rust-clippy/clippy_lints/src/shadow.rs

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use crate::reexport::Name;
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use crate::utils::{contains_name, higher, iter_input_pats, snippet, span_lint_and_then};
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use rustc_hir::intravisit::FnKind;
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use rustc_hir::{
Block, Body, Expr, ExprKind, FnDecl, Guard, HirId, Local, MutTy, Pat, PatKind, Path, QPath, StmtKind, Ty, TyKind,
UnOp,
};
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use rustc_lint::{LateContext, LateLintPass, LintContext};
use rustc_middle::lint::in_external_macro;
use rustc_middle::ty;
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use rustc_session::{declare_lint_pass, declare_tool_lint};
use rustc_span::source_map::Span;
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declare_clippy_lint! {
/// **What it does:** Checks for bindings that shadow other bindings already in
/// scope, while just changing reference level or mutability.
///
/// **Why is this bad?** Not much, in fact it's a very common pattern in Rust
/// code. Still, some may opt to avoid it in their code base, they can set this
/// lint to `Warn`.
///
/// **Known problems:** This lint, as the other shadowing related lints,
/// currently only catches very simple patterns.
///
/// **Example:**
/// ```rust
/// # let x = 1;
/// let x = &x;
/// ```
pub SHADOW_SAME,
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restriction,
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"rebinding a name to itself, e.g., `let mut x = &mut x`"
}
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declare_clippy_lint! {
/// **What it does:** Checks for bindings that shadow other bindings already in
/// scope, while reusing the original value.
///
/// **Why is this bad?** Not too much, in fact it's a common pattern in Rust
/// code. Still, some argue that name shadowing like this hurts readability,
/// because a value may be bound to different things depending on position in
/// the code.
///
/// **Known problems:** This lint, as the other shadowing related lints,
/// currently only catches very simple patterns.
///
/// **Example:**
/// ```rust
/// let x = 2;
/// let x = x + 1;
/// ```
/// use different variable name:
/// ```rust
/// let x = 2;
/// let y = x + 1;
/// ```
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pub SHADOW_REUSE,
restriction,
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"rebinding a name to an expression that re-uses the original value, e.g., `let x = x + 1`"
}
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declare_clippy_lint! {
/// **What it does:** Checks for bindings that shadow other bindings already in
/// scope, either without a initialization or with one that does not even use
/// the original value.
///
/// **Why is this bad?** Name shadowing can hurt readability, especially in
/// large code bases, because it is easy to lose track of the active binding at
/// any place in the code. This can be alleviated by either giving more specific
/// names to bindings or introducing more scopes to contain the bindings.
///
/// **Known problems:** This lint, as the other shadowing related lints,
/// currently only catches very simple patterns.
///
/// **Example:**
/// ```rust
/// # let y = 1;
/// # let z = 2;
/// let x = y;
/// let x = z; // shadows the earlier binding
/// ```
pub SHADOW_UNRELATED,
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pedantic,
"rebinding a name without even using the original value"
}
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declare_lint_pass!(Shadow => [SHADOW_SAME, SHADOW_REUSE, SHADOW_UNRELATED]);
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impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Shadow {
fn check_fn(
&mut self,
cx: &LateContext<'a, 'tcx>,
_: FnKind<'tcx>,
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decl: &'tcx FnDecl<'_>,
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body: &'tcx Body<'_>,
_: Span,
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_: HirId,
) {
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if in_external_macro(cx.sess(), body.value.span) {
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return;
}
check_fn(cx, decl, body);
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}
}
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fn check_fn<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, decl: &'tcx FnDecl<'_>, body: &'tcx Body<'_>) {
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let mut bindings = Vec::with_capacity(decl.inputs.len());
for arg in iter_input_pats(decl, body) {
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if let PatKind::Binding(.., ident, _) = arg.pat.kind {
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bindings.push((ident.name, ident.span))
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}
}
check_expr(cx, &body.value, &mut bindings);
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}
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fn check_block<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, block: &'tcx Block<'_>, bindings: &mut Vec<(Name, Span)>) {
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let len = bindings.len();
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for stmt in block.stmts {
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match stmt.kind {
StmtKind::Local(ref local) => check_local(cx, local, bindings),
StmtKind::Expr(ref e) | StmtKind::Semi(ref e) => check_expr(cx, e, bindings),
StmtKind::Item(..) => {},
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}
}
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if let Some(ref o) = block.expr {
check_expr(cx, o, bindings);
}
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bindings.truncate(len);
}
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fn check_local<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, local: &'tcx Local<'_>, bindings: &mut Vec<(Name, Span)>) {
if in_external_macro(cx.sess(), local.span) {
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return;
}
if higher::is_from_for_desugar(local) {
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return;
}
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let Local {
ref pat,
ref ty,
ref init,
span,
..
} = *local;
if let Some(ref t) = *ty {
check_ty(cx, t, bindings)
}
if let Some(ref o) = *init {
check_expr(cx, o, bindings);
check_pat(cx, pat, Some(o), span, bindings);
} else {
check_pat(cx, pat, None, span, bindings);
}
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}
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fn is_binding(cx: &LateContext<'_, '_>, pat_id: HirId) -> bool {
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let var_ty = cx.tables.node_type_opt(pat_id);
if let Some(var_ty) = var_ty {
match var_ty.kind {
ty::Adt(..) => false,
_ => true,
}
} else {
false
}
}
fn check_pat<'a, 'tcx>(
cx: &LateContext<'a, 'tcx>,
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pat: &'tcx Pat<'_>,
init: Option<&'tcx Expr<'_>>,
span: Span,
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bindings: &mut Vec<(Name, Span)>,
) {
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// TODO: match more stuff / destructuring
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match pat.kind {
PatKind::Binding(.., ident, ref inner) => {
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let name = ident.name;
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if is_binding(cx, pat.hir_id) {
let mut new_binding = true;
for tup in bindings.iter_mut() {
if tup.0 == name {
lint_shadow(cx, name, span, pat.span, init, tup.1);
tup.1 = ident.span;
new_binding = false;
break;
}
}
if new_binding {
bindings.push((name, ident.span));
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}
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}
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if let Some(ref p) = *inner {
check_pat(cx, p, init, span, bindings);
}
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},
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PatKind::Struct(_, pfields, _) => {
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if let Some(init_struct) = init {
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if let ExprKind::Struct(_, ref efields, _) = init_struct.kind {
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for field in pfields {
let name = field.ident.name;
let efield = efields
.iter()
.find_map(|f| if f.ident.name == name { Some(&*f.expr) } else { None });
check_pat(cx, &field.pat, efield, span, bindings);
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}
} else {
for field in pfields {
check_pat(cx, &field.pat, init, span, bindings);
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}
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}
} else {
for field in pfields {
check_pat(cx, &field.pat, None, span, bindings);
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}
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}
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},
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PatKind::Tuple(inner, _) => {
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if let Some(init_tup) = init {
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if let ExprKind::Tup(ref tup) = init_tup.kind {
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for (i, p) in inner.iter().enumerate() {
check_pat(cx, p, Some(&tup[i]), p.span, bindings);
}
} else {
for p in inner {
check_pat(cx, p, init, span, bindings);
}
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}
} else {
for p in inner {
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check_pat(cx, p, None, span, bindings);
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}
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}
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},
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PatKind::Box(ref inner) => {
if let Some(initp) = init {
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if let ExprKind::Box(ref inner_init) = initp.kind {
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check_pat(cx, inner, Some(&**inner_init), span, bindings);
} else {
check_pat(cx, inner, init, span, bindings);
}
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} else {
check_pat(cx, inner, init, span, bindings);
}
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},
PatKind::Ref(ref inner, _) => check_pat(cx, inner, init, span, bindings),
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// PatVec(Vec<P<Pat>>, Option<P<Pat>>, Vec<P<Pat>>),
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_ => (),
}
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}
fn lint_shadow<'a, 'tcx>(
cx: &LateContext<'a, 'tcx>,
name: Name,
span: Span,
pattern_span: Span,
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init: Option<&'tcx Expr<'_>>,
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prev_span: Span,
) {
if let Some(expr) = init {
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if is_self_shadow(name, expr) {
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span_lint_and_then(
cx,
SHADOW_SAME,
span,
&format!(
"`{}` is shadowed by itself in `{}`",
snippet(cx, pattern_span, "_"),
snippet(cx, expr.span, "..")
),
|diag| {
diag.span_note(prev_span, "previous binding is here");
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},
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);
} else if contains_name(name, expr) {
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span_lint_and_then(
cx,
SHADOW_REUSE,
pattern_span,
&format!(
"`{}` is shadowed by `{}` which reuses the original value",
snippet(cx, pattern_span, "_"),
snippet(cx, expr.span, "..")
),
|diag| {
diag.span_note(expr.span, "initialization happens here");
diag.span_note(prev_span, "previous binding is here");
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},
);
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} else {
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span_lint_and_then(
cx,
SHADOW_UNRELATED,
pattern_span,
&format!(
"`{}` is shadowed by `{}`",
snippet(cx, pattern_span, "_"),
snippet(cx, expr.span, "..")
),
|diag| {
diag.span_note(expr.span, "initialization happens here");
diag.span_note(prev_span, "previous binding is here");
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},
);
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}
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} else {
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span_lint_and_then(
cx,
SHADOW_UNRELATED,
span,
&format!("`{}` shadows a previous declaration", snippet(cx, pattern_span, "_")),
|diag| {
diag.span_note(prev_span, "previous binding is here");
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},
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);
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}
}
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fn check_expr<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr<'_>, bindings: &mut Vec<(Name, Span)>) {
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if in_external_macro(cx.sess(), expr.span) {
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return;
}
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match expr.kind {
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ExprKind::Unary(_, ref e)
| ExprKind::Field(ref e, _)
| ExprKind::AddrOf(_, _, ref e)
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| ExprKind::Box(ref e) => check_expr(cx, e, bindings),
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ExprKind::Block(ref block, _) | ExprKind::Loop(ref block, _, _) => check_block(cx, block, bindings),
// ExprKind::Call
// ExprKind::MethodCall
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ExprKind::Array(v) | ExprKind::Tup(v) => {
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for e in v {
check_expr(cx, e, bindings)
}
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},
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ExprKind::Match(ref init, arms, _) => {
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check_expr(cx, init, bindings);
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let len = bindings.len();
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for arm in arms {
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check_pat(cx, &arm.pat, Some(&**init), arm.pat.span, bindings);
// This is ugly, but needed to get the right type
if let Some(ref guard) = arm.guard {
match guard {
Guard::If(if_expr) => check_expr(cx, if_expr, bindings),
}
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}
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check_expr(cx, &arm.body, bindings);
bindings.truncate(len);
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}
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},
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_ => (),
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}
}
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fn check_ty<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, ty: &'tcx Ty<'_>, bindings: &mut Vec<(Name, Span)>) {
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match ty.kind {
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TyKind::Slice(ref sty) => check_ty(cx, sty, bindings),
TyKind::Array(ref fty, ref anon_const) => {
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check_ty(cx, fty, bindings);
check_expr(cx, &cx.tcx.hir().body(anon_const.body).value, bindings);
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},
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TyKind::Ptr(MutTy { ty: ref mty, .. }) | TyKind::Rptr(_, MutTy { ty: ref mty, .. }) => {
check_ty(cx, mty, bindings)
},
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TyKind::Tup(tup) => {
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for t in tup {
check_ty(cx, t, bindings)
}
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},
TyKind::Typeof(ref anon_const) => check_expr(cx, &cx.tcx.hir().body(anon_const.body).value, bindings),
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_ => (),
}
}
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fn is_self_shadow(name: Name, expr: &Expr<'_>) -> bool {
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match expr.kind {
ExprKind::Box(ref inner) | ExprKind::AddrOf(_, _, ref inner) => is_self_shadow(name, inner),
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ExprKind::Block(ref block, _) => {
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block.stmts.is_empty() && block.expr.as_ref().map_or(false, |e| is_self_shadow(name, e))
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},
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ExprKind::Unary(op, ref inner) => (UnOp::UnDeref == op) && is_self_shadow(name, inner),
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ExprKind::Path(QPath::Resolved(_, ref path)) => path_eq_name(name, path),
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_ => false,
}
}
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fn path_eq_name(name: Name, path: &Path<'_>) -> bool {
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!path.is_global() && path.segments.len() == 1 && path.segments[0].ident.as_str() == name.as_str()
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}