clippy_lints/src/entry.rs

   1 use crate::utils::SpanlessEq;
   2 use crate::utils::{get_item_name, higher, 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_lint_pass, declare_tool_lint};
   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 declare_lint_pass!(HashMapPass => [MAP_ENTRY]);
  41
  42 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for HashMapPass {
  43     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
  44         if let Some((ref check, ref then_block, ref else_block)) = higher::if_block(&expr) {
  45             if let ExprKind::Unary(UnOp::UnNot, ref check) = check.node {
  46                 if let Some((ty, map, key)) = check_cond(cx, check) {
  47                     // in case of `if !m.contains_key(&k) { m.insert(k, v); }`
  48                     // we can give a better error message
  49                     let sole_expr = {
  50                         else_block.is_none()
  51                             && if let ExprKind::Block(ref then_block, _) = then_block.node {
  52                                 (then_block.expr.is_some() as usize) + then_block.stmts.len() == 1
  53                             } else {
  54                                 true
  55                             }
  56                     };
  57
  58                     let mut visitor = InsertVisitor {
  59                         cx,
  60                         span: expr.span,
  61                         ty,
  62                         map,
  63                         key,
  64                         sole_expr,
  65                     };
  66
  67                     walk_expr(&mut visitor, &**then_block);
  68                 }
  69             } else if let Some(ref else_block) = *else_block {
  70                 if let Some((ty, map, key)) = check_cond(cx, check) {
  71                     let mut visitor = InsertVisitor {
  72                         cx,
  73                         span: expr.span,
  74                         ty,
  75                         map,
  76                         key,
  77                         sole_expr: false,
  78                     };
  79
  80                     walk_expr(&mut visitor, else_block);
  81                 }
  82             }
  83         }
  84     }
  85 }
  86
  87 fn check_cond<'a, 'tcx, 'b>(
  88     cx: &'a LateContext<'a, 'tcx>,
  89     check: &'b Expr,
  90 ) -> Option<(&'static str, &'b Expr, &'b Expr)> {
  91     if_chain! {
  92         if let ExprKind::MethodCall(ref path, _, ref params) = check.node;
  93         if params.len() >= 2;
  94         if path.ident.name == sym!(contains_key);
  95         if let ExprKind::AddrOf(_, ref key) = params[1].node;
  96         then {
  97             let map = &params[0];
  98             let obj_ty = walk_ptrs_ty(cx.tables.expr_ty(map));
  99
 100             return if match_type(cx, obj_ty, &paths::BTREEMAP) {
 101                 Some(("BTreeMap", map, key))
 102             }
 103             else if match_type(cx, obj_ty, &paths::HASHMAP) {
 104                 Some(("HashMap", map, key))
 105             }
 106             else {
 107                 None
 108             };
 109         }
 110     }
 111
 112     None
 113 }
 114
 115 struct InsertVisitor<'a, 'tcx: 'a, 'b> {
 116     cx: &'a LateContext<'a, 'tcx>,
 117     span: Span,
 118     ty: &'static str,
 119     map: &'b Expr,
 120     key: &'b Expr,
 121     sole_expr: bool,
 122 }
 123
 124 impl<'a, 'tcx, 'b> Visitor<'tcx> for InsertVisitor<'a, 'tcx, 'b> {
 125     fn visit_expr(&mut self, expr: &'tcx Expr) {
 126         if_chain! {
 127             if let ExprKind::MethodCall(ref path, _, ref params) = expr.node;
 128             if params.len() == 3;
 129             if path.ident.name == sym!(insert);
 130             if get_item_name(self.cx, self.map) == get_item_name(self.cx, &params[0]);
 131             if SpanlessEq::new(self.cx).eq_expr(self.key, &params[1]);
 132             then {
 133                 span_lint_and_then(self.cx, MAP_ENTRY, self.span,
 134                                    &format!("usage of `contains_key` followed by `insert` on a `{}`", self.ty), |db| {
 135                     if self.sole_expr {
 136                         let help = format!("{}.entry({}).or_insert({})",
 137                                            snippet(self.cx, self.map.span, "map"),
 138                                            snippet(self.cx, params[1].span, ".."),
 139                                            snippet(self.cx, params[2].span, ".."));
 140
 141                         db.span_suggestion(
 142                             self.span,
 143                             "consider using",
 144                             help,
 145                             Applicability::MachineApplicable, // snippet
 146                         );
 147                     }
 148                     else {
 149                         let help = format!("{}.entry({})",
 150                                            snippet(self.cx, self.map.span, "map"),
 151                                            snippet(self.cx, params[1].span, ".."));
 152
 153                         db.span_suggestion(
 154                             self.span,
 155                             "consider using",
 156                             help,
 157                             Applicability::MachineApplicable, // snippet
 158                         );
 159                     }
 160                 });
 161             }
 162         }
 163
 164         if !self.sole_expr {
 165             walk_expr(self, expr);
 166         }
 167     }
 168     fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
 169         NestedVisitorMap::None
 170     }
 171 }