🚦 Add composite action for caching cargo installs

The `cargo install` commands are taking quite a while due to it
producing long build-times. This adds a caching mechanism to keep the
dependencies between builds so that installation times don't have to
suffer.

.github/actions/cargo-install/action.yaml

@@ -0,0 +1,29 @@
+name: cargo-install
+description: "Performs a cargo install for the specified component, with caching"
+
+inputs:
+  target:
+    required: true
+    description: "The component to install"
+
+runs:
+  using: "composite"
+  steps:
+    - name: Cache installation
+      id: cargo-install
+      uses: actions/cache@v3
+      with:
+        path: .cargo/bin/${{ inputs.target }}
+        key: cargo-install-${{ inputs.target }}
+
+    - name: Update git submodules
+      if: steps.cargo-install.outputs.cache-hit != 'true'
+      shell: bash
+      run: |
+        mkdir -p .cargo/bin
+        cargo install --locked ${{ inputs.target }} --root ./.cargo
+
+    - name: Update PATH
+      shell: bash
+      run: |
+        echo "$(pwd)/.cargo/bin" >> "${GITHUB_PATH}"

.github/workflows/build.yaml

@@ -61,8 +61,15 @@ jobs:
       - name: Install toolchain
         uses: ./.github/actions/rust-toolchain
 
-      - name: Install cargo-deny and cargo-about
-        run: cargo install --locked cargo-deny cargo-about
+      - name: Install cargo-deny
+        uses: ./.github/actions/cargo-install
+        with:
+          target: cargo-deny
+
+      - name: Install cargo-about
+        uses: ./.github/actions/cargo-install
+        with:
+          target: cargo-about
 
       - name: Check cargo-deny
         run: cargo deny check
@@ -98,8 +105,15 @@ jobs:
         with:
           components: clippy
 
-      - name: Install required cargo
-        run: cargo install clippy-sarif sarif-fmt
+      - name: Install clippy-sarif
+        uses: ./.github/actions/cargo-install
+        with:
+          target: clippy-sarif
+
+      - name: Install sarif-fmt
+        uses: ./.github/actions/cargo-install
+        with:
+          target: sarif-fmt
 
       - name: Check clippy
         continue-on-error: true

.github/workflows/docs.yaml

@@ -21,8 +21,14 @@ jobs:
           rust: nightly
 
       - name: Install mdbook
-        run: |
-          cargo install --locked mdbook
+        uses: ./.github/actions/cargo-install
+        with:
+          target: mdbook
+
+      - name: Install cargo-about
+        uses: ./.github/actions/cargo-install
+        with:
+          target: cargo-about
 
       - name: Install cargo-llvm-cov
         uses: taiki-e/install-action@cargo-llvm-cov

.gitignore

@@ -1,2 +1,3 @@
 /target
 /Cargo.lock
+/.cargo