HeaderCheck: It checks some of your headers

CMakeLists.txt

@@ -250,6 +250,9 @@ if(NOT "${SERENITY_ARCH}" STREQUAL "aarch64")
     add_subdirectory(Userland)
     add_subdirectory(Tests)
 endif()
+if (ENABLE_COMPILETIME_HEADER_CHECK)
+    add_subdirectory(Meta/HeaderCheck)
+endif()
 
 export_components("${CMAKE_BINARY_DIR}/components.ini")
 

Meta/CMake/common_options.cmake

@@ -7,6 +7,7 @@ serenity_option(ENABLE_UNDEFINED_SANITIZER OFF CACHE BOOL "Enable undefined beha
 
 serenity_option(ENABLE_ALL_THE_DEBUG_MACROS OFF CACHE BOOL "Enable all debug macros to validate they still compile")
 serenity_option(ENABLE_ALL_DEBUG_FACILITIES OFF CACHE BOOL "Enable all noisy debug symbols and options. Not recommended for normal developer use")
+serenity_option(ENABLE_COMPILETIME_HEADER_CHECK OFF CACHE BOOL "Enable compiletime check that each library header compiles stand-alone")
 
 serenity_option(ENABLE_UNICODE_DATABASE_DOWNLOAD ON CACHE BOOL "Enable download of Unicode UCD and CLDR files at build time")
 serenity_option(INCLUDE_WASM_SPEC_TESTS OFF CACHE BOOL "Download and include the WebAssembly spec testsuite")

Meta/HeaderCheck/.gitignore

@@ -0,0 +1 @@
+CMakeLists.txt

Meta/HeaderCheck/CMakeLists.txt

@@ -0,0 +1,4 @@
+execute_process(COMMAND "${CMAKE_CURRENT_SOURCE_DIR}/generate_all.py" "${SERENITY_ARCH}" OUTPUT_VARIABLE SOURCES_STRING)
+string(REPLACE "\n" ";" SOURCES_LIST ${SOURCES_STRING})
+
+add_library(HeaderCheck OBJECT ${SOURCES_LIST})

Meta/HeaderCheck/generate_all.py

@@ -0,0 +1,70 @@
+#!/usr/bin/env python3
+
+import os
+import sys
+import subprocess
+
+TEST_FILE_TEMPLATE = '''\
+#include <{filename}>
+// Check idempotency:
+#include <{filename}>
+'''
+
+
+def get_headers_here():
+    result = subprocess.run(['git', 'ls-files', 'Userland/Libraries/*.h'], check=True, capture_output=True, text=True)
+    assert result.stderr == ''
+    output = result.stdout.split('\n')
+    assert output[-1] == ''  # Trailing newline
+    assert len(output) > 500, 'There should be well over a thousand headers, not only {}?!'.format(len(output))
+    return output[:-1]
+
+
+def as_filename(header_path):
+    return header_path.replace('/', '__') + '__test.cpp'
+
+
+def verbosely_write(path, new_content):
+    print(path)
+    # FIXME: Ensure directory exists
+    if os.path.exists(path):
+        with open(path, 'r') as fp:
+            old_data = fp.read()
+        if old_data == new_content:
+            # Fast path! Don't trigger ninja
+            return
+    with open(path, 'w') as fp:
+        fp.write(new_content)
+
+
+def generate_part(header):
+    content = TEST_FILE_TEMPLATE.format(filename=header)
+    if header.startswith('Kernel/'):
+        content += '#define KERNEL\n'
+    verbosely_write(as_filename(header), content)
+
+
+def run(root_path, arch):
+    os.chdir(root_path)
+    headers_list = get_headers_here()
+
+    generated_files_path = os.path.join(root_path, 'Build', arch, 'Meta', 'HeaderCheck')
+    if not os.path.exists(generated_files_path):
+        os.mkdir(generated_files_path)
+    os.chdir(generated_files_path)
+    for header in headers_list:
+        generate_part(header)
+
+
+if __name__ == '__main__':
+    if 'SERENITY_SOURCE_DIR' not in os.environ:
+        print('Must set SERENITY_SOURCE_DIR first!', file=sys.stderr)
+        exit(1)
+    if len(sys.argv) == 2:
+        with open('/tmp/the_arg', 'w') as fp:
+            fp.write(sys.argv[1])
+        run(os.environ['SERENITY_SOURCE_DIR'], sys.argv[1])
+    else:
+        print('Usage: SERENITY_SOURCE_DIR=/path/to/serenity {} SERENITY_BUILD_ARCH'
+              .format(sys.argv[0]), file=sys.stderr)
+        exit(1)