clippy_lints/src/entry.rs

   1 use crate::utils::SpanlessEq;
   2 use crate::utils::{get_item_name, higher, match_type, paths, snippet, snippet_opt};
   3 use crate::utils::{snippet_with_applicability, 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     /// # use std::collections::HashMap;
  21     /// # let mut map = HashMap::new();
  22     /// # let v = 1;
  23     /// # let k = 1;
  24     /// if !map.contains_key(&k) {
  25     ///     map.insert(k.clone(), v);
  26     /// }
  27     /// ```
  28     ///
  29     /// **Example:**
  30     /// ```rust
  31     /// # use std::collections::HashMap;
  32     /// # let mut map = HashMap::new();
  33     /// # let k = 1;
  34     /// # let v = 1;
  35     /// if !map.contains_key(&k) {
  36     ///     map.insert(k, v);
  37     /// }
  38     /// ```
  39     /// can both be rewritten as:
  40     /// ```rust
  41     /// # use std::collections::HashMap;
  42     /// # let mut map = HashMap::new();
  43     /// # let k = 1;
  44     /// # let v = 1;
  45     /// map.entry(k).or_insert(v);
  46     /// ```
  47     pub MAP_ENTRY,
  48     perf,
  49     "use of `contains_key` followed by `insert` on a `HashMap` or `BTreeMap`"
  50 }
  51
  52 declare_lint_pass!(HashMapPass => [MAP_ENTRY]);
  53
  54 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for HashMapPass {
  55     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
  56         if let Some((ref check, ref then_block, ref else_block)) = higher::if_block(&expr) {
  57             if let ExprKind::Unary(UnOp::UnNot, ref check) = check.node {
  58                 if let Some((ty, map, key)) = check_cond(cx, check) {
  59                     // in case of `if !m.contains_key(&k) { m.insert(k, v); }`
  60                     // we can give a better error message
  61                     let sole_expr = {
  62                         else_block.is_none()
  63                             && if let ExprKind::Block(ref then_block, _) = then_block.node {
  64                                 (then_block.expr.is_some() as usize) + then_block.stmts.len() == 1
  65                             } else {
  66                                 true
  67                             }
  68                     };
  69
  70                     let mut visitor = InsertVisitor {
  71                         cx,
  72                         span: expr.span,
  73                         ty,
  74                         map,
  75                         key,
  76                         sole_expr,
  77                     };
  78
  79                     walk_expr(&mut visitor, &**then_block);
  80                 }
  81             } else if let Some(ref else_block) = *else_block {
  82                 if let Some((ty, map, key)) = check_cond(cx, check) {
  83                     let mut visitor = InsertVisitor {
  84                         cx,
  85                         span: expr.span,
  86                         ty,
  87                         map,
  88                         key,
  89                         sole_expr: false,
  90                     };
  91
  92                     walk_expr(&mut visitor, else_block);
  93                 }
  94             }
  95         }
  96     }
  97 }
  98
  99 fn check_cond<'a, 'tcx, 'b>(
 100     cx: &'a LateContext<'a, 'tcx>,
 101     check: &'b Expr,
 102 ) -> Option<(&'static str, &'b Expr, &'b Expr)> {
 103     if_chain! {
 104         if let ExprKind::MethodCall(ref path, _, ref params) = check.node;
 105         if params.len() >= 2;
 106         if path.ident.name == sym!(contains_key);
 107         if let ExprKind::AddrOf(_, ref key) = params[1].node;
 108         then {
 109             let map = &params[0];
 110             let obj_ty = walk_ptrs_ty(cx.tables.expr_ty(map));
 111
 112             return if match_type(cx, obj_ty, &paths::BTREEMAP) {
 113                 Some(("BTreeMap", map, key))
 114             }
 115             else if match_type(cx, obj_ty, &paths::HASHMAP) {
 116                 Some(("HashMap", map, key))
 117             }
 118             else {
 119                 None
 120             };
 121         }
 122     }
 123
 124     None
 125 }
 126
 127 struct InsertVisitor<'a, 'tcx, 'b> {
 128     cx: &'a LateContext<'a, 'tcx>,
 129     span: Span,
 130     ty: &'static str,
 131     map: &'b Expr,
 132     key: &'b Expr,
 133     sole_expr: bool,
 134 }
 135
 136 impl<'a, 'tcx, 'b> Visitor<'tcx> for InsertVisitor<'a, 'tcx, 'b> {
 137     fn visit_expr(&mut self, expr: &'tcx Expr) {
 138         if_chain! {
 139             if let ExprKind::MethodCall(ref path, _, ref params) = expr.node;
 140             if params.len() == 3;
 141             if path.ident.name == sym!(insert);
 142             if get_item_name(self.cx, self.map) == get_item_name(self.cx, &params[0]);
 143             if SpanlessEq::new(self.cx).eq_expr(self.key, &params[1]);
 144             if snippet_opt(self.cx, self.map.span) == snippet_opt(self.cx, params[0].span);
 145             then {
 146                 span_lint_and_then(self.cx, MAP_ENTRY, self.span,
 147                                    &format!("usage of `contains_key` followed by `insert` on a `{}`", self.ty), |db| {
 148                     if self.sole_expr {
 149                         let mut app = Applicability::MachineApplicable;
 150                         let help = format!("{}.entry({}).or_insert({})",
 151                                            snippet_with_applicability(self.cx, self.map.span, "map", &mut app),
 152                                            snippet_with_applicability(self.cx, params[1].span, "..", &mut app),
 153                                            snippet_with_applicability(self.cx, params[2].span, "..", &mut app));
 154
 155                         db.span_suggestion(
 156                             self.span,
 157                             "consider using",
 158                             help,
 159                             Applicability::MachineApplicable, // snippet
 160                         );
 161                     }
 162                     else {
 163                         let help = format!("consider using `{}.entry({})`",
 164                                            snippet(self.cx, self.map.span, "map"),
 165                                            snippet(self.cx, params[1].span, ".."));
 166
 167                         db.span_help(
 168                             self.span,
 169                             &help,
 170                         );
 171                     }
 172                 });
 173             }
 174         }
 175
 176         if !self.sole_expr {
 177             walk_expr(self, expr);
 178         }
 179     }
 180     fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
 181         NestedVisitorMap::None
 182     }
 183 }