src/tools/clippy/clippy_lints/src/suspicious_trait_impl.rs

   1 use clippy_utils::diagnostics::span_lint;
   2 use clippy_utils::{binop_traits, trait_ref_of_method, BINOP_TRAITS, OP_ASSIGN_TRAITS};
   3 use if_chain::if_chain;
   4 use rustc_hir as hir;
   5 use rustc_hir::intravisit::{walk_expr, NestedVisitorMap, Visitor};
   6 use rustc_lint::{LateContext, LateLintPass};
   7 use rustc_middle::hir::map::Map;
   8 use rustc_session::{declare_lint_pass, declare_tool_lint};
   9
  10 declare_clippy_lint! {
  11     /// ### What it does
  12     /// Lints for suspicious operations in impls of arithmetic operators, e.g.
  13     /// subtracting elements in an Add impl.
  14     ///
  15     /// ### Why is this bad?
  16     /// This is probably a typo or copy-and-paste error and not intended.
  17     ///
  18     /// ### Example
  19     /// ```ignore
  20     /// impl Add for Foo {
  21     ///     type Output = Foo;
  22     ///
  23     ///     fn add(self, other: Foo) -> Foo {
  24     ///         Foo(self.0 - other.0)
  25     ///     }
  26     /// }
  27     /// ```
  28     pub SUSPICIOUS_ARITHMETIC_IMPL,
  29     suspicious,
  30     "suspicious use of operators in impl of arithmetic trait"
  31 }
  32
  33 declare_clippy_lint! {
  34     /// ### What it does
  35     /// Lints for suspicious operations in impls of OpAssign, e.g.
  36     /// subtracting elements in an AddAssign impl.
  37     ///
  38     /// ### Why is this bad?
  39     /// This is probably a typo or copy-and-paste error and not intended.
  40     ///
  41     /// ### Example
  42     /// ```ignore
  43     /// impl AddAssign for Foo {
  44     ///     fn add_assign(&mut self, other: Foo) {
  45     ///         *self = *self - other;
  46     ///     }
  47     /// }
  48     /// ```
  49     pub SUSPICIOUS_OP_ASSIGN_IMPL,
  50     suspicious,
  51     "suspicious use of operators in impl of OpAssign trait"
  52 }
  53
  54 declare_lint_pass!(SuspiciousImpl => [SUSPICIOUS_ARITHMETIC_IMPL, SUSPICIOUS_OP_ASSIGN_IMPL]);
  55
  56 impl<'tcx> LateLintPass<'tcx> for SuspiciousImpl {
  57     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'_>) {
  58         if_chain! {
  59             if let hir::ExprKind::Binary(binop, _, _) | hir::ExprKind::AssignOp(binop, ..) = expr.kind;
  60             if let Some((binop_trait_lang, op_assign_trait_lang)) = binop_traits(binop.node);
  61             if let Ok(binop_trait_id) = cx.tcx.lang_items().require(binop_trait_lang);
  62             if let Ok(op_assign_trait_id) = cx.tcx.lang_items().require(op_assign_trait_lang);
  63
  64             // Check for more than one binary operation in the implemented function
  65             // Linting when multiple operations are involved can result in false positives
  66             let parent_fn = cx.tcx.hir().get_parent_item(expr.hir_id);
  67             if let hir::Node::ImplItem(impl_item) = cx.tcx.hir().get(parent_fn);
  68             if let hir::ImplItemKind::Fn(_, body_id) = impl_item.kind;
  69             let body = cx.tcx.hir().body(body_id);
  70             let parent_fn = cx.tcx.hir().get_parent_item(expr.hir_id);
  71             if let Some(trait_ref) = trait_ref_of_method(cx, parent_fn);
  72             let trait_id = trait_ref.path.res.def_id();
  73             if ![binop_trait_id, op_assign_trait_id].contains(&trait_id);
  74             if let Some(&(_, lint)) = [
  75                 (&BINOP_TRAITS, SUSPICIOUS_ARITHMETIC_IMPL),
  76                 (&OP_ASSIGN_TRAITS, SUSPICIOUS_OP_ASSIGN_IMPL),
  77             ]
  78                 .iter()
  79                 .find(|&(ts, _)| ts.iter().any(|&t| Ok(trait_id) == cx.tcx.lang_items().require(t)));
  80             if count_binops(&body.value) == 1;
  81             then {
  82                 span_lint(
  83                     cx,
  84                     lint,
  85                     binop.span,
  86                     &format!("suspicious use of `{}` in `{}` impl", binop.node.as_str(), cx.tcx.item_name(trait_id)),
  87                 );
  88             }
  89         }
  90     }
  91 }
  92
  93 fn count_binops(expr: &hir::Expr<'_>) -> u32 {
  94     let mut visitor = BinaryExprVisitor::default();
  95     visitor.visit_expr(expr);
  96     visitor.nb_binops
  97 }
  98
  99 #[derive(Default)]
 100 struct BinaryExprVisitor {
 101     nb_binops: u32,
 102 }
 103
 104 impl<'tcx> Visitor<'tcx> for BinaryExprVisitor {
 105     type Map = Map<'tcx>;
 106
 107     fn visit_expr(&mut self, expr: &'tcx hir::Expr<'_>) {
 108         match expr.kind {
 109             hir::ExprKind::Binary(..)
 110             | hir::ExprKind::Unary(hir::UnOp::Not | hir::UnOp::Neg, _)
 111             | hir::ExprKind::AssignOp(..) => self.nb_binops += 1,
 112             _ => {},
 113         }
 114
 115         walk_expr(self, expr);
 116     }
 117
 118     fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
 119         NestedVisitorMap::None
 120     }
 121 }