chore: no-default-features check due to feature-based compiles

.github/workflows/rust.yml

@@ -52,8 +52,6 @@ jobs:
     - name: Check build of deployed Omicron packages
       run: cargo run --bin omicron-package -- -t default check
 
-  # Note that `cargo clippy` includes `cargo check, so this ends up checking all
-  # of our code.
   clippy-lint:
     runs-on: ubuntu-22.04
     env:
@@ -82,6 +80,31 @@ jobs:
     - name: Run Clippy Lints
       run: cargo xtask clippy
 
+  check-features:
+    runs-on: ubuntu-22.04
+    env:
+      CARGO_INCREMENTAL: 0
+    steps:
+    # This repo is unstable and unnecessary: https://github.com/microsoft/linux-package-repositories/issues/34
+    - name: Disable packages.microsoft.com repo
+      run: sudo rm -f /etc/apt/sources.list.d/microsoft-prod.list
+    - uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11 # v4.1.1
+      with:
+        ref: ${{ github.event.pull_request.head.sha }} # see omicron#4461
+    - uses: Swatinem/rust-cache@23bce251a8cd2ffc3c1075eaa2367cf899916d84 # v2.7.3
+      if: ${{ github.ref != 'refs/heads/main' }}
+    - name: Report cargo version
+      run: cargo --version
+      run: source "./env.sh"; echo "PATH=$PATH" >> "$GITHUB_ENV"
+    - name: Print PATH
+      run: echo $PATH
+    - name: Print GITHUB_ENV
+      run: cat "$GITHUB_ENV"
+    - name: Install Pre-Requisites
+      run: ./tools/install_builder_prerequisites.sh -y
+    - name: Run Cargo Check (No Default Features)
+      run: cargo check --no-default-features
+
   # This is just a test build of docs.  Publicly available docs are built via
   # the separate "rustdocs" repo.
   build-docs: