[libc++] improve feature test macro script

I've been playing a bit with the `generate_feature_test_macro_components.py` script and replaced some hardcoded values with extra code generation (generate ALL the things).
The output is the same and it makes updating the script less work for the coming 25 C++ standards (until 2 digit number overflow).

Feel free to 'veto' if you think it's overkill.

Differential Revision: https://reviews.llvm.org/D94530

diff --git a/libcxx/utils/generate_feature_test_macro_components.py b/libcxx/utils/generate_feature_test_macro_components.py
index c08771f..2ce7960 100755 (executable)
--- a/libcxx/utils/generate_feature_test_macro_components.py
+++ b/libcxx/utils/generate_feature_test_macro_components.py
@@ -704,6 +704,8 @@ def get_for_std(d, std):
       return d[s]
   return None
 
+def get_std_number(std):
+    return std.replace('c++', '')
 
 """
   Functions to produce the <version> header
@@ -732,7 +734,22 @@ def produce_macros_definition_for_std(std):
     result += "\n"
     if 'depends' in tc.keys():
       result += "# endif\n"
-  return result
+  return result.strip()
+
+def produce_macros_definitions():
+  macro_definition_template = """#if _LIBCPP_STD_VER > {previous_std_number}
+{macro_definition}
+#endif"""
+
+  macros_definitions = []
+  previous_std_number = '11'
+  for std in get_std_dialects():
+    macros_definitions.append(
+      macro_definition_template.format(previous_std_number=previous_std_number,
+                                       macro_definition=produce_macros_definition_for_std(std)))
+    previous_std_number = get_std_number(std)
+
+  return '\n\n'.join(macros_definitions)
 
 def chunks(l, n):
   """Yield successive n-sized chunks from l."""
@@ -799,31 +816,14 @@ def produce_version_header():
 #pragma GCC system_header
 #endif
 
-#if _LIBCPP_STD_VER > 11
-{cxx14_macros}
-#endif
-
-#if _LIBCPP_STD_VER > 14
-{cxx17_macros}
-#endif
-
-#if _LIBCPP_STD_VER > 17
-{cxx20_macros}
-#endif
-
-#if _LIBCPP_STD_VER > 20
-{cxx2b_macros}
-#endif
+{cxx_macros}
 
 #endif // _LIBCPP_VERSIONH
 """
 
   version_str = template.format(
       synopsis=produce_version_synopsis().strip(),
-      cxx14_macros=produce_macros_definition_for_std('c++14').strip(),
-      cxx17_macros=produce_macros_definition_for_std('c++17').strip(),
-      cxx20_macros=produce_macros_definition_for_std('c++20').strip(),
-      cxx2b_macros=produce_macros_definition_for_std('c++2b').strip())
+      cxx_macros=produce_macros_definitions())
   version_header_path = os.path.join(include_path, 'version')
   with open(version_header_path, 'w', newline='\n') as f:
     f.write(version_str)
@@ -894,7 +894,36 @@ def generate_std_test(test_list, std):
       result += test_types["depends"].format(name=tc["name"], value=val, std=std, depends=tc["depends"])
     else:
       result +=  test_types["defined"].format(name=tc["name"], value=val, std=std)
-  return result
+  return result.strip()
+
+def generate_std_tests(test_list):
+  std_tests_template = """#if TEST_STD_VER < {first_std_number}
+
+{pre_std_test}
+
+{other_std_tests}
+
+#elif TEST_STD_VER > {penultimate_std_number}
+
+{last_std_test}
+
+#endif // TEST_STD_VER > {penultimate_std_number}"""
+
+  std_dialects = get_std_dialects()
+  assert not get_std_number(std_dialects[-1]).isnumeric()
+
+  other_std_tests = []
+  for std in std_dialects[:-1]:
+    other_std_tests.append('#elif TEST_STD_VER == ' + get_std_number(std))
+    other_std_tests.append(generate_std_test(test_list, std))
+
+  std_tests = std_tests_template.format(first_std_number=get_std_number(std_dialects[0]),
+                                        pre_std_test=generate_std_test(test_list, 'c++11'),
+                                        other_std_tests='\n\n'.join(other_std_tests),
+                                        penultimate_std_number=get_std_number(std_dialects[-2]),
+                                        last_std_test=generate_std_test(test_list, std_dialects[-1]))
+
+  return std_tests
 
 def generate_synopsis(test_list):
     max_name_len = max([len(tc["name"]) for tc in test_list])
@@ -944,38 +973,14 @@ def produce_tests():
 #include <{header}>
 #include "test_macros.h"
 
-#if TEST_STD_VER < 14
-
-{cxx11_tests}
-
-#elif TEST_STD_VER == 14
-
-{cxx14_tests}
-
-#elif TEST_STD_VER == 17
-
-{cxx17_tests}
-
-#elif TEST_STD_VER == 20
-
-{cxx20_tests}
-
-#elif TEST_STD_VER > 20
-
-{cxx2b_tests}
-
-#endif // TEST_STD_VER > 20
+{cxx_tests}
 
 int main(int, char**) {{ return 0; }}
 """.format(script_name=script_name,
            header=h,
            markup=('\n{}\n'.format(markup) if markup else ''),
            synopsis=generate_synopsis(test_list),
-           cxx11_tests=generate_std_test(test_list, 'c++11').strip(),
-           cxx14_tests=generate_std_test(test_list, 'c++14').strip(),
-           cxx17_tests=generate_std_test(test_list, 'c++17').strip(),
-           cxx20_tests=generate_std_test(test_list, 'c++20').strip(),
-           cxx2b_tests=generate_std_test(test_list, 'c++2b').strip())
+           cxx_tests=generate_std_tests(test_list))
     test_name = "{header}.version.pass.cpp".format(header=h)
     out_path = os.path.join(macro_test_path, test_name)
     with open(out_path, 'w', newline='\n') as f: