clippy_lints/src/entry.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::utils::SpanlessEq;
  11 use crate::utils::{get_item_name, match_type, paths, snippet, span_lint_and_then, walk_ptrs_ty};
  12 use if_chain::if_chain;
  13 use rustc::hir::intravisit::{walk_expr, NestedVisitorMap, Visitor};
  14 use rustc::hir::*;
  15 use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
  16 use rustc::{declare_tool_lint, lint_array};
  17 use rustc_errors::Applicability;
  18 use syntax::source_map::Span;
  19
  20 /// **What it does:** Checks for uses of `contains_key` + `insert` on `HashMap`
  21 /// or `BTreeMap`.
  22 ///
  23 /// **Why is this bad?** Using `entry` is more efficient.
  24 ///
  25 /// **Known problems:** Some false negatives, eg.:
  26 /// ```rust
  27 /// let k = &key;
  28 /// if !m.contains_key(k) {
  29 ///     m.insert(k.clone(), v);
  30 /// }
  31 /// ```
  32 ///
  33 /// **Example:**
  34 /// ```rust
  35 /// if !m.contains_key(&k) {
  36 ///     m.insert(k, v)
  37 /// }
  38 /// ```
  39 /// can be rewritten as:
  40 /// ```rust
  41 /// m.entry(k).or_insert(v);
  42 /// ```
  43 declare_clippy_lint! {
  44     pub MAP_ENTRY,
  45     perf,
  46     "use of `contains_key` followed by `insert` on a `HashMap` or `BTreeMap`"
  47 }
  48
  49 #[derive(Copy, Clone)]
  50 pub struct HashMapLint;
  51
  52 impl LintPass for HashMapLint {
  53     fn get_lints(&self) -> LintArray {
  54         lint_array!(MAP_ENTRY)
  55     }
  56 }
  57
  58 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for HashMapLint {
  59     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
  60         if let ExprKind::If(ref check, ref then_block, ref else_block) = expr.node {
  61             if let ExprKind::Unary(UnOp::UnNot, ref check) = check.node {
  62                 if let Some((ty, map, key)) = check_cond(cx, check) {
  63                     // in case of `if !m.contains_key(&k) { m.insert(k, v); }`
  64                     // we can give a better error message
  65                     let sole_expr = {
  66                         else_block.is_none()
  67                             && if let ExprKind::Block(ref then_block, _) = then_block.node {
  68                                 (then_block.expr.is_some() as usize) + then_block.stmts.len() == 1
  69                             } else {
  70                                 true
  71                             }
  72                     };
  73
  74                     let mut visitor = InsertVisitor {
  75                         cx,
  76                         span: expr.span,
  77                         ty,
  78                         map,
  79                         key,
  80                         sole_expr,
  81                     };
  82
  83                     walk_expr(&mut visitor, &**then_block);
  84                 }
  85             } else if let Some(ref else_block) = *else_block {
  86                 if let Some((ty, map, key)) = check_cond(cx, check) {
  87                     let mut visitor = InsertVisitor {
  88                         cx,
  89                         span: expr.span,
  90                         ty,
  91                         map,
  92                         key,
  93                         sole_expr: false,
  94                     };
  95
  96                     walk_expr(&mut visitor, else_block);
  97                 }
  98             }
  99         }
 100     }
 101 }
 102
 103 fn check_cond<'a, 'tcx, 'b>(
 104     cx: &'a LateContext<'a, 'tcx>,
 105     check: &'b Expr,
 106 ) -> Option<(&'static str, &'b Expr, &'b Expr)> {
 107     if_chain! {
 108         if let ExprKind::MethodCall(ref path, _, ref params) = check.node;
 109         if params.len() >= 2;
 110         if path.ident.name == "contains_key";
 111         if let ExprKind::AddrOf(_, ref key) = params[1].node;
 112         then {
 113             let map = &params[0];
 114             let obj_ty = walk_ptrs_ty(cx.tables.expr_ty(map));
 115
 116             return if match_type(cx, obj_ty, &paths::BTREEMAP) {
 117                 Some(("BTreeMap", map, key))
 118             }
 119             else if match_type(cx, obj_ty, &paths::HASHMAP) {
 120                 Some(("HashMap", map, key))
 121             }
 122             else {
 123                 None
 124             };
 125         }
 126     }
 127
 128     None
 129 }
 130
 131 struct InsertVisitor<'a, 'tcx: 'a, 'b> {
 132     cx: &'a LateContext<'a, 'tcx>,
 133     span: Span,
 134     ty: &'static str,
 135     map: &'b Expr,
 136     key: &'b Expr,
 137     sole_expr: bool,
 138 }
 139
 140 impl<'a, 'tcx, 'b> Visitor<'tcx> for InsertVisitor<'a, 'tcx, 'b> {
 141     fn visit_expr(&mut self, expr: &'tcx Expr) {
 142         if_chain! {
 143             if let ExprKind::MethodCall(ref path, _, ref params) = expr.node;
 144             if params.len() == 3;
 145             if path.ident.name == "insert";
 146             if get_item_name(self.cx, self.map) == get_item_name(self.cx, &params[0]);
 147             if SpanlessEq::new(self.cx).eq_expr(self.key, &params[1]);
 148             then {
 149                 span_lint_and_then(self.cx, MAP_ENTRY, self.span,
 150                                    &format!("usage of `contains_key` followed by `insert` on a `{}`", self.ty), |db| {
 151                     if self.sole_expr {
 152                         let help = format!("{}.entry({}).or_insert({})",
 153                                            snippet(self.cx, self.map.span, "map"),
 154                                            snippet(self.cx, params[1].span, ".."),
 155                                            snippet(self.cx, params[2].span, ".."));
 156
 157                         db.span_suggestion_with_applicability(
 158                             self.span,
 159                             "consider using",
 160                             help,
 161                             Applicability::MachineApplicable, // snippet
 162                         );
 163                     }
 164                     else {
 165                         let help = format!("{}.entry({})",
 166                                            snippet(self.cx, self.map.span, "map"),
 167                                            snippet(self.cx, params[1].span, ".."));
 168
 169                         db.span_suggestion_with_applicability(
 170                             self.span,
 171                             "consider using",
 172                             help,
 173                             Applicability::MachineApplicable, // snippet
 174                         );
 175                     }
 176                 });
 177             }
 178         }
 179
 180         if !self.sole_expr {
 181             walk_expr(self, expr);
 182         }
 183     }
 184     fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
 185         NestedVisitorMap::None
 186     }
 187 }