Actions: Various CI improvements

- Test against MSRV
- Parallel linting
- Compile benchmarks on nightly

.github/workflows/rust.yml

@@ -3,45 +3,60 @@ name: Rust
 on: [push, pull_request]
 
 jobs:
+  lint:
+    name: Lint
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v1
+      - uses: actions-rs/toolchain@v1
+        with:
+          toolchain: 1.37.0
+          override: true
+
+      # Ensure all code has been formatted with rustfmt
+      - run: rustup component add rustfmt
+      - name: Check formatting
+        uses: actions-rs/cargo@v1
+        with:
+          command: fmt
+          args: --all -- --check --color always
+
   test:
     name: Test on ${{ matrix.os }}
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        os: [ubuntu-latest, windows-latest]
+        os: [ubuntu-latest, windows-latest, macOS-latest]
 
     steps:
-    - uses: actions/checkout@v1
-    - name: Check formatting
-      run: cargo fmt --all -- --check
-    - name: Build
-      run: cargo build --verbose --release --all
-    - name: Run tests
-      run: cargo test --verbose --release --all
-    - name: Run slow tests
-      run: cargo test --verbose --release --all -- --ignored
-
-  macOS:
-    name: Test on macOS-latest
-    runs-on: macOS-latest
-
-    steps:
-    - name: Install Rust
-      run: curl https://sh.rustup.rs -sSf | sh -s -- -y
-    - name: Install rustfmt
-      run: $HOME/.cargo/bin/rustup component add rustfmt
-    - uses: actions/checkout@v1
-    - name: Check formatting
-      run: $HOME/.cargo/bin/cargo fmt --all -- --check
-    - name: Build
-      run: $HOME/.cargo/bin/cargo build --verbose --release --all
-    - name: Run tests
-      run: $HOME/.cargo/bin/cargo test --verbose --release --all
-    - name: Run slow tests
-      run: $HOME/.cargo/bin/cargo test --verbose --release --all -- --ignored
+      - uses: actions/checkout@v1
+      - uses: actions-rs/toolchain@v1
+        with:
+          toolchain: 1.37.0
+          override: true
+      - name: cargo fetch
+        uses: actions-rs/cargo@v1
+        with:
+          command: fetch
+      - name: Build tests
+        uses: actions-rs/cargo@v1
+        with:
+          command: build
+          args: --verbose --release --all --tests
+      - name: Run tests
+        uses: actions-rs/cargo@v1
+        with:
+          command: test
+          args: --verbose --release --all
+      - name: Run slow tests
+        uses: actions-rs/cargo@v1
+        with:
+          command: test
+          args: --verbose --release --all -- --ignored
 
   doc-links:
-    name: Check intra-doc links
+    name: Nightly lint
     runs-on: ubuntu-latest
 
     steps:
@@ -50,7 +65,22 @@ jobs:
         with:
           toolchain: nightly
           override: true
-      - uses: actions-rs/cargo@v1
+      - name: cargo fetch
+        uses: actions-rs/cargo@v1
+        with:
+          command: fetch
+
+      # Ensure intra-documentation links all resolve correctly
+      # Requires #![deny(intra_doc_link_resolution_failure)] in crates.
+      - name: Check intra-doc links
+        uses: actions-rs/cargo@v1
         with:
           command: doc
-          args: --document-private-items
+          args: --all --document-private-items
+
+      # Build benchmarks to prevent bitrot
+      - name: Build benchmarks
+        uses: actions-rs/cargo@v1
+        with:
+          command: build
+          args: --verbose --all --benches