src/tools/clippy/clippy_lints/src/entry.rs

   1 use crate::utils::SpanlessEq;
   2 use crate::utils::{get_item_name, is_type_diagnostic_item, match_type, paths, snippet, snippet_opt};
   3 use crate::utils::{snippet_with_applicability, span_lint_and_then};
   4 use if_chain::if_chain;
   5 use rustc_errors::Applicability;
   6 use rustc_hir::intravisit::{walk_expr, NestedVisitorMap, Visitor};
   7 use rustc_hir::{BorrowKind, Expr, ExprKind, UnOp};
   8 use rustc_lint::{LateContext, LateLintPass};
   9 use rustc_middle::hir::map::Map;
  10 use rustc_session::{declare_lint_pass, declare_tool_lint};
  11 use rustc_span::source_map::Span;
  12 use rustc_span::sym;
  13
  14 declare_clippy_lint! {
  15     /// **What it does:** Checks for uses of `contains_key` + `insert` on `HashMap`
  16     /// or `BTreeMap`.
  17     ///
  18     /// **Why is this bad?** Using `entry` is more efficient.
  19     ///
  20     /// **Known problems:** Some false negatives, eg.:
  21     /// ```rust
  22     /// # use std::collections::HashMap;
  23     /// # let mut map = HashMap::new();
  24     /// # let v = 1;
  25     /// # let k = 1;
  26     /// if !map.contains_key(&k) {
  27     ///     map.insert(k.clone(), v);
  28     /// }
  29     /// ```
  30     ///
  31     /// **Example:**
  32     /// ```rust
  33     /// # use std::collections::HashMap;
  34     /// # let mut map = HashMap::new();
  35     /// # let k = 1;
  36     /// # let v = 1;
  37     /// if !map.contains_key(&k) {
  38     ///     map.insert(k, v);
  39     /// }
  40     /// ```
  41     /// can both be rewritten as:
  42     /// ```rust
  43     /// # use std::collections::HashMap;
  44     /// # let mut map = HashMap::new();
  45     /// # let k = 1;
  46     /// # let v = 1;
  47     /// map.entry(k).or_insert(v);
  48     /// ```
  49     pub MAP_ENTRY,
  50     perf,
  51     "use of `contains_key` followed by `insert` on a `HashMap` or `BTreeMap`"
  52 }
  53
  54 declare_lint_pass!(HashMapPass => [MAP_ENTRY]);
  55
  56 impl<'tcx> LateLintPass<'tcx> for HashMapPass {
  57     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
  58         if let ExprKind::If(ref check, ref then_block, ref else_block) = expr.kind {
  59             if let ExprKind::Unary(UnOp::Not, ref check) = check.kind {
  60                 if let Some((ty, map, key)) = check_cond(cx, check) {
  61                     // in case of `if !m.contains_key(&k) { m.insert(k, v); }`
  62                     // we can give a better error message
  63                     let sole_expr = {
  64                         else_block.is_none()
  65                             && if let ExprKind::Block(ref then_block, _) = then_block.kind {
  66                                 (then_block.expr.is_some() as usize) + then_block.stmts.len() == 1
  67                             } else {
  68                                 true
  69                             }
  70                         // XXXManishearth we can also check for if/else blocks containing `None`.
  71                     };
  72
  73                     let mut visitor = InsertVisitor {
  74                         cx,
  75                         span: expr.span,
  76                         ty,
  77                         map,
  78                         key,
  79                         sole_expr,
  80                     };
  81
  82                     walk_expr(&mut visitor, &**then_block);
  83                 }
  84             } else if let Some(ref else_block) = *else_block {
  85                 if let Some((ty, map, key)) = check_cond(cx, check) {
  86                     let mut visitor = InsertVisitor {
  87                         cx,
  88                         span: expr.span,
  89                         ty,
  90                         map,
  91                         key,
  92                         sole_expr: false,
  93                     };
  94
  95                     walk_expr(&mut visitor, else_block);
  96                 }
  97             }
  98         }
  99     }
 100 }
 101
 102 fn check_cond<'a>(cx: &LateContext<'_>, check: &'a Expr<'a>) -> Option<(&'static str, &'a Expr<'a>, &'a Expr<'a>)> {
 103     if_chain! {
 104         if let ExprKind::MethodCall(ref path, _, ref params, _) = check.kind;
 105         if params.len() >= 2;
 106         if path.ident.name == sym!(contains_key);
 107         if let ExprKind::AddrOf(BorrowKind::Ref, _, ref key) = params[1].kind;
 108         then {
 109             let map = &params[0];
 110             let obj_ty = cx.typeck_results().expr_ty(map).peel_refs();
 111
 112             return if match_type(cx, obj_ty, &paths::BTREEMAP) {
 113                 Some(("BTreeMap", map, key))
 114             }
 115             else if is_type_diagnostic_item(cx, obj_ty, sym::hashmap_type) {
 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<'tcx>,
 129     span: Span,
 130     ty: &'static str,
 131     map: &'b Expr<'b>,
 132     key: &'b Expr<'b>,
 133     sole_expr: bool,
 134 }
 135
 136 impl<'a, 'tcx, 'b> Visitor<'tcx> for InsertVisitor<'a, 'tcx, 'b> {
 137     type Map = Map<'tcx>;
 138
 139     fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
 140         if_chain! {
 141             if let ExprKind::MethodCall(ref path, _, ref params, _) = expr.kind;
 142             if params.len() == 3;
 143             if path.ident.name == sym!(insert);
 144             if get_item_name(self.cx, self.map) == get_item_name(self.cx, &params[0]);
 145             if SpanlessEq::new(self.cx).eq_expr(self.key, &params[1]);
 146             if snippet_opt(self.cx, self.map.span) == snippet_opt(self.cx, params[0].span);
 147             then {
 148                 span_lint_and_then(self.cx, MAP_ENTRY, self.span,
 149                                    &format!("usage of `contains_key` followed by `insert` on a `{}`", self.ty), |diag| {
 150                     if self.sole_expr {
 151                         let mut app = Applicability::MachineApplicable;
 152                         let help = format!("{}.entry({}).or_insert({});",
 153                                            snippet_with_applicability(self.cx, self.map.span, "map", &mut app),
 154                                            snippet_with_applicability(self.cx, params[1].span, "..", &mut app),
 155                                            snippet_with_applicability(self.cx, params[2].span, "..", &mut app));
 156
 157                         diag.span_suggestion(
 158                             self.span,
 159                             "consider using",
 160                             help,
 161                             Applicability::MachineApplicable, // snippet
 162                         );
 163                     }
 164                     else {
 165                         let help = format!("consider using `{}.entry({})`",
 166                                            snippet(self.cx, self.map.span, "map"),
 167                                            snippet(self.cx, params[1].span, ".."));
 168
 169                         diag.span_label(
 170                             self.span,
 171                             &help,
 172                         );
 173                     }
 174                 });
 175             }
 176         }
 177
 178         if !self.sole_expr {
 179             walk_expr(self, expr);
 180         }
 181     }
 182     fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
 183         NestedVisitorMap::None
 184     }
 185 }