1 use clippy_utils::diagnostics::span_lint_and_note;
2 use clippy_utils::source::snippet;
3 use clippy_utils::visitors::is_local_used;
4 use rustc_data_structures::fx::FxHashMap;
5 use rustc_hir::def::Res;
6 use rustc_hir::def_id::LocalDefId;
7 use rustc_hir::hir_id::ItemLocalId;
8 use rustc_hir::{Block, Body, BodyOwnerKind, Expr, ExprKind, HirId, Node, Pat, PatKind, QPath, UnOp};
9 use rustc_lint::{LateContext, LateLintPass};
10 use rustc_session::{declare_tool_lint, impl_lint_pass};
11 use rustc_span::{Span, Symbol};
13 declare_clippy_lint! {
15 /// Checks for bindings that shadow other bindings already in
16 /// scope, while just changing reference level or mutability.
18 /// ### Why is this bad?
19 /// Not much, in fact it's a very common pattern in Rust
20 /// code. Still, some may opt to avoid it in their code base, they can set this
30 /// let y = &x; // use different variable name
32 #[clippy::version = "pre 1.29.0"]
35 "rebinding a name to itself, e.g., `let mut x = &mut x`"
38 declare_clippy_lint! {
40 /// Checks for bindings that shadow other bindings already in
41 /// scope, while reusing the original value.
43 /// ### Why is this bad?
44 /// Not too much, in fact it's a common pattern in Rust
45 /// code. Still, some argue that name shadowing like this hurts readability,
46 /// because a value may be bound to different things depending on position in
54 /// use different variable name:
59 #[clippy::version = "pre 1.29.0"]
62 "rebinding a name to an expression that re-uses the original value, e.g., `let x = x + 1`"
65 declare_clippy_lint! {
67 /// Checks for bindings that shadow other bindings already in
68 /// scope, either without an initialization or with one that does not even use
69 /// the original value.
71 /// ### Why is this bad?
72 /// Name shadowing can hurt readability, especially in
73 /// large code bases, because it is easy to lose track of the active binding at
74 /// any place in the code. This can be alleviated by either giving more specific
75 /// names to bindings or introducing more scopes to contain the bindings.
84 /// let x = z; // shadows the earlier binding
87 /// let w = z; // use different variable name
89 #[clippy::version = "pre 1.29.0"]
92 "rebinding a name without even using the original value"
96 pub(crate) struct Shadow {
97 bindings: Vec<FxHashMap<Symbol, Vec<ItemLocalId>>>,
100 impl_lint_pass!(Shadow => [SHADOW_SAME, SHADOW_REUSE, SHADOW_UNRELATED]);
102 impl<'tcx> LateLintPass<'tcx> for Shadow {
103 fn check_pat(&mut self, cx: &LateContext<'tcx>, pat: &'tcx Pat<'_>) {
104 let (id, ident) = match pat.kind {
105 PatKind::Binding(_, hir_id, ident, _) => (hir_id, ident),
108 if ident.span.from_expansion() || ident.span.is_dummy() {
111 let HirId { owner, local_id } = id;
113 // get (or insert) the list of items for this owner and symbol
114 let data = self.bindings.last_mut().unwrap();
115 let items_with_name = data.entry(ident.name).or_default();
117 // check other bindings with the same name, most recently seen first
118 for &prev in items_with_name.iter().rev() {
119 if prev == local_id {
120 // repeated binding in an `Or` pattern
124 if is_shadow(cx, owner, prev, local_id) {
125 let prev_hir_id = HirId { owner, local_id: prev };
126 lint_shadow(cx, pat, prev_hir_id, ident.span);
127 // only lint against the "nearest" shadowed binding
132 items_with_name.push(local_id);
135 fn check_body(&mut self, cx: &LateContext<'_>, body: &Body<'_>) {
136 let hir = cx.tcx.hir();
137 if !matches!(hir.body_owner_kind(hir.body_owner(body.id())), BodyOwnerKind::Closure) {
138 self.bindings.push(FxHashMap::default());
142 fn check_body_post(&mut self, cx: &LateContext<'_>, body: &Body<'_>) {
143 let hir = cx.tcx.hir();
144 if !matches!(hir.body_owner_kind(hir.body_owner(body.id())), BodyOwnerKind::Closure) {
150 fn is_shadow(cx: &LateContext<'_>, owner: LocalDefId, first: ItemLocalId, second: ItemLocalId) -> bool {
151 let scope_tree = cx.tcx.region_scope_tree(owner.to_def_id());
152 let first_scope = scope_tree.var_scope(first);
153 let second_scope = scope_tree.var_scope(second);
154 scope_tree.is_subscope_of(second_scope, first_scope)
157 fn lint_shadow(cx: &LateContext<'_>, pat: &Pat<'_>, shadowed: HirId, span: Span) {
158 let (lint, msg) = match find_init(cx, pat.hir_id) {
159 Some(expr) if is_self_shadow(cx, pat, expr, shadowed) => {
161 "`{}` is shadowed by itself in `{}`",
162 snippet(cx, pat.span, "_"),
163 snippet(cx, expr.span, "..")
167 Some(expr) if is_local_used(cx, expr, shadowed) => {
168 let msg = format!("`{}` is shadowed", snippet(cx, pat.span, "_"));
172 let msg = format!("`{}` shadows a previous, unrelated binding", snippet(cx, pat.span, "_"));
173 (SHADOW_UNRELATED, msg)
181 Some(cx.tcx.hir().span(shadowed)),
182 "previous binding is here",
186 /// Returns true if the expression is a simple transformation of a local binding such as `&x`
187 fn is_self_shadow(cx: &LateContext<'_>, pat: &Pat<'_>, mut expr: &Expr<'_>, hir_id: HirId) -> bool {
188 let hir = cx.tcx.hir();
189 let is_direct_binding = hir
190 .parent_iter(pat.hir_id)
191 .map_while(|(_id, node)| match node {
192 Node::Pat(pat) => Some(pat),
195 .all(|pat| matches!(pat.kind, PatKind::Ref(..) | PatKind::Or(_)));
196 if !is_direct_binding {
200 expr = match expr.kind {
202 | ExprKind::AddrOf(_, _, e)
211 | ExprKind::Unary(UnOp::Deref, e) => e,
212 ExprKind::Path(QPath::Resolved(None, path)) => break path.res == Res::Local(hir_id),
218 /// Finds the "init" expression for a pattern: `let <pat> = <init>;` or
219 /// `match <init> { .., <pat> => .., .. }`
220 fn find_init<'tcx>(cx: &LateContext<'tcx>, hir_id: HirId) -> Option<&'tcx Expr<'tcx>> {
221 for (_, node) in cx.tcx.hir().parent_iter(hir_id) {
222 let init = match node {
223 Node::Arm(_) | Node::Pat(_) => continue,
224 Node::Expr(expr) => match expr.kind {
225 ExprKind::Match(e, _, _) => Some(e),
228 Node::Local(local) => local.init,