Add Free Pascal ABI Dependencies with fpc-depends

Ship a Free Pascal package without the right ABI dependency and it installs fine, then breaks the day the compiler moves on. Running fpc-depends adds the Free Pascal ABI substitution to a Debian package, and you check the generated substvars data before the control metadata is built. Allow about 15 minutes if the package already has a debhelper workflow. This guide targets the Debian Free Pascal 3.2.2 implementation installed from fp-compiler-3.2.2.

1. Check the package layout

Work from the root of a Debian source package. You need:

• A debian/ directory.
• A package name in debian/control.
• A normal debhelper build.
• The documented build dependency:

Build-Depends: fp-utils (>= 2.4.2-1)

The command is not part of debhelper itself. It is a debhelper-like helper shipped with the Free Pascal packaging. Its manual page describes it as the program that generates the ${fpc-abi:Depends} substitution and adds it to substvars files.

Confirm the installed version and the selected executable before editing any packaging files.

$ command -v fpc-depends
/usr/bin/fpc-depends
$ readlink -f /usr/bin/fpc-depends
/usr/bin/fpc-depends-3.2.2
$ dpkg-query -W -f='${Package} ${Version}\n' fp-compiler-3.2.2
fp-compiler-3.2.2 3.2.2+dfsg-32

2. Add the helper to the build

Run fpc-depends before dh_gencontrol, so the substitution exists when Debian control files are expanded. If your package already has an override_dh_gencontrol target, add the helper there:

#!/usr/bin/make -f

%:
	dh $@

override_dh_gencontrol:
	fpc-depends
	dh_gencontrol

3. Run the helper and inspect its output

Build the package as usual, or run the helper from the package root while you diagnose the packaging step:

$ fpc-depends
$ find debian -maxdepth 2 -type f -name '*.substvars' -print
debian/hello.substvars

The file name depends on your binary package. Inspect it without editing it:

$ sed -n '1,80p' debian/hello.substvars
fpc-abi:Depends=fpc-abi-3.2.2

The installed 3.2.2 implementation removes any previous fpc-abi:Depends value and adds fpc-abi-3.2.2 for every package in debhelper's package list. That makes it safe to rerun during a build: the value is regenerated, not appended again and again. Other substvars in the same file belong to other helpers and stay intact.

4. Let dh_gencontrol expand it

Now let the normal debhelper target consume the substitution:

$ dh_gencontrol
$ grep -R '^Depends:' debian/*/DEBIAN/control debian/*/DEBIAN/control 2>/dev/null
debian/hello/DEBIAN/control:Depends: fpc-abi-3.2.2, ...

The exact dependency line depends on the package. The ellipsis stands for other dependencies and is not literal output. Inspect the generated control file for the ABI dependency, then build or run your package's normal Debian checks.

5. Diagnose a helper that stops at once

On this machine the installed executable exists but cannot start, because the Perl module Debian::Debhelper::Dh_Lib is missing. The observed failure:

$ fpc-depends
Can't locate Debian/Debhelper/Dh_Lib.pm in @INC ...
BEGIN failed--compilation aborted ...

This is an installation problem, not evidence that your Pascal package has no ABI dependency. Restore the normal debhelper Perl support through your distribution's package manager, then rerun the command as the build user. Do not silence the error or write a local replacement module.

• Runs but nothing changes? Confirm you are in the package root and that debhelper selected the package you expect. Check the package list and generated file paths before touching the rules file.
• Wrong ABI value? Check which versioned fpc-depends executable the alternatives link selects.

6. Clean up generated files only

After a failed diagnostic run, remove only the generated substvars file, and only if it is untracked and your build policy allows it. A standard clean target is better:

$ debian/rules clean