Add Build-Depends and Depends by default?

[WilliamDEdwards]

I'm looking to build debs for a few PyPI packages, for which our own packaging tooling is overkill. While testing fpm, it caught my attention that Build-Depends and Depends are not set. I'd expect them to be set to something like:

Build-Depends: python3-all, dh-python, debhelper (>= 10), python3-setuptools
Depends: python3, ${misc:Depends}

After all, fpm has the information it needs to set these lines. E.g. by looking at the Python version of the specified --python-bin.

[jordansissel]

From what I recall, Build-Depends is a feature of the debian package build tooling and instructs the build system (dhmake, pbuilder I think, etc) on what dependencies are required to build a package from source, not to install it.

Because fpm produces what Debian calls a "binary" package(1), I don't think adding "Build-Depends" into the .deb can be useful. In fact, if I make fpm include Build-Depends, lintian reports an unknown field:

(1) as opposed to a source package which is used to build a binary package with Debian tooling.

% ar p example_1.0_all.deb control.tar.gz | tar -zxO ./control  | grep Depends
Build-Depends: gcc

% lintian example_1.0_all.deb
...
W: example: unknown-field Build-Depends

[jordansissel]

Checking an existing system to see what fields are included in binary packages:

% find /var/cache/apt/archives -name '*.deb' | wc -l
145

% ls /var/cache/apt/archives/*.deb | xargs -n1 sh -c 'ar p $1 control.tar.xz | tar -JxO ./control' -  | fex :1 | sort | uniq -c | sort -n | grep Depends

     14 Pre-Depends
    130 Depends

Of 145 .deb binary packages in apt's local cache, only Depends and Pre-Depends are used on my Ubuntu system. In binary packages, I can't see documentation indicating that Build-Depends is valid - https://www.debian.org/doc/debian-policy/ch-relationships.html#binary-dependencies-depends-recommends-suggests-enhances-pre-depends

[WilliamDEdwards]

Build-Depends can only be set for source packages.

As it's possible to pass --deb-build-depends to fpm, which is included in the control file of the binary package, I assumed that fpm intends to build a source package. (Is this a bug?)

Regardless, I think it'd be more correct if fpm sets the Build-Depends line I mentioned for the source package which I assume it builds before building the binary package. I also think it'd be more correct to add ${misc:Depends} to Depends by default. It is substituted at build time.

If the source package is for internal use only, both points probably won't make any difference in practice.

However, adding python3 as a dependency by default is not only more correct, it could also make a difference in practice.

P.S. It's admirable how involved you still are with a project that's been going for so long!

[jordansissel]

I assumed that fpm intends to build a source package

fpm doesn't currently build source packages, though some work is being done to do this for fpm's rpm output in #1657. In #1657, the "source rpm" output would largely be a way to trick rpm-based build systems into packaging files without any meaningful "build" step because fpm had already previously done that work. If #1657 proceeds (and I hope it will!), then we can assume that debian source packages could soon come to fpm, and for that, Build-Depends would be useful to keep.

The --deb-build-depends flag was added in #451 thought not for the purposes of debian "source packages" I suppose, but could be reused for a future feature where fpm can produce debian source packages.