libstdc++: Disable std::string{,_view} construction from nullptr (P2166R1)

Implement this C++23 feature. Because construction from a null pointer
is undefined, we can implement it for C++11 and up, turning undefined
behaviour into a compilation error.

libstdc++-v3/ChangeLog:

	* include/bits/basic_string.h (basic_string(nullptr_t)): Define
	as deleted.
	(operator=(nullptr_t)): Likewise.
	* include/bits/cow_string.h (basic_string(nullptr_t)): Likewise.
	(operator=(nullptr_t)): Likewise.
	* include/std/string_view (basic_string_view(nullptr_t)):
	Likewise.
	* testsuite/21_strings/basic_string/cons/char/nullptr.cc: New test.
	* testsuite/21_strings/basic_string_view/cons/char/nonnull.cc:
	Change dg-warning to dg-error.
	* testsuite/21_strings/basic_string_view/cons/wchar_t/nonnull.cc:
	Likewise.

diff --git a/libstdc++-v3/include/bits/basic_string.h b/libstdc++-v3/include/bits/basic_string.h
index 24c454d..68c3884 100644 (file)
--- a/libstdc++-v3/include/bits/basic_string.h
+++ b/libstdc++-v3/include/bits/basic_string.h
@@ -623,6 +623,8 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
          _M_construct(__str.begin(), __str.end());
       }
 
+      basic_string(nullptr_t) = delete;
+      basic_string& operator=(nullptr_t) = delete;
 #endif // C++11
 
       /**

diff --git a/libstdc++-v3/include/bits/cow_string.h b/libstdc++-v3/include/bits/cow_string.h
index ba4a8cc..f054012 100644 (file)
--- a/libstdc++-v3/include/bits/cow_string.h
+++ b/libstdc++-v3/include/bits/cow_string.h
@@ -667,6 +667,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
        else
          _M_dataplus._M_p = _S_construct(__str.begin(), __str.end(), __a);
       }
+
+      basic_string(nullptr_t) = delete;
+      basic_string& operator=(nullptr_t) = delete;
 #endif // C++11
 
       /**

diff --git a/libstdc++-v3/include/std/string_view b/libstdc++-v3/include/std/string_view
index d8cbee9..996b03f 100644 (file)
--- a/libstdc++-v3/include/std/string_view
+++ b/libstdc++-v3/include/std/string_view
@@ -168,6 +168,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 #endif // C++23
 #endif // C++20
 
+      basic_string_view(nullptr_t) = delete;
+
       constexpr basic_string_view&
       operator=(const basic_string_view&) noexcept = default;
 

diff --git a/libstdc++-v3/testsuite/21_strings/basic_string/cons/char/nullptr.cc b/libstdc++-v3/testsuite/21_strings/basic_string/cons/char/nullptr.cc
new file mode 100644 (file)
index 0000000..fdb24ae
--- /dev/null
+++ b/libstdc++-v3/testsuite/21_strings/basic_string/cons/char/nullptr.cc
@@ -0,0 +1,4 @@
+// { dg-do compile { target c++11 } }
+#include <string>
+
+std::string s = nullptr; // { dg-error "deleted" "P2166R1" }

diff --git a/libstdc++-v3/testsuite/21_strings/basic_string_view/cons/char/nonnull.cc b/libstdc++-v3/testsuite/21_strings/basic_string_view/cons/char/nonnull.cc
index b33af08..f42f95e 100644 (file)
--- a/libstdc++-v3/testsuite/21_strings/basic_string_view/cons/char/nonnull.cc
+++ b/libstdc++-v3/testsuite/21_strings/basic_string_view/cons/char/nonnull.cc
@@ -25,5 +25,5 @@ test01()
 {
   std::string_view s((const char*)nullptr); // { dg-warning "\\\[-Wnonnull" }
   std::string_view t((char*)nullptr);      // { dg-warning "\\\[-Wnonnull" }
-  std::string_view u(nullptr);             // { dg-warning "\\\[-Wnonnull" }
+  std::string_view u(nullptr);             // { dg-error "deleted" }
 }

diff --git a/libstdc++-v3/testsuite/21_strings/basic_string_view/cons/wchar_t/nonnull.cc b/libstdc++-v3/testsuite/21_strings/basic_string_view/cons/wchar_t/nonnull.cc
index 4c10131..e480f7c 100644 (file)
--- a/libstdc++-v3/testsuite/21_strings/basic_string_view/cons/wchar_t/nonnull.cc
+++ b/libstdc++-v3/testsuite/21_strings/basic_string_view/cons/wchar_t/nonnull.cc
@@ -25,5 +25,5 @@ test01()
 {
   std::wstring_view s((const wchar_t*)nullptr);        // { dg-warning "\\\[-Wnonnull" }
   std::wstring_view t((wchar_t*)nullptr);      // { dg-warning "\\\[-Wnonnull" }
-  std::wstring_view u(nullptr);                        // { dg-warning "\\\[-Wnonnull" }
+  std::wstring_view u(nullptr);                        // { dg-error "deleted" }
 }