diff --git a/libcxx/.clang-tidy b/libcxx/.clang-tidy
--- a/libcxx/.clang-tidy
+++ b/libcxx/.clang-tidy
@@ -50,6 +50,14 @@
     value: lower_case
   - key:   readability-identifier-naming.LocalVariablePrefix
     value: __
+  - key:   readability-identifier-naming.TemplateParameterCase
+    value: CamelCase
+  - key:   readability-identifier-naming.TemplateParameterPrefix
+    value: _
+  - key:   readability-identifier-naming.TemplateParameterIgnoredRegexp
+    value: (.*\:auto|expr-type) # This is https://llvm.org/PR56464
+  - key:   readability-identifier-naming.ValueTemplateParameterIgnoredRegexp # TODO: enforce naming of variable parameters
+    value: .*
 
 # TODO: investigate these checks
 # bugprone-branch-clone,
diff --git a/libcxx/include/__bit_reference b/libcxx/include/__bit_reference
--- a/libcxx/include/__bit_reference
+++ b/libcxx/include/__bit_reference
@@ -731,12 +731,12 @@
 
 // swap_ranges
 
-template <class __C1, class __C2>
-_LIBCPP_HIDE_FROM_ABI __bit_iterator<__C2, false>
-__swap_ranges_aligned(__bit_iterator<__C1, false> __first, __bit_iterator<__C1, false> __last,
-                      __bit_iterator<__C2, false> __result)
+template <class _Cl, class _Cr>
+_LIBCPP_HIDE_FROM_ABI __bit_iterator<_Cr, false>
+__swap_ranges_aligned(__bit_iterator<_Cl, false> __first, __bit_iterator<_Cl, false> __last,
+                      __bit_iterator<_Cr, false> __result)
 {
-    typedef __bit_iterator<__C1, false> _I1;
+    typedef __bit_iterator<_Cl, false> _I1;
     typedef  typename _I1::difference_type difference_type;
     typedef typename _I1::__storage_type __storage_type;
     const int __bits_per_word = _I1::__bits_per_word;
@@ -781,12 +781,12 @@
     return __result;
 }
 
-template <class __C1, class __C2>
-_LIBCPP_HIDE_FROM_ABI __bit_iterator<__C2, false>
-__swap_ranges_unaligned(__bit_iterator<__C1, false> __first, __bit_iterator<__C1, false> __last,
-                        __bit_iterator<__C2, false> __result)
+template <class _Cl, class _Cr>
+_LIBCPP_HIDE_FROM_ABI __bit_iterator<_Cr, false>
+__swap_ranges_unaligned(__bit_iterator<_Cl, false> __first, __bit_iterator<_Cl, false> __last,
+                        __bit_iterator<_Cr, false> __result)
 {
-    typedef __bit_iterator<__C1, false> _I1;
+    typedef __bit_iterator<_Cl, false> _I1;
     typedef  typename _I1::difference_type difference_type;
     typedef typename _I1::__storage_type __storage_type;
     const int __bits_per_word = _I1::__bits_per_word;
@@ -881,11 +881,11 @@
     return __result;
 }
 
-template <class __C1, class __C2>
+template <class _Cl, class _Cr>
 inline _LIBCPP_INLINE_VISIBILITY
-__bit_iterator<__C2, false>
-swap_ranges(__bit_iterator<__C1, false> __first1, __bit_iterator<__C1, false> __last1,
-            __bit_iterator<__C2, false> __first2)
+__bit_iterator<_Cr, false>
+swap_ranges(__bit_iterator<_Cl, false> __first1, __bit_iterator<_Cl, false> __last1,
+            __bit_iterator<_Cr, false> __first2)
 {
     if (__first1.__ctz_ == __first2.__ctz_)
         return _VSTD::__swap_ranges_aligned(__first1, __last1, __first2);
@@ -1314,15 +1314,15 @@
     friend __bit_iterator<_Dp, false> copy_backward(__bit_iterator<_Dp, _IC> __first,
                                                     __bit_iterator<_Dp, _IC> __last,
                                                     __bit_iterator<_Dp, false> __result);
-    template <class __C1, class __C2>friend __bit_iterator<__C2, false> __swap_ranges_aligned(__bit_iterator<__C1, false>,
-                                                                                           __bit_iterator<__C1, false>,
-                                                                                           __bit_iterator<__C2, false>);
-    template <class __C1, class __C2>friend __bit_iterator<__C2, false> __swap_ranges_unaligned(__bit_iterator<__C1, false>,
-                                                                                             __bit_iterator<__C1, false>,
-                                                                                             __bit_iterator<__C2, false>);
-    template <class __C1, class __C2>friend __bit_iterator<__C2, false> swap_ranges(__bit_iterator<__C1, false>,
-                                                                                 __bit_iterator<__C1, false>,
-                                                                                 __bit_iterator<__C2, false>);
+    template <class _Cl, class _Cr>friend __bit_iterator<_Cr, false> __swap_ranges_aligned(__bit_iterator<_Cl, false>,
+                                                                                           __bit_iterator<_Cl, false>,
+                                                                                           __bit_iterator<_Cr, false>);
+    template <class _Cl, class _Cr>friend __bit_iterator<_Cr, false> __swap_ranges_unaligned(__bit_iterator<_Cl, false>,
+                                                                                             __bit_iterator<_Cl, false>,
+                                                                                             __bit_iterator<_Cr, false>);
+    template <class _Cl, class _Cr>friend __bit_iterator<_Cr, false> swap_ranges(__bit_iterator<_Cl, false>,
+                                                                                 __bit_iterator<_Cl, false>,
+                                                                                 __bit_iterator<_Cr, false>);
     template <class _Dp>
     _LIBCPP_CONSTEXPR_SINCE_CXX20
     friend __bit_iterator<_Dp, false> rotate(__bit_iterator<_Dp, false>,
diff --git a/libcxx/include/__chrono/calendar.h b/libcxx/include/__chrono/calendar.h
--- a/libcxx/include/__chrono/calendar.h
+++ b/libcxx/include/__chrono/calendar.h
@@ -26,8 +26,8 @@
 {
 
 struct local_t {};
-template<class Duration>
-using local_time  = time_point<local_t, Duration>;
+template<class _Duration>
+using local_time  = time_point<local_t, _Duration>;
 using local_seconds = local_time<seconds>;
 using local_days    = local_time<days>;
 
diff --git a/libcxx/include/__format/format_context.h b/libcxx/include/__format/format_context.h
--- a/libcxx/include/__format/format_context.h
+++ b/libcxx/include/__format/format_context.h
@@ -120,9 +120,9 @@
   // TODO FMT Validate whether lazy creation is the best solution.
   optional<_VSTD::locale> __loc_;
 
-  template <class __OutIt, class __CharT>
-  friend _LIBCPP_HIDE_FROM_ABI basic_format_context<__OutIt, __CharT>
-  __format_context_create(__OutIt, basic_format_args<basic_format_context<__OutIt, __CharT>>,
+  template <class _OtherOutIt, class _OtherCharT>
+  friend _LIBCPP_HIDE_FROM_ABI basic_format_context<_OtherOutIt, _OtherCharT>
+  __format_context_create(_OtherOutIt, basic_format_args<basic_format_context<_OtherOutIt, _OtherCharT>>,
                           optional<_VSTD::locale>&&);
 
   // Note: the Standard doesn't specify the required constructors.
@@ -133,9 +133,9 @@
       : __out_it_(_VSTD::move(__out_it)), __args_(__args),
         __loc_(_VSTD::move(__loc)) {}
 #else
-  template <class __OutIt, class __CharT>
-  friend _LIBCPP_HIDE_FROM_ABI basic_format_context<__OutIt, __CharT>
-      __format_context_create(__OutIt, basic_format_args<basic_format_context<__OutIt, __CharT>>);
+  template <class _OtherOutIt, class _OtherCharT>
+  friend _LIBCPP_HIDE_FROM_ABI basic_format_context<_OtherOutIt, _OtherCharT>
+      __format_context_create(_OtherOutIt, basic_format_args<basic_format_context<_OtherOutIt, _OtherCharT>>);
 
   _LIBCPP_HIDE_FROM_ABI
   explicit basic_format_context(_OutIt __out_it,
diff --git a/libcxx/include/__format/range_default_formatter.h b/libcxx/include/__format/range_default_formatter.h
--- a/libcxx/include/__format/range_default_formatter.h
+++ b/libcxx/include/__format/range_default_formatter.h
@@ -111,8 +111,9 @@
     return __underlying_.parse(__ctx);
   }
 
-  template <class FormatContext>
-  _LIBCPP_HIDE_FROM_ABI typename FormatContext::iterator format(__maybe_const_r& __range, FormatContext& __ctx) const {
+  template <class _FormatContext>
+  _LIBCPP_HIDE_FROM_ABI typename _FormatContext::iterator
+  format(__maybe_const_r& __range, _FormatContext& __ctx) const {
     return __underlying_.format(__range, __ctx);
   }
 };
diff --git a/libcxx/include/__functional/binder1st.h b/libcxx/include/__functional/binder1st.h
--- a/libcxx/include/__functional/binder1st.h
+++ b/libcxx/include/__functional/binder1st.h
@@ -21,30 +21,30 @@
 
 #if _LIBCPP_STD_VER <= 14 || defined(_LIBCPP_ENABLE_CXX17_REMOVED_BINDERS)
 
-template <class __Operation>
+template <class _Operation>
 class _LIBCPP_TEMPLATE_VIS _LIBCPP_DEPRECATED_IN_CXX11 binder1st
-    : public __unary_function<typename __Operation::second_argument_type, typename __Operation::result_type>
+    : public __unary_function<typename _Operation::second_argument_type, typename _Operation::result_type>
 {
 protected:
-    __Operation                               op;
-    typename __Operation::first_argument_type value;
+    _Operation                               op;
+    typename _Operation::first_argument_type value;
 public:
-    _LIBCPP_INLINE_VISIBILITY binder1st(const __Operation& __x,
-                               const typename __Operation::first_argument_type __y)
+    _LIBCPP_INLINE_VISIBILITY binder1st(const _Operation& __x,
+                               const typename _Operation::first_argument_type __y)
         : op(__x), value(__y) {}
-    _LIBCPP_INLINE_VISIBILITY typename __Operation::result_type operator()
-        (typename __Operation::second_argument_type& __x) const
+    _LIBCPP_INLINE_VISIBILITY typename _Operation::result_type operator()
+        (typename _Operation::second_argument_type& __x) const
             {return op(value, __x);}
-    _LIBCPP_INLINE_VISIBILITY typename __Operation::result_type operator()
-        (const typename __Operation::second_argument_type& __x) const
+    _LIBCPP_INLINE_VISIBILITY typename _Operation::result_type operator()
+        (const typename _Operation::second_argument_type& __x) const
             {return op(value, __x);}
 };
 
-template <class __Operation, class _Tp>
+template <class _Operation, class _Tp>
 _LIBCPP_DEPRECATED_IN_CXX11 inline _LIBCPP_INLINE_VISIBILITY
-binder1st<__Operation>
-bind1st(const __Operation& __op, const _Tp& __x)
-    {return binder1st<__Operation>(__op, __x);}
+binder1st<_Operation>
+bind1st(const _Operation& __op, const _Tp& __x)
+    {return binder1st<_Operation>(__op, __x);}
 
 #endif // _LIBCPP_STD_VER <= 14 || defined(_LIBCPP_ENABLE_CXX17_REMOVED_BINDERS)
 
diff --git a/libcxx/include/__functional/binder2nd.h b/libcxx/include/__functional/binder2nd.h
--- a/libcxx/include/__functional/binder2nd.h
+++ b/libcxx/include/__functional/binder2nd.h
@@ -21,30 +21,30 @@
 
 #if _LIBCPP_STD_VER <= 14 || defined(_LIBCPP_ENABLE_CXX17_REMOVED_BINDERS)
 
-template <class __Operation>
+template <class _Operation>
 class _LIBCPP_TEMPLATE_VIS _LIBCPP_DEPRECATED_IN_CXX11 binder2nd
-    : public __unary_function<typename __Operation::first_argument_type, typename __Operation::result_type>
+    : public __unary_function<typename _Operation::first_argument_type, typename _Operation::result_type>
 {
 protected:
-    __Operation                                op;
-    typename __Operation::second_argument_type value;
+    _Operation                                op;
+    typename _Operation::second_argument_type value;
 public:
     _LIBCPP_INLINE_VISIBILITY
-    binder2nd(const __Operation& __x, const typename __Operation::second_argument_type __y)
+    binder2nd(const _Operation& __x, const typename _Operation::second_argument_type __y)
         : op(__x), value(__y) {}
-    _LIBCPP_INLINE_VISIBILITY typename __Operation::result_type operator()
-        (      typename __Operation::first_argument_type& __x) const
+    _LIBCPP_INLINE_VISIBILITY typename _Operation::result_type operator()
+        (      typename _Operation::first_argument_type& __x) const
             {return op(__x, value);}
-    _LIBCPP_INLINE_VISIBILITY typename __Operation::result_type operator()
-        (const typename __Operation::first_argument_type& __x) const
+    _LIBCPP_INLINE_VISIBILITY typename _Operation::result_type operator()
+        (const typename _Operation::first_argument_type& __x) const
             {return op(__x, value);}
 };
 
-template <class __Operation, class _Tp>
+template <class _Operation, class _Tp>
 _LIBCPP_DEPRECATED_IN_CXX11 inline _LIBCPP_INLINE_VISIBILITY
-binder2nd<__Operation>
-bind2nd(const __Operation& __op, const _Tp& __x)
-    {return binder2nd<__Operation>(__op, __x);}
+binder2nd<_Operation>
+bind2nd(const _Operation& __op, const _Tp& __x)
+    {return binder2nd<_Operation>(__op, __x);}
 
 #endif // _LIBCPP_STD_VER <= 14 || defined(_LIBCPP_ENABLE_CXX17_REMOVED_BINDERS)
 
diff --git a/libcxx/include/__fwd/mdspan.h b/libcxx/include/__fwd/mdspan.h
--- a/libcxx/include/__fwd/mdspan.h
+++ b/libcxx/include/__fwd/mdspan.h
@@ -32,13 +32,13 @@
 
 // Layout policy with a mapping which corresponds to FORTRAN-style array layouts
 struct layout_left {
-  template <class Extents>
+  template <class _Extents>
   class mapping;
 };
 
 // Layout policy with a mapping which corresponds to C-style array layouts
 struct layout_right {
-  template <class Extents>
+  template <class _Extents>
   class mapping;
 };
 
diff --git a/libcxx/include/__stop_token/stop_callback.h b/libcxx/include/__stop_token/stop_callback.h
--- a/libcxx/include/__stop_token/stop_callback.h
+++ b/libcxx/include/__stop_token/stop_callback.h
@@ -89,8 +89,8 @@
   }
 };
 
-template <class Callback>
-_LIBCPP_AVAILABILITY_SYNC stop_callback(stop_token, Callback) -> stop_callback<Callback>;
+template <class _Callback>
+_LIBCPP_AVAILABILITY_SYNC stop_callback(stop_token, _Callback) -> stop_callback<_Callback>;
 
 #endif // _LIBCPP_STD_VER >= 20
 
diff --git a/libcxx/include/experimental/propagate_const b/libcxx/include/experimental/propagate_const
--- a/libcxx/include/experimental/propagate_const
+++ b/libcxx/include/experimental/propagate_const
@@ -284,8 +284,8 @@
     return get();
   }
 
-  template <class _Tp_ = _Tp, class _Up = enable_if_t<is_convertible<
-                                  const _Tp_, const element_type *>::value>>
+  template <class _Dummy = _Tp, class _Up = enable_if_t<is_convertible<
+                                  const _Dummy, const element_type *>::value>>
   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR operator const element_type *() const {
     return get();
   }
@@ -300,8 +300,8 @@
     return get();
   }
 
-  template <class _Tp_ = _Tp, class _Up = enable_if_t<
-                                  is_convertible<_Tp_, element_type *>::value>>
+  template <class _Dummy = _Tp, class _Up = enable_if_t<
+                                  is_convertible<_Dummy, element_type *>::value>>
   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR operator element_type *() {
     return get();
   }
diff --git a/libcxx/include/experimental/type_traits b/libcxx/include/experimental/type_traits
--- a/libcxx/include/experimental/type_traits
+++ b/libcxx/include/experimental/type_traits
@@ -132,20 +132,20 @@
 template <template<class...> class _Op, class... _Args>
   _LIBCPP_CONSTEXPR bool is_detected_v = is_detected<_Op, _Args...>::value;
 
-template <class Default, template<class...> class _Op, class... _Args>
-  using detected_or = _DETECTOR<Default, void, _Op, _Args...>;
-template <class Default, template<class...> class _Op, class... _Args>
-  using detected_or_t = typename detected_or<Default, _Op, _Args...>::type;
-
-template <class Expected, template<class...> class _Op, class... _Args>
-  using is_detected_exact = is_same<Expected, detected_t<_Op, _Args...>>;
-template <class Expected, template<class...> class _Op, class... _Args>
-  _LIBCPP_CONSTEXPR bool is_detected_exact_v = is_detected_exact<Expected, _Op, _Args...>::value;
-
-template <class To, template<class...> class _Op, class... _Args>
-  using is_detected_convertible = is_convertible<detected_t<_Op, _Args...>, To>;
-template <class To, template<class...> class _Op, class... _Args>
-  _LIBCPP_CONSTEXPR bool is_detected_convertible_v = is_detected_convertible<To, _Op, _Args...>::value;
+template <class _Default, template<class...> class _Op, class... _Args>
+  using detected_or = _DETECTOR<_Default, void, _Op, _Args...>;
+template <class _Default, template<class...> class _Op, class... _Args>
+  using detected_or_t = typename detected_or<_Default, _Op, _Args...>::type;
+
+template <class _Expected, template<class...> class _Op, class... _Args>
+  using is_detected_exact = is_same<_Expected, detected_t<_Op, _Args...>>;
+template <class _Expected, template<class...> class _Op, class... _Args>
+  _LIBCPP_CONSTEXPR bool is_detected_exact_v = is_detected_exact<_Expected, _Op, _Args...>::value;
+
+template <class _To, template<class...> class _Op, class... _Args>
+  using is_detected_convertible = is_convertible<detected_t<_Op, _Args...>, _To>;
+template <class _To, template<class...> class _Op, class... _Args>
+  _LIBCPP_CONSTEXPR bool is_detected_convertible_v = is_detected_convertible<_To, _Op, _Args...>::value;
 
 
 _LIBCPP_END_NAMESPACE_LFTS
diff --git a/libcxx/include/locale b/libcxx/include/locale
--- a/libcxx/include/locale
+++ b/libcxx/include/locale
@@ -3593,15 +3593,15 @@
 #endif
 
 template<class _Codecvt, class _Elem = wchar_t,
-         class _Wide_alloc = allocator<_Elem>,
-         class _Byte_alloc = allocator<char> >
+         class _WideAlloc = allocator<_Elem>,
+         class _ByteAlloc = allocator<char> >
 class _LIBCPP_TEMPLATE_VIS _LIBCPP_DEPRECATED_IN_CXX17 wstring_convert
 {
 public:
-    typedef basic_string<char, char_traits<char>, _Byte_alloc>   byte_string;
-    typedef basic_string<_Elem, char_traits<_Elem>, _Wide_alloc> wide_string;
-    typedef typename _Codecvt::state_type                        state_type;
-    typedef typename wide_string::traits_type::int_type          int_type;
+    typedef basic_string<char, char_traits<char>, _ByteAlloc>   byte_string;
+    typedef basic_string<_Elem, char_traits<_Elem>, _WideAlloc> wide_string;
+    typedef typename _Codecvt::state_type                       state_type;
+    typedef typename wide_string::traits_type::int_type         int_type;
 
 private:
     byte_string __byte_err_string_;
@@ -3663,25 +3663,25 @@
 };
 
 _LIBCPP_SUPPRESS_DEPRECATED_PUSH
-template<class _Codecvt, class _Elem, class _Wide_alloc, class _Byte_alloc>
+template<class _Codecvt, class _Elem, class _WideAlloc, class _ByteAlloc>
 inline
-wstring_convert<_Codecvt, _Elem, _Wide_alloc, _Byte_alloc>::
+wstring_convert<_Codecvt, _Elem, _WideAlloc, _ByteAlloc>::
     wstring_convert(_Codecvt* __pcvt)
         : __cvtptr_(__pcvt), __cvtstate_(), __cvtcount_(0)
 {
 }
 _LIBCPP_SUPPRESS_DEPRECATED_POP
 
-template<class _Codecvt, class _Elem, class _Wide_alloc, class _Byte_alloc>
+template<class _Codecvt, class _Elem, class _WideAlloc, class _ByteAlloc>
 inline
-wstring_convert<_Codecvt, _Elem, _Wide_alloc, _Byte_alloc>::
+wstring_convert<_Codecvt, _Elem, _WideAlloc, _ByteAlloc>::
     wstring_convert(_Codecvt* __pcvt, state_type __state)
         : __cvtptr_(__pcvt), __cvtstate_(__state), __cvtcount_(0)
 {
 }
 
-template<class _Codecvt, class _Elem, class _Wide_alloc, class _Byte_alloc>
-wstring_convert<_Codecvt, _Elem, _Wide_alloc, _Byte_alloc>::
+template<class _Codecvt, class _Elem, class _WideAlloc, class _ByteAlloc>
+wstring_convert<_Codecvt, _Elem, _WideAlloc, _ByteAlloc>::
     wstring_convert(const byte_string& __byte_err, const wide_string& __wide_err)
         : __byte_err_string_(__byte_err), __wide_err_string_(__wide_err),
           __cvtstate_(), __cvtcount_(0)
@@ -3691,9 +3691,9 @@
 
 #ifndef _LIBCPP_CXX03_LANG
 
-template<class _Codecvt, class _Elem, class _Wide_alloc, class _Byte_alloc>
+template<class _Codecvt, class _Elem, class _WideAlloc, class _ByteAlloc>
 inline
-wstring_convert<_Codecvt, _Elem, _Wide_alloc, _Byte_alloc>::
+wstring_convert<_Codecvt, _Elem, _WideAlloc, _ByteAlloc>::
     wstring_convert(wstring_convert&& __wc)
         : __byte_err_string_(_VSTD::move(__wc.__byte_err_string_)),
           __wide_err_string_(_VSTD::move(__wc.__wide_err_string_)),
@@ -3706,15 +3706,15 @@
 #endif // _LIBCPP_CXX03_LANG
 
 _LIBCPP_SUPPRESS_DEPRECATED_PUSH
-template<class _Codecvt, class _Elem, class _Wide_alloc, class _Byte_alloc>
-wstring_convert<_Codecvt, _Elem, _Wide_alloc, _Byte_alloc>::~wstring_convert()
+template<class _Codecvt, class _Elem, class _WideAlloc, class _ByteAlloc>
+wstring_convert<_Codecvt, _Elem, _WideAlloc, _ByteAlloc>::~wstring_convert()
 {
     delete __cvtptr_;
 }
 
-template<class _Codecvt, class _Elem, class _Wide_alloc, class _Byte_alloc>
-typename wstring_convert<_Codecvt, _Elem, _Wide_alloc, _Byte_alloc>::wide_string
-wstring_convert<_Codecvt, _Elem, _Wide_alloc, _Byte_alloc>::
+template<class _Codecvt, class _Elem, class _WideAlloc, class _ByteAlloc>
+typename wstring_convert<_Codecvt, _Elem, _WideAlloc, _ByteAlloc>::wide_string
+wstring_convert<_Codecvt, _Elem, _WideAlloc, _ByteAlloc>::
     from_bytes(const char* __frm, const char* __frm_end)
 {
 _LIBCPP_SUPPRESS_DEPRECATED_POP
@@ -3774,9 +3774,9 @@
     return __wide_err_string_;
 }
 
-template<class _Codecvt, class _Elem, class _Wide_alloc, class _Byte_alloc>
-typename wstring_convert<_Codecvt, _Elem, _Wide_alloc, _Byte_alloc>::byte_string
-wstring_convert<_Codecvt, _Elem, _Wide_alloc, _Byte_alloc>::
+template<class _Codecvt, class _Elem, class _WideAlloc, class _ByteAlloc>
+typename wstring_convert<_Codecvt, _Elem, _WideAlloc, _ByteAlloc>::byte_string
+wstring_convert<_Codecvt, _Elem, _WideAlloc, _ByteAlloc>::
     to_bytes(const _Elem* __frm, const _Elem* __frm_end)
 {
     __cvtcount_ = 0;
diff --git a/libcxx/include/optional b/libcxx/include/optional
--- a/libcxx/include/optional
+++ b/libcxx/include/optional
@@ -683,7 +683,7 @@
 #if _LIBCPP_STD_VER >= 20
 
 template <class _Tp>
-concept __is_derived_from_optional = requires(const _Tp& __t) { []<class __Up>(const optional<__Up>&) {}(__t); };
+concept __is_derived_from_optional = requires(const _Tp& __t) { []<class _Up>(const optional<_Up>&) {}(__t); };
 
 #  endif // _LIBCPP_STD_VER >= 20
 
diff --git a/libcxx/include/queue b/libcxx/include/queue
--- a/libcxx/include/queue
+++ b/libcxx/include/queue
@@ -453,17 +453,17 @@
 
     _LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI const _Container& __get_container() const { return c; }
 
-    template <class _T1, class _C1>
+    template <class _T1, class _OtherContainer>
     friend
     _LIBCPP_INLINE_VISIBILITY
     bool
-    operator==(const queue<_T1, _C1>& __x,const queue<_T1, _C1>& __y);
+    operator==(const queue<_T1, _OtherContainer>& __x,const queue<_T1, _OtherContainer>& __y);
 
-    template <class _T1, class _C1>
+    template <class _T1, class _OtherContainer>
     friend
     _LIBCPP_INLINE_VISIBILITY
     bool
-    operator< (const queue<_T1, _C1>& __x,const queue<_T1, _C1>& __y);
+    operator< (const queue<_T1, _OtherContainer>& __x,const queue<_T1, _OtherContainer>& __y);
 };
 
 #if _LIBCPP_STD_VER >= 17
diff --git a/libcxx/include/semaphore b/libcxx/include/semaphore
--- a/libcxx/include/semaphore
+++ b/libcxx/include/semaphore
@@ -116,11 +116,11 @@
         };
         __cxx_atomic_wait(&__a_.__a_, __test_fn);
     }
-    template <class Rep, class Period>
+    template <class _Rep, class _Period>
     _LIBCPP_AVAILABILITY_SYNC _LIBCPP_INLINE_VISIBILITY
-    bool try_acquire_for(chrono::duration<Rep, Period> const& __rel_time)
+    bool try_acquire_for(chrono::duration<_Rep, _Period> const& __rel_time)
     {
-        if (__rel_time == chrono::duration<Rep, Period>::zero())
+        if (__rel_time == chrono::duration<_Rep, _Period>::zero())
             return try_acquire();
         auto const __test_fn = [this]() { return try_acquire(); };
         return std::__libcpp_thread_poll_with_backoff(__test_fn, __libcpp_timed_backoff_policy(), __rel_time);
@@ -178,9 +178,9 @@
     {
         __semaphore_.acquire();
     }
-    template<class Rep, class Period>
+    template<class _Rep, class _Period>
     _LIBCPP_AVAILABILITY_SYNC _LIBCPP_INLINE_VISIBILITY
-    bool try_acquire_for(chrono::duration<Rep, Period> const& __rel_time)
+    bool try_acquire_for(chrono::duration<_Rep, _Period> const& __rel_time)
     {
         return __semaphore_.try_acquire_for(chrono::duration_cast<chrono::nanoseconds>(__rel_time));
     }
@@ -189,11 +189,11 @@
     {
         return __semaphore_.try_acquire();
     }
-    template <class Clock, class Duration>
+    template <class _Clock, class _Duration>
     _LIBCPP_AVAILABILITY_SYNC _LIBCPP_INLINE_VISIBILITY
-    bool try_acquire_until(chrono::time_point<Clock, Duration> const& __abs_time)
+    bool try_acquire_until(chrono::time_point<_Clock, _Duration> const& __abs_time)
     {
-        auto const __current = Clock::now();
+        auto const __current = _Clock::now();
         if (__current >= __abs_time)
             return try_acquire();
         else
diff --git a/libcxx/include/shared_mutex b/libcxx/include/shared_mutex
--- a/libcxx/include/shared_mutex
+++ b/libcxx/include/shared_mutex
@@ -370,10 +370,10 @@
 
   _LIBCPP_HIDE_FROM_ABI void lock();
   _LIBCPP_HIDE_FROM_ABI bool try_lock();
-  template <class Rep, class Period>
-  _LIBCPP_HIDE_FROM_ABI bool try_lock_for(const chrono::duration<Rep, Period>& __rel_time);
-  template <class Clock, class Duration>
-  _LIBCPP_HIDE_FROM_ABI bool try_lock_until(const chrono::time_point<Clock, Duration>& __abs_time);
+  template <class _Rep, class _Period>
+  _LIBCPP_HIDE_FROM_ABI bool try_lock_for(const chrono::duration<_Rep, _Period>& __rel_time);
+  template <class _Clock, class _Duration>
+  _LIBCPP_HIDE_FROM_ABI bool try_lock_until(const chrono::time_point<_Clock, _Duration>& __abs_time);
   _LIBCPP_HIDE_FROM_ABI void unlock();
 
   // Setters
diff --git a/libcxx/include/stack b/libcxx/include/stack
--- a/libcxx/include/stack
+++ b/libcxx/include/stack
@@ -304,15 +304,15 @@
 
     _LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI const _Container& __get_container() const { return c; }
 
-    template <class T1, class _C1>
+    template <class _T1, class _OtherContainer>
     friend
     bool
-    operator==(const stack<T1, _C1>& __x, const stack<T1, _C1>& __y);
+    operator==(const stack<_T1, _OtherContainer>& __x, const stack<_T1, _OtherContainer>& __y);
 
-    template <class T1, class _C1>
+    template <class _T1, class _OtherContainer>
     friend
     bool
-    operator< (const stack<T1, _C1>& __x, const stack<T1, _C1>& __y);
+    operator< (const stack<_T1, _OtherContainer>& __x, const stack<_T1, _OtherContainer>& __y);
 };
 
 #if _LIBCPP_STD_VER >= 17
diff --git a/libcxx/include/tuple b/libcxx/include/tuple
--- a/libcxx/include/tuple
+++ b/libcxx/include/tuple
@@ -960,13 +960,13 @@
 
     // tuple(const pair<U1, U2>&) constructors (including allocator_arg_t variants)
 
-    template <template <class...> class Pred, class _Pair, class _DecayedPair = __remove_cvref_t<_Pair>, class _Tuple = tuple>
+    template <template <class...> class _Pred, class _Pair, class _DecayedPair = __remove_cvref_t<_Pair>, class _Tuple = tuple>
     struct _CtorPredicateFromPair : false_type{};
 
-    template <template <class...> class Pred, class _Pair, class _Up1, class _Up2, class _Tp1, class _Tp2>
-    struct _CtorPredicateFromPair<Pred, _Pair, pair<_Up1, _Up2>, tuple<_Tp1, _Tp2> > : _And<
-        Pred<_Tp1, __copy_cvref_t<_Pair, _Up1> >,
-        Pred<_Tp2, __copy_cvref_t<_Pair, _Up2> >
+    template <template <class...> class _Pred, class _Pair, class _Up1, class _Up2, class _Tp1, class _Tp2>
+    struct _CtorPredicateFromPair<_Pred, _Pair, pair<_Up1, _Up2>, tuple<_Tp1, _Tp2> > : _And<
+        _Pred<_Tp1, __copy_cvref_t<_Pair, _Up1> >,
+        _Pred<_Tp2, __copy_cvref_t<_Pair, _Up2> >
     > {};
 
     template <class _Pair>
@@ -1207,15 +1207,15 @@
     }
 #endif // _LIBCPP_STD_VER >= 23
 
-    template <template<class...> class Pred, bool _Const,
+    template <template<class...> class _Pred, bool _Const,
               class _Pair, class _DecayedPair = __remove_cvref_t<_Pair>, class _Tuple = tuple>
     struct _AssignPredicateFromPair : false_type {};
 
-    template <template<class...> class Pred, bool _Const,
+    template <template<class...> class _Pred, bool _Const,
               class _Pair, class _Up1, class _Up2, class _Tp1, class _Tp2>
-    struct _AssignPredicateFromPair<Pred, _Const, _Pair, pair<_Up1, _Up2>, tuple<_Tp1, _Tp2> > :
-        _And<Pred<__maybe_const<_Const, _Tp1>&, __copy_cvref_t<_Pair, _Up1> >,
-             Pred<__maybe_const<_Const, _Tp2>&, __copy_cvref_t<_Pair, _Up2> >
+    struct _AssignPredicateFromPair<_Pred, _Const, _Pair, pair<_Up1, _Up2>, tuple<_Tp1, _Tp2> > :
+        _And<_Pred<__maybe_const<_Const, _Tp1>&, __copy_cvref_t<_Pair, _Up1> >,
+             _Pred<__maybe_const<_Const, _Tp2>&, __copy_cvref_t<_Pair, _Up2> >
             > {};
 
     template <bool _Const, class _Pair>
diff --git a/libcxx/include/variant b/libcxx/include/variant
--- a/libcxx/include/variant
+++ b/libcxx/include/variant
@@ -1274,7 +1274,7 @@
   using _Bases::operator()...;
 };
 
-template <class IdxSeq>
+template <class _IdxSeq>
 struct __make_overloads_imp;
 
 template <size_t ..._Idx>
diff --git a/libcxx/include/vector b/libcxx/include/vector
--- a/libcxx/include/vector
+++ b/libcxx/include/vector
@@ -3419,12 +3419,12 @@
 #endif // _LIBCPP_STD_VER >= 20
 
 #if _LIBCPP_STD_VER >= 23
-template <class _Tp, class CharT>
+template <class _Tp, class _CharT>
 // Since is-vector-bool-reference is only used once it's inlined here.
   requires same_as<typename _Tp::__container, vector<bool, typename _Tp::__container::allocator_type>>
-struct _LIBCPP_TEMPLATE_VIS formatter<_Tp, CharT> {
+struct _LIBCPP_TEMPLATE_VIS formatter<_Tp, _CharT> {
 private:
-  formatter<bool, CharT> __underlying_;
+  formatter<bool, _CharT> __underlying_;
 
 public:
   template <class _ParseContext>