clippy_lints/src/entry.rs

   1 use crate::utils::sym;
   2 use crate::utils::SpanlessEq;
   3 use crate::utils::{get_item_name, higher, match_type, paths, snippet, span_lint_and_then, walk_ptrs_ty};
   4 use if_chain::if_chain;
   5 use rustc::hir::intravisit::{walk_expr, NestedVisitorMap, Visitor};
   6 use rustc::hir::*;
   7 use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
   8 use rustc::{declare_lint_pass, declare_tool_lint};
   9 use rustc_errors::Applicability;
  10 use syntax::source_map::Span;
  11
  12 declare_clippy_lint! {
  13     /// **What it does:** Checks for uses of `contains_key` + `insert` on `HashMap`
  14     /// or `BTreeMap`.
  15     ///
  16     /// **Why is this bad?** Using `entry` is more efficient.
  17     ///
  18     /// **Known problems:** Some false negatives, eg.:
  19     /// ```rust
  20     /// let k = &key;
  21     /// if !m.contains_key(k) {
  22     ///     m.insert(k.clone(), v);
  23     /// }
  24     /// ```
  25     ///
  26     /// **Example:**
  27     /// ```rust
  28     /// if !m.contains_key(&k) {
  29     ///     m.insert(k, v)
  30     /// }
  31     /// ```
  32     /// can be rewritten as:
  33     /// ```rust
  34     /// m.entry(k).or_insert(v);
  35     /// ```
  36     pub MAP_ENTRY,
  37     perf,
  38     "use of `contains_key` followed by `insert` on a `HashMap` or `BTreeMap`"
  39 }
  40
  41 declare_lint_pass!(HashMapPass => [MAP_ENTRY]);
  42
  43 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for HashMapPass {
  44     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
  45         if let Some((ref check, ref then_block, ref else_block)) = higher::if_block(&expr) {
  46             if let ExprKind::Unary(UnOp::UnNot, ref check) = check.node {
  47                 if let Some((ty, map, key)) = check_cond(cx, check) {
  48                     // in case of `if !m.contains_key(&k) { m.insert(k, v); }`
  49                     // we can give a better error message
  50                     let sole_expr = {
  51                         else_block.is_none()
  52                             && 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 == *sym::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 == *sym::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(
 143                             self.span,
 144                             "consider using",
 145                             help,
 146                             Applicability::MachineApplicable, // snippet
 147                         );
 148                     }
 149                     else {
 150                         let help = format!("{}.entry({})",
 151                                            snippet(self.cx, self.map.span, "map"),
 152                                            snippet(self.cx, params[1].span, ".."));
 153
 154                         db.span_suggestion(
 155                             self.span,
 156                             "consider using",
 157                             help,
 158                             Applicability::MachineApplicable, // snippet
 159                         );
 160                     }
 161                 });
 162             }
 163         }
 164
 165         if !self.sole_expr {
 166             walk_expr(self, expr);
 167         }
 168     }
 169     fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
 170         NestedVisitorMap::None
 171     }
 172 }