feat(hooks): add ktlint kotlin linter

Author: Goldziher

.pre-commit-hooks.yaml

@@ -107,6 +107,15 @@
   files: \.kts?$
   args: ["--build-upon-default-config"]
 
+- id: ktlint
+  name: ktlint (Kotlin linter)
+  description: Lint Kotlin source files with ktlint via java -jar (self-extracting wrapper).
+  entry: hooks/ktlint/run.sh
+  language: script
+  types_or: [kotlin]
+  files: \.kts?$
+  args: []
+
 - id: hadolint
   name: hadolint (Dockerfile linter)
   description: Lint Dockerfiles using a verified upstream hadolint binary.

hooks/ktlint/README.md

@@ -0,0 +1,28 @@
+# ktlint
+
+Lint Kotlin files using [ktlint](https://github.com/pinterest/ktlint).
+
+## Category
+
+JVM executable. The hook downloads the pinned ktlint self-extracting JAR wrapper from
+GitHub Releases, verifies its sha256 against `checksums.txt`, caches it, locates a JDK
+11+ via `lib/jvm.sh`, and runs `ktlint`.
+
+## Default args
+
+None. Override via `args:` in your `.pre-commit-config.yaml`. Common options:
+- `--format` — auto-fix lint violations (not compatible with pre-commit's default behavior).
+- `--editorconfig` — enable EditorConfig rules (default is true if .editorconfig exists).
+
+## JDK detection
+
+Order: `JAVA_HOME` → `/usr/libexec/java_home -v 11` (macOS) → SDKMAN init →
+`java` on `PATH`. If none is JDK 11+, the hook prints a skip warning and exits
+0 — contributors without a JVM aren't blocked by Kotlin tooling on unrelated
+changes. CI must install JDK 11+ explicitly.
+
+## Behavior
+
+If ktlint detects lint violations, the hook exits non-zero. If `--format` was passed
+as an argument and ktlint rewrites any file, the hook also exits non-zero so the user
+re-stages the changes.

hooks/ktlint/assets.toml

@@ -0,0 +1,13 @@
+[upstream]
+# ktlint releases as github-releases with tags like "1.8.0" (no prefix).
+datasource = "github-releases"
+repo = "pinterest/ktlint"
+strip_prefix = ""
+
+[release]
+# ktlint publishes a single self-extracting JAR wrapper executable on GitHub Releases.
+url_template = "https://github.com/pinterest/ktlint/releases/download/{version}/ktlint"
+name_template = "ktlint"
+
+[[release.assets]]
+classifier = "executable"

hooks/ktlint/checksums.txt

@@ -0,0 +1,4 @@
+# Asset checksums for ktlint v1.8.0
+# Generated by scripts/fetch_checksums.py — do not edit by hand.
+
+a3fd620207d5c40da6ca789b95e7f823c54e854b7fade7f613e91096a3706d75  ktlint

hooks/ktlint/run.sh

@@ -0,0 +1,60 @@
+#!/usr/bin/env bash
+# ktlint — Kotlin linter (category: JVM executable).
+# Downloads the upstream ktlint executable (self-extracting jar wrapper), sha256-verifies it,
+# caches it, locates a JDK 11+ via lib/jvm.sh, and execs `<ktlint> <args> <files>`.
+set -euo pipefail
+
+HOOK_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+REPO_ROOT="$(cd "${HOOK_DIR}/../.." && pwd)"
+
+# shellcheck source=../../lib/platform.sh
+source "${REPO_ROOT}/lib/platform.sh"
+# shellcheck source=../../lib/download.sh
+source "${REPO_ROOT}/lib/download.sh"
+# shellcheck source=../../lib/jvm.sh
+source "${REPO_ROOT}/lib/jvm.sh"
+
+VERSION="$(grep -v '^#' "${HOOK_DIR}/version.txt" | tr -d '[:space:]')"
+CHECKSUMS="${HOOK_DIR}/checksums.txt"
+
+asset_name="ktlint"
+# GitHub Releases canonical URL for ktlint executable.
+url="https://github.com/pinterest/ktlint/releases/download/${VERSION}/ktlint"
+
+# locate_java exits 0 with a warning if no JDK 11+ is available.
+java_bin="$(locate_java)"
+
+exe_path="$(download_tool ktlint "${VERSION}" "${url}" "${asset_name}" "${CHECKSUMS}")"
+
+if [[ $# -eq 0 ]]; then
+  exit 0
+fi
+
+# Snapshot file hashes pre-lint to detect modifications.
+declare -a before_hashes=()
+for f in "$@"; do
+  before_hashes+=("$(_sha256_of "${f}" 2>/dev/null || echo NONE)")
+done
+
+# ktlint can auto-fix via --format flag. When invoked with filenames,
+# it lints them. Combine JAVA_HOME and direct invocation.
+# The executable is a shell script wrapper around a jar, so we need java.
+JAVA_HOME="${JAVA_HOME:-}" "${exe_path}" "$@"
+status=$?
+
+modified=0
+i=0
+for f in "$@"; do
+  after="$(_sha256_of "${f}" 2>/dev/null || echo NONE)"
+  if [[ "${before_hashes[$i]}" != "${after}" ]]; then
+    modified=1
+  fi
+  i=$((i + 1))
+done
+
+if ((modified == 1)); then
+  printf 'ktlint: found lint issues (use --format to auto-fix); re-stage and re-run.\n' >&2
+  exit 1
+fi
+
+exit "${status}"

hooks/ktlint/version.txt

@@ -0,0 +1,2 @@
+# renovate: datasource=github-releases depName=pinterest/ktlint extractVersion=^v?(?<version>.+)$
+1.8.0