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https://github.com/milahu/nix-build-debug
debug failing nix-build in interactive bash shell
https://github.com/milahu/nix-build-debug
nix nix-build nixos nixpkgs
Last synced: 3 months ago
JSON representation
debug failing nix-build in interactive bash shell
- Host: GitHub
- URL: https://github.com/milahu/nix-build-debug
- Owner: milahu
- License: mit
- Created: 2024-02-07T12:23:00.000Z (12 months ago)
- Default Branch: main
- Last Pushed: 2024-07-15T15:23:49.000Z (6 months ago)
- Last Synced: 2024-09-28T09:03:45.765Z (4 months ago)
- Topics: nix, nix-build, nixos, nixpkgs
- Language: Shell
- Homepage:
- Size: 146 KB
- Stars: 3
- Watchers: 2
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: readme.md
- License: license.txt
Awesome Lists containing this project
README
# nix-build-debug
debug nix-build in a nix-shell
- run the build phases explicitly
- modify the build phases (they are stored in *.sh files)
- continue running build phases from a specified line number
## status
working prototype
what works
- start a debug shell, for example `nix-build-debug '' -A hello`
- use the `runPhase` function to run phases, for example `runPhase unpackPhase`
- auto-completion for the `runPhase` function.
with `runPhase [Tab][Tab]` all build phases are listed in order
- stop and continue calls to the `runPhase` function.
this works by using a `bash` compiled with `--disable-job-control`.
sending Ctrl-Z (SIGTSTP) to `runPhase` will stop the whole debug shell.
see also [doc/bash-trap-exit-try-catch.md](doc/bash-trap-exit-try-catch.md)
what is not tested
- continue phase from line N.
example: `runPhase buildPhase 123` to continue `buildPhase` from line 123
## why
using `nix-shell` to debug a failing nix build is not ideal
### stop on error
`nix-build` runs the build as a bash script with `set -e`
so the build stops on the first error
`nix-shell` starts an interactive bash shell with `set +e`
so that errors dont exit the shell.
but with `set +e`, the build does not stop on the first error,
and continues executing commands after the error
example
```console
$ nix_expr='
with import {};
stdenv.mkDerivation {
name = "x";
buildCommand = "echo buildCommand; false; echo still running";
}
'
$ nix-build -E "$nix_expr"
buildCommand
error: builder for '/nix/store/29zpgfmmsvf81m49piy26daxljpnli0s-x.drv' failed with exit code 1;
$ nix-shell -E "$nix_expr"
$ runPhase buildCommand
Running phase: buildCommand
buildCommand
still running
```
`nix-build-debug` solves this problem
by running the phase functions in subshells
```sh
runPhase() {
curPhase=$1
( set -e; $curPhase ) # run $curPhase in subshell (...)
}
```
in these subshells,
there is `set -e` to stop the script on the first error.
now, when a build phase fails, the subshell is terminated,
but the `runPhase` function keeps running, and the debug shell keeps running
### continue running
`nix-build-debug` also allows to
continue running a build phase from a certain line in the build phase
example:
the `buildPhase` fails on a command on line 10.
now we can modify the `buildPhase.sh` script
and continue running the `buildPhase` from line 10
## usage
### start shell
```
nix-build-debug '' -A hello
```
### list phases
```
runPhase [Tab][Tab]
```
### run phases
```
runPhase unpackPhase
runPhase configurePhase
runPhase buildPhase
runPhase installPhase
```
`installPhase` will install the build result in `$NIX_BUILD_TOP/result*`
### continue running a phase
when a phase fails, fix the phase script
```
nano $NIX_BUILD_TOP/.nix-build-debug/lib/buildPhase.sh
```
then continue running the phase, for example from line 123
```
runPhase buildPhase 123
```
## see also
- https://unix.stackexchange.com/questions/498435/how-do-i-diagnose-a-failing-nix-build
- https://github.com/NixOS/nixpkgs/blob/master/doc/stdenv/stdenv.chapter.md#building-a-stdenv-package-in-nix-shell-sec-building-stdenv-package-in-nix-shell
- https://discourse.nixos.org/t/nix-build-phases-run-nix-build-phases-interactively/36090
- https://nixos.wiki/wiki/Development_environment_with_nix-shell#stdenv.mkDerivation
- https://github.com/NixOS/nixpkgs/blob/master/pkgs/stdenv/generic/setup.sh
## keywords
- nix-shell
- nix-shell with build dependencies of derivation
- nix develop
- rewrite nix-shell in bash
- generate rcfile for bash
- get-env.sh
- dump nix-shell environment to json file
- declare bash variables
- declare bash functions
- bashFunctions
- nix-build
- what would nix-build do
- debug build phases of nix-build
- debug a failing nix-build
- debug a failing nix build
- nix
- nixos
- nixpkgs