CI: Break out lint as a job, and pass RUSTFLAGS=-Dwarnings.

This will cause the CI job to actually fail on rustc or clippy warnings,
rather than passing and thus requiring us to manually check the output.

.github/workflows/ci.yml

@@ -173,17 +173,13 @@ jobs:
 
     - run: df -h .
 
-    # Run clippy and docs to get warnings.
-    - name: Lint
-      run: cargo xtask --scope=only-normal lint --timings
-
     # Save timing reports so we can download and view them
     # (for understanding build performance in CI)
     - name: Save cargo --timings output
       if: ${{ always() }}
       uses: actions/upload-artifact@v4
       with:
-        name: cargo-timings ${{ matrix.os }} ${{ matrix.toolchain }} ${{ matrix.depversions }}
+        name: cargo-timings build ${{ matrix.os }} ${{ matrix.toolchain }} ${{ matrix.depversions }}
         path: |
           target/cargo-timings/cargo-timing-*.html
 
@@ -228,9 +224,76 @@ jobs:
       env:
         GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
 
+  # Run `xtask lint`.
+  #
+  # This job is separate from the main "build" job so that:
+  # * Lint results are delivered quickly by running them in parallel with other jobs.
+  # * We build with `-Dwarnings` so the failures aren't silent, but don't want this to
+  #   cause *re*building in the main build job and its cache.
+  lint:
+    strategy:
+      fail-fast: false
+      matrix:
+        toolchain: ["stable", "nightly", "beta"]
+
+    runs-on: ubuntu-latest
+    continue-on-error: false
+
+    steps:
+    - uses: actions/checkout@v4
+
+    - name: Set Rust toolchain
+      # The rust-toolchain.toml file specifies the targets and components we need,
+      # but we may want to override the toolchain.
+      if: ${{ matrix.toolchain != 'stable' }}
+      run: |
+          sed -i.origstable "s/stable/${{ matrix.toolchain }}/" rust-toolchain.toml
+          rustup show  # triggers installation of selected toolchain
+
+    - name: Install native libraries
+      if: ${{ runner.os == 'Linux' }}
+      run: |
+          sudo apt update
+          sudo apt-get -y install libxrandr-dev xorg-dev libx11-xcb-dev libwayland-dev libasound2-dev libudev-dev
+
+    - run: df -h .
+
+    - uses: Swatinem/[email protected]
+      with:
+        # We cannot reuse the cache from the `build` job, because `RUSTFLAGS=-Dwarnings`
+        # would invalidate all cached artifacts anyway.
+        prefix-key: "v1-rust-${{ matrix.toolchain }}"
+        shared-key: "lint"
+
+    - name: Install tools
+      run: |
+        cargo install --locked [email protected]
+
+    - run: df -h .
+
+    # Kludge: Avoid dependency on `cargo-about` by making the generated license info file look fresh.
+    - name: Skip license generation
+      run: touch all-is-cubes-wasm/static/third-party-licenses.html
+
+    - name: Lint
+      run: cargo xtask --scope=only-normal lint --timings
+      env:
+        RUSTFLAGS: '-Dwarnings'
+
+    - run: df -h .
+
+    - name: Save cargo --timings output
+      if: ${{ always() }}
+      uses: actions/upload-artifact@v4
+      with:
+        name: cargo-timings lint ${{ matrix.toolchain }}
+        path: |
+          target/cargo-timings/cargo-timing-*.html
+
   # Run `xtask test-more` to look for broken `features`.
   features:
     # Don't spend time on this if the normal builds failed.
+    # Also, we reuse the cache from it.
     needs: build
     runs-on: ubuntu-latest
     continue-on-error: false
@@ -249,17 +312,13 @@ jobs:
       run: |
           sudo apt update
           sudo apt-get -y install libxrandr-dev xorg-dev libx11-xcb-dev libwayland-dev libasound2-dev libudev-dev
-      # libxrandr-dev xorg-dev libx11-xcb-dev libwayland-dev: needed for windowing
-      # Note that `libwayland-dev` provides the library called `wayland-client`
-      # libasound2-dev: needed for audio via `kira`
-      # libudev-dev: needed for gamepad input via `gilrs`
 
     # Load cache before doing any Rust builds
     - uses: Swatinem/[email protected]
       with:
         # Reuse the cache from the normal `build` job instead of creating an independent one,
         # to reduce redundant work and save disk space — but don't *write* to that cache, so
-        # we don't bloat it.
+        # we don't bloat it or conflict.
         prefix-key: "v1-rust-ubuntu-stable-locked"
         shared-key: "build"
         save-if: false

.github/workflows/unstable-ci.yml

@@ -11,6 +11,7 @@
 # * no deployment
 # * no testing of multiple feature configurations
 # * no concept of a "primary" matrix configuration
+# * no separate lint job
 
 name: Unstable Rust Features