Include doctests for code coverage

Author: pitdicker

.github/workflows/codecov.yml

@@ -12,12 +12,13 @@ jobs:
       CARGO_TERM_COLOR: always
     steps:
       - uses: actions/checkout@v3
-      - name: Install Rust
-        run: rustup update stable
+      # nightly is required for --doctests, see cargo-llvm-cov#2
+      - name: Install Rust (nightly)
+        run: rustup update nightly
       - name: Install cargo-llvm-cov
         uses: taiki-e/install-action@cargo-llvm-cov
       - name: Generate code coverage
-        run: cargo llvm-cov --all-features --workspace --lcov --output-path lcov.info
+        run: cargo +nightly llvm-cov --all-features --workspace --lcov --doctests --output-path lcov.info
       - name: Upload coverage to Codecov
         uses: codecov/codecov-action@v3
         env: