Run 'cargo xtask codegen' in CI and check that there are no diffs

.github/workflows/checks.yml

@@ -56,7 +56,7 @@ jobs:
       - name: Setup mdBook
         uses: peaceiris/actions-mdbook@v1
         with:
-          # if this changes, change it in cli/Cargo.toml and .github/workflows/publish-docs.yml as well
+          # if this changes, change it in .github/workflows/publish-docs.yml as well
           mdbook-version: '0.4.10'
 
       - run: mdbook test taskchampion/docs
@@ -80,3 +80,39 @@ jobs:
           command: fmt
           args: --all -- --check
 
+  codegen:
+    runs-on: ubuntu-latest
+    name: "codegen"
+    steps:
+      - uses: actions/checkout@v3
+
+      - name: Cache cargo registry
+        uses: actions/cache@v3
+        with:
+          path: ~/.cargo/registry
+          key: ${{ runner.os }}-cargo-registry-${{ hashFiles('**/Cargo.lock') }}
+
+      - name: Cache cargo build
+        uses: actions/cache@v3
+        with:
+          path: target
+          key: ${{ runner.os }}-cargo-build-target-${{ hashFiles('**/Cargo.lock') }}
+
+      - uses: actions-rs/toolchain@v1
+        with:
+          # Same as the MSRV in rust-tests.yml
+          toolchain: "1.64"
+          override: true
+
+      - uses: actions-rs/cargo@v1.0.3
+        with:
+          command: run
+          args: --package xtask -- codegen
+
+      - name: check for changes
+        run: |
+          if ! git diff; then
+            echo "Generated code not up-to-date;
+            run `cargo run --package xtask -- codegen` and commit the result";
+            exit 1;
+          fi

.github/workflows/publish-docs.yml

@@ -18,7 +18,7 @@ jobs:
       - name: Setup mdBook
         uses: peaceiris/actions-mdbook@v1
         with:
-          # if this changes, change it in cli/Cargo.toml and .github/workflows/publish-docs.yml as well
+          # if this changes, change it in .github/workflows/publish-docs.yml as well
           mdbook-version: '0.4.10'
 
       - run: mdbook build taskchampion/docs