Re: [PATCH RFA] libstdc++: add ADL friends

[Jason Merrill]

On 11/3/25 5:26 PM, Patrick Palka wrote:

On Sun, 2 Nov 2025, Jason Merrill wrote:

Tested x86_64-pc-linux-gnu, OK for trunk?

-- 8< --

Since the implementation namespaces __detail and __exception_ptr aren't
exported from std, ADL can't find these functions there.  Adding friend
declarations makes it work.

I thought Nathaniel's module ADL fixes (for 121705 and/or 117658) would
make this unnecessary?

I don't think they help here, because e.g. in
18_support/exception_ptr/rethrow_exception.cc there is no instantiation 
context for the call

    rethrow_exception(make_exception_ptr(0));

which happens in a non-template function.  I don't see anything in 
[basic.lookup.argdep] that would cause us to look into the interface 
unit of std in this case.
libstdc++-v3/ChangeLog:

        * include/bits/quoted_string.h: Add ADL friends.
        * libsupc++/exception_ptr.h: Add ADL friend.
---
  libstdc++-v3/include/bits/quoted_string.h | 23 +++++++++++++++++++++++
  libstdc++-v3/libsupc++/exception_ptr.h    |  4 ++++
  2 files changed, 27 insertions(+)

diff --git a/libstdc++-v3/include/bits/quoted_string.h 
b/libstdc++-v3/include/bits/quoted_string.h
index 3a828d5eab9..9a51aa367fe 100644
--- a/libstdc++-v3/include/bits/quoted_string.h
+++ b/libstdc++-v3/include/bits/quoted_string.h
@@ -61,6 +61,23 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
        _Quoted_string&
        operator=(_Quoted_string&) = delete;
  
+	// Friends for ADL with module std.
+       template<typename _CharT2, typename _Traits>
+       friend std::basic_ostream<_CharT2, _Traits>&
+       operator<<(std::basic_ostream<_CharT2, _Traits>& __os,
+                  const _Quoted_string<const _CharT2*, _CharT2>& __str);
+
+       template<typename _CharT2, typename _Traits, typename _String2>
+       friend std::basic_ostream<_CharT2, _Traits>&
+       operator<<(std::basic_ostream<_CharT2, _Traits>& __os,
+                  const _Quoted_string<_String2, _CharT2>& __str);
+
+       template<typename _CharT2, typename _Traits, typename _Alloc>
+       friend std::basic_istream<_CharT2, _Traits>&
+       operator>>(std::basic_istream<_CharT2, _Traits>& __is,
+                  const _Quoted_string<basic_string<_CharT2, _Traits, _Alloc>&,
+                  _CharT2>& __str);
+
        _String _M_string;
        _CharT _M_delim;
        _CharT _M_escape;
@@ -78,6 +95,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
        _Quoted_string&
        operator=(_Quoted_string&) = delete;
  
+	// Friend for ADL with module std.
+       template<typename _CharT2, typename _Traits2, typename _String2>
+       friend std::basic_ostream<_CharT2, _Traits2>&
+       operator<<(std::basic_ostream<_CharT2, _Traits2>& __os,
+                  const _Quoted_string<_String2, _CharT2>& __str);
+
        basic_string_view<_CharT, _Traits> _M_string;
        _CharT _M_delim;
        _CharT _M_escape;
diff --git a/libstdc++-v3/libsupc++/exception_ptr.h 
b/libstdc++-v3/libsupc++/exception_ptr.h
index f673a334333..76482db3756 100644
--- a/libstdc++-v3/libsupc++/exception_ptr.h
+++ b/libstdc++-v3/libsupc++/exception_ptr.h
@@ -214,6 +214,10 @@ namespace std _GLIBCXX_VISIBILITY(default)
        { return __x._M_exception_object != __y._M_exception_object; }
  #endif
  
+      // Friend for ADL with module std.
+      friend _GLIBCXX26_CONSTEXPR void
+      swap(exception_ptr& __lhs, exception_ptr& __rhs);
+
        const class std::type_info*
        __cxa_exception_type() const _GLIBCXX_USE_NOEXCEPT
        __attribute__ ((__pure__));

base-commit: 2be505ace7e5e29a29ab53025762cf1a100a6d76
--
2.51.0