clippy_lints/src/entry.rs

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