/usr/bin/clang-tidy-diff-3.7.py is in clang-tidy-3.7 1:3.7.1-2ubuntu2.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/bin/../lib/llvm-3.7/share/clang/clang-tidy-diff.py
/usr/bin/../lib/llvm-3.7/share/clang/clang-tidy-diff.py