clippy_lints/src/entry.rs

   1 use crate::utils::SpanlessEq;
   2 use crate::utils::{get_item_name, higher, match_type, paths, snippet, snippet_opt};
   3 use crate::utils::{snippet_with_applicability, span_lint_and_then, walk_ptrs_ty};
   4 use if_chain::if_chain;
   5 use rustc::declare_lint_pass;
   6 use rustc::hir::map::Map;
   7 use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
   8 use rustc_errors::Applicability;
   9 use rustc_hir::intravisit::{walk_expr, NestedVisitorMap, Visitor};
  10 use rustc_hir::*;
  11 use rustc_session::declare_tool_lint;
  12 use rustc_span::source_map::Span;
  13
  14 declare_clippy_lint! {
  15     /// **What it does:** Checks for uses of `contains_key` + `insert` on `HashMap`
  16     /// or `BTreeMap`.
  17     ///
  18     /// **Why is this bad?** Using `entry` is more efficient.
  19     ///
  20     /// **Known problems:** Some false negatives, eg.:
  21     /// ```rust
  22     /// # use std::collections::HashMap;
  23     /// # let mut map = HashMap::new();
  24     /// # let v = 1;
  25     /// # let k = 1;
  26     /// if !map.contains_key(&k) {
  27     ///     map.insert(k.clone(), v);
  28     /// }
  29     /// ```
  30     ///
  31     /// **Example:**
  32     /// ```rust
  33     /// # use std::collections::HashMap;
  34     /// # let mut map = HashMap::new();
  35     /// # let k = 1;
  36     /// # let v = 1;
  37     /// if !map.contains_key(&k) {
  38     ///     map.insert(k, v);
  39     /// }
  40     /// ```
  41     /// can both be rewritten as:
  42     /// ```rust
  43     /// # use std::collections::HashMap;
  44     /// # let mut map = HashMap::new();
  45     /// # let k = 1;
  46     /// # let v = 1;
  47     /// map.entry(k).or_insert(v);
  48     /// ```
  49     pub MAP_ENTRY,
  50     perf,
  51     "use of `contains_key` followed by `insert` on a `HashMap` or `BTreeMap`"
  52 }
  53
  54 declare_lint_pass!(HashMapPass => [MAP_ENTRY]);
  55
  56 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for HashMapPass {
  57     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr<'_>) {
  58         if let Some((ref check, ref then_block, ref else_block)) = higher::if_block(&expr) {
  59             if let ExprKind::Unary(UnOp::UnNot, ref check) = check.kind {
  60                 if let Some((ty, map, key)) = check_cond(cx, check) {
  61                     // in case of `if !m.contains_key(&k) { m.insert(k, v); }`
  62                     // we can give a better error message
  63                     let sole_expr = {
  64                         else_block.is_none()
  65                             && if let ExprKind::Block(ref then_block, _) = then_block.kind {
  66                                 (then_block.expr.is_some() as usize) + then_block.stmts.len() == 1
  67                             } else {
  68                                 true
  69                             }
  70                         // XXXManishearth we can also check for if/else blocks containing `None`.
  71                     };
  72
  73                     let mut visitor = InsertVisitor {
  74                         cx,
  75                         span: expr.span,
  76                         ty,
  77                         map,
  78                         key,
  79                         sole_expr,
  80                     };
  81
  82                     walk_expr(&mut visitor, &**then_block);
  83                 }
  84             } else if let Some(ref else_block) = *else_block {
  85                 if let Some((ty, map, key)) = check_cond(cx, check) {
  86                     let mut visitor = InsertVisitor {
  87                         cx,
  88                         span: expr.span,
  89                         ty,
  90                         map,
  91                         key,
  92                         sole_expr: false,
  93                     };
  94
  95                     walk_expr(&mut visitor, else_block);
  96                 }
  97             }
  98         }
  99     }
 100 }
 101
 102 fn check_cond<'a, 'tcx, 'b>(
 103     cx: &'a LateContext<'a, 'tcx>,
 104     check: &'b Expr<'b>,
 105 ) -> Option<(&'static str, &'b Expr<'b>, &'b Expr<'b>)> {
 106     if_chain! {
 107         if let ExprKind::MethodCall(ref path, _, ref params) = check.kind;
 108         if params.len() >= 2;
 109         if path.ident.name == sym!(contains_key);
 110         if let ExprKind::AddrOf(BorrowKind::Ref, _, ref key) = params[1].kind;
 111         then {
 112             let map = &params[0];
 113             let obj_ty = walk_ptrs_ty(cx.tables.expr_ty(map));
 114
 115             return if match_type(cx, obj_ty, &paths::BTREEMAP) {
 116                 Some(("BTreeMap", map, key))
 117             }
 118             else if match_type(cx, obj_ty, &paths::HASHMAP) {
 119                 Some(("HashMap", map, key))
 120             }
 121             else {
 122                 None
 123             };
 124         }
 125     }
 126
 127     None
 128 }
 129
 130 struct InsertVisitor<'a, 'tcx, 'b> {
 131     cx: &'a LateContext<'a, 'tcx>,
 132     span: Span,
 133     ty: &'static str,
 134     map: &'b Expr<'b>,
 135     key: &'b Expr<'b>,
 136     sole_expr: bool,
 137 }
 138
 139 impl<'a, 'tcx, 'b> Visitor<'tcx> for InsertVisitor<'a, 'tcx, 'b> {
 140     type Map = Map<'tcx>;
 141
 142     fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
 143         if_chain! {
 144             if let ExprKind::MethodCall(ref path, _, ref params) = expr.kind;
 145             if params.len() == 3;
 146             if path.ident.name == sym!(insert);
 147             if get_item_name(self.cx, self.map) == get_item_name(self.cx, &params[0]);
 148             if SpanlessEq::new(self.cx).eq_expr(self.key, &params[1]);
 149             if snippet_opt(self.cx, self.map.span) == snippet_opt(self.cx, params[0].span);
 150             then {
 151                 span_lint_and_then(self.cx, MAP_ENTRY, self.span,
 152                                    &format!("usage of `contains_key` followed by `insert` on a `{}`", self.ty), |db| {
 153                     if self.sole_expr {
 154                         let mut app = Applicability::MachineApplicable;
 155                         let help = format!("{}.entry({}).or_insert({});",
 156                                            snippet_with_applicability(self.cx, self.map.span, "map", &mut app),
 157                                            snippet_with_applicability(self.cx, params[1].span, "..", &mut app),
 158                                            snippet_with_applicability(self.cx, params[2].span, "..", &mut app));
 159
 160                         db.span_suggestion(
 161                             self.span,
 162                             "consider using",
 163                             help,
 164                             Applicability::MachineApplicable, // snippet
 165                         );
 166                     }
 167                     else {
 168                         let help = format!("consider using `{}.entry({})`",
 169                                            snippet(self.cx, self.map.span, "map"),
 170                                            snippet(self.cx, params[1].span, ".."));
 171
 172                         db.span_label(
 173                             self.span,
 174                             &help,
 175                         );
 176                     }
 177                 });
 178             }
 179         }
 180
 181         if !self.sole_expr {
 182             walk_expr(self, expr);
 183         }
 184     }
 185     fn nested_visit_map(&mut self) -> NestedVisitorMap<'_, Self::Map> {
 186         NestedVisitorMap::None
 187     }
 188 }