fix(detekt): translate positional file args to --input <comma-separated>

Author: Goldziher

CHANGELOG.md

@@ -9,6 +9,11 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Fixed
 
+- `detekt`: hook now translates pre-commit's positional file arguments into
+  the detekt CLI's `--input <comma-separated>` form. Previously detekt CLI
+  rejected positional args with `Was passed main parameter '<file>' but no
+  main parameter was defined in your arg class`, which broke the hook for
+  every downstream consumer.
 - `detekt`: regenerate `checksums.txt` for detekt-cli 1.23.8 (Renovate had
   bumped `version.txt` without re-running `scripts/fetch_checksums.py`,
   breaking the hook for downstream consumers).

hooks/detekt/run.sh

@@ -24,4 +24,29 @@ java_bin="$(locate_java)"
 
 jar_path="$(download_tool detekt "${VERSION}" "${url}" "${asset_name}" "${CHECKSUMS}")"
 
-exec "${java_bin}" -jar "${jar_path}" "$@"
+# detekt-cli does not accept positional file arguments — it requires
+# `--input <path>[,path...]`. pre-commit/prek pass staged files as
+# positional args at the end of the invocation (after any manifest `args:`),
+# so split flags from file paths and re-assemble as `--input <csv>`.
+flags=()
+files=()
+for arg in "$@"; do
+  case "${arg}" in
+    -*) flags+=("${arg}") ;;
+    *) files+=("${arg}") ;;
+  esac
+done
+
+cmd=("${java_bin}" -jar "${jar_path}")
+if [ "${#flags[@]}" -gt 0 ]; then
+  cmd+=("${flags[@]}")
+fi
+if [ "${#files[@]}" -gt 0 ]; then
+  # Join file paths with commas without leaking IFS to the rest of the script.
+  input_paths="$(
+    IFS=','
+    printf '%s' "${files[*]}"
+  )"
+  cmd+=(--input "${input_paths}")
+fi
+exec "${cmd[@]}"