Add GitHub Actions workflow to run Clippy

.github/workflows/clippy.yml

@@ -0,0 +1,32 @@
+name: Clippy
+
+on:
+  push:
+  schedule: [cron: "40 1 * * *"]
+
+jobs:
+  stable:
+    name: Clippy ${{matrix.dir}}
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - dir: serde
+            features: rc,unstable
+          - dir: serde_derive
+          - dir: serde_test
+          - dir: test_suite
+            features: unstable
+            tests: true
+          - dir: test_suite/no_std
+    steps:
+      - uses: actions/checkout@v2
+      - uses: dtolnay/rust-toolchain@nightly
+        with:
+          components: clippy
+        # The need for -Aredundant_field_names here is a Clippy bug.
+        # https://github.com/rust-lang/rust-clippy/issues/5356
+      - name: cargo clippy ${{matrix.features && format('--features {0}', matrix.features)}}
+        run: cargo clippy --features '${{matrix.features}}' ${{matrix.tests && '--tests'}} -- -Dclippy::all -Aclippy::redundant_field_names
+        working-directory: ${{matrix.dir}}