GitHub Actions: Run Clippy on stubs

.github/workflows/tests.yml

@@ -137,11 +137,16 @@ jobs:
       - name: Install Clippy
         run: rustup component add clippy
 
-      - name: Clippy
+      - name: Clippy tests
         env:
           CLIPPY: true
         run: ./_test/check-exercises.sh
 
+      - name: Clippy stubs
+        env:
+          CLIPPY: true
+        run: sh ./_test/ensure-stubs-compile.sh
+
   nightly-compilation:
     name: Check exercises on nightly (benchmark enabled)
     runs-on: ubuntu-latest

_test/ensure-stubs-compile.sh

@@ -30,21 +30,40 @@ for dir in $changed_exercises; do
 	cp -r $dir/tests $dir/tests.orig
 	cp $dir/src/lib.rs $dir/lib.rs.orig
 
-	# This sed serves two purposes:
-	# First, in Travis CI, we may have already compiled using the example solution.
-	# Edit the src/lib.rs file so that we surely recompile using the stub.
-	# Second, ensures that the stub compiles without warnings.
-	sed -i -e '1i #![deny(warnings)]' "$dir/src/lib.rs"
+  # In CI, we may have already compiled using the example solution.
+  # So we want to touch the src/lib.rs in some way,
+  # so that we surely recompile using the stub.
+  if [ -n "$CLIPPY" ]; then
+    # We don't deny warnings in clippy mode,
+    # just because there are many we don't want to deal with right now.
+    # So in clippy mode it's just a touch.
+    touch "$dir/src/lib.rs"
+  else
+    # In non-clippy mode, we do want to compile without warnings.
+    sed -i -e '1i #![deny(warnings)]' "$dir/src/lib.rs"
+  fi
 
 	# Deny warnings in the tests that may result from compiling the stubs.
 	# This helps avoid, for example, an overflowing literal warning
 	# that could be caused by a stub with a type that is too small.
 	sed -i -e '1i #![deny(warnings)]' $dir/tests/*.rs
 
-	if ! (cd $dir && cargo test --quiet --no-run); then
-	  echo "$exercise's stub does not compile; please make it compile"
-	  broken="$broken\n$exercise"
-	fi
+  if [ -n "$CLIPPY" ]; then
+    if ! (cd $dir && cargo clippy --lib --tests --color always 2>clippy.log); then
+      cat $dir/clippy.log
+      broken="$broken\n$exercise"
+    elif grep -q warning $dir/clippy.log; then
+      # Warnings will be outputted, but do not fail the build.
+      echo "clippy $exercise WARN"
+      cat $dir/clippy.log
+    else
+      # Just to show progress
+      echo "clippy $exercise OK"
+    fi
+  elif ! (cd $dir && cargo test --quiet --no-run); then
+    echo "$exercise's stub does not compile; please make it compile"
+    broken="$broken\n$exercise"
+  fi
 
 	# Restore tests and stub.
 	mv $dir/lib.rs.orig $dir/src/lib.rs