src/entry.rs

   1 use rustc::hir::*;
   2 use rustc::hir::intravisit::{Visitor, walk_expr, walk_block};
   3 use rustc::lint::*;
   4 use syntax::codemap::Span;
   5 use utils::SpanlessEq;
   6 use utils::{get_item_name, match_type, paths, snippet, span_lint_and_then, walk_ptrs_ty};
   7
   8 /// **What it does:** This lint checks for uses of `contains_key` + `insert` on `HashMap` or
   9 /// `BTreeMap`.
  10 ///
  11 /// **Why is this bad?** Using `entry` is more efficient.
  12 ///
  13 /// **Known problems:** Some false negatives, eg.:
  14 /// ```
  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_lint! {
  28     pub MAP_ENTRY,
  29     Warn,
  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 LateLintPass for HashMapLint {
  43     fn check_expr(&mut self, cx: &LateContext, expr: &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 = else_block.is_none() &&
  50                                     ((then_block.expr.is_some() as usize) + then_block.stmts.len() == 1);
  51
  52                     let mut visitor = InsertVisitor {
  53                         cx: cx,
  54                         span: expr.span,
  55                         ty: ty,
  56                         map: map,
  57                         key: key,
  58                         sole_expr: sole_expr,
  59                     };
  60
  61                     walk_block(&mut visitor, then_block);
  62                 }
  63             } else if let Some(ref else_block) = *else_block {
  64                 if let Some((ty, map, key)) = check_cond(cx, check) {
  65                     let mut visitor = InsertVisitor {
  66                         cx: cx,
  67                         span: expr.span,
  68                         ty: ty,
  69                         map: map,
  70                         key: key,
  71                         sole_expr: false,
  72                     };
  73
  74                     walk_expr(&mut visitor, else_block);
  75                 }
  76             }
  77         }
  78     }
  79 }
  80
  81 fn check_cond<'a, 'tcx, 'b>(cx: &'a LateContext<'a, 'tcx>, check: &'b Expr) -> Option<(&'static str, &'b Expr, &'b Expr)> {
  82     if_let_chain! {[
  83         let ExprMethodCall(ref name, _, ref params) = check.node,
  84         params.len() >= 2,
  85         name.node.as_str() == "contains_key",
  86         let ExprAddrOf(_, ref key) = params[1].node
  87     ], {
  88         let map = &params[0];
  89         let obj_ty = walk_ptrs_ty(cx.tcx.expr_ty(map));
  90
  91         return if match_type(cx, obj_ty, &paths::BTREEMAP) {
  92             Some(("BTreeMap", map, key))
  93         }
  94         else if match_type(cx, obj_ty, &paths::HASHMAP) {
  95             Some(("HashMap", map, key))
  96         }
  97         else {
  98             None
  99         };
 100     }}
 101
 102     None
 103 }
 104
 105 struct InsertVisitor<'a, 'tcx: 'a, 'b> {
 106     cx: &'a LateContext<'a, 'tcx>,
 107     span: Span,
 108     ty: &'static str,
 109     map: &'b Expr,
 110     key: &'b Expr,
 111     sole_expr: bool,
 112 }
 113
 114 impl<'a, 'tcx, 'v, 'b> Visitor<'v> for InsertVisitor<'a, 'tcx, 'b> {
 115     fn visit_expr(&mut self, expr: &'v Expr) {
 116         if_let_chain! {[
 117             let ExprMethodCall(ref name, _, ref params) = expr.node,
 118             params.len() == 3,
 119             name.node.as_str() == "insert",
 120             get_item_name(self.cx, self.map) == get_item_name(self.cx, &*params[0]),
 121             SpanlessEq::new(self.cx).eq_expr(self.key, &params[1])
 122         ], {
 123
 124             span_lint_and_then(self.cx, MAP_ENTRY, self.span,
 125                                &format!("usage of `contains_key` followed by `insert` on `{}`", self.ty), |db| {
 126                 if self.sole_expr {
 127                     let help = format!("{}.entry({}).or_insert({})",
 128                                        snippet(self.cx, self.map.span, "map"),
 129                                        snippet(self.cx, params[1].span, ".."),
 130                                        snippet(self.cx, params[2].span, ".."));
 131
 132                     db.span_suggestion(self.span, "Consider using", help);
 133                 }
 134                 else {
 135                     let help = format!("Consider using `{}.entry({})`",
 136                                        snippet(self.cx, self.map.span, "map"),
 137                                        snippet(self.cx, params[1].span, ".."));
 138
 139                     db.span_note(self.span, &help);
 140                 }
 141             });
 142         }}
 143
 144         if !self.sole_expr {
 145             walk_expr(self, expr);
 146         }
 147     }
 148 }