Debugging
When writing a package definition, you will likely experience that you try to build the resulting derivation and it fails.
When this happens, one way of debugging the issue is to trigger a breakpoint at the point of failure, enter into the build environment and poke around to (hopefully) determine the cause of the issue.
First, add breakpointHook to the nativeBuildInputs list for your derivation.
You will likely also have to add breakpointHook as an argument to the function
which returns your derivation. E.g.:
{ stdenv
, #....
, breakpointHook
}:
stdenv.mkDerivation rec {
# ...
nativeBuildInputs = [
# ...
breakpointHook
];
# ...
}
Then build your derivation once more. When it fails, breakpointHook will
cause the process to pause and print a message mentioning the cntr command to
run to enter the environment:
$ nix build .#libvfn
[1/0/1 built, 0.0 MiB DL] building libvfn-1.0.0 (buildPhase): cntr attach -t command cntr-/nix/store/ijr3l638sv0ln4yzsczydz6xmnlx3fcp-libvfn
Run this command as root. cntr is not available in most distros, one way of
getting it is via Nix, for example:
cntr will exit in error, but reveal its location in the nix store, copy this
path and re-run the command shown above:
/nix/store/inb57qmalb4knr6g3dl5k5y6gbbchl4h-cntr-1.5.1/bin/cntr attach -t command cntr-/nix/store/inb57qmalb4knr6g3dl5k5y6gbbchl4h-cntr-1.5.1/bin/cntr
Warning
Take care to update the store paths to point to your copy of cntr and
your failing derivation!
Once inside the container, run the following to load the build environment:
What now ?
The build sources are in /build. Try to build the package manually, step by
step and see if there are any errors.
Note that the environment may hold flags which should be passed to the build
tool. For instance, in meson projects, $mesonFlags hold all the flags which
should be passed to meson setup.