maintainers/haskell/eval-pkg-sets.sh: add script for checking eval

This checks the eval of all package sets, even those neither CI nor
Hydra will evaluate (completely).

maintainers/scripts/haskell/eval-pkg-sets.sh

@@ -0,0 +1,39 @@
+#!/usr/bin/env nix-shell
+#!nix-shell -i bash
+#!nix-shell -p jq git
+# shellcheck shell=bash
+#
+# Usage: eval-pkg-sets.sh [extra flags for nix-* commands ...]
+#
+# Must be executed in a git checkout of Nixpkgs.
+
+set -euo pipefail
+
+NIXPKGS="$(git rev-parse --show-toplevel)"
+PKGSETS="$(nix-env --readonly-mode --json --drv-path -f "$NIXPKGS" -qaP -A haskell.compiler "$@" \
+  | jq -r 'to_entries | unique_by(.value.drvPath) .[] .key | sub("^haskell.compiler";"haskell.packages")')"
+
+trap 'exit 1' SIGINT SIGTERM
+
+set +e
+
+badsets=""
+for set in $PKGSETS; do
+  # Confirm an equivalent package set to haskell.compiler.$entry exists and is usable
+  if ! nix-instantiate --readonly-mode -A "$set.ghc" "$@" > /dev/null 2>&1; then
+    echo "Skipping $set... ($set.ghc does not evaluate)"
+  else
+    echo "Evaluating $set..."
+
+    if ! nix-env --readonly-mode -f "$NIXPKGS" -qaP --drv-path -A "$set" "$@" > /dev/null; then
+      badsets+="$set "
+    fi
+  fi
+done
+
+if [ -n "$badsets" ]; then
+  echo "Found potential eval issues in the following sets:" >&2
+  # shellcheck disable=SC2086
+  printf '%s\n' $badsets
+  exit 1
+fi