diff --git a/libcxx/CMakeLists.txt b/libcxx/CMakeLists.txt
--- a/libcxx/CMakeLists.txt
+++ b/libcxx/CMakeLists.txt
@@ -568,9 +568,15 @@
   else()
     target_add_compile_flags_if_supported(${target} PRIVATE -Wall)
   endif()
-  target_add_compile_flags_if_supported(${target} PRIVATE -Wextra -W -Wwrite-strings
-                                                          -Wno-unused-parameter -Wno-long-long
-                                                          -Werror=return-type -Wextra-semi -Wundef
+  target_add_compile_flags_if_supported(${target} PRIVATE -Wextra
+                                                          -W
+                                                          -Wwrite-strings
+                                                          -Wno-unused-parameter
+                                                          -Wno-long-long
+                                                          -Werror=return-type
+                                                          -Wextra-semi
+                                                          -Wundef
+                                                          -Wunused-template
                                                           -Wformat-nonliteral)
   if ("${CMAKE_CXX_COMPILER_ID}" MATCHES "Clang")
     target_add_compile_flags_if_supported(${target} PRIVATE
diff --git a/libcxx/include/__algorithm/make_projected.h b/libcxx/include/__algorithm/make_projected.h
--- a/libcxx/include/__algorithm/make_projected.h
+++ b/libcxx/include/__algorithm/make_projected.h
@@ -60,7 +60,7 @@
           __enable_if_t<!(!is_member_pointer<typename decay<_Pred>::type>::value &&
                             __is_identity<typename decay<_Proj>::type>::value),
                         int> = 0>
-_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR static _ProjectedPred<_Pred, _Proj>
+_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR inline _ProjectedPred<_Pred, _Proj>
 __make_projected(_Pred& __pred, _Proj& __proj) {
   return _ProjectedPred<_Pred, _Proj>(__pred, __proj);
 }
@@ -73,7 +73,7 @@
           __enable_if_t<!is_member_pointer<typename decay<_Pred>::type>::value &&
                           __is_identity<typename decay<_Proj>::type>::value,
                         int> = 0>
-_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR static _Pred& __make_projected(_Pred& __pred, _Proj&) {
+_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR inline _Pred& __make_projected(_Pred& __pred, _Proj&) {
   return __pred;
 }
 
@@ -86,7 +86,7 @@
 namespace ranges {
 
 template <class _Comp, class _Proj1, class _Proj2>
-_LIBCPP_HIDE_FROM_ABI constexpr static
+_LIBCPP_HIDE_FROM_ABI constexpr inline
 decltype(auto) __make_projected_comp(_Comp& __comp, _Proj1& __proj1, _Proj2& __proj2) {
   if constexpr (__is_identity<decay_t<_Proj1>>::value && __is_identity<decay_t<_Proj2>>::value &&
                 !is_member_pointer_v<decay_t<_Comp>>) {
diff --git a/libcxx/include/__config b/libcxx/include/__config
--- a/libcxx/include/__config
+++ b/libcxx/include/__config
@@ -1251,13 +1251,13 @@
 // macro is used to mark them as such, which suppresses the
 // '-Wctad-maybe-unsupported' compiler warning when CTAD is used in user code
 // with these classes.
-#if _LIBCPP_STD_VER >= 17
+#  if _LIBCPP_STD_VER >= 17
 #    define _LIBCPP_CTAD_SUPPORTED_FOR_TYPE(_ClassName)                                                                \
-      template <class ..._Tag>                                                                                         \
-      _ClassName(typename _Tag::__allow_ctad...) -> _ClassName<_Tag...>
-#else
-#  define _LIBCPP_CTAD_SUPPORTED_FOR_TYPE(_ClassName) static_assert(true, "")
-#endif
+      template <class... _Tag>                                                                                         \
+      [[maybe_unused]] _ClassName(typename _Tag::__allow_ctad...)->_ClassName<_Tag...>
+#  else
+#    define _LIBCPP_CTAD_SUPPORTED_FOR_TYPE(_ClassName) static_assert(true, "")
+#  endif
 
 #endif // __cplusplus
 
diff --git a/libcxx/include/__memory/shared_ptr.h b/libcxx/include/__memory/shared_ptr.h
--- a/libcxx/include/__memory/shared_ptr.h
+++ b/libcxx/include/__memory/shared_ptr.h
@@ -433,10 +433,10 @@
 
 template <class _Dp, class _Pt,
     class = decltype(std::declval<_Dp>()(std::declval<_Pt>()))>
-static true_type __well_formed_deleter_test(int);
+inline true_type __well_formed_deleter_test(int);
 
 template <class, class>
-static false_type __well_formed_deleter_test(...);
+inline false_type __well_formed_deleter_test(...);
 
 template <class _Dp, class _Pt>
 struct __well_formed_deleter : decltype(std::__well_formed_deleter_test<_Dp, _Pt>(0)) {};
diff --git a/libcxx/include/__type_traits/is_nothrow_convertible.h b/libcxx/include/__type_traits/is_nothrow_convertible.h
--- a/libcxx/include/__type_traits/is_nothrow_convertible.h
+++ b/libcxx/include/__type_traits/is_nothrow_convertible.h
@@ -27,10 +27,10 @@
 #if _LIBCPP_STD_VER >= 20
 
 template <typename _Tp>
-static void __test_noexcept(_Tp) noexcept;
+inline void __test_noexcept(_Tp) noexcept;
 
 template<typename _Fm, typename _To>
-static bool_constant<noexcept(_VSTD::__test_noexcept<_To>(std::declval<_Fm>()))>
+inline bool_constant<noexcept(_VSTD::__test_noexcept<_To>(std::declval<_Fm>()))>
 __is_nothrow_convertible_test();
 
 template <typename _Fm, typename _To>
diff --git a/libcxx/src/filesystem/filesystem_common.h b/libcxx/src/filesystem/filesystem_common.h
--- a/libcxx/src/filesystem/filesystem_common.h
+++ b/libcxx/src/filesystem/filesystem_common.h
@@ -44,9 +44,11 @@
 #endif
 #endif
 
+// TODO: Check whether these functions actually need internal linkage, or if they can be made normal header functions
 _LIBCPP_DIAGNOSTIC_PUSH
 _LIBCPP_GCC_DIAGNOSTIC_IGNORED("-Wunused-function")
 _LIBCPP_CLANG_DIAGNOSTIC_IGNORED("-Wunused-function")
+_LIBCPP_CLANG_DIAGNOSTIC_IGNORED("-Wunused-template")
 
 #if defined(_LIBCPP_WIN32API)
 #  define PATHSTR(x) (L##x)
diff --git a/libcxx/test/std/time/time.hms/time.hms.nonmembers/ostream.pass.cpp b/libcxx/test/std/time/time.hms/time.hms.nonmembers/ostream.pass.cpp
--- a/libcxx/test/std/time/time.hms/time.hms.nonmembers/ostream.pass.cpp
+++ b/libcxx/test/std/time/time.hms/time.hms.nonmembers/ostream.pass.cpp
@@ -53,15 +53,6 @@
   return sstr.str();
 }
 
-template <class CharT, class Duration>
-static std::basic_string<CharT> stream_ja_JP_locale(std::chrono::hh_mm_ss<Duration> hms) {
-  std::basic_stringstream<CharT> sstr;
-  const std::locale locale(LOCALE_ja_JP_UTF_8);
-  sstr.imbue(locale);
-  sstr << hms;
-  return sstr.str();
-}
-
 template <class CharT>
 static void test() {
   // Note std::atto can't be tested since the ratio conversion from std::atto
diff --git a/libcxx/utils/libcxx/test/params.py b/libcxx/utils/libcxx/test/params.py
--- a/libcxx/utils/libcxx/test/params.py
+++ b/libcxx/utils/libcxx/test/params.py
@@ -17,6 +17,7 @@
   '-Wextra',
   '-Wshadow',
   '-Wundef',
+  '-Wunused-template',
   '-Wno-unused-command-line-argument',
   '-Wno-attributes',
   '-Wno-pessimizing-move',