There is a bug with pip 6.14.0. I just use pip-compile --allow-unsafe --generate-hashes --output-file=requirements/test.txt --resolver=backtracking --strip-extras requirements/test.in
but now it adds --config=pyproject.toml even there is no configuration in pyproject.toml
When running pip-compile click context has no src_files, so select_config_file returns pyproject.toml, but after compiling click context has src_files as requirements/test.in, so select_config_file returns None and so pyproject.toml != None

Making --config is_eager=False works

Originally posted by @q0w in #1893 (comment)