Add GitHub Actions CI with toolchain-scoped caches

Author: kipcole9

.github/workflows/ci.yml

@@ -0,0 +1,110 @@
+name: Elixir CI
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+
+env:
+  MIX_ENV: test
+
+permissions:
+  contents: read
+
+jobs:
+  test:
+    name: "Elixir ${{ matrix.elixir }} / OTP ${{ matrix.otp }}${{ matrix.lint && ' (lint)' || '' }}"
+    runs-on: ubuntu-latest
+
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          # Elixir 1.17 — supports OTP 25–27
+          - elixir: "1.17-otp-26"
+            otp: "26"
+          - elixir: "1.17-otp-27"
+            otp: "27"
+
+          # Elixir 1.18 — supports OTP 25–27
+          - elixir: "1.18-otp-26"
+            otp: "26"
+          - elixir: "1.18-otp-27"
+            otp: "27"
+
+          # Elixir 1.19 — supports OTP 26–28
+          - elixir: "1.19-otp-26"
+            otp: "26"
+          - elixir: "1.19-otp-27"
+            otp: "27"
+          - elixir: "1.19-otp-28"
+            otp: "28"
+
+          # Elixir 1.20 — supports OTP 27–29
+          - elixir: "1.20.2-otp-27"
+            otp: "27"
+          - elixir: "1.20.2-otp-28"
+            otp: "28"
+          - elixir: "1.20.2-otp-29"
+            otp: "29"
+            lint: true
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v5
+
+      - name: Set up Elixir
+        uses: erlef/setup-beam@v1
+        with:
+          elixir-version: ${{ matrix.elixir }}
+          otp-version: ${{ matrix.otp }}
+
+      - name: Restore dependency cache
+        uses: actions/cache@v5
+        with:
+          path: |
+            deps
+            _build
+          key: mix-${{ matrix.elixir }}-${{ matrix.otp }}-${{ hashFiles('mix.lock') }}
+          restore-keys: |
+            mix-${{ matrix.elixir }}-${{ matrix.otp }}-
+
+      - name: Install dependencies
+        run: mix deps.get
+
+      - name: Check formatting
+        if: matrix.lint
+        run: mix format --check-formatted
+
+      - name: Compile (warnings as errors)
+        run: mix compile --warnings-as-errors
+
+      - name: Run tests
+        if: ${{ !matrix.lint }}
+        run: mix test
+
+      - name: Run tests with coverage
+        if: matrix.lint
+        run: mix test --cover
+
+      - name: Build docs (warnings as errors)
+        if: matrix.lint
+        env:
+          MIX_ENV: release
+        run: mix docs --warnings-as-errors
+
+      - name: Restore PLT cache
+        if: matrix.lint
+        uses: actions/cache@v5
+        with:
+          path: _build/dev/dialyxir_*
+          key: plt-${{ matrix.elixir }}-${{ matrix.otp }}-${{ hashFiles('mix.lock') }}
+          restore-keys: |
+            plt-${{ matrix.elixir }}-${{ matrix.otp }}-
+
+      - name: Run dialyzer
+        if: matrix.lint
+        env:
+          MIX_ENV: dev
+        run: mix dialyzer