Add CI.

.github/workflows/ci.yaml

@@ -0,0 +1,79 @@
+# Inspired by a combination of:
+# - https://github.com/rrrene/credo/blob/master/.github/workflows/ci-workflow.yml
+# - https://elixirforum.com/t/using-github-action-cache/37922/2
+name: "Lint and test"
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+    branches:
+      - main
+
+jobs:
+  test:
+    runs-on: ubuntu-22.04
+    env:
+      ImageOS: ubuntu22
+    steps:
+      - uses: actions/checkout@v3
+      - uses: erlef/setup-beam@v1
+        id: beam
+        with:
+          otp-version: '25'
+          elixir-version: '1.15'
+
+      # Dependencies.
+      - name: Restore dependencies cache
+        uses: actions/cache@v2
+        id: deps_cache
+        with:
+          key: |
+            ${{ runner.os }}-${{ steps.beam.outputs.elixir-version }}-${{ steps.beam.outputs.otp-version }}-deps-${{ hashFiles(format('{0}{1}', github.workspace, '/mix.lock')) }}
+          restore-keys: |
+            ${{ runner.os }}-${{ steps.beam.outputs.elixir-version }}-${{ steps.beam.outputs.otp-version }}-deps
+          path: |
+            deps
+      - name: Download dependencies
+        run: mix deps.get
+      - name: Compile dependencies
+        run: mix deps.compile
+
+      # Build.
+      - name: Restore build cache
+        uses: actions/cache@v2
+        id: build_cache
+        with:
+          key: |
+            ${{ runner.os }}-${{ steps.beam.outputs.elixir-version }}-${{ steps.beam.outputs.otp-version }}-build-${{ hashFiles(format('{0}{1}', github.workspace, '/mix.lock')) }}
+          restore-keys: |
+            ${{ runner.os }}-${{ steps.beam.outputs.elixir-version }}-${{ steps.beam.outputs.otp-version }}-build
+          path: |
+            _build
+      - name: Compile project
+        run: mix compile --warnings-as-errors
+
+      # Formatting, linting, and type checking.
+      - name: Check formatting
+        run: mix format --check-formatted
+      - name: Check lint
+        run: mix credo --strict
+      - name: Restore PLT cache
+        uses: actions/cache@v2
+        id: plt_cache
+        with:
+          key: |
+            ${{ runner.os }}-${{ steps.beam.outputs.elixir-version }}-${{ steps.beam.outputs.otp-version }}-plt
+          restore-keys: |
+            ${{ runner.os }}-${{ steps.beam.outputs.elixir-version }}-${{ steps.beam.outputs.otp-version }}-plt
+          path: |
+            priv/plts
+      - name: Create PLTs
+        if: steps.plt_cache.outputs.cache-hit != 'true'
+        run: mix dialyzer --plt
+      - name: Check typespecs
+        run: mix dialyzer --format github
+
+      # Tests.
+      - name: Check tests
+        run: mix test