flake/generate-files: add --commit command + fixes

- Added `--commit` with a git-based message
- `nix fmt` only operates on files known to git
- ensure `generated` directory exists

flake-modules/updates/default.nix

@@ -9,6 +9,21 @@
           repo_root=$(git rev-parse --show-toplevel)
           generated_dir=$repo_root/generated
 
+          commit=
+          while [ $# -gt 0 ]; do
+            case "$1" in
+            --commit) commit=1
+              ;;
+            --*) echo "unknown option $1"
+              ;;
+            *) echo "unexpected argument $1"
+              ;;
+            esac
+            shift
+          done
+
+          mkdir -p "$generated_dir"
+
           echo "Rust-Analyzer"
           nix build .#rust-analyzer-options
           cat ./result >"$generated_dir"/rust-analyzer.nix
@@ -21,7 +36,40 @@
           nix build .#none-ls-builtins
           cat ./result >"$generated_dir"/none-ls.nix
 
+          git add --intent-to-add "$generated_dir"
           nix fmt
+
+          if [ -n "$commit" ]; then
+            cd "$generated_dir"
+            git add .
+
+            # Construct a msg body from `git status`
+            body=$(
+              git status \
+                --short \
+                --ignored=no \
+                --untracked-files=no \
+                --no-ahead-behind \
+              | sed \
+                -e 's/^\s*\([A-Z]\)\s*/\1 /' \
+                -e 's/^A/Added/' \
+                -e 's/^M/Updated/' \
+                -e 's/^R/Renamed/' \
+                -e 's/^D/Removed/' \
+                -e 's/^/- /'
+            )
+
+            # Construct the commit message based on the body
+            count=$(echo "$body" | wc -l)
+            if [ "$count" -gt 1 ] || [ ''${#body} -gt 50 ]; then
+              msg=$(echo -e "generated: Update\n\n$body")
+            else
+              msg="generated:''${body:1}"
+            fi
+
+            # Commit if there are changes
+            [ "$count" -gt 0 ] && git commit -m "$msg" --no-verify
+          fi
         '';
       };