update github actions

* Node.js 16 actions are deprecated; update checkout
* action-rs/* are archived; switch to dtolnay/rust-toolchain
  (unclear how to properly configure cache)

.github/workflows/rust.yml

@@ -5,179 +5,89 @@ name: Rust CI
 jobs:
   # if this fails we don't try anything else on stable
   #
-  # we use multiple jobs so no single check prevents others from being run;
-  # but use a cache to speedup steps after build
   # (if initial build fails nothing else is checked)
+  #
+  # TODO: unclear how to setup cache with dtolnay/rust-toolchain
   build:
     name: Build
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2
-      - name: Cache stable
-        uses: actions/cache@v2
-        with:
-          key: build-stable-${{ github.run_id }}
-          path: |
-            /usr/share/rust/.cargo/
-            target/
-      - uses: actions-rs/toolchain@v1
-        with:
-          profile: minimal
-          toolchain: stable
-          override: true
-      - name: Build
-        uses: actions-rs/cargo@v1
-        with:
-          command: build
+      - uses: actions/checkout@v4
+      - uses: dtolnay/rust-toolchain@stable
+      - name: Build default features
+        run: cargo build
       - name: Build with all features
-        uses: actions-rs/cargo@v1
-        with:
-          command: build
-          args: --all-features
+        run: cargo build --all-features
 
   check:
     name: Check
     runs-on: ubuntu-latest
     needs: build
     steps:
-      - uses: actions/checkout@v2
-      - name: Cache stable
-        uses: actions/cache@v2
-        with:
-          key: build-stable-${{ github.run_id }}
-          path: |
-            /usr/share/rust/.cargo/
-            target/
-      - uses: actions-rs/toolchain@v1
-        with:
-          profile: minimal
-          toolchain: stable
-          override: true
+      - uses: actions/checkout@v4
+      - uses: dtolnay/rust-toolchain@stable
       - name: Check
-        uses: actions-rs/cargo@v1
-        with:
-          command: check
-          args: --all-features
+        run: cargo check --all-features
 
   test:
     name: Test Suite
     runs-on: ubuntu-latest
     needs: build
     steps:
-      - uses: actions/checkout@v2
-      - name: Cache stable
-        uses: actions/cache@v2
-        with:
-          key: build-stable-${{ github.run_id }}
-          path: |
-            /usr/share/rust/.cargo/
-            target/
-      - uses: actions-rs/toolchain@v1
-        with:
-          profile: minimal
-          toolchain: stable
-          override: true
+      - uses: actions/checkout@v4
+      - uses: dtolnay/rust-toolchain@stable
       - name: Test
-        uses: actions-rs/cargo@v1
-        with:
-          command: test
-          args: --all-features
+        run: cargo test --all-features
 
   clippy:
     name: Clippy
     runs-on: ubuntu-latest
     needs: build
     steps:
-      - uses: actions/checkout@v2
-      - name: Cache stable
-        uses: actions/cache@v2
-        with:
-          key: build-stable-${{ github.run_id }}
-          path: |
-            /usr/share/rust/.cargo/
-            target/
-      - uses: actions-rs/toolchain@v1
-        with:
-          profile: minimal
-          toolchain: stable
-          override: true
-          components: clippy
+      - uses: actions/checkout@v4
+      - uses: dtolnay/rust-toolchain@stable
       - name: Clippy
-        uses: actions-rs/cargo@v1
-        with:
-          command: clippy
-          args: -- -D warnings
+        run: cargo clippy -- -D warnings
 
   doc:
     name: Rustdoc
     runs-on: ubuntu-latest
     needs: build
     steps:
-      - uses: actions/checkout@v2
-      - name: Cache stable
-        uses: actions/cache@v2
-        with:
-          key: build-stable-${{ github.run_id }}
-          path: |
-            /usr/share/rust/.cargo/
-            target/
-      - uses: actions-rs/toolchain@v1
-        with:
-          profile: minimal
-          toolchain: stable
-          override: true
+      - uses: actions/checkout@v4
+      - uses: dtolnay/rust-toolchain@stable
       - name: Rustdoc
-        uses: actions-rs/cargo@v1
-        with:
-          command: doc
-          args: --all-features
+        run: cargo doc --all-features
 
   # no cache for nightly, run all steps in same job - if one fails, the others won't be tried
   build-nightly:
     name: Build [nightly]
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2
-      - uses: actions-rs/toolchain@v1
+      - uses: actions/checkout@v4
+      - uses: dtolnay/rust-toolchain@nightly
         with:
-          profile: minimal
-          toolchain: nightly
-          override: true
           components: rustfmt
       # nightly fmt
       - name: Rustfmt [nightly]
-        uses: actions-rs/cargo@v1
-        with:
-          command: fmt
-          args: --all -- --check
+        run: cargo fmt --all -- --check
       # nightly build
       - name: Build [nightly]
-        uses: actions-rs/cargo@v1
-        with:
-          command: build
+        run: cargo build
       # nightly build all features
       - name: Build with all features [nightly]
-        uses: actions-rs/cargo@v1
-        with:
-          command: build
-          args: --all-features
+        run: cargo build --all-features
       # check
       - name: Check [nightly]
-        uses: actions-rs/cargo@v1
-        with:
-          command: check
-          args: --all-features
+        run: cargo check --all-features
       # doc_cfg not stable yet
       # https://doc.rust-lang.org/unstable-book/language-features/doc-cfg.html
       # https://github.com/rust-lang/rust/issues/43781
       - name: Rustdoc [nightly]
-        uses: actions-rs/cargo@v1
         env:
           # this should need nightly
           RUSTDOCFLAGS: "--cfg doc_cfg"
-        with:
-          command: doc
-          args: --all-features
+        run: cargo doc --all-features
       # deploy docs from nightly for doc_cfg feature
       # (for stable we'd create a new job and use the cache)
       - name: Deploy docs