Run Dialyzer in CI (#10)

Author: whatyouhide

.github/workflows/main.yml

@@ -35,19 +35,30 @@ jobs:
           elixir-version: ${{matrix.elixir}}
 
       - name: Install dependencies
-        run: mix deps.get --only test
+        run: mix deps.get --only test, deps.compile
+
+      # Don't cache PLTs based on mix.lock hash, as Dialyzer can incrementally update even old ones
+      # Cache key based on Elixir & Erlang version (also useful when running in matrix)
+      - name: Cache Dialyzer's PLT
+        uses: actions/cache@v2
+        id: cache-plt
+        with:
+          path: priv/plts
+          key: ${{ runner.os }}-otp${{ matrix.otp }}-elixir${{ matrix.elixir }}
+
+      # Create PLTs if no cache was found
+      - name: Create PLTs
+        if: steps.cache-plt.outputs.cache-hit != 'true'
+        run: mix do deps.get, dialyzer --plt
 
       - name: Check formatting
         run: mix format --check-formatted
         if: ${{matrix.lint}}
 
       - name: Check for unused dependencies
-        run: mix deps.get && mix deps.unlock --check-unused
+        run: mix do deps.get, deps.unlock --check-unused
         if: ${{matrix.lint}}
 
-      - name: Compile dependencies
-        run: mix deps.compile
-
       - name: Compile with --warnings-as-errors
         run: mix compile --warnings-as-errors
         if: ${{matrix.lint}}
@@ -59,3 +70,6 @@ jobs:
       - name: Run tests with coverage
         run: mix coveralls.github --trace
         if: ${{matrix.coverage}}
+
+      - name: Run Dialyzer
+        run: mix dialyzer