clippy_lints/src/entry.rs

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