diff --git a/libcxx/.clang-format b/libcxx/.clang-format
--- a/libcxx/.clang-format
+++ b/libcxx/.clang-format
@@ -4,10 +4,24 @@
 Language: Cpp
 Standard: Cpp03
 
+# Lots of code uses indent of 4, but that's not consistent.
+# AccessModifierOffset: -4
+# IndentWidth: 4
+AlignConsecutiveAssignments: true
+AlignTrailingComments: true
+# BreakBeforeBraces: Allman # Usage is not consistent.
+# AlwaysBreakAfterReturnType: All # Do we want it only in templates? We could request and addition of AlwaysBreakBeforeReturnType as well.
+
 AlwaysBreakTemplateDeclarations: true
 PointerAlignment: Left
+IndentPPDirectives: AfterHash
+# SpacesBeforeTrailingComments: 2 # Already inconsistent
 
 # Disable formatting options which may break tests.
 SortIncludes: false
 ReflowComments: false
+# Alternative solution: we can have a different .clang-format in test/. E.g. with:
+# CommentPragmas: '^ expected-' # Alternative to disabling ReflowComments.
+
+# Caveat currently released versions of clang-format mishandle concepts and consider boolean operators as rvalue references, hence using PointerAlignment.
 ---
diff --git a/libcxx/utils/generate_feature_test_macro_components.py b/libcxx/utils/generate_feature_test_macro_components.py
--- a/libcxx/utils/generate_feature_test_macro_components.py
+++ b/libcxx/utils/generate_feature_test_macro_components.py
@@ -561,14 +561,14 @@
   for tc in feature_test_macros:
     if std not in tc["values"]:
       continue
-    inner_indent = 1
+    inner_indent = 2
     if 'depends' in tc.keys():
       assert 'internal_depends' in tc.keys()
-      result += "# if %s\n" % tc["internal_depends"]
+      result += "#  if %s\n" % tc["internal_depends"]
       inner_indent += 2
     if get_value_before(tc["values"], std) is not None:
       assert 'depends' not in tc.keys()
-      result += "# undef  %s\n" % tc["name"]
+      result += "#  undef %s\n" % tc["name"]
     line = "#%sdefine %s" % ((" " * inner_indent), tc["name"])
     line += " " * (indent - len(line))
     line += "%sL" % tc["values"][std]
@@ -577,7 +577,7 @@
     result += line
     result += "\n"
     if 'depends' in tc.keys():
-      result += "# endif\n"
+      result += "#  endif\n"
   return result
 
 def chunks(l, n):
@@ -642,9 +642,11 @@
 #include <__config>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
-#pragma GCC system_header
+#  pragma GCC system_header
 #endif
 
+// clang-format off
+
 #if _LIBCPP_STD_VER > 11
 {cxx14_macros}
 #endif
@@ -657,6 +659,8 @@
 {cxx2a_macros}
 #endif
 
+// clang-format on
+
 #endif // _LIBCPP_VERSIONH
 """
 
@@ -677,48 +681,48 @@
 
 test_types = {
   "undefined": """
-# ifdef {name}
-#   error "{name} should not be defined before {std_first}"
-# endif
+#  ifdef {name}
+#    error "{name} should not be defined before {std_first}"
+#  endif
 """,
 
   "depends": """
-# if {depends}
-#   ifndef {name}
-#     error "{name} should be defined in {std}"
-#   endif
-#   if {name} != {value}
-#     error "{name} should have the value {value} in {std}"
-#   endif
-# else
-#   ifdef {name}
-#     error "{name} should not be defined when {depends} is not defined!"
-#   endif
-# endif
+#  if {depends}
+#    ifndef {name}
+#      error "{name} should be defined in {std}"
+#    endif
+#    if {name} != {value}
+#      error "{name} should have the value {value} in {std}"
+#    endif
+#  else
+#    ifdef {name}
+#      error "{name} should not be defined when {depends} is not defined!"
+#    endif
+#  endif
 """,
 
   "unimplemented": """
-# if !defined(_LIBCPP_VERSION)
-#   ifndef {name}
-#     error "{name} should be defined in {std}"
-#   endif
-#   if {name} != {value}
-#     error "{name} should have the value {value} in {std}"
-#   endif
-# else // _LIBCPP_VERSION
-#   ifdef {name}
-#     error "{name} should not be defined because it is unimplemented in libc++!"
-#   endif
-# endif
+#  if !defined(_LIBCPP_VERSION)
+#    ifndef {name}
+#      error "{name} should be defined in {std}"
+#    endif
+#    if {name} != {value}
+#      error "{name} should have the value {value} in {std}"
+#    endif
+#  else // _LIBCPP_VERSION
+#    ifdef {name}
+#      error "{name} should not be defined because it is unimplemented in libc++!"
+#    endif
+#  endif
 """,
 
   "defined":"""
-# ifndef {name}
-#   error "{name} should be defined in {std}"
-# endif
-# if {name} != {value}
-#   error "{name} should have the value {value} in {std}"
-# endif
+#  ifndef {name}
+#    error "{name} should be defined in {std}"
+#  endif
+#  if {name} != {value}
+#    error "{name} should have the value {value} in {std}"
+#  endif
 """
 }
 
@@ -784,6 +788,8 @@
 #include <{header}>
 #include "test_macros.h"
 
+// clang-format off
+
 #if TEST_STD_VER < 14
 
 {cxx11_tests}
@@ -802,6 +808,8 @@
 
 #endif // TEST_STD_VER > 17
 
+// clang-format on
+
 int main(int, char**) {{ return 0; }}
 """.format(script_name=script_name,
            header=h,