Introduce a cargo clippy run (#2025)

This might help catch stylistic problems in our Rust code.

Related to #2587.

.github/workflows/build.yml

@@ -11,38 +11,6 @@ env:
   CARGO_TERM_COLOR: always
 
 jobs:
-  format:
-    runs-on: ubuntu-latest
-    env:
-      NIGHTLY_VERSION: nightly-2025-09-01
-    steps:
-      - name: Checkout
-        uses: actions/checkout@v5
-
-      - name: Install formatting dependencies
-        run: |
-          sudo apt update
-          sudo apt install gettext yapf3
-
-      - name: Install pinned nightly for rustfmt
-        run: |
-          rustup toolchain install --profile minimal "$NIGHTLY_VERSION"
-          rustup component add rustfmt --toolchain "$NIGHTLY_VERSION"
-
-      - name: Check formatting
-        uses: dprint/check@v2.3
-
-  typos:
-    runs-on: ubuntu-latest
-    steps:
-      - name: Checkout
-        uses: actions/checkout@v5
-
-      - name: Check for typos
-        uses: crate-ci/typos@v1.35.7
-        with:
-          config: ./.github/typos.toml
-
   cargo:
     strategy:
       matrix:

.github/workflows/lint.yml

@@ -0,0 +1,55 @@
+name: Lint
+
+on:
+  pull_request:
+  push:
+    branches:
+      - main
+
+env:
+  CARGO_TERM_COLOR: always
+
+jobs:
+  clippy:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v5
+
+      - name: Setup Rust cache
+        uses: ./.github/workflows/setup-rust-cache
+
+      - name: Clippy
+        run: cargo clippy -- -Dwarnings
+
+  format:
+    runs-on: ubuntu-latest
+    env:
+      NIGHTLY_VERSION: nightly-2025-09-01
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v5
+
+      - name: Install formatting dependencies
+        run: |
+          sudo apt update
+          sudo apt install gettext yapf3
+
+      - name: Install pinned nightly for rustfmt
+        run: |
+          rustup toolchain install --profile minimal "$NIGHTLY_VERSION"
+          rustup component add rustfmt --toolchain "$NIGHTLY_VERSION"
+
+      - name: Check formatting
+        uses: dprint/check@v2.3
+
+  typos:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v5
+
+      - name: Check for typos
+        uses: crate-ci/typos@v1.35.7
+        with:
+          config: ./.github/typos.toml

mdbook-course/src/bin/course-schedule.rs

@@ -48,7 +48,7 @@ fn timediff(actual: u64, target: u64, slop: u64) -> String {
     } else if actual + slop < target {
         format!("{}: ({} short)", duration(actual), duration(target - actual),)
     } else {
-        format!("{}", duration(actual))
+        duration(actual).to_string()
     }
 }
 

mdbook-course/src/bin/mdbook-course.rs

@@ -29,7 +29,7 @@ fn main() {
         );
     let matches = app.get_matches();
 
-    if let Some(_) = matches.subcommand_matches("supports") {
+    if matches.subcommand_matches("supports").is_some() {
         // Support all renderers.
         process::exit(0);
     }

mdbook-course/src/course.rs

@@ -156,7 +156,7 @@ impl Courses {
     fn course_mut(&mut self, name: impl AsRef<str>) -> &mut Course {
         let name = name.as_ref();
         if let Some(found_idx) =
-            self.courses.iter().position(|course| &course.name == name)
+            self.courses.iter().position(|course| course.name == name)
         {
             return &mut self.courses[found_idx];
         }
@@ -177,9 +177,7 @@ impl Courses {
         &self,
         chapter: &Chapter,
     ) -> Option<(&Course, &Session, &Segment, &Slide)> {
-        let Some(ref source_path) = chapter.source_path else {
-            return None;
-        };
+        let source_path = chapter.source_path.as_ref()?;
 
         for course in self {
             for session in course {
@@ -193,7 +191,7 @@ impl Courses {
             }
         }
 
-        return None;
+        None
     }
 }
 
@@ -202,7 +200,7 @@ impl<'a> IntoIterator for &'a Courses {
     type IntoIter = std::slice::Iter<'a, Course>;
 
     fn into_iter(self) -> Self::IntoIter {
-        (&self.courses).into_iter()
+        self.courses.iter()
     }
 }
 
@@ -216,7 +214,7 @@ impl Course {
     fn session_mut(&mut self, name: impl AsRef<str>) -> &mut Session {
         let name = name.as_ref();
         if let Some(found_idx) =
-            self.sessions.iter().position(|session| &session.name == name)
+            self.sessions.iter().position(|session| session.name == name)
         {
             return &mut self.sessions[found_idx];
         }
@@ -275,7 +273,7 @@ impl<'a> IntoIterator for &'a Course {
     type IntoIter = std::slice::Iter<'a, Session>;
 
     fn into_iter(self) -> Self::IntoIter {
-        (&self.sessions).into_iter()
+        self.sessions.iter()
     }
 }
 
@@ -348,7 +346,7 @@ impl<'a> IntoIterator for &'a Session {
     type IntoIter = std::slice::Iter<'a, Segment>;
 
     fn into_iter(self) -> Self::IntoIter {
-        (&self.segments).into_iter()
+        self.segments.iter()
     }
 }
 
@@ -401,7 +399,7 @@ impl<'a> IntoIterator for &'a Segment {
     type IntoIter = std::slice::Iter<'a, Slide>;
 
     fn into_iter(self) -> Self::IntoIter {
-        (&self.slides).into_iter()
+        self.slides.iter()
     }
 }
 
@@ -449,7 +447,7 @@ impl Slide {
     pub fn is_sub_chapter(&self, chapter: &Chapter) -> bool {
         // The first `source_path` in the slide is the "parent" chapter, so anything
         // else is a sub-chapter.
-        chapter.source_path.as_ref() != self.source_paths.get(0)
+        chapter.source_path.as_ref() != self.source_paths.first()
     }
 
     /// Return the total duration of this slide.

mdbook-course/src/markdown.rs

@@ -83,7 +83,7 @@ impl<const N: usize> Table<N> {
         for cell in iter {
             write!(f, " {} |", cell)?;
         }
-        write!(f, "\n")
+        writeln!(f)
     }
 }
 

mdbook-course/src/replacements.rs

@@ -51,7 +51,7 @@ pub fn replace(
                 ["course", "outline", course_name @ ..] => {
                     let course_name = course_name.join(" ");
                     let Some(course) = courses.find_course(course_name) else {
-                        return format!("not found - {}", captures[0].to_string());
+                        return format!("not found - {}", &captures[0]);
                     };
                     course.schedule()
                 }

src/concurrency/async-exercises/chat-async/src/bin/client.rs

@@ -41,7 +41,7 @@ async fn main() -> Result<(), tokio_websockets::Error> {
                             println!("From server: {}", text);
                         }
                     },
-                    Some(Err(err)) => return Err(err.into()),
+                    Some(Err(err)) => return Err(err),
                     None => return Ok(()),
                 }
             }

src/lifetimes/exercise.rs

@@ -116,7 +116,7 @@ fn unpack_tag(tag: u64) -> (u64, WireType) {
 
 // ANCHOR: parse_field
 /// Parse a field, returning the remaining bytes
-fn parse_field(data: &[u8]) -> (Field, &[u8]) {
+fn parse_field(data: &[u8]) -> (Field<'_>, &[u8]) {
     let (tag, remainder) = parse_varint(data);
     let (field_num, wire_type) = unpack_tag(tag);
     let (fieldvalue, remainder) = match wire_type {

src/tuples-and-arrays/exercise.rs

@@ -12,6 +12,8 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+// Iterators are covered later.
+#[allow(clippy::needless_range_loop)]
 // ANCHOR: solution
 // ANCHOR: transpose
 fn transpose(matrix: [[i32; 3]; 3]) -> [[i32; 3]; 3] {

src/types-and-values/exercise.rs

@@ -12,6 +12,8 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+// Omitting `return` is covered later.
+#[allow(clippy::needless_return)]
 // ANCHOR: solution
 // ANCHOR: fib
 fn fib(n: u32) -> u32 {

src/unsafe-rust/exercise.rs

@@ -12,6 +12,8 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+// `DIR` matches name of C struct.
+#[allow(clippy::upper_case_acronyms)]
 // ANCHOR: solution
 // ANCHOR: ffi
 mod ffi {
@@ -40,7 +42,7 @@ mod ffi {
     }
 
     // Layout according to the macOS man page for dir(5).
-    #[cfg(all(target_os = "macos"))]
+    #[cfg(target_os = "macos")]
     #[repr(C)]
     pub struct dirent {
         pub d_fileno: u64,

third_party/rust-on-exercism/health-statistics.rs

@@ -29,7 +29,7 @@ impl User {
     // ANCHOR_END: setup
 
     // ANCHOR: User_visit_doctor
-    pub fn visit_doctor(&mut self, measurements: Measurements) -> HealthReport {
+    pub fn visit_doctor(&mut self, measurements: Measurements) -> HealthReport<'_> {
         // ANCHOR_END: User_visit_doctor
         self.visit_count += 1;
         let bp = measurements.blood_pressure;
@@ -37,12 +37,9 @@ impl User {
             patient_name: &self.name,
             visit_count: self.visit_count,
             height_change: measurements.height - self.height,
-            blood_pressure_change: match self.last_blood_pressure {
-                Some(lbp) => {
-                    Some((bp.0 as i32 - lbp.0 as i32, bp.1 as i32 - lbp.1 as i32))
-                }
-                None => None,
-            },
+            blood_pressure_change: self
+                .last_blood_pressure
+                .map(|lbp| (bp.0 as i32 - lbp.0 as i32, bp.1 as i32 - lbp.1 as i32)),
         };
         self.height = measurements.height;
         self.last_blood_pressure = Some(bp);