Can i git bisect a flake?

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1

I’ve used things like https://github.com/timokau/nix-bisect , to bisect problems encounted with nixpkgs to track down bugs and SQUASH them. (or a least collect them in a jar, and release them back into the wild).

Is it possible to bisect a flake in this way?

if so, how would i go about it.

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2

Sure.

nix-bisect does not really support Flakes but as long as the flake in question uses flake-compat for all the relevant git commits, nix-build-status should still work as usual.

If you need to bisect against a different repo than the Nix derivation is in, it gets more complicated since nix-build-status does not support the flake CLI flags.

In that case, you will need to either:

  1. use a plain nix build
    For example, I recently bisected Node.js repo to diagnose a build failure in a JS project. I applied the following patch to Nixpkgs:

    --- a/pkgs/development/web/nodejs/v18.nix
+++ b/pkgs/development/web/nodejs/v18.nix
@@ -5,11 +5,11 @@ let
     python = python3;
   };
 in
-buildNodejs {
+(buildNodejs {
   inherit enableNpm;
   version = "18.6.0";
   sha256 = "0k05phvlpwf467sbaxcvdzr4ncclm9fpldml8fbfrjigl4rhr2sz";
   patches = [
     ./disable-darwin-v8-system-instrumentation.patch
   ];
-}
+}).overrideAttrs (attrs: { src = /home/jtojnar/Projects/node; })

    And then run the following command in the Node.js checkout:

    git bisect run nix build ~/Projects/nixfiles#pengu -L --keep-failed --impure --override-input nixpkgs ~/Projects/nixpkgs

  2. Create a custom build expression file utilizing flake-compat and run nix-build-status with -f flag pointing to the file.

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