Add auto-generation notices for generated files

This directs new devs to look for the source files instead of
wasting time editing generated files.

cmake/dbGenZod.cmake

@@ -16,6 +16,7 @@ function(cppbessot_add_db_gen_zod_target version)
   set(_openapi_file "${_version_dir}/openapi/openapi.yaml")
   set(_output_dir "${_version_dir}/generated-zod")
   set(_output_file "${_output_dir}/schemas.ts")
+  set(_prepend_notice_script "${CMAKE_CURRENT_LIST_DIR}/scripts/prepend_cppbessot_notice.cmake")
 
   add_custom_target(db_gen_zod
     COMMAND ${CMAKE_COMMAND} -E make_directory "${_output_dir}"
@@ -23,6 +24,9 @@ function(cppbessot_add_db_gen_zod_target version)
             "${_openapi_file}"
             --output "${_output_file}"
             --export-schemas
+    COMMAND ${CMAKE_COMMAND}
+            -DCPPBESSOT_TARGET_FILE="${_output_file}"
+            -P "${_prepend_notice_script}"
     COMMENT "Generating Zod schemas for ${version}"
     VERBATIM
   )

cmake/scripts/prepend_cppbessot_notice.cmake

@@ -0,0 +1,20 @@
+if(NOT DEFINED CPPBESSOT_TARGET_FILE OR "${CPPBESSOT_TARGET_FILE}" STREQUAL "")
+  message(FATAL_ERROR "CPPBESSOT_TARGET_FILE is required")
+endif()
+
+# Some CMake command invocations can pass wrapped quotes through -D values.
+set(_target_file "${CPPBESSOT_TARGET_FILE}")
+string(REGEX REPLACE "^\"(.*)\"$" "\\1" _target_file "${_target_file}")
+
+if(NOT EXISTS "${_target_file}")
+  message(FATAL_ERROR "Target file does not exist: ${_target_file}")
+endif()
+
+file(READ "${_target_file}" _content)
+
+if(_content MATCHES "AUTO-GENERATED BY CppBeSsot")
+  return()
+endif()
+
+set(_notice "/*\n * AUTO-GENERATED BY CppBeSsot.\n * Direct edits are pointless: this file is regenerated.\n * Update the OpenAPI schema and/or CppBeSsot templates, then regenerate generated-* outputs.\n */\n\n")
+file(WRITE "${_target_file}" "${_notice}${_content}")