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