add code coverage

.github/workflows/coverage.yml

@@ -0,0 +1,34 @@
+---
+on:
+  pull_request:
+    types: [review_requested, ready_for_review]
+
+name: Execute code coverage
+
+jobs:
+  nightly-coverage:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions-rs/toolchain@v1
+        with:
+          toolchain: nightly
+          override: true
+      - uses: actions-rs/cargo@v1
+        with:
+          command: clean
+      - uses: actions-rs/cargo@v1
+        with:
+          command: test
+          args: --all-features --no-fail-fast
+        env:
+          CARGO_INCREMENTAL: "0"
+          RUSTFLAGS: "-Zprofile -Ccodegen-units=1 -Cinline-threshold=0 -Clink-dead-code -Coverflow-checks=off -Cpanic=unwind -Zpanic_abort_tests"
+      - uses: actions-rs/grcov@v0.1
+      - name: Upload coverage to Codecov
+        uses: codecov/codecov-action@v1
+        with:
+          token: ${{ secrets.CODECOV_TOKEN }}
+          file: ${{ steps.coverage.outputs.report }}
+          yml: ./codecov.yml
+          fail_ci_if_error: true