clippy_lints/src/entry.rs

   1 use clippy_utils::diagnostics::span_lint_and_then;
   2 use clippy_utils::source::{snippet, snippet_opt, snippet_with_applicability};
   3 use clippy_utils::ty::{is_type_diagnostic_item, match_type};
   4 use clippy_utils::SpanlessEq;
   5 use clippy_utils::{get_item_name, paths};
   6 use if_chain::if_chain;
   7 use rustc_errors::Applicability;
   8 use rustc_hir::intravisit::{walk_expr, NestedVisitorMap, Visitor};
   9 use rustc_hir::{BorrowKind, Expr, ExprKind, UnOp};
  10 use rustc_lint::{LateContext, LateLintPass};
  11 use rustc_middle::hir::map::Map;
  12 use rustc_session::{declare_lint_pass, declare_tool_lint};
  13 use rustc_span::source_map::Span;
  14 use rustc_span::sym;
  15
  16 declare_clippy_lint! {
  17     /// **What it does:** Checks for uses of `contains_key` + `insert` on `HashMap`
  18     /// or `BTreeMap`.
  19     ///
  20     /// **Why is this bad?** Using `entry` is more efficient.
  21     ///
  22     /// **Known problems:** Some false negatives, eg.:
  23     /// ```rust
  24     /// # use std::collections::HashMap;
  25     /// # let mut map = HashMap::new();
  26     /// # let v = 1;
  27     /// # let k = 1;
  28     /// if !map.contains_key(&k) {
  29     ///     map.insert(k.clone(), v);
  30     /// }
  31     /// ```
  32     ///
  33     /// **Example:**
  34     /// ```rust
  35     /// # use std::collections::HashMap;
  36     /// # let mut map = HashMap::new();
  37     /// # let k = 1;
  38     /// # let v = 1;
  39     /// if !map.contains_key(&k) {
  40     ///     map.insert(k, v);
  41     /// }
  42     /// ```
  43     /// can both be rewritten as:
  44     /// ```rust
  45     /// # use std::collections::HashMap;
  46     /// # let mut map = HashMap::new();
  47     /// # let k = 1;
  48     /// # let v = 1;
  49     /// map.entry(k).or_insert(v);
  50     /// ```
  51     pub MAP_ENTRY,
  52     perf,
  53     "use of `contains_key` followed by `insert` on a `HashMap` or `BTreeMap`"
  54 }
  55
  56 declare_lint_pass!(HashMapPass => [MAP_ENTRY]);
  57
  58 impl<'tcx> LateLintPass<'tcx> for HashMapPass {
  59     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
  60         if let ExprKind::If(check, then_block, ref else_block) = expr.kind {
  61             if let ExprKind::Unary(UnOp::Not, check) = check.kind {
  62                 if let Some((ty, map, key)) = check_cond(cx, check) {
  63                     // in case of `if !m.contains_key(&k) { m.insert(k, v); }`
  64                     // we can give a better error message
  65                     let sole_expr = {
  66                         else_block.is_none()
  67                             && if let ExprKind::Block(then_block, _) = then_block.kind {
  68                                 (then_block.expr.is_some() as usize) + then_block.stmts.len() == 1
  69                             } else {
  70                                 true
  71                             }
  72                         // XXXManishearth we can also check for if/else blocks containing `None`.
  73                     };
  74
  75                     let mut visitor = InsertVisitor {
  76                         cx,
  77                         span: expr.span,
  78                         ty,
  79                         map,
  80                         key,
  81                         sole_expr,
  82                     };
  83
  84                     walk_expr(&mut visitor, then_block);
  85                 }
  86             } else if let Some(else_block) = *else_block {
  87                 if let Some((ty, map, key)) = check_cond(cx, check) {
  88                     let mut visitor = InsertVisitor {
  89                         cx,
  90                         span: expr.span,
  91                         ty,
  92                         map,
  93                         key,
  94                         sole_expr: false,
  95                     };
  96
  97                     walk_expr(&mut visitor, else_block);
  98                 }
  99             }
 100         }
 101     }
 102 }
 103
 104 fn check_cond<'a>(cx: &LateContext<'_>, check: &'a Expr<'a>) -> Option<(&'static str, &'a Expr<'a>, &'a Expr<'a>)> {
 105     if_chain! {
 106         if let ExprKind::MethodCall(path, _, params, _) = check.kind;
 107         if params.len() >= 2;
 108         if path.ident.name == sym!(contains_key);
 109         if let ExprKind::AddrOf(BorrowKind::Ref, _, key) = params[1].kind;
 110         then {
 111             let map = &params[0];
 112             let obj_ty = cx.typeck_results().expr_ty(map).peel_refs();
 113
 114             return if match_type(cx, obj_ty, &paths::BTREEMAP) {
 115                 Some(("BTreeMap", map, key))
 116             }
 117             else if is_type_diagnostic_item(cx, obj_ty, sym::hashmap_type) {
 118                 Some(("HashMap", map, key))
 119             }
 120             else {
 121                 None
 122             };
 123         }
 124     }
 125
 126     None
 127 }
 128
 129 struct InsertVisitor<'a, 'tcx, 'b> {
 130     cx: &'a LateContext<'tcx>,
 131     span: Span,
 132     ty: &'static str,
 133     map: &'b Expr<'b>,
 134     key: &'b Expr<'b>,
 135     sole_expr: bool,
 136 }
 137
 138 impl<'a, 'tcx, 'b> Visitor<'tcx> for InsertVisitor<'a, 'tcx, 'b> {
 139     type Map = Map<'tcx>;
 140
 141     fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
 142         if_chain! {
 143             if let ExprKind::MethodCall(path, _, params, _) = expr.kind;
 144             if params.len() == 3;
 145             if path.ident.name == sym!(insert);
 146             if get_item_name(self.cx, self.map) == get_item_name(self.cx, &params[0]);
 147             if SpanlessEq::new(self.cx).eq_expr(self.key, &params[1]);
 148             if snippet_opt(self.cx, self.map.span) == snippet_opt(self.cx, params[0].span);
 149             then {
 150                 span_lint_and_then(self.cx, MAP_ENTRY, self.span,
 151                                    &format!("usage of `contains_key` followed by `insert` on a `{}`", self.ty), |diag| {
 152                     if self.sole_expr {
 153                         let mut app = Applicability::MachineApplicable;
 154                         let help = format!("{}.entry({}).or_insert({});",
 155                                            snippet_with_applicability(self.cx, self.map.span, "map", &mut app),
 156                                            snippet_with_applicability(self.cx, params[1].span, "..", &mut app),
 157                                            snippet_with_applicability(self.cx, params[2].span, "..", &mut app));
 158
 159                         diag.span_suggestion(
 160                             self.span,
 161                             "consider using",
 162                             help,
 163                             Applicability::MachineApplicable, // snippet
 164                         );
 165                     }
 166                     else {
 167                         let help = format!("consider using `{}.entry({})`",
 168                                            snippet(self.cx, self.map.span, "map"),
 169                                            snippet(self.cx, params[1].span, ".."));
 170
 171                         diag.span_label(
 172                             self.span,
 173                             &help,
 174                         );
 175                     }
 176                 });
 177             }
 178         }
 179
 180         if !self.sole_expr {
 181             walk_expr(self, expr);
 182         }
 183     }
 184     fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
 185         NestedVisitorMap::None
 186     }
 187 }