clippy_lints/src/entry.rs

   1 use crate::utils::SpanlessEq;
   2 use crate::utils::{get_item_name, match_type, paths, snippet, span_lint_and_then, walk_ptrs_ty};
   3 use if_chain::if_chain;
   4 use rustc::hir::intravisit::{walk_expr, NestedVisitorMap, Visitor};
   5 use rustc::hir::*;
   6 use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
   7 use rustc::{declare_tool_lint, lint_array};
   8 use rustc_errors::Applicability;
   9 use syntax::source_map::Span;
  10
  11 /// **What it does:** Checks for uses of `contains_key` + `insert` on `HashMap`
  12 /// or `BTreeMap`.
  13 ///
  14 /// **Why is this bad?** Using `entry` is more efficient.
  15 ///
  16 /// **Known problems:** Some false negatives, eg.:
  17 /// ```rust
  18 /// let k = &key;
  19 /// if !m.contains_key(k) {
  20 ///     m.insert(k.clone(), v);
  21 /// }
  22 /// ```
  23 ///
  24 /// **Example:**
  25 /// ```rust
  26 /// if !m.contains_key(&k) {
  27 ///     m.insert(k, v)
  28 /// }
  29 /// ```
  30 /// can be rewritten as:
  31 /// ```rust
  32 /// m.entry(k).or_insert(v);
  33 /// ```
  34 declare_clippy_lint! {
  35     pub MAP_ENTRY,
  36     perf,
  37     "use of `contains_key` followed by `insert` on a `HashMap` or `BTreeMap`"
  38 }
  39
  40 #[derive(Copy, Clone)]
  41 pub struct HashMapLint;
  42
  43 impl LintPass for HashMapLint {
  44     fn get_lints(&self) -> LintArray {
  45         lint_array!(MAP_ENTRY)
  46     }
  47 }
  48
  49 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for HashMapLint {
  50     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
  51         if let ExprKind::If(ref check, ref then_block, ref else_block) = expr.node {
  52             if let ExprKind::Unary(UnOp::UnNot, ref check) = check.node {
  53                 if let Some((ty, map, key)) = check_cond(cx, check) {
  54                     // in case of `if !m.contains_key(&k) { m.insert(k, v); }`
  55                     // we can give a better error message
  56                     let sole_expr = {
  57                         else_block.is_none()
  58                             && if let ExprKind::Block(ref then_block, _) = then_block.node {
  59                                 (then_block.expr.is_some() as usize) + then_block.stmts.len() == 1
  60                             } else {
  61                                 true
  62                             }
  63                     };
  64
  65                     let mut visitor = InsertVisitor {
  66                         cx,
  67                         span: expr.span,
  68                         ty,
  69                         map,
  70                         key,
  71                         sole_expr,
  72                     };
  73
  74                     walk_expr(&mut visitor, &**then_block);
  75                 }
  76             } else if let Some(ref else_block) = *else_block {
  77                 if let Some((ty, map, key)) = check_cond(cx, check) {
  78                     let mut visitor = InsertVisitor {
  79                         cx,
  80                         span: expr.span,
  81                         ty,
  82                         map,
  83                         key,
  84                         sole_expr: false,
  85                     };
  86
  87                     walk_expr(&mut visitor, else_block);
  88                 }
  89             }
  90         }
  91     }
  92 }
  93
  94 fn check_cond<'a, 'tcx, 'b>(
  95     cx: &'a LateContext<'a, 'tcx>,
  96     check: &'b Expr,
  97 ) -> Option<(&'static str, &'b Expr, &'b Expr)> {
  98     if_chain! {
  99         if let ExprKind::MethodCall(ref path, _, ref params) = check.node;
 100         if params.len() >= 2;
 101         if path.ident.name == "contains_key";
 102         if let ExprKind::AddrOf(_, ref key) = params[1].node;
 103         then {
 104             let map = &params[0];
 105             let obj_ty = walk_ptrs_ty(cx.tables.expr_ty(map));
 106
 107             return if match_type(cx, obj_ty, &paths::BTREEMAP) {
 108                 Some(("BTreeMap", map, key))
 109             }
 110             else if match_type(cx, obj_ty, &paths::HASHMAP) {
 111                 Some(("HashMap", map, key))
 112             }
 113             else {
 114                 None
 115             };
 116         }
 117     }
 118
 119     None
 120 }
 121
 122 struct InsertVisitor<'a, 'tcx: 'a, 'b> {
 123     cx: &'a LateContext<'a, 'tcx>,
 124     span: Span,
 125     ty: &'static str,
 126     map: &'b Expr,
 127     key: &'b Expr,
 128     sole_expr: bool,
 129 }
 130
 131 impl<'a, 'tcx, 'b> Visitor<'tcx> for InsertVisitor<'a, 'tcx, 'b> {
 132     fn visit_expr(&mut self, expr: &'tcx Expr) {
 133         if_chain! {
 134             if let ExprKind::MethodCall(ref path, _, ref params) = expr.node;
 135             if params.len() == 3;
 136             if path.ident.name == "insert";
 137             if get_item_name(self.cx, self.map) == get_item_name(self.cx, &params[0]);
 138             if SpanlessEq::new(self.cx).eq_expr(self.key, &params[1]);
 139             then {
 140                 span_lint_and_then(self.cx, MAP_ENTRY, self.span,
 141                                    &format!("usage of `contains_key` followed by `insert` on a `{}`", self.ty), |db| {
 142                     if self.sole_expr {
 143                         let help = format!("{}.entry({}).or_insert({})",
 144                                            snippet(self.cx, self.map.span, "map"),
 145                                            snippet(self.cx, params[1].span, ".."),
 146                                            snippet(self.cx, params[2].span, ".."));
 147
 148                         db.span_suggestion_with_applicability(
 149                             self.span,
 150                             "consider using",
 151                             help,
 152                             Applicability::MachineApplicable, // snippet
 153                         );
 154                     }
 155                     else {
 156                         let help = format!("{}.entry({})",
 157                                            snippet(self.cx, self.map.span, "map"),
 158                                            snippet(self.cx, params[1].span, ".."));
 159
 160                         db.span_suggestion_with_applicability(
 161                             self.span,
 162                             "consider using",
 163                             help,
 164                             Applicability::MachineApplicable, // snippet
 165                         );
 166                     }
 167                 });
 168             }
 169         }
 170
 171         if !self.sole_expr {
 172             walk_expr(self, expr);
 173         }
 174     }
 175     fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
 176         NestedVisitorMap::None
 177     }
 178 }