use rustc::hir::*; use rustc::hir::intravisit::{walk_expr, NestedVisitorMap, Visitor}; use rustc::lint::*; use syntax::codemap::Span; use utils::SpanlessEq; use utils::{get_item_name, match_type, paths, snippet, span_lint_and_then, walk_ptrs_ty}; /// **What it does:** Checks for uses of `contains_key` + `insert` on `HashMap` /// or `BTreeMap`. /// /// **Why is this bad?** Using `entry` is more efficient. /// /// **Known problems:** Some false negatives, eg.: /// ```rust /// let k = &key; /// if !m.contains_key(k) { m.insert(k.clone(), v); } /// ``` /// /// **Example:** /// ```rust /// if !m.contains_key(&k) { m.insert(k, v) } /// ``` /// can be rewritten as: /// ```rust /// m.entry(k).or_insert(v); /// ``` declare_clippy_lint! { pub MAP_ENTRY, perf, "use of `contains_key` followed by `insert` on a `HashMap` or `BTreeMap`" } #[derive(Copy, Clone)] pub struct HashMapLint; impl LintPass for HashMapLint { fn get_lints(&self) -> LintArray { lint_array!(MAP_ENTRY) } } impl<'a, 'tcx> LateLintPass<'a, 'tcx> for HashMapLint { fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) { if let ExprIf(ref check, ref then_block, ref else_block) = expr.node { if let ExprUnary(UnOp::UnNot, ref check) = check.node { if let Some((ty, map, key)) = check_cond(cx, check) { // in case of `if !m.contains_key(&k) { m.insert(k, v); }` // we can give a better error message let sole_expr = { else_block.is_none() && if let ExprBlock(ref then_block, _) = then_block.node { (then_block.expr.is_some() as usize) + then_block.stmts.len() == 1 } else { true } }; let mut visitor = InsertVisitor { cx, span: expr.span, ty, map, key, sole_expr, }; walk_expr(&mut visitor, &**then_block); } } else if let Some(ref else_block) = *else_block { if let Some((ty, map, key)) = check_cond(cx, check) { let mut visitor = InsertVisitor { cx, span: expr.span, ty, map, key, sole_expr: false, }; walk_expr(&mut visitor, else_block); } } } } } fn check_cond<'a, 'tcx, 'b>( cx: &'a LateContext<'a, 'tcx>, check: &'b Expr, ) -> Option<(&'static str, &'b Expr, &'b Expr)> { if_chain! { if let ExprMethodCall(ref path, _, ref params) = check.node; if params.len() >= 2; if path.name == "contains_key"; if let ExprAddrOf(_, ref key) = params[1].node; then { let map = ¶ms[0]; let obj_ty = walk_ptrs_ty(cx.tables.expr_ty(map)); return if match_type(cx, obj_ty, &paths::BTREEMAP) { Some(("BTreeMap", map, key)) } else if match_type(cx, obj_ty, &paths::HASHMAP) { Some(("HashMap", map, key)) } else { None }; } } None } struct InsertVisitor<'a, 'tcx: 'a, 'b> { cx: &'a LateContext<'a, 'tcx>, span: Span, ty: &'static str, map: &'b Expr, key: &'b Expr, sole_expr: bool, } impl<'a, 'tcx, 'b> Visitor<'tcx> for InsertVisitor<'a, 'tcx, 'b> { fn visit_expr(&mut self, expr: &'tcx Expr) { if_chain! { if let ExprMethodCall(ref path, _, ref params) = expr.node; if params.len() == 3; if path.name == "insert"; if get_item_name(self.cx, self.map) == get_item_name(self.cx, ¶ms[0]); if SpanlessEq::new(self.cx).eq_expr(self.key, ¶ms[1]); then { span_lint_and_then(self.cx, MAP_ENTRY, self.span, &format!("usage of `contains_key` followed by `insert` on a `{}`", self.ty), |db| { if self.sole_expr { let help = format!("{}.entry({}).or_insert({})", snippet(self.cx, self.map.span, "map"), snippet(self.cx, params[1].span, ".."), snippet(self.cx, params[2].span, "..")); db.span_suggestion(self.span, "consider using", help); } else { let help = format!("{}.entry({})", snippet(self.cx, self.map.span, "map"), snippet(self.cx, params[1].span, "..")); db.span_suggestion(self.span, "consider using", help); } }); } } if !self.sole_expr { walk_expr(self, expr); } } fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> { NestedVisitorMap::None } }