clippy_lints/src/entry.rs

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