.cc
> @@ -31,11 +31,11 @@ auto first = std::begin(r), last = std::end(r);
>   
>   // span(It, size_type)
>   std::span<int> s1 = {first, 2};
> -std::span<int, 2> s2 = {first, 2}; // { dg-error "could not convert" }
> +std::span<int, 2> s2 = {first, 2}; // { dg-error "explicit constructor" }
>   
>   // span(It, End)
>   std::span<int> s3 = {first, last};
> -std::span<int, 2> s4 = {first, last}; // { dg-error "could not convert" }
> +std::span<int, 2> s4 = {first, last}; // { dg-error "explicit constructor" }
>   
>   // span(R&&)
>   std::span<int> s5 = r;
> 
> base-commit: fbd50e867e6a782c7b56c9727bf7e1e74dae4b94