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
34 "rebinding a name to itself, e.g., `let mut x = &mut x`"
37 declare_clippy_lint! {
39 /// Checks for bindings that shadow other bindings already in
40 /// scope, while reusing the original value.
42 /// ### Why is this bad?
43 /// Not too much, in fact it's a common pattern in Rust
44 /// code. Still, some argue that name shadowing like this hurts readability,
45 /// because a value may be bound to different things depending on position in
53 /// use different variable name:
60 "rebinding a name to an expression that re-uses the original value, e.g., `let x = x + 1`"
63 declare_clippy_lint! {
65 /// Checks for bindings that shadow other bindings already in
66 /// scope, either without an initialization or with one that does not even use
67 /// the original value.
69 /// ### Why is this bad?
70 /// Name shadowing can hurt readability, especially in
71 /// large code bases, because it is easy to lose track of the active binding at
72 /// any place in the code. This can be alleviated by either giving more specific
73 /// names to bindings or introducing more scopes to contain the bindings.
82 /// let x = z; // shadows the earlier binding
85 /// let w = z; // use different variable name
89 "rebinding a name without even using the original value"
93 pub(crate) struct Shadow {
94 bindings: Vec<FxHashMap<Symbol, Vec<ItemLocalId>>>,
97 impl_lint_pass!(Shadow => [SHADOW_SAME, SHADOW_REUSE, SHADOW_UNRELATED]);
99 impl<'tcx> LateLintPass<'tcx> for Shadow {
100 fn check_pat(&mut self, cx: &LateContext<'tcx>, pat: &'tcx Pat<'_>) {
101 let (id, ident) = match pat.kind {
102 PatKind::Binding(_, hir_id, ident, _) => (hir_id, ident),
105 if ident.span.from_expansion() || ident.span.is_dummy() {
108 let HirId { owner, local_id } = id;
110 // get (or insert) the list of items for this owner and symbol
111 let data = self.bindings.last_mut().unwrap();
112 let items_with_name = data.entry(ident.name).or_default();
114 // check other bindings with the same name, most recently seen first
115 for &prev in items_with_name.iter().rev() {
116 if prev == local_id {
117 // repeated binding in an `Or` pattern
121 if is_shadow(cx, owner, prev, local_id) {
122 let prev_hir_id = HirId { owner, local_id: prev };
123 lint_shadow(cx, pat, prev_hir_id, ident.span);
124 // only lint against the "nearest" shadowed binding
129 items_with_name.push(local_id);
132 fn check_body(&mut self, cx: &LateContext<'_>, body: &Body<'_>) {
133 let hir = cx.tcx.hir();
134 if !matches!(hir.body_owner_kind(hir.body_owner(body.id())), BodyOwnerKind::Closure) {
135 self.bindings.push(FxHashMap::default());
139 fn check_body_post(&mut self, cx: &LateContext<'_>, body: &Body<'_>) {
140 let hir = cx.tcx.hir();
141 if !matches!(hir.body_owner_kind(hir.body_owner(body.id())), BodyOwnerKind::Closure) {
147 fn is_shadow(cx: &LateContext<'_>, owner: LocalDefId, first: ItemLocalId, second: ItemLocalId) -> bool {
148 let scope_tree = cx.tcx.region_scope_tree(owner.to_def_id());
149 let first_scope = scope_tree.var_scope(first);
150 let second_scope = scope_tree.var_scope(second);
151 scope_tree.is_subscope_of(second_scope, first_scope)
154 fn lint_shadow(cx: &LateContext<'_>, pat: &Pat<'_>, shadowed: HirId, span: Span) {
155 let (lint, msg) = match find_init(cx, pat.hir_id) {
156 Some(expr) if is_self_shadow(cx, pat, expr, shadowed) => {
158 "`{}` is shadowed by itself in `{}`",
159 snippet(cx, pat.span, "_"),
160 snippet(cx, expr.span, "..")
164 Some(expr) if is_local_used(cx, expr, shadowed) => {
166 "`{}` is shadowed by `{}` which reuses the original value",
167 snippet(cx, pat.span, "_"),
168 snippet(cx, expr.span, "..")
173 let msg = format!("`{}` shadows a previous, unrelated binding", snippet(cx, pat.span, "_"));
174 (SHADOW_UNRELATED, msg)
182 Some(cx.tcx.hir().span(shadowed)),
183 "previous binding is here",
187 /// Returns true if the expression is a simple transformation of a local binding such as `&x`
188 fn is_self_shadow(cx: &LateContext<'_>, pat: &Pat<'_>, mut expr: &Expr<'_>, hir_id: HirId) -> bool {
189 let hir = cx.tcx.hir();
190 let is_direct_binding = hir
191 .parent_iter(pat.hir_id)
192 .map_while(|(_id, node)| match node {
193 Node::Pat(pat) => Some(pat),
196 .all(|pat| matches!(pat.kind, PatKind::Ref(..) | PatKind::Or(_)));
197 if !is_direct_binding {
201 expr = match expr.kind {
203 | ExprKind::AddrOf(_, _, e)
212 | ExprKind::Unary(UnOp::Deref, e) => e,
213 ExprKind::Path(QPath::Resolved(None, path)) => break path.res == Res::Local(hir_id),
219 /// Finds the "init" expression for a pattern: `let <pat> = <init>;` or
220 /// `match <init> { .., <pat> => .., .. }`
221 fn find_init<'tcx>(cx: &LateContext<'tcx>, hir_id: HirId) -> Option<&'tcx Expr<'tcx>> {
222 for (_, node) in cx.tcx.hir().parent_iter(hir_id) {
223 let init = match node {
224 Node::Arm(_) | Node::Pat(_) => continue,
225 Node::Expr(expr) => match expr.kind {
226 ExprKind::Match(e, _, _) => Some(e),
229 Node::Local(local) => local.init,