GitHub Actions: Run Clippy on tests

.github/workflows/tests.yml

@@ -121,6 +121,46 @@ jobs:
         run: sh ./_test/check-exercise-crate.sh
         continue-on-error: ${{ matrix.rust == 'beta' && matrix.deny_warnings == '1' }}
 
+  clippy:
+    name: Clippy
+    runs-on: ubuntu-latest
+
+    strategy:
+      matrix:
+        rust: ["stable", "beta"]
+
+    steps:
+      - name: Checkout master
+        uses: actions/checkout@v2
+        with:
+          ref: master
+
+      - name: Checkout code
+        uses: actions/checkout@v2
+
+      # We actually think explicitly installing Clippy isn't necessary,
+      # as it is currently installed by default.
+      # But we'll include this step anyway just in case that changes.
+      - name: Install Clippy
+        run: rustup component add clippy
+
+      - name: Setup toolchain
+        uses: actions-rs/toolchain@v1
+        with:
+          toolchain: ${{ matrix.rust }}
+          default: true
+
+      - name: Clippy tests
+        env:
+          CLIPPY: tests/
+        run: ./_test/check-exercises.sh
+
+      # Our examples currently have too much Clippy output to consider this.
+      # But maybe in the future.
+      #- name: Clippy examples
+      #  env:
+      #    CLIPPY: src/lib.rs
+      #  run: ./_test/check-exercises.sh
   nightly-compilation:
     name: Check exercises on nightly (benchmark enabled)
     runs-on: ubuntu-latest

_test/check-exercises.sh

@@ -11,9 +11,10 @@ if [ ! -x "./bin/test-exercise" ]; then
    exit 1
 fi
 
-# In DENYWARNINGS mode, do not set -e so that we run all tests.
+# In DENYWARNINGS or CLIPPY mode, do not set -e so that we run all tests.
 # This allows us to see all warnings.
-if [ -z "$DENYWARNINGS" ]; then
+# If we are in neither DENYWARNINGS nor CLIPPY mode, do set -e.
+if [ -z "$DENYWARNINGS" ] && [ -z "$CLIPPY" ]; then
     set -e
 fi
 

bin/test-exercise

@@ -82,6 +82,19 @@ done
 # (use subshell so we auto-reset to current pwd after)
 (
    cd $exercise
-   # this is the last command; its exit code is what's passed on
-   time cargo $command "$@"
+   if [ -n "$CLIPPY" ]; then
+     cargo clippy --all-targets --color always "$@" 2>clippy.log
+     # Only consider it a failure if output contains the string in CLIPPY.
+     # For example, if we're only looking in tests, CLIPPY contains tests/
+     if grep -q $CLIPPY clippy.log; then
+       cat clippy.log
+       exit 1
+     else
+       # Just to show progress
+       echo "clippy $exercise OK"
+     fi
+   else
+     # this is the last command; its exit code is what's passed on
+     time cargo $command "$@"
+   fi
 )