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.kind {
  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.kind {
  64                                 (then_block.expr.is_some() as usize) + then_block.stmts.len() == 1
  65                             } else {
  66                                 true
  67                             }
  68                         // XXXManishearth we can also check for if/else blocks containing `None`.
  69                     };
  70
  71                     let mut visitor = InsertVisitor {
  72                         cx,
  73                         span: expr.span,
  74                         ty,
  75                         map,
  76                         key,
  77                         sole_expr,
  78                     };
  79
  80                     walk_expr(&mut visitor, &**then_block);
  81                 }
  82             } else if let Some(ref else_block) = *else_block {
  83                 if let Some((ty, map, key)) = check_cond(cx, check) {
  84                     let mut visitor = InsertVisitor {
  85                         cx,
  86                         span: expr.span,
  87                         ty,
  88                         map,
  89                         key,
  90                         sole_expr: false,
  91                     };
  92
  93                     walk_expr(&mut visitor, else_block);
  94                 }
  95             }
  96         }
  97     }
  98 }
  99
 100 fn check_cond<'a, 'tcx, 'b>(
 101     cx: &'a LateContext<'a, 'tcx>,
 102     check: &'b Expr,
 103 ) -> Option<(&'static str, &'b Expr, &'b Expr)> {
 104     if_chain! {
 105         if let ExprKind::MethodCall(ref path, _, ref params) = check.kind;
 106         if params.len() >= 2;
 107         if path.ident.name == sym!(contains_key);
 108         if let ExprKind::AddrOf(_, ref key) = params[1].kind;
 109         then {
 110             let map = &params[0];
 111             let obj_ty = walk_ptrs_ty(cx.tables.expr_ty(map));
 112
 113             return if match_type(cx, obj_ty, &paths::BTREEMAP) {
 114                 Some(("BTreeMap", map, key))
 115             }
 116             else if match_type(cx, obj_ty, &paths::HASHMAP) {
 117                 Some(("HashMap", map, key))
 118             }
 119             else {
 120                 None
 121             };
 122         }
 123     }
 124
 125     None
 126 }
 127
 128 struct InsertVisitor<'a, 'tcx, 'b> {
 129     cx: &'a LateContext<'a, 'tcx>,
 130     span: Span,
 131     ty: &'static str,
 132     map: &'b Expr,
 133     key: &'b Expr,
 134     sole_expr: bool,
 135 }
 136
 137 impl<'a, 'tcx, 'b> Visitor<'tcx> for InsertVisitor<'a, 'tcx, 'b> {
 138     fn visit_expr(&mut self, expr: &'tcx Expr) {
 139         if_chain! {
 140             if let ExprKind::MethodCall(ref path, _, ref params) = expr.kind;
 141             if params.len() == 3;
 142             if path.ident.name == sym!(insert);
 143             if get_item_name(self.cx, self.map) == get_item_name(self.cx, &params[0]);
 144             if SpanlessEq::new(self.cx).eq_expr(self.key, &params[1]);
 145             if snippet_opt(self.cx, self.map.span) == snippet_opt(self.cx, params[0].span);
 146             then {
 147                 span_lint_and_then(self.cx, MAP_ENTRY, self.span,
 148                                    &format!("usage of `contains_key` followed by `insert` on a `{}`", self.ty), |db| {
 149                     if self.sole_expr {
 150                         let mut app = Applicability::MachineApplicable;
 151                         let help = format!("{}.entry({}).or_insert({});",
 152                                            snippet_with_applicability(self.cx, self.map.span, "map", &mut app),
 153                                            snippet_with_applicability(self.cx, params[1].span, "..", &mut app),
 154                                            snippet_with_applicability(self.cx, params[2].span, "..", &mut app));
 155
 156                         db.span_suggestion(
 157                             self.span,
 158                             "consider using",
 159                             help,
 160                             Applicability::MachineApplicable, // snippet
 161                         );
 162                     }
 163                     else {
 164                         let help = format!("consider using `{}.entry({})`",
 165                                            snippet(self.cx, self.map.span, "map"),
 166                                            snippet(self.cx, params[1].span, ".."));
 167
 168                         db.span_label(
 169                             self.span,
 170                             &help,
 171                         );
 172                     }
 173                 });
 174             }
 175         }
 176
 177         if !self.sole_expr {
 178             walk_expr(self, expr);
 179         }
 180     }
 181     fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
 182         NestedVisitorMap::None
 183     }
 184 }