[useless_vec]: detect unnecessary vec![_]
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y21
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f93df98b84
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1 changed files with 42 additions and 55 deletions
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@ -8,7 +8,6 @@ use clippy_utils::ty::is_copy;
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use clippy_utils::visitors::for_each_local_use_after_expr;
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use clippy_utils::{get_parent_expr, higher, is_trait_method};
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use if_chain::if_chain;
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use rustc_ast::BindingAnnotation;
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use rustc_errors::Applicability;
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use rustc_hir::{BorrowKind, Expr, ExprKind, Mutability, Node, PatKind};
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use rustc_lint::{LateContext, LateLintPass};
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@ -54,11 +53,7 @@ declare_clippy_lint! {
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impl_lint_pass!(UselessVec => [USELESS_VEC]);
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fn adjusts_to_slice(cx: &LateContext<'_>, e: &Expr<'_>) -> bool {
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if let ty::Ref(_, ty, _) = cx.typeck_results().expr_ty_adjusted(e).kind() {
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ty.is_slice()
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} else {
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false
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}
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matches!(cx.typeck_results().expr_ty_adjusted(e).kind(), ty::Ref(_, ty, _) if ty.is_slice())
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}
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/// Checks if the given expression is a method call to a `Vec` method
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@ -76,13 +71,21 @@ fn is_allowed_vec_method(cx: &LateContext<'_>, e: &Expr<'_>) -> bool {
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impl<'tcx> LateLintPass<'tcx> for UselessVec {
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fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
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// search for `&vec![_]` expressions where the adjusted type is `&[_]`
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// search for `&vec![_]` or `vec![_]` expressions where the adjusted type is `&[_]`
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if_chain! {
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if adjusts_to_slice(cx, expr);
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if let ExprKind::AddrOf(BorrowKind::Ref, mutability, addressee) = expr.kind;
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if let Some(vec_args) = higher::VecArgs::hir(cx, addressee);
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if let Some(vec_args) = higher::VecArgs::hir(cx, expr.peel_borrows());
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then {
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self.check_vec_macro(cx, &vec_args, mutability, expr.span, SuggestSlice::Yes);
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let (suggest_slice, span) = if let ExprKind::AddrOf(BorrowKind::Ref, mutability, _) = expr.kind {
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// `expr` is `&vec![_]`, so suggest `&[_]` (or `&mut[_]` resp.)
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(SuggestedType::SliceRef(mutability), expr.span)
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} else {
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// `expr` is the `vec![_]` expansion, so suggest `[_]`
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// and also use the span of the actual `vec![_]` expression
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(SuggestedType::Array, expr.span.ctxt().outer_expn_data().call_site)
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};
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self.check_vec_macro(cx, &vec_args, span, suggest_slice);
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}
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}
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@ -93,7 +96,7 @@ impl<'tcx> LateLintPass<'tcx> for UselessVec {
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// for now ignore locals with type annotations.
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// this is to avoid compile errors when doing the suggestion here: let _: Vec<_> = vec![..];
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&& local.ty.is_none()
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&& let PatKind::Binding(BindingAnnotation(_, mutbl), id, ..) = local.pat.kind
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&& let PatKind::Binding(_, id, ..) = local.pat.kind
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&& is_copy(cx, vec_type(cx.typeck_results().expr_ty_adjusted(expr)))
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{
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let only_slice_uses = for_each_local_use_after_expr(cx, id, expr.hir_id, |expr| {
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@ -113,9 +116,8 @@ impl<'tcx> LateLintPass<'tcx> for UselessVec {
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self.check_vec_macro(
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cx,
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&vec_args,
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mutbl,
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expr.span.ctxt().outer_expn_data().call_site,
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SuggestSlice::No
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SuggestedType::Array
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);
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}
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}
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@ -128,7 +130,7 @@ impl<'tcx> LateLintPass<'tcx> for UselessVec {
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then {
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// report the error around the `vec!` not inside `<std macros>:`
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let span = arg.span.ctxt().outer_expn_data().call_site;
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self.check_vec_macro(cx, &vec_args, Mutability::Not, span, SuggestSlice::No);
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self.check_vec_macro(cx, &vec_args, span, SuggestedType::Array);
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}
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}
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}
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@ -137,11 +139,11 @@ impl<'tcx> LateLintPass<'tcx> for UselessVec {
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}
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#[derive(Copy, Clone)]
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enum SuggestSlice {
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enum SuggestedType {
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/// Suggest using a slice `&[..]` / `&mut [..]`
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Yes,
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SliceRef(Mutability),
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/// Suggest using an array: `[..]`
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No,
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Array,
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}
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impl UselessVec {
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@ -149,17 +151,11 @@ impl UselessVec {
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&mut self,
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cx: &LateContext<'tcx>,
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vec_args: &higher::VecArgs<'tcx>,
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mutability: Mutability,
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span: Span,
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suggest_slice: SuggestSlice,
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suggest_slice: SuggestedType,
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) {
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let mut applicability = Applicability::MachineApplicable;
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let (borrow_prefix_mut, borrow_prefix) = match suggest_slice {
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SuggestSlice::Yes => ("&mut ", "&"),
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SuggestSlice::No => ("", ""),
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};
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let snippet = match *vec_args {
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higher::VecArgs::Repeat(elem, len) => {
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if let Some(Constant::Int(len_constant)) = constant(cx, cx.typeck_results(), len) {
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@ -168,21 +164,13 @@ impl UselessVec {
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return;
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}
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match mutability {
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Mutability::Mut => {
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format!(
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"{borrow_prefix_mut}[{}; {}]",
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snippet_with_applicability(cx, elem.span, "elem", &mut applicability),
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snippet_with_applicability(cx, len.span, "len", &mut applicability)
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)
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},
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Mutability::Not => {
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format!(
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"{borrow_prefix}[{}; {}]",
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snippet_with_applicability(cx, elem.span, "elem", &mut applicability),
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snippet_with_applicability(cx, len.span, "len", &mut applicability)
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)
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},
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let elem = snippet_with_applicability(cx, elem.span, "elem", &mut applicability);
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let len = snippet_with_applicability(cx, len.span, "len", &mut applicability);
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match suggest_slice {
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SuggestedType::SliceRef(Mutability::Mut) => format!("&mut [{elem}; {len}]"),
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SuggestedType::SliceRef(Mutability::Not) => format!("&[{elem}; {len}]"),
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SuggestedType::Array => format!("[{elem}; {len}]"),
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}
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} else {
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return;
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@ -194,25 +182,24 @@ impl UselessVec {
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return;
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}
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let span = args[0].span.to(last.span);
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let args = snippet_with_applicability(cx, span, "..", &mut applicability);
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match mutability {
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Mutability::Mut => {
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format!(
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"{borrow_prefix_mut}[{}]",
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snippet_with_applicability(cx, span, "..", &mut applicability)
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)
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match suggest_slice {
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SuggestedType::SliceRef(Mutability::Mut) => {
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format!("&mut [{args}]")
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},
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Mutability::Not => {
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format!(
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"{borrow_prefix}[{}]",
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snippet_with_applicability(cx, span, "..", &mut applicability)
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)
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SuggestedType::SliceRef(Mutability::Not) => {
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format!("&[{args}]")
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},
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SuggestedType::Array => {
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format!("[{args}]")
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},
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}
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} else {
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match mutability {
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Mutability::Mut => format!("{borrow_prefix_mut}[]"),
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Mutability::Not => format!("{borrow_prefix}[]"),
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match suggest_slice {
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SuggestedType::SliceRef(Mutability::Mut) => "&mut []".to_owned(),
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SuggestedType::SliceRef(Mutability::Not) => "&[]".to_owned(),
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SuggestedType::Array => "[]".to_owned(),
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}
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}
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},
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@ -226,8 +213,8 @@ impl UselessVec {
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&format!(
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"you can use {} directly",
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match suggest_slice {
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SuggestSlice::Yes => "a slice",
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SuggestSlice::No => "an array",
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SuggestedType::SliceRef(_) => "a slice",
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SuggestedType::Array => "an array",
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}
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),
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snippet,
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