clippy_lints/src/entry.rs

   1 use crate::rustc::hir::*;
   2 use crate::rustc::hir::intravisit::{walk_expr, NestedVisitorMap, Visitor};
   3 use crate::rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
   4 use crate::rustc::{declare_tool_lint, lint_array};
   5 use if_chain::if_chain;
   6 use crate::syntax::source_map::Span;
   7 use crate::utils::SpanlessEq;
   8 use crate::utils::{get_item_name, match_type, paths, snippet, span_lint_and_then, walk_ptrs_ty};
   9 use crate::rustc_errors::Applicability;
  10
  11 /// **What it does:** Checks for uses of `contains_key` + `insert` on `HashMap`
  12 /// or `BTreeMap`.
  13 ///
  14 /// **Why is this bad?** Using `entry` is more efficient.
  15 ///
  16 /// **Known problems:** Some false negatives, eg.:
  17 /// ```rust
  18 /// let k = &key;
  19 /// if !m.contains_key(k) { m.insert(k.clone(), v); }
  20 /// ```
  21 ///
  22 /// **Example:**
  23 /// ```rust
  24 /// if !m.contains_key(&k) { m.insert(k, v) }
  25 /// ```
  26 /// can be rewritten as:
  27 /// ```rust
  28 /// m.entry(k).or_insert(v);
  29 /// ```
  30 declare_clippy_lint! {
  31     pub MAP_ENTRY,
  32     perf,
  33     "use of `contains_key` followed by `insert` on a `HashMap` or `BTreeMap`"
  34 }
  35
  36 #[derive(Copy, Clone)]
  37 pub struct HashMapLint;
  38
  39 impl LintPass for HashMapLint {
  40     fn get_lints(&self) -> LintArray {
  41         lint_array!(MAP_ENTRY)
  42     }
  43 }
  44
  45 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for HashMapLint {
  46     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
  47         if let ExprKind::If(ref check, ref then_block, ref else_block) = expr.node {
  48             if let ExprKind::Unary(UnOp::UnNot, ref check) = check.node {
  49                 if let Some((ty, map, key)) = check_cond(cx, check) {
  50                     // in case of `if !m.contains_key(&k) { m.insert(k, v); }`
  51                     // we can give a better error message
  52                     let sole_expr = {
  53                         else_block.is_none() && if let ExprKind::Block(ref then_block, _) = then_block.node {
  54                             (then_block.expr.is_some() as usize) + then_block.stmts.len() == 1
  55                         } else {
  56                             true
  57                         }
  58                     };
  59
  60                     let mut visitor = InsertVisitor {
  61                         cx,
  62                         span: expr.span,
  63                         ty,
  64                         map,
  65                         key,
  66                         sole_expr,
  67                     };
  68
  69                     walk_expr(&mut visitor, &**then_block);
  70                 }
  71             } else if let Some(ref else_block) = *else_block {
  72                 if let Some((ty, map, key)) = check_cond(cx, check) {
  73                     let mut visitor = InsertVisitor {
  74                         cx,
  75                         span: expr.span,
  76                         ty,
  77                         map,
  78                         key,
  79                         sole_expr: false,
  80                     };
  81
  82                     walk_expr(&mut visitor, else_block);
  83                 }
  84             }
  85         }
  86     }
  87 }
  88
  89 fn check_cond<'a, 'tcx, 'b>(
  90     cx: &'a LateContext<'a, 'tcx>,
  91     check: &'b Expr,
  92 ) -> Option<(&'static str, &'b Expr, &'b Expr)> {
  93     if_chain! {
  94         if let ExprKind::MethodCall(ref path, _, ref params) = check.node;
  95         if params.len() >= 2;
  96         if path.ident.name == "contains_key";
  97         if let ExprKind::AddrOf(_, ref key) = params[1].node;
  98         then {
  99             let map = &params[0];
 100             let obj_ty = walk_ptrs_ty(cx.tables.expr_ty(map));
 101
 102             return if match_type(cx, obj_ty, &paths::BTREEMAP) {
 103                 Some(("BTreeMap", map, key))
 104             }
 105             else if match_type(cx, obj_ty, &paths::HASHMAP) {
 106                 Some(("HashMap", map, key))
 107             }
 108             else {
 109                 None
 110             };
 111         }
 112     }
 113
 114     None
 115 }
 116
 117 struct InsertVisitor<'a, 'tcx: 'a, 'b> {
 118     cx: &'a LateContext<'a, 'tcx>,
 119     span: Span,
 120     ty: &'static str,
 121     map: &'b Expr,
 122     key: &'b Expr,
 123     sole_expr: bool,
 124 }
 125
 126 impl<'a, 'tcx, 'b> Visitor<'tcx> for InsertVisitor<'a, 'tcx, 'b> {
 127     fn visit_expr(&mut self, expr: &'tcx Expr) {
 128         if_chain! {
 129             if let ExprKind::MethodCall(ref path, _, ref params) = expr.node;
 130             if params.len() == 3;
 131             if path.ident.name == "insert";
 132             if get_item_name(self.cx, self.map) == get_item_name(self.cx, &params[0]);
 133             if SpanlessEq::new(self.cx).eq_expr(self.key, &params[1]);
 134             then {
 135                 span_lint_and_then(self.cx, MAP_ENTRY, self.span,
 136                                    &format!("usage of `contains_key` followed by `insert` on a `{}`", self.ty), |db| {
 137                     if self.sole_expr {
 138                         let help = format!("{}.entry({}).or_insert({})",
 139                                            snippet(self.cx, self.map.span, "map"),
 140                                            snippet(self.cx, params[1].span, ".."),
 141                                            snippet(self.cx, params[2].span, ".."));
 142
 143                         db.span_suggestion_with_applicability(
 144                             self.span,
 145                             "consider using",
 146                             help,
 147                             Applicability::Unspecified,
 148                         );
 149                     }
 150                     else {
 151                         let help = format!("{}.entry({})",
 152                                            snippet(self.cx, self.map.span, "map"),
 153                                            snippet(self.cx, params[1].span, ".."));
 154
 155                         db.span_suggestion_with_applicability(
 156                             self.span,
 157                             "consider using",
 158                             help,
 159                             Applicability::Unspecified,
 160                         );
 161                     }
 162                 });
 163             }
 164         }
 165
 166         if !self.sole_expr {
 167             walk_expr(self, expr);
 168         }
 169     }
 170     fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
 171         NestedVisitorMap::None
 172     }
 173 }