build: add linting formatting tools

.github/dependabot.yml

@@ -0,0 +1,7 @@
+version: 2
+updates:
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      # Check for updates to GitHub Actions every week
+      interval: "monthly"

.github/shellcheck-actions.sh

@@ -0,0 +1,19 @@
+#!/usr/bin/env bash
+set -euo pipefail
+info() { echo -e "\e[92m[+] $@\e[0m"; }
+error() { echo >&2 -e "\e[31m[!] $@\e[0m"; exit 1; }
+warn() { echo -e "\e[33m[-] $@\e[0m"; }
+DIR=$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )
+
+export SHELLCHECK_OPTS=(
+    "-s" "bash"
+    "-e" "2296"
+    "-e" "2157"
+    "-e" "2129"
+    "-e" "2154"
+)
+
+for f in "$DIR"/../**/*.yaml; do
+    echo $f
+    yq '.runs.steps[].run' "$f" | grep -v -P "^null$" | shellcheck "${SHELLCHECK_OPTS[@]}" -
+done

.github/workflows/lint.yaml

@@ -0,0 +1,33 @@
+name: Lint
+
+on:
+  pull_request:
+  push:
+
+jobs:
+  lint:
+    name: Lint
+    runs-on: ubuntu-22.04
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Setup Node
+        uses: actions/setup-node@v4
+
+      - name: Run linters
+        run: |
+          make lint
+
+      - name: Run formatters
+        run: |
+          make format
+
+      - name: Check for modifications to generated files
+        run: |
+          if [[ -n "$(git status -s)" ]]; then
+            echo "Please run 'make format' then commit/push changes"
+            echo
+            git diff
+            exit 1
+          fi

Makefile

@@ -0,0 +1,15 @@
+.PHONY: help
+help:
+	@echo "Usage:"
+	@sed -n 's/^##//p' ${MAKEFILE_LIST} | column -t -s ':' |  sed -e 's/^/ /'
+
+.PHONY: lint
+lint:
+## lint: Lint the codebase with Prettier
+	npx prettier --print-width=99 --check .
+	bash ${CURDIR}/.github/shellcheck-actions.sh
+
+.PHONY: format
+format:
+## format: Formats both Markdown documents and YAML documents to preferred repository style.
+	npx prettier --print-width=99 --write .

README.md

@@ -23,3 +23,25 @@ You can see examples of these actions in use in the following repos:
 - [signal-desktop](https://github.com/snapcrafters/signal-desktop/main/.github/workflows)
 - [mattermost-desktop](https://github.com/snapcrafters/mattermost-desktop/main/.github/workflows)
 - [discord](https://github.com/snapcrafters/discord/main/.github/workflows)
+
+## Contributing
+
+If you'd like to contribute to this repository, please feel free to fork and create a pull request.
+
+There are a few style guidelines to keep in mind:
+
+- Code should be linted using [Prettier](https://prettier.io/). You can achieve this with `make
+lint` and `make format`. The only requirements are [`npx`](https://www.npmjs.com/package/npx) and
+  [`shellcheck`](https://github.com/koalaman/shellcheck).
+- When defining inputs/outputs in `action.yaml`, or listing them in the tables within `README.md`,
+  they should be listed in alphabetical order for easy reading and updating.
+- Github Action inputs/outputs should be named all lowercase, separated by `-` where needed. The
+  applies to inputs/outputs to actions themselves, and for individual steps within the actions. For
+  example: `snap-name` or `token`.
+- Environment variables referring to repository level secrets and variables should be named all
+  uppercase, and separated by `_`. For example: `SNAPCRAFTERS_BOT_COMMIT`.
+- Step/job level environment variables should be named all lowercase, and separated by `_`. For
+  example: `snap_name` or `yaml_path`.
+- All `bash` variables should be quoted.
+- Scripts of all kinds, including those within actions `run:|` directives should follow the [Google
+  styleguide](https://google.github.io/styleguide/shellguide.html)