src/tools/clippy/clippy_lints/src/assign_ops.rs

   1 use clippy_utils::diagnostics::span_lint_and_then;
   2 use clippy_utils::source::snippet_opt;
   3 use clippy_utils::ty::implements_trait;
   4 use clippy_utils::{binop_traits, sugg};
   5 use clippy_utils::{eq_expr_value, trait_ref_of_method};
   6 use if_chain::if_chain;
   7 use rustc_errors::Applicability;
   8 use rustc_hir as hir;
   9 use rustc_hir::intravisit::{walk_expr, NestedVisitorMap, Visitor};
  10 use rustc_lint::{LateContext, LateLintPass};
  11 use rustc_middle::hir::map::Map;
  12 use rustc_session::{declare_lint_pass, declare_tool_lint};
  13
  14 declare_clippy_lint! {
  15     /// ### What it does
  16     /// Checks for `a = a op b` or `a = b commutative_op a`
  17     /// patterns.
  18     ///
  19     /// ### Why is this bad?
  20     /// These can be written as the shorter `a op= b`.
  21     ///
  22     /// ### Known problems
  23     /// While forbidden by the spec, `OpAssign` traits may have
  24     /// implementations that differ from the regular `Op` impl.
  25     ///
  26     /// ### Example
  27     /// ```rust
  28     /// let mut a = 5;
  29     /// let b = 0;
  30     /// // ...
  31     /// // Bad
  32     /// a = a + b;
  33     ///
  34     /// // Good
  35     /// a += b;
  36     /// ```
  37     pub ASSIGN_OP_PATTERN,
  38     style,
  39     "assigning the result of an operation on a variable to that same variable"
  40 }
  41
  42 declare_clippy_lint! {
  43     /// ### What it does
  44     /// Checks for `a op= a op b` or `a op= b op a` patterns.
  45     ///
  46     /// ### Why is this bad?
  47     /// Most likely these are bugs where one meant to write `a
  48     /// op= b`.
  49     ///
  50     /// ### Known problems
  51     /// Clippy cannot know for sure if `a op= a op b` should have
  52     /// been `a = a op a op b` or `a = a op b`/`a op= b`. Therefore, it suggests both.
  53     /// If `a op= a op b` is really the correct behaviour it should be
  54     /// written as `a = a op a op b` as it's less confusing.
  55     ///
  56     /// ### Example
  57     /// ```rust
  58     /// let mut a = 5;
  59     /// let b = 2;
  60     /// // ...
  61     /// a += a + b;
  62     /// ```
  63     pub MISREFACTORED_ASSIGN_OP,
  64     suspicious,
  65     "having a variable on both sides of an assign op"
  66 }
  67
  68 declare_lint_pass!(AssignOps => [ASSIGN_OP_PATTERN, MISREFACTORED_ASSIGN_OP]);
  69
  70 impl<'tcx> LateLintPass<'tcx> for AssignOps {
  71     #[allow(clippy::too_many_lines)]
  72     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'_>) {
  73         match &expr.kind {
  74             hir::ExprKind::AssignOp(op, lhs, rhs) => {
  75                 if let hir::ExprKind::Binary(binop, l, r) = &rhs.kind {
  76                     if op.node != binop.node {
  77                         return;
  78                     }
  79                     // lhs op= l op r
  80                     if eq_expr_value(cx, lhs, l) {
  81                         lint_misrefactored_assign_op(cx, expr, *op, rhs, lhs, r);
  82                     }
  83                     // lhs op= l commutative_op r
  84                     if is_commutative(op.node) && eq_expr_value(cx, lhs, r) {
  85                         lint_misrefactored_assign_op(cx, expr, *op, rhs, lhs, l);
  86                     }
  87                 }
  88             },
  89             hir::ExprKind::Assign(assignee, e, _) => {
  90                 if let hir::ExprKind::Binary(op, l, r) = &e.kind {
  91                     let lint = |assignee: &hir::Expr<'_>, rhs: &hir::Expr<'_>| {
  92                         let ty = cx.typeck_results().expr_ty(assignee);
  93                         let rty = cx.typeck_results().expr_ty(rhs);
  94                         if_chain! {
  95                             if let Some((_, lang_item)) = binop_traits(op.node);
  96                             if let Ok(trait_id) = cx.tcx.lang_items().require(lang_item);
  97                             let parent_fn = cx.tcx.hir().get_parent_item(e.hir_id);
  98                             if trait_ref_of_method(cx, parent_fn)
  99                                 .map_or(true, |t| t.path.res.def_id() != trait_id);
 100                             if implements_trait(cx, ty, trait_id, &[rty.into()]);
 101                             then {
 102                                 span_lint_and_then(
 103                                     cx,
 104                                     ASSIGN_OP_PATTERN,
 105                                     expr.span,
 106                                     "manual implementation of an assign operation",
 107                                     |diag| {
 108                                         if let (Some(snip_a), Some(snip_r)) =
 109                                             (snippet_opt(cx, assignee.span), snippet_opt(cx, rhs.span))
 110                                         {
 111                                             diag.span_suggestion(
 112                                                 expr.span,
 113                                                 "replace it with",
 114                                                 format!("{} {}= {}", snip_a, op.node.as_str(), snip_r),
 115                                                 Applicability::MachineApplicable,
 116                                             );
 117                                         }
 118                                     },
 119                                 );
 120                             }
 121                         }
 122                     };
 123
 124                     let mut visitor = ExprVisitor {
 125                         assignee,
 126                         counter: 0,
 127                         cx,
 128                     };
 129
 130                     walk_expr(&mut visitor, e);
 131
 132                     if visitor.counter == 1 {
 133                         // a = a op b
 134                         if eq_expr_value(cx, assignee, l) {
 135                             lint(assignee, r);
 136                         }
 137                         // a = b commutative_op a
 138                         // Limited to primitive type as these ops are know to be commutative
 139                         if eq_expr_value(cx, assignee, r) && cx.typeck_results().expr_ty(assignee).is_primitive_ty() {
 140                             match op.node {
 141                                 hir::BinOpKind::Add
 142                                 | hir::BinOpKind::Mul
 143                                 | hir::BinOpKind::And
 144                                 | hir::BinOpKind::Or
 145                                 | hir::BinOpKind::BitXor
 146                                 | hir::BinOpKind::BitAnd
 147                                 | hir::BinOpKind::BitOr => {
 148                                     lint(assignee, l);
 149                                 },
 150                                 _ => {},
 151                             }
 152                         }
 153                     }
 154                 }
 155             },
 156             _ => {},
 157         }
 158     }
 159 }
 160
 161 fn lint_misrefactored_assign_op(
 162     cx: &LateContext<'_>,
 163     expr: &hir::Expr<'_>,
 164     op: hir::BinOp,
 165     rhs: &hir::Expr<'_>,
 166     assignee: &hir::Expr<'_>,
 167     rhs_other: &hir::Expr<'_>,
 168 ) {
 169     span_lint_and_then(
 170         cx,
 171         MISREFACTORED_ASSIGN_OP,
 172         expr.span,
 173         "variable appears on both sides of an assignment operation",
 174         |diag| {
 175             if let (Some(snip_a), Some(snip_r)) = (snippet_opt(cx, assignee.span), snippet_opt(cx, rhs_other.span)) {
 176                 let a = &sugg::Sugg::hir(cx, assignee, "..");
 177                 let r = &sugg::Sugg::hir(cx, rhs, "..");
 178                 let long = format!("{} = {}", snip_a, sugg::make_binop(op.node.into(), a, r));
 179                 diag.span_suggestion(
 180                     expr.span,
 181                     &format!(
 182                         "did you mean `{} = {} {} {}` or `{}`? Consider replacing it with",
 183                         snip_a,
 184                         snip_a,
 185                         op.node.as_str(),
 186                         snip_r,
 187                         long
 188                     ),
 189                     format!("{} {}= {}", snip_a, op.node.as_str(), snip_r),
 190                     Applicability::MaybeIncorrect,
 191                 );
 192                 diag.span_suggestion(
 193                     expr.span,
 194                     "or",
 195                     long,
 196                     Applicability::MaybeIncorrect, // snippet
 197                 );
 198             }
 199         },
 200     );
 201 }
 202
 203 #[must_use]
 204 fn is_commutative(op: hir::BinOpKind) -> bool {
 205     use rustc_hir::BinOpKind::{
 206         Add, And, BitAnd, BitOr, BitXor, Div, Eq, Ge, Gt, Le, Lt, Mul, Ne, Or, Rem, Shl, Shr, Sub,
 207     };
 208     match op {
 209         Add | Mul | And | Or | BitXor | BitAnd | BitOr | Eq | Ne => true,
 210         Sub | Div | Rem | Shl | Shr | Lt | Le | Ge | Gt => false,
 211     }
 212 }
 213
 214 struct ExprVisitor<'a, 'tcx> {
 215     assignee: &'a hir::Expr<'a>,
 216     counter: u8,
 217     cx: &'a LateContext<'tcx>,
 218 }
 219
 220 impl<'a, 'tcx> Visitor<'tcx> for ExprVisitor<'a, 'tcx> {
 221     type Map = Map<'tcx>;
 222
 223     fn visit_expr(&mut self, expr: &'tcx hir::Expr<'_>) {
 224         if eq_expr_value(self.cx, self.assignee, expr) {
 225             self.counter += 1;
 226         }
 227
 228         walk_expr(self, expr);
 229     }
 230     fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
 231         NestedVisitorMap::None
 232     }
 233 }