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

Jason Merrill via Gcc-patches Mon, 20 Mar 2023 11:41:10 -0700

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

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

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