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