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),
109 if pat.span.desugaring_kind().is_some() {
113 if ident.span.from_expansion() || ident.span.is_dummy() {
117 let HirId { owner, local_id } = id;
118 // get (or insert) the list of items for this owner and symbol
119 let data = self.bindings.last_mut().unwrap();
120 let items_with_name = data.entry(ident.name).or_default();
122 // check other bindings with the same name, most recently seen first
123 for &prev in items_with_name.iter().rev() {
124 if prev == local_id {
125 // repeated binding in an `Or` pattern
129 if is_shadow(cx, owner, prev, local_id) {
130 let prev_hir_id = HirId { owner, local_id: prev };
131 lint_shadow(cx, pat, prev_hir_id, ident.span);
132 // only lint against the "nearest" shadowed binding
137 items_with_name.push(local_id);
140 fn check_body(&mut self, cx: &LateContext<'_>, body: &Body<'_>) {
141 let hir = cx.tcx.hir();
142 if !matches!(hir.body_owner_kind(hir.body_owner(body.id())), BodyOwnerKind::Closure) {
143 self.bindings.push(FxHashMap::default());
147 fn check_body_post(&mut self, cx: &LateContext<'_>, body: &Body<'_>) {
148 let hir = cx.tcx.hir();
149 if !matches!(hir.body_owner_kind(hir.body_owner(body.id())), BodyOwnerKind::Closure) {
155 fn is_shadow(cx: &LateContext<'_>, owner: LocalDefId, first: ItemLocalId, second: ItemLocalId) -> bool {
156 let scope_tree = cx.tcx.region_scope_tree(owner.to_def_id());
157 let first_scope = scope_tree.var_scope(first);
158 let second_scope = scope_tree.var_scope(second);
159 scope_tree.is_subscope_of(second_scope, first_scope)
162 fn lint_shadow(cx: &LateContext<'_>, pat: &Pat<'_>, shadowed: HirId, span: Span) {
163 let (lint, msg) = match find_init(cx, pat.hir_id) {
164 Some(expr) if is_self_shadow(cx, pat, expr, shadowed) => {
166 "`{}` is shadowed by itself in `{}`",
167 snippet(cx, pat.span, "_"),
168 snippet(cx, expr.span, "..")
172 Some(expr) if is_local_used(cx, expr, shadowed) => {
173 let msg = format!("`{}` is shadowed", snippet(cx, pat.span, "_"));
177 let msg = format!("`{}` shadows a previous, unrelated binding", snippet(cx, pat.span, "_"));
178 (SHADOW_UNRELATED, msg)
186 Some(cx.tcx.hir().span(shadowed)),
187 "previous binding is here",
191 /// Returns true if the expression is a simple transformation of a local binding such as `&x`
192 fn is_self_shadow(cx: &LateContext<'_>, pat: &Pat<'_>, mut expr: &Expr<'_>, hir_id: HirId) -> bool {
193 let hir = cx.tcx.hir();
194 let is_direct_binding = hir
195 .parent_iter(pat.hir_id)
196 .map_while(|(_id, node)| match node {
197 Node::Pat(pat) => Some(pat),
200 .all(|pat| matches!(pat.kind, PatKind::Ref(..) | PatKind::Or(_)));
201 if !is_direct_binding {
205 expr = match expr.kind {
207 | ExprKind::AddrOf(_, _, e)
216 | ExprKind::Unary(UnOp::Deref, e) => e,
217 ExprKind::Path(QPath::Resolved(None, path)) => break path.res == Res::Local(hir_id),
223 /// Finds the "init" expression for a pattern: `let <pat> = <init>;` or
224 /// `match <init> { .., <pat> => .., .. }`
225 fn find_init<'tcx>(cx: &LateContext<'tcx>, hir_id: HirId) -> Option<&'tcx Expr<'tcx>> {
226 for (_, node) in cx.tcx.hir().parent_iter(hir_id) {
227 let init = match node {
228 Node::Arm(_) | Node::Pat(_) => continue,
229 Node::Expr(expr) => match expr.kind {
230 ExprKind::Match(e, _, _) => Some(e),
233 Node::Local(local) => local.init,