Run cmake-init and setup flake.nix and default.nix

cmake/lint.cmake

@@ -0,0 +1,51 @@
+cmake_minimum_required(VERSION 3.14)
+
+macro(default name)
+  if(NOT DEFINED "${name}")
+    set("${name}" "${ARGN}")
+  endif()
+endmacro()
+
+default(FORMAT_COMMAND clang-format)
+default(
+    PATTERNS
+    source/*.cpp source/*.hpp
+    include/*.hpp
+    test/*.cpp test/*.hpp
+)
+default(FIX NO)
+
+set(flag --output-replacements-xml)
+set(args OUTPUT_VARIABLE output)
+if(FIX)
+  set(flag -i)
+  set(args "")
+endif()
+
+file(GLOB_RECURSE files ${PATTERNS})
+set(badly_formatted "")
+set(output "")
+string(LENGTH "${CMAKE_SOURCE_DIR}/" path_prefix_length)
+
+foreach(file IN LISTS files)
+  execute_process(
+      COMMAND "${FORMAT_COMMAND}" --style=file "${flag}" "${file}"
+      WORKING_DIRECTORY "${CMAKE_SOURCE_DIR}"
+      RESULT_VARIABLE result
+      ${args}
+  )
+  if(NOT result EQUAL "0")
+    message(FATAL_ERROR "'${file}': formatter returned with ${result}")
+  endif()
+  if(NOT FIX AND output MATCHES "\n<replacement offset")
+    string(SUBSTRING "${file}" "${path_prefix_length}" -1 relative_file)
+    list(APPEND badly_formatted "${relative_file}")
+  endif()
+  set(output "")
+endforeach()
+
+if(NOT badly_formatted STREQUAL "")
+  list(JOIN badly_formatted "\n" bad_list)
+  message("The following files are badly formatted:\n\n${bad_list}\n")
+  message(FATAL_ERROR "Run again with FIX=YES to fix these files.")
+endif()