Separate check for docs into its own job

.github/workflows/ci.yml

@@ -117,6 +117,17 @@ jobs:
       - name: loom
         run: ./ci/crossbeam-epoch-loom.sh
 
+  # Check if the document can be generated without warning.
+  docs:
+    name: docs
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - name: Install Rust
+        run: rustup update nightly && rustup default nightly
+      - name: docs
+        run: ./ci/docs.sh
+
   # This job doesn't actually test anything, but they're used to tell bors the
   # build completed, as there is no practical way to detect when a workflow is
   # successful listening to webhooks only.
@@ -133,6 +144,7 @@ jobs:
       - rustfmt
       - clippy
       - loom
+      - docs
     runs-on: ubuntu-latest
     steps:
       - name: Mark the job as a success

ci/docs.sh

@@ -0,0 +1,8 @@
+#!/bin/bash
+
+cd "$(dirname "$0")"/..
+set -ex
+
+export RUSTDOCFLAGS="-D warnings"
+
+cargo doc --no-deps --all --all-features

ci/test.sh

@@ -22,8 +22,6 @@ if [[ "$RUST_VERSION" == "nightly"* ]]; then
     # Some crates have `nightly` feature, so run tests with --all-features.
     cargo test --all --all-features --exclude benchmarks -- --test-threads=1
 
-    RUSTDOCFLAGS="-D warnings" cargo doc --no-deps --all --all-features
-
     # Benchmarks are only checked on nightly because depending on unstable features.
     cargo check --all --benches
     cd crossbeam-channel/benchmarks