Enable CI for macOS runners

Unfortunately the store redirection used on Linux to enable caching of
the nix store is not supported on macOS as you cannot easily `chroot` in
userspace. While we may be able to do better in the future, for now we
just do not cache the nix store on macOS, and install all of the
development dependencies from scratch.

.github/workflows/ci.yml

@@ -8,22 +8,22 @@ on:
 
 # Environment variables that will be set on all runners
 env:
-  CI_DEV_SHELL: "nix --store ~/nix_store develop '.#ci'"
+  DEV_SHELL_LINUX: "nix --store ~/nix_store develop '.#ci'"
+  DEV_SHELL_MACOS: "nix develop '.#ci'"
   CARGO_TERM_COLOR: always   # Always colour Cargo's output.
   CARGO_INCREMENTAL: 0       # Always run without incremental builds on CI.
   CARGO_PROFILE_DEV_DEBUG: 0 # Don't embed debug info even though the build is a dev build.
 
 # Configuration for individual jobs
 jobs:
 
-  # This job is responsible for running the unit and integration tests.
+  # This job is responsible for running the unit and integration tests
   test:
     name: "Test"
     strategy:
       fail-fast: false
       matrix:
-#        os: [ "ubuntu-latest", "macos-latest" ]
-         os: [ "ubuntu-latest" ]
+        os: [ "ubuntu-latest", "macos-latest" ]
     runs-on: ${{ matrix.os }}
     steps:
       - name: Checkout Code
@@ -32,8 +32,19 @@ jobs:
         shell: "bash"
         run: |
           curl -sSf -L https://install.lix.systems/lix | sh -s -- install --no-confirm
+      - name: Setup Devshell Command
+        shell: "bash"
+        run: |
+          if [ "$RUNNER_OS" == "Linux" ]; then
+              echo "DEV_SHELL=${{ env.DEV_SHELL_LINUX }}" >> $GITHUB_ENV
+          elif [ "$RUNNER_OS" == "macOS" ]; then
+              echo "DEV_SHELL=${{ env.DEV_SHELL_MACOS }}" >> $GITHUB_ENV
+          else
+              exit 1
+          fi
       - name: Restore Nix Cache
         uses: actions/cache@v3
+        if: runner.os != 'macOS'
         continue-on-error: true
         with:
           path: |
@@ -49,15 +60,15 @@ jobs:
       - name: Build Lix Dependencies
         shell: "bash"
         run: |
-          ${{ env.CI_DEV_SHELL }}
+          eval "$DEV_SHELL"
       - name: Build Tests
         shell: "bash"
         run: |
-          ${{ env.CI_DEV_SHELL }} --command cargo test --all-targets --no-run
+          eval "$DEV_SHELL --command cargo test --all-targets --no-run"
       - name: Run Tests
         shell: "bash"
         run: |
-          ${{ env.CI_DEV_SHELL }} --command cargo test --all-targets -- --nocapture
+          eval "$DEV_SHELL --command cargo test --all-targets -- --nocapture"
 
   # This job runs the linter.
   lint:
@@ -67,7 +78,7 @@ jobs:
       - name: Checkout Code
         uses: actions/checkout@v3
       - name: Install Lix
-        shell: "bash"
+        shell: bash
         run: |
           curl -sSf -L https://install.lix.systems/lix | sh -s -- install --no-confirm
       - name: Restore Nix Cache
@@ -85,13 +96,13 @@ jobs:
             target/
           key: rust-${{ hashFiles('**/Cargo.lock') }}-ubuntu-latest
       - name: Build Lix Dependencies
-        shell: "bash"
+        shell: bash
         run: |
-          ${{ env.CI_DEV_SHELL }}
+          ${{ env.DEV_SHELL_LINUX }}
       - name: Lint Code
-        shell: "bash"
+        shell: bash
         run: |
-          ${{ env.CI_DEV_SHELL }} --command cargo clippy --all-targets
+          ${{ env.DEV_SHELL_LINUX }} --command cargo clippy --all-targets
 
   # This job checks the code formatting.
   formatting:
@@ -101,7 +112,7 @@ jobs:
       - name: Checkout Code
         uses: actions/checkout@v3
       - name: Install Lix
-        shell: "bash"
+        shell: bash
         run: |
           curl -sSf -L https://install.lix.systems/lix | sh -s -- install --no-confirm
       - name: Restore Nix Cache
@@ -119,10 +130,10 @@ jobs:
             target/
           key: rust-${{ hashFiles('**/Cargo.lock') }}-ubuntu-latest
       - name: Build Lix Dependencies
-        shell: "bash"
+        shell: bash
         run: |
-          ${{ env.CI_DEV_SHELL }}
+          ${{ env.DEV_SHELL_LINUX }}
       - name: Check Formatting
-        shell: "bash"
+        shell: bash
         run: |
-          ${{ env.CI_DEV_SHELL }} --command cargo fmt --all -- --check
+          ${{ env.DEV_SHELL_LINUX }} --command cargo fmt --all -- --check