maintainers/scripts/haskell: add unbreak.nu script

The new script runs through all packages marked as broken in
broken.yaml, tries to build them, and removes them from the file if they
do.

maintainers/scripts/haskell/unbreak.nu

@@ -0,0 +1,31 @@
+#! /usr/bin/env nix-shell
+#! nix-shell -i nu -p nushell flock gnused -I nixpkgs=.
+
+# This script tests to build all packages listed in broken.yaml, expecting a build failure.
+# It will remove all packages that build fine from the list.
+
+# Attention: For unknown reasons, the script can't be easily cancelled and needs to be killed manually if it shouldn't run to completion.
+
+use std log
+
+let broken_config = "pkgs/development/haskell-modules/configuration-hackage2nix/broken.yaml"
+
+def is-broken [package : string]: nothing -> bool {
+    let res = with-env { NIXPKGS_ALLOW_BROKEN: "1" } {
+        # rather high timeout of half an hour, just to prevent never-ending builds
+        ^nix-build --no-out-link -j 1 --cores 1 --timeout 1800 -A $"haskellPackages.($package)" | complete
+    }
+    if $res.exit_code == 0 {
+      log warning $"($package) is not broken anymore!"
+      return false
+    } else {
+      log info $"($package) is still broken."
+      log debug $"($package) build log:\n($res.stderr)"
+      return true
+    }
+}
+
+def main [] {
+    $broken_config | open | get broken-packages
+      | par-each {|package| if not (is-broken $package) { ^flock -x $broken_config -c $"sed -i -e '/^  - ($package) /d' ($broken_config)" }}
+}