Lint for suspicious implementations of arithmetic std::ops traits

clippy_lints/src/lib.rs

@@ -158,6 +158,7 @@ pub mod returns;
 pub mod serde_api;
 pub mod shadow;
 pub mod strings;
+pub mod suspicious_trait_impl;
 pub mod swap;
 pub mod temporary_assignment;
 pub mod transmute;
@@ -373,6 +374,7 @@ pub fn register_plugins(reg: &mut rustc_plugin::Registry) {
     reg.register_late_lint_pass(box types::UnitArg);
     reg.register_late_lint_pass(box double_comparison::DoubleComparisonPass);
     reg.register_late_lint_pass(box question_mark::QuestionMarkPass);
+    reg.register_late_lint_pass(box suspicious_trait_impl::SuspiciousImpl);
 
     reg.register_lint_group("clippy_restrictions", vec![
         arithmetic::FLOAT_ARITHMETIC,
@@ -599,6 +601,8 @@ pub fn register_plugins(reg: &mut rustc_plugin::Registry) {
         returns::NEEDLESS_RETURN,
         serde_api::SERDE_API_MISUSE,
         strings::STRING_LIT_AS_BYTES,
+        suspicious_trait_impl::SUSPICIOUS_ARITHMETIC_IMPL,
+        suspicious_trait_impl::SUSPICIOUS_OP_ASSIGN_IMPL,
         swap::ALMOST_SWAPPED,
         swap::MANUAL_SWAP,
         temporary_assignment::TEMPORARY_ASSIGNMENT,

clippy_lints/src/suspicious_trait_impl.rs

@@ -0,0 +1,192 @@
+use rustc::lint::*;
+use rustc::hir;
+use rustc::hir::intravisit::{walk_expr, NestedVisitorMap, Visitor};
+use syntax::ast;
+use utils::{get_trait_def_id, span_lint};
+
+/// **What it does:** Lints for suspicious operations in impls of arithmetic operators, e.g.
+/// subtracting elements in an Add impl.
+///
+/// **Why this is bad?** This is probably a typo or copy-and-paste error and not intended.
+///
+/// **Known problems:** None.
+///
+/// **Example:**
+/// ```rust
+/// impl Add for Foo {
+///     type Output = Foo;
+///
+///     fn add(self, other: Foo) -> Foo {
+///         Foo(self.0 - other.0)
+///     }
+/// }
+/// ```
+declare_lint! {
+    pub SUSPICIOUS_ARITHMETIC_IMPL,
+    Warn,
+    "suspicious use of operators in impl of arithmetic trait"
+}
+
+/// **What it does:** Lints for suspicious operations in impls of OpAssign, e.g.
+/// subtracting elements in an AddAssign impl.
+///
+/// **Why this is bad?** This is probably a typo or copy-and-paste error and not intended.
+///
+/// **Known problems:** None.
+///
+/// **Example:**
+/// ```rust
+/// impl AddAssign for Foo {
+///     fn add_assign(&mut self, other: Foo) {
+///         *self = *self - other;
+///     }
+/// }
+/// ```
+declare_lint! {
+    pub SUSPICIOUS_OP_ASSIGN_IMPL,
+    Warn,
+    "suspicious use of operators in impl of OpAssign trait"
+}
+
+#[derive(Copy, Clone)]
+pub struct SuspiciousImpl;
+
+impl LintPass for SuspiciousImpl {
+    fn get_lints(&self) -> LintArray {
+        lint_array![SUSPICIOUS_ARITHMETIC_IMPL, SUSPICIOUS_OP_ASSIGN_IMPL]
+    }
+}
+
+impl<'a, 'tcx> LateLintPass<'a, 'tcx> for SuspiciousImpl {
+    fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx hir::Expr) {
+        use rustc::hir::BinOp_::*;
+        if let hir::ExprBinary(binop, _, _) = expr.node {
+            // Check if the binary expression is part of another binary expression
+            // as a child node
+            let mut parent_expr = cx.tcx.hir.get_parent_node(expr.id);
+            while parent_expr != ast::CRATE_NODE_ID {
+                if_chain! {
+                    if let hir::map::Node::NodeExpr(e) = cx.tcx.hir.get(parent_expr);
+                    if let hir::ExprBinary(_, _, _) = e.node;
+                    then {
+                        return
+                    }
+                }
+
+                parent_expr = cx.tcx.hir.get_parent_node(parent_expr);
+            }
+            // as a parent node
+            let mut visitor = BinaryExprVisitor {
+                in_binary_expr: false,
+            };
+            walk_expr(&mut visitor, expr);
+
+            if visitor.in_binary_expr {
+                return;
+            }
+
+            if let Some(impl_trait) = check_binop(
+                cx,
+                expr,
+                &binop.node,
+                &["Add", "Sub", "Mul", "Div"],
+                &[BiAdd, BiSub, BiMul, BiDiv],
+            ) {
+                span_lint(
+                    cx,
+                    SUSPICIOUS_ARITHMETIC_IMPL,
+                    binop.span,
+                    &format!(
+                        r#"Suspicious use of binary operator in `{}` impl"#,
+                        impl_trait
+                    ),
+                );
+            }
+
+            if let Some(impl_trait) = check_binop(
+                cx,
+                expr,
+                &binop.node,
+                &[
+                    "AddAssign",
+                    "SubAssign",
+                    "MulAssign",
+                    "DivAssign",
+                    "BitAndAssign",
+                    "BitOrAssign",
+                    "BitXorAssign",
+                    "RemAssign",
+                    "ShlAssign",
+                    "ShrAssign",
+                ],
+                &[
+                    BiAdd, BiSub, BiMul, BiDiv, BiBitAnd, BiBitOr, BiBitXor, BiRem, BiShl, BiShr
+                ],
+            ) {
+                span_lint(
+                    cx,
+                    SUSPICIOUS_OP_ASSIGN_IMPL,
+                    binop.span,
+                    &format!(
+                        r#"Suspicious use of binary operator in `{}` impl"#,
+                        impl_trait
+                    ),
+                );
+            }
+        }
+    }
+}
+
+fn check_binop<'a>(
+    cx: &LateContext,
+    expr: &hir::Expr,
+    binop: &hir::BinOp_,
+    traits: &[&'a str],
+    expected_ops: &[hir::BinOp_],
+) -> Option<&'a str> {
+    let mut trait_ids = vec![];
+    let [krate, module] = ::utils::paths::OPS_MODULE;
+
+    for t in traits {
+        let path = [krate, module, t];
+        if let Some(trait_id) = get_trait_def_id(cx, &path) {
+            trait_ids.push(trait_id);
+        } else {
+            return None;
+        }
+    }
+
+    // Get the actually implemented trait
+    let parent_fn = cx.tcx.hir.get_parent(expr.id);
+    let parent_impl = cx.tcx.hir.get_parent(parent_fn);
+
+    if_chain! {
+        if parent_impl != ast::CRATE_NODE_ID;
+        if let hir::map::Node::NodeItem(item) = cx.tcx.hir.get(parent_impl);
+        if let hir::Item_::ItemImpl(_, _, _, _, Some(ref trait_ref), _, _) = item.node;
+        if let Some(idx) = trait_ids.iter().position(|&tid| tid == trait_ref.path.def.def_id());
+        if *binop != expected_ops[idx];
+        then{
+            return Some(traits[idx])
+        }
+    }
+
+    None
+}
+
+struct BinaryExprVisitor {
+    in_binary_expr: bool,
+}
+
+impl<'a, 'tcx: 'a> Visitor<'tcx> for BinaryExprVisitor {
+    fn visit_expr(&mut self, expr: &'tcx hir::Expr) {
+        if let hir::ExprBinary(_, _, _) = expr.node {
+            self.in_binary_expr = true;
+        }
+
+        walk_expr(self, expr);
+    }
+    fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
+        NestedVisitorMap::None
+    }
+}

tests/ui/suspicious_arithmetic_impl.rs

@@ -0,0 +1,52 @@
+
+
+
+#![warn(suspicious_arithmetic_impl)]
+use std::ops::{Add, AddAssign, Mul, Sub, Div};
+
+#[derive(Copy, Clone)]
+struct Foo(u32);
+
+impl Add for Foo {
+    type Output = Foo;
+
+    fn add(self, other: Self) -> Self {
+        Foo(self.0 - other.0)
+    }
+}
+
+impl AddAssign for Foo {
+    fn add_assign(&mut self, other: Foo) {
+        *self = *self - other;
+    }
+}
+
+impl Mul for Foo {
+    type Output = Foo;
+
+    fn mul(self, other: Foo) -> Foo {
+        Foo(self.0 * other.0 % 42) // OK: BiRem part of BiExpr as parent node
+    }
+}
+
+impl Sub for Foo {
+    type Output = Foo;
+
+    fn sub(self, other: Self) -> Self {
+        Foo(self.0 * other.0 - 42) // OK: BiMul part of BiExpr as child node
+    }
+}
+
+impl Div for Foo {
+    type Output = Foo;
+
+    fn div(self, other: Self) -> Self {
+        Foo(do_nothing(self.0 + other.0) / 42) // OK: BiAdd part of BiExpr as child node
+    }
+}
+
+fn main() {}
+
+fn do_nothing(x: u32) -> u32 {
+    x
+}

tests/ui/suspicious_arithmetic_impl.stderr

@@ -0,0 +1,18 @@
+error: Suspicious use of binary operator in `Add` impl
+  --> $DIR/suspicious_arithmetic_impl.rs:14:20
+   |
+14 |         Foo(self.0 - other.0)
+   |                    ^
+   |
+   = note: `-D suspicious-arithmetic-impl` implied by `-D warnings`
+
+error: Suspicious use of binary operator in `AddAssign` impl
+  --> $DIR/suspicious_arithmetic_impl.rs:20:23
+   |
+20 |         *self = *self - other;
+   |                       ^
+   |
+   = note: `-D suspicious-op-assign-impl` implied by `-D warnings`
+
+error: aborting due to 2 previous errors
+