clippy_lints/src/eq_op.rs

   1 // Copyright 2014-2018 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution.
   3 //
   4 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   5 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   6 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   7 // option. This file may not be copied, modified, or distributed
   8 // except according to those terms.
   9
  10
  11 use crate::rustc::hir::*;
  12 use crate::rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
  13 use crate::rustc::{declare_tool_lint, lint_array};
  14 use crate::utils::{in_macro, implements_trait, is_copy, multispan_sugg, snippet, span_lint, span_lint_and_then, SpanlessEq};
  15 use crate::rustc_errors::Applicability;
  16
  17 /// **What it does:** Checks for equal operands to comparison, logical and
  18 /// bitwise, difference and division binary operators (`==`, `>`, etc., `&&`,
  19 /// `||`, `&`, `|`, `^`, `-` and `/`).
  20 ///
  21 /// **Why is this bad?** This is usually just a typo or a copy and paste error.
  22 ///
  23 /// **Known problems:** False negatives: We had some false positives regarding
  24 /// calls (notably [racer](https://github.com/phildawes/racer) had one instance
  25 /// of `x.pop() && x.pop()`), so we removed matching any function or method
  26 /// calls. We may introduce a whitelist of known pure functions in the future.
  27 ///
  28 /// **Example:**
  29 /// ```rust
  30 /// x + 1 == x + 1
  31 /// ```
  32 declare_clippy_lint! {
  33     pub EQ_OP,
  34     correctness,
  35     "equal operands on both sides of a comparison or bitwise combination (e.g. `x == x`)"
  36 }
  37
  38 /// **What it does:** Checks for arguments to `==` which have their address
  39 /// taken to satisfy a bound
  40 /// and suggests to dereference the other argument instead
  41 ///
  42 /// **Why is this bad?** It is more idiomatic to dereference the other argument.
  43 ///
  44 /// **Known problems:** None
  45 ///
  46 /// **Example:**
  47 /// ```rust
  48 /// &x == y
  49 /// ```
  50 declare_clippy_lint! {
  51     pub OP_REF,
  52     style,
  53     "taking a reference to satisfy the type constraints on `==`"
  54 }
  55
  56 #[derive(Copy, Clone)]
  57 pub struct EqOp;
  58
  59 impl LintPass for EqOp {
  60     fn get_lints(&self) -> LintArray {
  61         lint_array!(EQ_OP, OP_REF)
  62     }
  63 }
  64
  65 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for EqOp {
  66     #[allow(clippy::similar_names)]
  67     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr) {
  68         if let ExprKind::Binary(op, ref left, ref right) = e.node {
  69             if in_macro(e.span) {
  70                 return;
  71             }
  72             if is_valid_operator(op) && SpanlessEq::new(cx).ignore_fn().eq_expr(left, right) {
  73                 span_lint(
  74                     cx,
  75                     EQ_OP,
  76                     e.span,
  77                     &format!("equal expressions as operands to `{}`", op.node.as_str()),
  78                 );
  79                 return;
  80             }
  81             let (trait_id, requires_ref) = match op.node {
  82                 BinOpKind::Add => (cx.tcx.lang_items().add_trait(), false),
  83                 BinOpKind::Sub => (cx.tcx.lang_items().sub_trait(), false),
  84                 BinOpKind::Mul => (cx.tcx.lang_items().mul_trait(), false),
  85                 BinOpKind::Div => (cx.tcx.lang_items().div_trait(), false),
  86                 BinOpKind::Rem => (cx.tcx.lang_items().rem_trait(), false),
  87                 // don't lint short circuiting ops
  88                 BinOpKind::And | BinOpKind::Or => return,
  89                 BinOpKind::BitXor => (cx.tcx.lang_items().bitxor_trait(), false),
  90                 BinOpKind::BitAnd => (cx.tcx.lang_items().bitand_trait(), false),
  91                 BinOpKind::BitOr => (cx.tcx.lang_items().bitor_trait(), false),
  92                 BinOpKind::Shl => (cx.tcx.lang_items().shl_trait(), false),
  93                 BinOpKind::Shr => (cx.tcx.lang_items().shr_trait(), false),
  94                 BinOpKind::Ne | BinOpKind::Eq => (cx.tcx.lang_items().eq_trait(), true),
  95                 BinOpKind::Lt | BinOpKind::Le | BinOpKind::Ge | BinOpKind::Gt => (cx.tcx.lang_items().ord_trait(), true),
  96             };
  97             if let Some(trait_id) = trait_id {
  98                 #[allow(clippy::match_same_arms)]
  99                 match (&left.node, &right.node) {
 100                     // do not suggest to dereference literals
 101                     (&ExprKind::Lit(..), _) | (_, &ExprKind::Lit(..)) => {},
 102                     // &foo == &bar
 103                     (&ExprKind::AddrOf(_, ref l), &ExprKind::AddrOf(_, ref r)) => {
 104                         let lty = cx.tables.expr_ty(l);
 105                         let rty = cx.tables.expr_ty(r);
 106                         let lcpy = is_copy(cx, lty);
 107                         let rcpy = is_copy(cx, rty);
 108                         // either operator autorefs or both args are copyable
 109                         if (requires_ref || (lcpy && rcpy)) && implements_trait(cx, lty, trait_id, &[rty.into()]) {
 110                             span_lint_and_then(
 111                                 cx,
 112                                 OP_REF,
 113                                 e.span,
 114                                 "needlessly taken reference of both operands",
 115                                 |db| {
 116                                     let lsnip = snippet(cx, l.span, "...").to_string();
 117                                     let rsnip = snippet(cx, r.span, "...").to_string();
 118                                     multispan_sugg(
 119                                         db,
 120                                         "use the values directly".to_string(),
 121                                         vec![(left.span, lsnip), (right.span, rsnip)],
 122                                     );
 123                                 },
 124                             )
 125                         } else if lcpy && !rcpy && implements_trait(cx, lty, trait_id, &[cx.tables.expr_ty(right).into()]) {
 126                             span_lint_and_then(cx, OP_REF, e.span, "needlessly taken reference of left operand", |db| {
 127                                 let lsnip = snippet(cx, l.span, "...").to_string();
 128                                 db.span_suggestion_with_applicability(
 129                                     left.span,
 130                                     "use the left value directly",
 131                                     lsnip,
 132                                     Applicability::MachineApplicable, // snippet
 133                                 );
 134                             })
 135                         } else if !lcpy && rcpy && implements_trait(cx, cx.tables.expr_ty(left), trait_id, &[rty.into()]) {
 136                             span_lint_and_then(
 137                                 cx,
 138                                 OP_REF,
 139                                 e.span,
 140                                 "needlessly taken reference of right operand",
 141                                 |db| {
 142                                     let rsnip = snippet(cx, r.span, "...").to_string();
 143                                     db.span_suggestion_with_applicability(
 144                                         right.span,
 145                                         "use the right value directly",
 146                                         rsnip,
 147                                         Applicability::MachineApplicable, // snippet
 148                                     );
 149                                 },
 150                             )
 151                         }
 152                     },
 153                     // &foo == bar
 154                     (&ExprKind::AddrOf(_, ref l), _) => {
 155                         let lty = cx.tables.expr_ty(l);
 156                         let lcpy = is_copy(cx, lty);
 157                         if (requires_ref || lcpy) && implements_trait(cx, lty, trait_id, &[cx.tables.expr_ty(right).into()]) {
 158                             span_lint_and_then(cx, OP_REF, e.span, "needlessly taken reference of left operand", |db| {
 159                                 let lsnip = snippet(cx, l.span, "...").to_string();
 160                                 db.span_suggestion_with_applicability(
 161                                     left.span,
 162                                     "use the left value directly",
 163                                     lsnip,
 164                                     Applicability::MachineApplicable, // snippet
 165                                 );
 166                             })
 167                         }
 168                     },
 169                     // foo == &bar
 170                     (_, &ExprKind::AddrOf(_, ref r)) => {
 171                         let rty = cx.tables.expr_ty(r);
 172                         let rcpy = is_copy(cx, rty);
 173                         if (requires_ref || rcpy) && implements_trait(cx, cx.tables.expr_ty(left), trait_id, &[rty.into()]) {
 174                             span_lint_and_then(cx, OP_REF, e.span, "taken reference of right operand", |db| {
 175                                 let rsnip = snippet(cx, r.span, "...").to_string();
 176                                 db.span_suggestion_with_applicability(
 177                                     right.span,
 178                                     "use the right value directly",
 179                                     rsnip,
 180                                     Applicability::MachineApplicable, // snippet
 181                                 );
 182                             })
 183                         }
 184                     },
 185                     _ => {},
 186                 }
 187             }
 188         }
 189     }
 190 }
 191
 192
 193 fn is_valid_operator(op: BinOp) -> bool {
 194     match op.node {
 195         BinOpKind::Sub | BinOpKind::Div | BinOpKind::Eq | BinOpKind::Lt | BinOpKind::Le | BinOpKind::Gt | BinOpKind::Ge | BinOpKind::Ne | BinOpKind::And | BinOpKind::Or | BinOpKind::BitXor | BinOpKind::BitAnd | BinOpKind::BitOr => true,
 196         _ => false,
 197     }
 198 }