Lintian tag information: missing-debian-source-format (type: warning)

Description (from lintian-explain-tags)

Explicitly selecting a source format by putting the format in
debian/source/format is recommended. This allows for future removal of the
1.0 default for the package source format and, depending on the source
format, may allow unambiguous declaration of whether this package is
native or non-native.

If you don't have a reason to stay with the old format for this package,
please consider switching to "3.0 (quilt)" (for packages with a separate
upstream tarball) or to "3.0 (native)" (for Debian native packages).

If you wish to keep using the old format, please create that file and put
"1.0" in it to be explicit about the source package version. If you have
problems with the 3.0 format, the dpkg maintainers are interested in
hearing, at debian-dpkg@lists.debian.org, the (technical) reasons why the
new formats do not suit you.

Please refer to the dpkg-source(1) manual page and
https://wiki.debian.org/Projects/DebSrc3.0 for details.

Visibility: warning
Show-Always: no
Check: debian/source-dir

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