maintainers/haskell/update-stackage.sh: make solver configurable

Accept either Nightly or LTS as the solver configuration variable in the
script. The Stackage version is now considered a tuple of solver and
version, allowing the script to handle updates and switches between
solvers gracefully.

Tested updating Nightly and updating from Nightly to LTS.

maintainers/scripts/haskell/update-stackage.sh

@@ -3,6 +3,15 @@
 
 set -eu -o pipefail
 
+# Stackage solver to use, LTS or Nightly
+# (should be capitalized like the display name)
+SOLVER=Nightly
+readonly SOLVER
+
+toLower() {
+    printf "%s" "$1" | tr '[:upper:]' '[:lower:]'
+}
+
 tmpfile=$(mktemp "update-stackage.XXXXXXX")
 # shellcheck disable=SC2064
 
@@ -11,16 +20,16 @@ stackage_config="pkgs/development/haskell-modules/configuration-hackage2nix/stac
 trap "rm ${tmpfile} ${tmpfile}.new" 0
 touch "$tmpfile" "$tmpfile.new" # Creating files here so that trap creates no errors.
 
-curl -L -s "https://stackage.org/nightly/cabal.config" >"$tmpfile"
-old_version=$(grep "# Stackage Nightly" $stackage_config | sed -E 's/.*([0-9]{4}-[0-9]{2}-[0-9]{2}).*/\1/')
-version=$(sed -rn "s/^--.*http:..(www.)?stackage.org.snapshot.nightly-//p" "$tmpfile")
+curl -L -s "https://stackage.org/$(toLower "$SOLVER")/cabal.config" >"$tmpfile"
+old_version=$(grep '^# Stackage' $stackage_config | sed -e 's/.\+ \([A-Za-z]\+ [0-9.-]\+\)$/\1/g')
+version="$SOLVER $(sed -rn "s/^--.*http:..(www.)?stackage.org.snapshot.$(toLower "$SOLVER")-//p" "$tmpfile")"
 
 if [[ "$old_version" == "$version" ]]; then
    echo "No new stackage version"
    exit 0 # Nothing to do
 fi
 
-echo "Updating Stackage Nightly from $old_version to $version."
+echo "Updating Stackage from $old_version to $version."
 
 # Create a simple yaml version of the file.
 sed -r \
@@ -33,7 +42,7 @@ sed -r \
     < "${tmpfile}" | sort --ignore-case >"${tmpfile}.new"
 
 cat > $stackage_config << EOF
-# Stackage Nightly $version
+# Stackage $version
 # This file is auto-generated by
 # maintainers/scripts/haskell/update-stackage.sh
 default-package-overrides:
@@ -51,7 +60,7 @@ sed -r \
 if [[ "${1:-}" == "--do-commit" ]]; then
 git add $stackage_config
 git commit -F - << EOF
-haskellPackages: stackage-nightly $old_version -> $version
+haskellPackages: stackage $old_version -> $version
 
 This commit has been generated by maintainers/scripts/haskell/update-stackage.sh
 EOF