1 files changed, 116 insertions, 0 deletions
diff --git a/src/tools/clippy/clippy_lints/src/suspicious_trait_impl.rs b/src/tools/clippy/clippy_lints/src/suspicious_trait_impl.rs
new file mode 100644
index 000000000..4294464db
--- /dev/null
+++ b/src/tools/clippy/clippy_lints/src/suspicious_trait_impl.rs
@@ -0,0 +1,116 @@
+use clippy_utils::diagnostics::span_lint;
+use clippy_utils::{binop_traits, trait_ref_of_method, BINOP_TRAITS, OP_ASSIGN_TRAITS};
+use if_chain::if_chain;
+use rustc_hir as hir;
+use rustc_hir::intravisit::{walk_expr, Visitor};
+use rustc_lint::{LateContext, LateLintPass};
+use rustc_session::{declare_lint_pass, declare_tool_lint};
+
+declare_clippy_lint! {
+    /// ### What it does
+    /// Lints for suspicious operations in impls of arithmetic operators, e.g.
+    /// subtracting elements in an Add impl.
+    ///
+    /// ### Why is this bad?
+    /// This is probably a typo or copy-and-paste error and not intended.
+    ///
+    /// ### Example
+    /// ```ignore
+    /// impl Add for Foo {
+    ///     type Output = Foo;
+    ///
+    ///     fn add(self, other: Foo) -> Foo {
+    ///         Foo(self.0 - other.0)
+    ///     }
+    /// }
+    /// ```
+    #[clippy::version = "pre 1.29.0"]
+    pub SUSPICIOUS_ARITHMETIC_IMPL,
+    suspicious,
+    "suspicious use of operators in impl of arithmetic trait"
+}
+
+declare_clippy_lint! {
+    /// ### What it does
+    /// Lints for suspicious operations in impls of OpAssign, e.g.
+    /// subtracting elements in an AddAssign impl.
+    ///
+    /// ### Why is this bad?
+    /// This is probably a typo or copy-and-paste error and not intended.
+    ///
+    /// ### Example
+    /// ```ignore
+    /// impl AddAssign for Foo {
+    ///     fn add_assign(&mut self, other: Foo) {
+    ///         *self = *self - other;
+    ///     }
+    /// }
+    /// ```
+    #[clippy::version = "pre 1.29.0"]
+    pub SUSPICIOUS_OP_ASSIGN_IMPL,
+    suspicious,
+    "suspicious use of operators in impl of OpAssign trait"
+}
+
+declare_lint_pass!(SuspiciousImpl => [SUSPICIOUS_ARITHMETIC_IMPL, SUSPICIOUS_OP_ASSIGN_IMPL]);
+
+impl<'tcx> LateLintPass<'tcx> for SuspiciousImpl {
+    fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'_>) {
+        if_chain! {
+            if let hir::ExprKind::Binary(binop, _, _) | hir::ExprKind::AssignOp(binop, ..) = expr.kind;
+            if let Some((binop_trait_lang, op_assign_trait_lang)) = binop_traits(binop.node);
+            if let Ok(binop_trait_id) = cx.tcx.lang_items().require(binop_trait_lang);
+            if let Ok(op_assign_trait_id) = cx.tcx.lang_items().require(op_assign_trait_lang);
+
+            // Check for more than one binary operation in the implemented function
+            // Linting when multiple operations are involved can result in false positives
+            let parent_fn = cx.tcx.hir().get_parent_item(expr.hir_id);
+            if let hir::Node::ImplItem(impl_item) = cx.tcx.hir().get_by_def_id(parent_fn);
+            if let hir::ImplItemKind::Fn(_, body_id) = impl_item.kind;
+            let body = cx.tcx.hir().body(body_id);
+            let parent_fn = cx.tcx.hir().get_parent_item(expr.hir_id);
+            if let Some(trait_ref) = trait_ref_of_method(cx, parent_fn);
+            let trait_id = trait_ref.path.res.def_id();
+            if ![binop_trait_id, op_assign_trait_id].contains(&trait_id);
+            if let Some(&(_, lint)) = [
+                (&BINOP_TRAITS, SUSPICIOUS_ARITHMETIC_IMPL),
+                (&OP_ASSIGN_TRAITS, SUSPICIOUS_OP_ASSIGN_IMPL),
+            ]
+                .iter()
+                .find(|&(ts, _)| ts.iter().any(|&t| Ok(trait_id) == cx.tcx.lang_items().require(t)));
+            if count_binops(&body.value) == 1;
+            then {
+                span_lint(
+                    cx,
+                    lint,
+                    binop.span,
+                    &format!("suspicious use of `{}` in `{}` impl", binop.node.as_str(), cx.tcx.item_name(trait_id)),
+                );
+            }
+        }
+    }
+}
+
+fn count_binops(expr: &hir::Expr<'_>) -> u32 {
+    let mut visitor = BinaryExprVisitor::default();
+    visitor.visit_expr(expr);
+    visitor.nb_binops
+}
+
+#[derive(Default)]
+struct BinaryExprVisitor {
+    nb_binops: u32,
+}
+
+impl<'tcx> Visitor<'tcx> for BinaryExprVisitor {
+    fn visit_expr(&mut self, expr: &'tcx hir::Expr<'_>) {
+        match expr.kind {
+            hir::ExprKind::Binary(..)
+            | hir::ExprKind::Unary(hir::UnOp::Not | hir::UnOp::Neg, _)
+            | hir::ExprKind::AssignOp(..) => self.nb_binops += 1,
+            _ => {},
+        }
+
+        walk_expr(self, expr);
+    }
+}