Implement formatter specializations for container adaptors (#4825)

Co-authored-by: Stephan T. Lavavej <[email protected]>

Author: frederick-vs-ja

stl/inc/format

@@ -4774,6 +4774,38 @@ public:
 private:
     _Fill_align_and_width_specs<_CharT> _Specs;
 };
+
+// Per LWG-3997, `_CharT` in library-provided `formatter` specializations is
+// constrained to character types supported by `format`.
+template <class _AdaptorType, _Format_supported_charT _CharT, template <class> class _RefView>
+struct _Adaptor_formatter_base {
+private:
+    using _Container             = _AdaptorType::container_type;
+    using _Maybe_const_container = _Fmt_maybe_const<_Container, _CharT>;
+    using _Maybe_const_adaptor   = _Maybe_const<is_const_v<_Maybe_const_container>, _AdaptorType>;
+
+    formatter<_RefView<_Maybe_const_container>, _CharT> _Underlying;
+
+public:
+    template <class _ParseCtx>
+    constexpr _ParseCtx::iterator parse(_ParseCtx& _Ctx) {
+        return _Underlying.parse(_Ctx);
+    }
+
+    template <class _FmtCtx>
+    _FmtCtx::iterator format(_Maybe_const_adaptor& _Adaptor, _FmtCtx& _Ctx) const {
+        struct _Container_exposer : _AdaptorType {
+            using _AdaptorType::c;
+
+            _Container_exposer(const _Container_exposer&)            = delete;
+            _Container_exposer& operator=(const _Container_exposer&) = delete;
+            ~_Container_exposer()                                    = delete;
+        };
+
+        constexpr auto _Mem_cont_ptr = &_Container_exposer::c;
+        return _Underlying.format(_Adaptor.*_Mem_cont_ptr, _Ctx);
+    }
+};
 #endif // _HAS_CXX23
 _STD_END
 

stl/inc/queue

@@ -18,6 +18,7 @@
 
 #if _HAS_CXX23
 #include <__msvc_ranges_to.hpp>
+#include <format>
 #include <iterator>
 #endif // _HAS_CXX23
 
@@ -223,6 +224,14 @@ void swap(queue<_Ty, _Container>& _Left, queue<_Ty, _Container>& _Right) noexcep
 template <class _Ty, class _Container, class _Alloc>
 struct uses_allocator<queue<_Ty, _Container>, _Alloc> : uses_allocator<_Container, _Alloc>::type {};
 
+#if _HAS_CXX23
+// Per LWG-3997, `_CharT` in library-provided `formatter` specializations is
+// constrained to character types supported by `format`.
+template <_Format_supported_charT _CharT, class _Ty, formattable<_CharT> _Container>
+struct formatter<queue<_Ty, _Container>, _CharT>
+    : _Adaptor_formatter_base<queue<_Ty, _Container>, _CharT, _RANGES ref_view> {};
+#endif // _HAS_CXX23
+
 _EXPORT_STD template <class _Ty, class _Container = vector<_Ty>, class _Pr = less<typename _Container::value_type>>
 class priority_queue {
 public:
@@ -490,6 +499,13 @@ void swap(priority_queue<_Ty, _Container, _Pr>& _Left, priority_queue<_Ty, _Cont
 template <class _Ty, class _Container, class _Pr, class _Alloc>
 struct uses_allocator<priority_queue<_Ty, _Container, _Pr>, _Alloc> : uses_allocator<_Container, _Alloc>::type {};
 
+#if _HAS_CXX23
+// Per LWG-3997, `_CharT` in library-provided `formatter` specializations is
+// constrained to character types supported by `format`.
+template <_Format_supported_charT _CharT, class _Ty, formattable<_CharT> _Container, class _Comp>
+struct formatter<priority_queue<_Ty, _Container, _Comp>, _CharT>
+    : _Adaptor_formatter_base<priority_queue<_Ty, _Container, _Comp>, _CharT, _RANGES ref_view> {};
+#endif // _HAS_CXX23
 _STD_END
 
 #pragma pop_macro("new")

stl/inc/stack

@@ -11,6 +11,7 @@
 
 #if _HAS_CXX23
 #include <__msvc_ranges_to.hpp>
+#include <format>
 #include <iterator>
 #endif // _HAS_CXX23
 
@@ -209,6 +210,14 @@ void swap(stack<_Ty, _Container>& _Left, stack<_Ty, _Container>& _Right) noexcep
 
 template <class _Ty, class _Container, class _Alloc>
 struct uses_allocator<stack<_Ty, _Container>, _Alloc> : uses_allocator<_Container, _Alloc>::type {};
+
+#if _HAS_CXX23
+// Per LWG-3997, `_CharT` in library-provided `formatter` specializations is
+// constrained to character types supported by `format`.
+template <_Format_supported_charT _CharT, class _Ty, formattable<_CharT> _Container>
+struct formatter<stack<_Ty, _Container>, _CharT>
+    : _Adaptor_formatter_base<stack<_Ty, _Container>, _CharT, _RANGES ref_view> {};
+#endif // _HAS_CXX23
 _STD_END
 
 #pragma pop_macro("new")

stl/inc/yvals_core.h

@@ -360,7 +360,6 @@
 // P2273R3 constexpr unique_ptr
 // P2278R4 cbegin Should Always Return A Constant Iterator
 // P2286R8 Formatting Ranges
-//     (only the '?' format specifier for strings and characters)
 // P2291R3 constexpr Integral <charconv>
 // P2302R4 ranges::contains, ranges::contains_subrange
 // P2321R2 zip
@@ -384,6 +383,7 @@
 // P2539R4 Synchronizing print() With The Underlying Stream
 // P2540R1 Empty Product For Certain Views
 // P2549R1 unexpected<E>::error()
+// P2585R1 Improve Default Container Formatting
 // P2599R2 mdspan: index_type, size_type
 // P2604R0 mdspan: data_handle_type, data_handle(), exhaustive
 // P2613R1 mdspan: empty()
@@ -1756,6 +1756,7 @@ _EMIT_STL_ERROR(STL1004, "C++98 unexpected() is incompatible with C++23 unexpect
 #define __cpp_lib_constexpr_typeinfo                202106L
 #define __cpp_lib_containers_ranges                 202202L
 #define __cpp_lib_expected                          202211L
+#define __cpp_lib_format_ranges                     202207L
 #define __cpp_lib_formatters                        202302L
 #define __cpp_lib_forward_like                      202207L
 #define __cpp_lib_freestanding_expected             202311L

tests/libcxx/expected_results.txt

@@ -244,14 +244,6 @@ std/language.support/support.limits/support.limits.general/cstdlib.version.compi
 # P2255R2 "Type Traits To Detect References Binding To Temporaries"
 std/language.support/support.limits/support.limits.general/type_traits.version.compile.pass.cpp FAIL
 
-# P2286R8 Formatting Ranges
-std/containers/container.adaptors/container.adaptors.format/format.functions.format.pass.cpp FAIL
-std/containers/container.adaptors/container.adaptors.format/format.functions.vformat.pass.cpp FAIL
-std/containers/container.adaptors/container.adaptors.format/format.pass.cpp FAIL
-std/containers/container.adaptors/container.adaptors.format/parse.pass.cpp FAIL
-std/containers/container.adaptors/container.adaptors.format/types.compile.pass.cpp FAIL
-std/utilities/format/format.formattable/concept.formattable.compile.pass.cpp FAIL
-
 
 # *** MISSING COMPILER FEATURES ***
 # P1169R4 static operator()
@@ -969,6 +961,7 @@ std/input.output/string.streams/stringstream/stringstream.members/str.allocator_
 # These formatter tests need to create basic_format_contexts, so test_format_context.h
 # says "Please create a vendor specific version of the test functions".
 # If we do, some of these tests should be able to work.
+std/containers/container.adaptors/container.adaptors.format/format.pass.cpp FAIL
 std/containers/sequences/vector.bool/vector.bool.fmt/format.pass.cpp FAIL
 std/thread/thread.threads/thread.thread.class/thread.thread.id/format.pass.cpp FAIL
 std/utilities/format/format.formatter/format.context/format.context/advance_to.pass.cpp FAIL

tests/std/test.lst

@@ -617,6 +617,7 @@ tests\P2278R4_const_span
 tests\P2278R4_ranges_const_iterator_machinery
 tests\P2278R4_ranges_const_range_machinery
 tests\P2278R4_views_as_const
+tests\P2286R8_text_formatting_container_adaptors
 tests\P2286R8_text_formatting_debug_enabled_specializations
 tests\P2286R8_text_formatting_escaping
 tests\P2286R8_text_formatting_escaping_legacy_text_encoding

tests/std/tests/P2286R8_text_formatting_container_adaptors/env.lst

@@ -0,0 +1,4 @@
+# Copyright (c) Microsoft Corporation.
+# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+RUNALL_INCLUDE ..\usual_latest_matrix.lst