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 use crate::rustc::hir::*;
  11 use crate::rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
  12 use crate::rustc::{declare_tool_lint, lint_array};
  13 use crate::rustc_errors::Applicability;
  14 use crate::utils::{
  15     implements_trait, in_macro, is_copy, multispan_sugg, snippet, span_lint, span_lint_and_then, SpanlessEq,
  16 };
  17
  18 /// **What it does:** Checks for equal operands to comparison, logical and
  19 /// bitwise, difference and division binary operators (`==`, `>`, etc., `&&`,
  20 /// `||`, `&`, `|`, `^`, `-` and `/`).
  21 ///
  22 /// **Why is this bad?** This is usually just a typo or a copy and paste error.
  23 ///
  24 /// **Known problems:** False negatives: We had some false positives regarding
  25 /// calls (notably [racer](https://github.com/phildawes/racer) had one instance
  26 /// of `x.pop() && x.pop()`), so we removed matching any function or method
  27 /// calls. We may introduce a whitelist of known pure functions in the future.
  28 ///
  29 /// **Example:**
  30 /// ```rust
  31 /// x + 1 == x + 1
  32 /// ```
  33 declare_clippy_lint! {
  34     pub EQ_OP,
  35     correctness,
  36     "equal operands on both sides of a comparison or bitwise combination (e.g. `x == x`)"
  37 }
  38
  39 /// **What it does:** Checks for arguments to `==` which have their address
  40 /// taken to satisfy a bound
  41 /// and suggests to dereference the other argument instead
  42 ///
  43 /// **Why is this bad?** It is more idiomatic to dereference the other argument.
  44 ///
  45 /// **Known problems:** None
  46 ///
  47 /// **Example:**
  48 /// ```rust
  49 /// &x == y
  50 /// ```
  51 declare_clippy_lint! {
  52     pub OP_REF,
  53     style,
  54     "taking a reference to satisfy the type constraints on `==`"
  55 }
  56
  57 #[derive(Copy, Clone)]
  58 pub struct EqOp;
  59
  60 impl LintPass for EqOp {
  61     fn get_lints(&self) -> LintArray {
  62         lint_array!(EQ_OP, OP_REF)
  63     }
  64 }
  65
  66 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for EqOp {
  67     #[allow(clippy::similar_names)]
  68     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr) {
  69         if let ExprKind::Binary(op, ref left, ref right) = e.node {
  70             if in_macro(e.span) {
  71                 return;
  72             }
  73             if is_valid_operator(op) && SpanlessEq::new(cx).ignore_fn().eq_expr(left, right) {
  74                 span_lint(
  75                     cx,
  76                     EQ_OP,
  77                     e.span,
  78                     &format!("equal expressions as operands to `{}`", op.node.as_str()),
  79                 );
  80                 return;
  81             }
  82             let (trait_id, requires_ref) = match op.node {
  83                 BinOpKind::Add => (cx.tcx.lang_items().add_trait(), false),
  84                 BinOpKind::Sub => (cx.tcx.lang_items().sub_trait(), false),
  85                 BinOpKind::Mul => (cx.tcx.lang_items().mul_trait(), false),
  86                 BinOpKind::Div => (cx.tcx.lang_items().div_trait(), false),
  87                 BinOpKind::Rem => (cx.tcx.lang_items().rem_trait(), false),
  88                 // don't lint short circuiting ops
  89                 BinOpKind::And | BinOpKind::Or => return,
  90                 BinOpKind::BitXor => (cx.tcx.lang_items().bitxor_trait(), false),
  91                 BinOpKind::BitAnd => (cx.tcx.lang_items().bitand_trait(), false),
  92                 BinOpKind::BitOr => (cx.tcx.lang_items().bitor_trait(), false),
  93                 BinOpKind::Shl => (cx.tcx.lang_items().shl_trait(), false),
  94                 BinOpKind::Shr => (cx.tcx.lang_items().shr_trait(), false),
  95                 BinOpKind::Ne | BinOpKind::Eq => (cx.tcx.lang_items().eq_trait(), true),
  96                 BinOpKind::Lt | BinOpKind::Le | BinOpKind::Ge | BinOpKind::Gt => {
  97                     (cx.tcx.lang_items().ord_trait(), true)
  98                 },
  99             };
 100             if let Some(trait_id) = trait_id {
 101                 #[allow(clippy::match_same_arms)]
 102                 match (&left.node, &right.node) {
 103                     // do not suggest to dereference literals
 104                     (&ExprKind::Lit(..), _) | (_, &ExprKind::Lit(..)) => {},
 105                     // &foo == &bar
 106                     (&ExprKind::AddrOf(_, ref l), &ExprKind::AddrOf(_, ref r)) => {
 107                         let lty = cx.tables.expr_ty(l);
 108                         let rty = cx.tables.expr_ty(r);
 109                         let lcpy = is_copy(cx, lty);
 110                         let rcpy = is_copy(cx, rty);
 111                         // either operator autorefs or both args are copyable
 112                         if (requires_ref || (lcpy && rcpy)) && implements_trait(cx, lty, trait_id, &[rty.into()]) {
 113                             span_lint_and_then(
 114                                 cx,
 115                                 OP_REF,
 116                                 e.span,
 117                                 "needlessly taken reference of both operands",
 118                                 |db| {
 119                                     let lsnip = snippet(cx, l.span, "...").to_string();
 120                                     let rsnip = snippet(cx, r.span, "...").to_string();
 121                                     multispan_sugg(
 122                                         db,
 123                                         "use the values directly".to_string(),
 124                                         vec![(left.span, lsnip), (right.span, rsnip)],
 125                                     );
 126                                 },
 127                             )
 128                         } else if lcpy
 129                             && !rcpy
 130                             && implements_trait(cx, lty, trait_id, &[cx.tables.expr_ty(right).into()])
 131                         {
 132                             span_lint_and_then(cx, OP_REF, e.span, "needlessly taken reference of left operand", |db| {
 133                                 let lsnip = snippet(cx, l.span, "...").to_string();
 134                                 db.span_suggestion_with_applicability(
 135                                     left.span,
 136                                     "use the left value directly",
 137                                     lsnip,
 138                                     Applicability::MachineApplicable, // snippet
 139                                 );
 140                             })
 141                         } else if !lcpy
 142                             && rcpy
 143                             && implements_trait(cx, cx.tables.expr_ty(left), trait_id, &[rty.into()])
 144                         {
 145                             span_lint_and_then(
 146                                 cx,
 147                                 OP_REF,
 148                                 e.span,
 149                                 "needlessly taken reference of right operand",
 150                                 |db| {
 151                                     let rsnip = snippet(cx, r.span, "...").to_string();
 152                                     db.span_suggestion_with_applicability(
 153                                         right.span,
 154                                         "use the right value directly",
 155                                         rsnip,
 156                                         Applicability::MachineApplicable, // snippet
 157                                     );
 158                                 },
 159                             )
 160                         }
 161                     },
 162                     // &foo == bar
 163                     (&ExprKind::AddrOf(_, ref l), _) => {
 164                         let lty = cx.tables.expr_ty(l);
 165                         let lcpy = is_copy(cx, lty);
 166                         if (requires_ref || lcpy)
 167                             && implements_trait(cx, lty, trait_id, &[cx.tables.expr_ty(right).into()])
 168                         {
 169                             span_lint_and_then(cx, OP_REF, e.span, "needlessly taken reference of left operand", |db| {
 170                                 let lsnip = snippet(cx, l.span, "...").to_string();
 171                                 db.span_suggestion_with_applicability(
 172                                     left.span,
 173                                     "use the left value directly",
 174                                     lsnip,
 175                                     Applicability::MachineApplicable, // snippet
 176                                 );
 177                             })
 178                         }
 179                     },
 180                     // foo == &bar
 181                     (_, &ExprKind::AddrOf(_, ref r)) => {
 182                         let rty = cx.tables.expr_ty(r);
 183                         let rcpy = is_copy(cx, rty);
 184                         if (requires_ref || rcpy)
 185                             && implements_trait(cx, cx.tables.expr_ty(left), trait_id, &[rty.into()])
 186                         {
 187                             span_lint_and_then(cx, OP_REF, e.span, "taken reference of right operand", |db| {
 188                                 let rsnip = snippet(cx, r.span, "...").to_string();
 189                                 db.span_suggestion_with_applicability(
 190                                     right.span,
 191                                     "use the right value directly",
 192                                     rsnip,
 193                                     Applicability::MachineApplicable, // snippet
 194                                 );
 195                             })
 196                         }
 197                     },
 198                     _ => {},
 199                 }
 200             }
 201         }
 202     }
 203 }
 204
 205 fn is_valid_operator(op: BinOp) -> bool {
 206     match op.node {
 207         BinOpKind::Sub
 208         | BinOpKind::Div
 209         | BinOpKind::Eq
 210         | BinOpKind::Lt
 211         | BinOpKind::Le
 212         | BinOpKind::Gt
 213         | BinOpKind::Ge
 214         | BinOpKind::Ne
 215         | BinOpKind::And
 216         | BinOpKind::Or
 217         | BinOpKind::BitXor
 218         | BinOpKind::BitAnd
 219         | BinOpKind::BitOr => true,
 220         _ => false,
 221     }
 222 }