nix-debug

A slightly nicer nix-shell debugging experience.

This is a very small wrapper around nix-shell that makes the stdenv-based derivation debugging experience ever so slightly nicer, by:

• adding convenient functions like run-next-phase and run-until <phase>
• using short, convenient aliases for some commands (r for runPhase, u for run-until, and n for run-next-phase)
• avoiding the unending cycle of rm -rf source/ && nix-shell ...
• having a shorter, informative prompt

You should be able to use this exactly like nix-shell (except for the fact that it'll be misleading for -p); if not please open an issue!

For known issues, see issue tracker, particularly the known issues list.

Usage & niceties

nix-debug currently provides the following commands and niceties. Note that these are only valid in an stdenv-based builder; if that is not the case (for example with a bare derivation), it will stop early and leave you with the basic nix-shell you would have gotten otherwise.

run-next-phase, n

run-next-phase
n

Runs the next phase, as described by stdenv's definePhases. The next phase is also indicated by the prompt and stored in the $nextPhase shell variable.

For example, after opening the shell, running run-next-phase will generally start the unpack phase; running it again afterwards will trigger the patch phase, etc.

run-until, u

run-until <phase>
u <phase>

Runs every phase up to but excluding the given <phase>, starting with the current phase.

For example, in a classic stdenv, if you have just finished the configure phase, running run-until install will run the build and check phase, letting you inspect your surroundings before running run-next-phase or runPhase installPhase (or even exit, if you want).

Note that the <phase> argument can be the prefix of a phase instead of the full phase name; if there are multiple matching phases it will throw an error and will have to be more specific. Thus, run-until b, run-until build and run-until buildPhase will all run the buildPhase phase.

run, r

run <phase>
r <phase>

A simple alias/wrapper for runPhase that allows <phase> to be a prefix instead of a full phase name. See the note on run-until for more information.

Automatically deleting the unpacked source

When starting, if the shell detects a source/ folder (such as those left by the unpack phase), it will ask you if you want to delete it before starting the session, since otherwise the unpack phase generally fails. To be safe, the default action is to keep the folder.

Similarly, before exiting, the shell will detect whether or not there is a source/ folder, and ask you if you want to delete it, since it's nice to be tidy :) Just like earlier, the default action is to keep the folder.

An informative prompt

I mean, look at the difference.

nix-shell's original prompt:

nix-debug's new prompt:

1. I barely ever go outside the original working directory in a debugging nix-shell, so relative directories are much more useful to me.
2. One of the most crucial pieces of information when fixing a derivation is which phase I'm currently running, and with a classic nix-shell there's basically no way to know that, you just have to guess.
3. Since I get easily distracted, I often end up opening a few terminals with different derivations, so instantly knowing what derivation this is relives some mental weight.

If you don't agree with those choices, you're very welcome to modify the __setup_prompt function (and even submit a PR if you want). I'm biased towards the shortest possible prompt (since I'm often working on limited screen space), but I'll gladly add a new prompt option if someone submits one.

License

This program is licensed under the GPLv3 or any later versions; the full text of the GPLv3 can be found in ./LICENSE.