1 use clippy_utils::diagnostics::span_lint_and_help;
2 use clippy_utils::ty::{match_type, peel_mid_ty_refs_is_mutable};
3 use clippy_utils::{fn_def_id, is_trait_method, path_to_local_id, paths, peel_ref_operators};
4 use rustc_ast::Mutability;
5 use rustc_hir::intravisit::{walk_expr, Visitor};
6 use rustc_hir::lang_items::LangItem;
7 use rustc_hir::{Block, Expr, ExprKind, HirId, Local, Node, PatKind, PathSegment, StmtKind};
8 use rustc_lint::{LateContext, LateLintPass};
9 use rustc_session::{declare_lint_pass, declare_tool_lint};
12 declare_clippy_lint! {
14 /// Checks for the creation of a `peekable` iterator that is never `.peek()`ed
16 /// ### Why is this bad?
17 /// Creating a peekable iterator without using any of its methods is likely a mistake,
18 /// or just a leftover after a refactor.
22 /// let collection = vec![1, 2, 3];
23 /// let iter = collection.iter().peekable();
25 /// for item in iter {
32 /// let collection = vec![1, 2, 3];
33 /// let iter = collection.iter();
35 /// for item in iter {
39 #[clippy::version = "1.64.0"]
42 "creating a peekable iterator without using any of its methods"
45 declare_lint_pass!(UnusedPeekable => [UNUSED_PEEKABLE]);
47 impl<'tcx> LateLintPass<'tcx> for UnusedPeekable {
48 fn check_block(&mut self, cx: &LateContext<'tcx>, block: &Block<'tcx>) {
49 // Don't lint `Peekable`s returned from a block
50 if let Some(expr) = block.expr
51 && let Some(ty) = cx.typeck_results().expr_ty_opt(peel_ref_operators(cx, expr))
52 && match_type(cx, ty, &paths::PEEKABLE)
57 for (idx, stmt) in block.stmts.iter().enumerate() {
58 if !stmt.span.from_expansion()
59 && let StmtKind::Local(local) = stmt.kind
60 && let PatKind::Binding(_, binding, ident, _) = local.pat.kind
61 && let Some(init) = local.init
62 && !init.span.from_expansion()
63 && let Some(ty) = cx.typeck_results().expr_ty_opt(init)
64 && let (ty, _, Mutability::Mut) = peel_mid_ty_refs_is_mutable(ty)
65 && match_type(cx, ty, &paths::PEEKABLE)
67 let mut vis = PeekableVisitor::new(cx, binding);
69 if idx + 1 == block.stmts.len() && block.expr.is_none() {
73 for stmt in &block.stmts[idx..] {
77 if let Some(expr) = block.expr {
81 if !vis.found_peek_call {
86 "`peek` never called on `Peekable` iterator",
88 "consider removing the call to `peekable`"
96 struct PeekableVisitor<'a, 'tcx> {
97 cx: &'a LateContext<'tcx>,
98 expected_hir_id: HirId,
99 found_peek_call: bool,
102 impl<'a, 'tcx> PeekableVisitor<'a, 'tcx> {
103 fn new(cx: &'a LateContext<'tcx>, expected_hir_id: HirId) -> Self {
107 found_peek_call: false,
112 impl<'tcx> Visitor<'_> for PeekableVisitor<'_, 'tcx> {
113 fn visit_expr(&mut self, ex: &'_ Expr<'_>) {
114 if self.found_peek_call {
118 if path_to_local_id(ex, self.expected_hir_id) {
119 for (_, node) in self.cx.tcx.hir().parent_iter(ex.hir_id) {
121 Node::Expr(expr) => {
123 // some_function(peekable)
125 // If the Peekable is passed to a function, stop
126 ExprKind::Call(_, args) => {
127 if let Some(func_did) = fn_def_id(self.cx, expr)
128 && let Ok(into_iter_did) = self
132 .require(LangItem::IntoIterIntoIter)
133 && func_did == into_iter_did
135 // Probably a for loop desugar, stop searching
139 if args.iter().any(|arg| {
140 matches!(arg.kind, ExprKind::Path(_)) && arg_is_mut_peekable(self.cx, arg)
142 self.found_peek_call = true;
146 // Catch anything taking a Peekable mutably
147 ExprKind::MethodCall(
149 ident: method_name_ident,
152 [self_arg, remaining_args @ ..],
155 let method_name = method_name_ident.name.as_str();
157 // `Peekable` methods
158 if matches!(method_name, "peek" | "peek_mut" | "next_if" | "next_if_eq")
159 && arg_is_mut_peekable(self.cx, self_arg)
161 self.found_peek_call = true;
165 // foo.some_method() excluding Iterator methods
166 if remaining_args.iter().any(|arg| arg_is_mut_peekable(self.cx, arg))
167 && !is_trait_method(self.cx, expr, sym::Iterator)
169 self.found_peek_call = true;
173 // foo.by_ref(), keep checking for `peek`
174 if method_name == "by_ref" {
180 ExprKind::AddrOf(_, Mutability::Mut, _) | ExprKind::Unary(..) | ExprKind::DropTemps(_) => {
182 ExprKind::AddrOf(_, Mutability::Not, _) => return,
184 self.found_peek_call = true;
189 Node::Local(Local { init: Some(init), .. }) => {
190 if arg_is_mut_peekable(self.cx, init) {
191 self.found_peek_call = true;
197 Node::Stmt(stmt) => match stmt.kind {
198 StmtKind::Expr(_) | StmtKind::Semi(_) => {},
200 self.found_peek_call = true;
204 Node::Block(_) | Node::ExprField(_) => {},
216 fn arg_is_mut_peekable(cx: &LateContext<'_>, arg: &Expr<'_>) -> bool {
217 if let Some(ty) = cx.typeck_results().expr_ty_opt(arg)
218 && let (ty, _, Mutability::Mut) = peel_mid_ty_refs_is_mutable(ty)
219 && match_type(cx, ty, &paths::PEEKABLE)