Update CI for mdbook-spec.

This makes a few changes to CI to handle mdbook-spec:

- Adds a new job for mdbook-spec itself.
- Removes caching, can set this up later.
- Moves `mdbook test` to a separate job. It can be useful to see in the
  CI results to see which jobs are passing or failing.
- Verifies the book builds with mdbook-spec.
- Fix a small oversight that `style-checks` should use `--locked`.
- Add a summary job to make it easier to work with merge queue and
  branch protections.

.github/workflows/main.yml

@@ -5,29 +5,18 @@ on:
 
 env:
   MDBOOK_VERSION: 0.4.40
-  # When updating, be sure to also update rust-lang/rust.
-  MDBOOK_SPEC_VERSION: 0.1.0
 
 jobs:
-  test:
-    name: Test
+  code-tests:
     runs-on: ubuntu-latest
     steps:
     - uses: actions/checkout@master
-    - name: Cache
-      uses: actions/cache@v4
-      with:
-        path: |
-          ~/.cargo/bin/
-          ~/.cargo/.crates.toml
-          ~/.cargo/.crates2.json
-        key: ms-${MDBOOK_SPEC_VERSION}
     - name: Update rustup
       run: rustup self update
     - name: Install Rust
       run: |
         rustup set profile minimal
-        rustup toolchain install nightly -c rust-docs,rustfmt
+        rustup toolchain install nightly
         rustup default nightly
     - name: Install mdbook
       run: |
@@ -39,13 +28,37 @@ jobs:
         rustup --version
         rustc -Vv
         mdbook --version
-    - name: Install mdbook-spec
-      run: cargo install --locked mdbook-spec@${MDBOOK_SPEC_VERSION}
     - name: Run tests
       run: mdbook test
+
+  style-tests:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@master
+    - name: Update rustup
+      run: rustup self update
+    - name: Install Rust
+      run: |
+        rustup set profile minimal
+        rustup toolchain install nightly -c rust-docs,rustfmt
+        rustup default nightly
+    - name: Install mdbook
+      run: |
+        mkdir bin
+        curl -sSL https://github.com/rust-lang/mdBook/releases/download/v${MDBOOK_VERSION}/mdbook-v${MDBOOK_VERSION}-x86_64-unknown-linux-gnu.tar.gz | tar -xz --directory=bin
+        echo "$(pwd)/bin" >> $GITHUB_PATH
+    - name: Report versions
+      run: |
+        rustup --version
+        rustc -Vv
+        mdbook --version
+    - name: Verify the book builds
+      env:
+        SPEC_DENY_WARNINGS: 1
+      run: mdbook build
     - name: Style checks
       working-directory: style-check
-      run: cargo run -- ../src
+      run: cargo run --locked -- ../src
     - name: Style fmt
       working-directory: style-check
       run: cargo fmt --check
@@ -54,3 +67,51 @@ jobs:
         curl -sSLo linkcheck.sh \
           https://raw.githubusercontent.com/rust-lang/rust/master/src/tools/linkchecker/linkcheck.sh
         sh linkcheck.sh --all reference
+
+  mdbook-spec:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@master
+    - name: Update rustup
+      run: rustup self update
+    - name: Install Rust
+      run: |
+        rustup set profile minimal
+        rustup toolchain install nightly -c rustfmt
+        rustup default nightly
+    - name: Install mdbook
+      run: |
+        mkdir bin
+        curl -sSL https://github.com/rust-lang/mdBook/releases/download/v${MDBOOK_VERSION}/mdbook-v${MDBOOK_VERSION}-x86_64-unknown-linux-gnu.tar.gz | tar -xz --directory=bin
+        echo "$(pwd)/bin" >> $GITHUB_PATH
+    - name: Report versions
+      run: |
+        rustup --version
+        rustc -Vv
+    - name: Verify mdbook-spec lockfile is current
+      working-directory: ./mdbook-spec
+      run: cargo update -p mdbook-spec --locked
+    - name: Test mdbook-spec
+      working-directory: ./mdbook-spec
+      run: cargo test
+    - name: Rustfmt check
+      working-directory: ./mdbook-spec
+      run: cargo fmt --check
+
+  # The success job is here to consolidate the total success/failure state of
+  # all other jobs. This job is then included in the GitHub branch protection
+  # rule which prevents merges unless all other jobs are passing. This makes
+  # it easier to manage the list of jobs via this yml file and to prevent
+  # accidentally adding new jobs without also updating the branch protections.
+  success:
+    name: Success gate
+    if: always()
+    needs:
+      - code-tests
+      - style-tests
+      - mdbook-spec
+    runs-on: ubuntu-latest
+    steps:
+      - run: jq --exit-status 'all(.result == "success")' <<< '${{ toJson(needs) }}'
+      - name: Done
+        run: exit 0