Fix Broken Builds

This skill orchestrates two parallel build processes to find and fix all broken packages contributed by ekapkgs. It targets ci/repos-packages.nix, which contains only the packages added by this repository (native packages from pkgs/ and top-level.nix, plus Python overrides from python-packages.nix).

Strategy

1. Background build — runs nix-build ./ci/repos-packages.nix -A buildable --max-jobs 5 --keep-going to build everything possible and populate the store with successful builds.
2. Foreground build loop — runs nix-build ./ci/repos-packages.nix -A buildable --max-jobs 1 which stops at the first failure. The agent diagnoses and fixes the failure, commits the fix, then re-runs the build. This repeats until the full build succeeds.

Procedure

Step 1: Launch the background build

Use the Bash tool with run_in_background: true:

nix-build ./ci/repos-packages.nix -A buildable --max-jobs 5 --keep-going 2>&1

This warms the store and builds everything it can in parallel. Do not wait for it.

Step 2: Run the foreground fix loop

Run this command (NOT in background):

nix-build ./ci/repos-packages.nix -A buildable --max-jobs 1 2>&1

Use a generous timeout (600000ms / 10 minutes). When it fails:

1. Parse the error — identify which package failed and the failure mode.
2. Read the build log — the error output contains the log path (/nix/store/...-<pkg>.drv). Run nix log /nix/store/...-<pkg>.drv or read the relevant portion of the stderr output to understand the failure.
3. Classify the failure — match it to one of the known patterns below.
4. Read the package source — find and read the Nix expression for the broken package.
5. Apply the fix — edit the Nix expression.
6. Validate — run nix-instantiate -A <package> then nix-build -A <package> to confirm the fix works before re-running the full build.
7. Commit — commit the fix following the repo's commit conventions. Do NOT add AI attribution.
8. Re-run — go back to running nix-build ./ci/repos-packages.nix -A buildable --max-jobs 1 and repeat until it succeeds.

Step 3: Confirm completion

When the foreground build completes successfully (exit code 0), all packages are building. Report the list of packages that were fixed.

Failure Classification

Obsolete patches

Symptom: "Reversed patch detected" or "Hunk FAILED" Fix: Remove the obsolete fetchpatch entry and unused function arguments.

Python build-system issues

Symptom: "Backend subprocess exited", setuptools-scm version errors, Cython mismatch, missing conftest.py Fix: Update build-system, patch pyproject.toml, use pythonRemoveDeps, or fix test file references.

CMake issues

Symptom: CMake install errors, missing build targets, feature flag renames Fix: Add explicit cmakeFlags for install dirs or updated option names.

Compiler errors (-Werror)

Symptom: [-Werror=...] errors Fix: Add env.NIX_CFLAGS_COMPILE = "-Wno-error=<specific-warning>"; — never suppress all warnings.

Hash mismatches (Rust/Go)

Symptom: "hash mismatch in fixed-output derivation" Fix: Replace cargoHash or vendorHash with the correct hash from the error message.

Dependency failures

Symptom: "Build failed due to failed dependency" referencing a different package Fix: Identify and fix the actual broken dependency first, then retry.

Structured attrs breakage

Symptom: Bash errors in phases — unbound variable, bad substitution, word splitting issues Fix: Convert bare $var iteration to "${var[@]}", fix array handling, move variables to env attrset.

Missing dependencies

Symptom: attribute '<name>' missing during evaluation Fix: Port the dependency or disable the feature with a TODO comment.

Missing build tools

Symptom: Program 'xxx' not found or cannot find -lxxx Fix: Add to nativeBuildInputs (build tools) or buildInputs (libraries).

Locating Package Source Files

• Standard packages: pkgs/<name>/default.nix
• Python overrides: python-packages.nix
• Aliases and variant wrappers: top-level.nix

The attribute path in the error maps to directory names — error in <name> means pkgs/<name>/default.nix.

To find a package file when the location is unclear:

find pkgs -name default.nix -path "*/<package-name>/*" 2>/dev/null

Commit Conventions

Each fix gets its own commit. Follow the repo conventions:

• <pkg>: fix build — for general build fixes
• <pkg>: remove obsolete patch — for patch removals
• <pkg>: fix structured attrs — for bash/structured attrs fixes
• <pkg>: update cargoHash / <pkg>: update vendorHash — for hash updates

Do NOT add Co-Authored-By or any AI attribution to commits.

Important Notes

• Always read the package source before making changes.
• Always validate individual package fixes before re-running the full build.
• Fix dependency failures bottom-up — fix the leaf dependency first.
• Use nix log to read full build logs when the inline error is insufficient.
• Run nix fmt on any edited .nix files before committing.