define toolchain and rule

.bazelproject

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+directories:
+  .
+
+derive_targets_from_directories: true

.bazelrc

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+# Bazel settings that apply to this repository.
+# Take care to document any settings that you expect users to apply.
+# Settings that apply only to CI are in .github/workflows/ci.bazelrc
+build --nolegacy_external_runfiles
+
+# Load any settings specific to the current user.
+# .bazelrc.user should appear in .gitignore so that settings are not shared with team members
+# This needs to be last statement in this
+# config, as the user configuration should be able to overwrite flags from this file.
+# See https://docs.bazel.build/versions/master/best-practices.html#bazelrc
+# (Note that we use .bazelrc.user so the file appears next to .bazelrc in directory listing,
+# rather than user.bazelrc as suggested in the Bazel docs)
+try-import %workspace%/.bazelrc.user

.bazelversion

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+5.1.1
+# The first line of this file is used by Bazelisk and Bazel to be sure
+# the right version of Bazel is used to build and test this repo.
+# This also defines which version is used on CI.
+#
+# Note that you should also run integration_tests against other Bazel
+# versions you support.

.github/workflows/ci.bazelrc

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+# Bazel settings to apply on CI only
+# Included with a --bazelrc option in the call to bazel
+build --announce_rc
+test --test_output=errors
+build --disk_cache=$HOME/.cache/bazel
+build --repository_cache=$HOME/.cache/bazel-repo
+test --test_env=XDG_CACHE_HOME

.github/workflows/ci.yaml

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+name: CI
+
+# Controls when the action will run.
+on:
+  # Triggers the workflow on push or pull request events but only for the main branch
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+
+  # Allows you to run this workflow manually from the Actions tab
+  workflow_dispatch:
+
+jobs:
+  test:
+    strategy:
+      fail-fast: false
+      matrix:
+        os:
+          - ubuntu-latest
+          - macos-latest
+          # builds on windows fail
+          # https://github.com/bazelbuild/rules_docker/issues/1524
+          # https://github.com/bazelbuild/rules_docker/issues/1438
+          # - windows-latest
+        bazel: [ 4.2.1, 5.1.1 ]
+    # The type of runner that the job will run on
+    runs-on: ${{ matrix.os }}
+
+    name: test-on-${{ matrix.os }}-with-bazel-${{ matrix.bazel }}
+
+    # Steps represent a sequence of tasks that will be executed as part of the job
+    steps:
+      # Checks-out your repository under $GITHUB_WORKSPACE, so your job can access it
+      - uses: actions/checkout@v3
+      - uses: bazelbuild/setup-bazelisk@v2
+      - name: Mount bazel action cache
+        uses: actions/cache@v3
+        with:
+          path: "~/.cache/bazel"
+          key: bazel
+      - name: Mount bazel repo cache
+        uses: actions/cache@v3
+        with:
+          path: "~/.cache/bazel-repo"
+          key: bazel-repo
+      - name: Set Bazelisk Version ${{ matrix.bazel }}
+        run: echo ${{ matrix.bazel }} > .bazelversion
+      - name: Build
+        shell: bash
+        env:
+          # Bazelisk will download bazel to here
+          XDG_CACHE_HOME: ~/.cache/bazel-repo
+        run: bazel --bazelrc=.github/workflows/ci.bazelrc --bazelrc=.bazelrc build ...
+      - name: Test
+        shell: bash
+        env:
+          # Bazelisk will download bazel to here
+          XDG_CACHE_HOME: ~/.cache/bazel-repo
+        run: bazel --bazelrc=.github/workflows/ci.bazelrc --bazelrc=.bazelrc test ...

.github/workflows/release.yml

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+# Cut a release whenever a new tag is pushed to the repo.
+# You should use an annotated tag, like `git tag -a v1.2.3`
+# and put the release notes into the commit message for the tag.
+name: Release
+
+on:
+  push:
+    tags:
+      - "*.*.*"
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v3
+      - uses: bazelbuild/setup-bazelisk@v2
+      - name: Check git state is clean
+        run: git status --porcelain
+      - name: Export release version
+        run: 'echo "RELEASE_VERSION=${GITHUB_REF##*/}" >> $GITHUB_ENV'
+      - name: Build release archive
+        env:
+          # Bazelisk will download bazel to here
+          XDG_CACHE_HOME: ~/.cache/bazel-repo
+        run: bazel --bazelrc=.github/workflows/ci.bazelrc --bazelrc=.bazelrc build //:slamdev_rules_helmdiff
+      - name: Set versioned archive name
+        run: cp bazel-bin/slamdev_rules_helmdiff.tar.gz bazel-bin/slamdev_rules_helmdiff-v${{ env.RELEASE_VERSION }}.tar.gz
+      - name: Export checksum
+        run: 'echo "RELEASE_CHECKSUM=$(shasum -b -a 256 bazel-bin/slamdev_rules_helmdiff-v${{ env.RELEASE_VERSION }}.tar.gz | cut -d " " -f 1)" >> $GITHUB_ENV'
+      - name: Upload release
+        uses: softprops/action-gh-release@v1
+        with:
+          files: bazel-bin/slamdev_rules_helmdiff-v${{ env.RELEASE_VERSION }}.tar.gz
+          fail_on_unmatched_files: true
+          body: |
+            ```starlark
+            http_archive(
+                name = "slamdev_rules_helmdiff",
+                sha256 = "${{ env.RELEASE_CHECKSUM }}",
+                url = "https://github.com/slamdev/rules_helmdiff/releases/download/${{ env.RELEASE_VERSION }}/slamdev_rules_helmdiff-v${{ env.RELEASE_VERSION }}.tar.gz",
+            )
+            ```

.gitignore

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+bazel-*
+.ijwb

.pre-commit-config.yaml

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+# See CONTRIBUTING.md for instructions.
+# See https://pre-commit.com for more information
+# See https://pre-commit.com/hooks.html for more hooks
+
+# Commitizen runs in commit-msg stage
+# but we don't want to run the other hooks on commit messages
+default_stages: [commit]
+
+repos:
+  # Check formatting and lint for starlark code
+  - repo: https://github.com/keith/pre-commit-buildifier
+    rev: 4.0.1.1
+    hooks:
+      - id: buildifier
+      - id: buildifier-lint
+  # Enforce that commit messages allow for later changelog generation
+  - repo: https://github.com/commitizen-tools/commitizen
+    rev: v2.18.0
+    hooks:
+      # Requires that commitizen is already installed
+      - id: commitizen
+        stages: [commit-msg]
+  - repo: https://github.com/pre-commit/mirrors-prettier
+    rev: "v2.4.0"
+    hooks:
+      - id: prettier

BUILD.bazel

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+load("@bazel_skylib//:bzl_library.bzl", "bzl_library")
+load("@rules_pkg//:pkg.bzl", "pkg_tar")
+load("@bazel_gazelle//:def.bzl", "gazelle", "gazelle_binary")
+
+gazelle_binary(
+    name = "gazelle_bin",
+    languages = ["@bazel_skylib//gazelle/bzl"],
+)
+
+gazelle(
+    name = "gazelle",
+    gazelle = "gazelle_bin",
+)
+
+# This declares the release artifact users
+pkg_tar(
+    name = "slamdev_rules_helmdiff",
+    srcs = [
+        "LICENSE",
+        "README.md",
+        "//helmdiff:package_content",
+    ],
+    extension = "tar.gz",
+    # It is all source code, so make it read-only.
+    mode = "0444",
+    # Make it owned by root so it does not have the uid of the CI robot.
+    owner = "0.0",
+    strip_prefix = ".",
+)
+
+bzl_library(
+    name = "internal_deps",
+    srcs = ["internal_deps.bzl"],
+    visibility = ["//visibility:public"],
+    deps = [
+        "@bazel_tools//tools/build_defs/repo:http.bzl",
+        "@bazel_tools//tools/build_defs/repo:utils.bzl",
+    ],
+)

CONTRIBUTING.md

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+# How to Contribute
+
+## Formatting
+
+Starlark files should be formatted by buildifier.
+We suggest using a pre-commit hook to automate this.
+First [install pre-commit](https://pre-commit.com/#installation),
+then run
+
+```shell
+pre-commit install
+```
+
+Otherwise later tooling on CI may yell at you about formatting/linting violations.
+
+## Updating BUILD files
+
+Some targets are generated from sources.
+Currently this is just the `bzl_library` targets.
+Run `bazel run //:gazelle` to keep them up-to-date.
+
+## Using this as a development dependency of other rules
+
+You'll commonly find that you develop in another WORKSPACE, such as
+some other ruleset that depends on rules_helmdiff, or in a nested
+WORKSPACE in the integration_tests folder.
+
+To always tell Bazel to use this directory rather than some release
+artifact or a version fetched from the internet, run this from this
+directory:
+
+```sh
+OVERRIDE="--override_repository=rules_helmdiff=$(pwd)/rules_helmdiff"
+echo "build $OVERRIDE" >> ~/.bazelrc
+echo "query $OVERRIDE" >> ~/.bazelrc
+```
+
+This means that any usage of `@rules_helmdiff` on your system will point to this folder.