/etc/bash_completion.d/gadap-config is in libgadap-dev 2.0-3.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 | # Simple bash completions for libgadap-dev
# Alastair McKinstry, <mckinstry@debian.org>, 2014-06-02
complete -W "--help --cc --cxx --cflags --libs --prefix --version" -f gadap-config
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