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use clippy_utils::diagnostics::span_lint_and_sugg;
use clippy_utils::last_path_segment;
use clippy_utils::source::snippet;
use if_chain::if_chain;
use rustc_errors::Applicability;
use rustc_hir::{self as hir, def_id::DefId, GenericArg, QPath, TyKind};
use rustc_hir_analysis::hir_ty_to_ty;
use rustc_lint::LateContext;
use rustc_middle::ty::layout::LayoutOf;
use rustc_middle::ty::TypeVisitable;
use rustc_span::symbol::sym;
use super::VEC_BOX;
pub(super) fn check(
cx: &LateContext<'_>,
hir_ty: &hir::Ty<'_>,
qpath: &QPath<'_>,
def_id: DefId,
box_size_threshold: u64,
) -> bool {
if cx.tcx.is_diagnostic_item(sym::Vec, def_id) {
if_chain! {
// Get the _ part of Vec<_>
if let Some(last) = last_path_segment(qpath).args;
if let Some(ty) = last.args.iter().find_map(|arg| match arg {
GenericArg::Type(ty) => Some(ty),
_ => None,
});
// ty is now _ at this point
if let TyKind::Path(ref ty_qpath) = ty.kind;
let res = cx.qpath_res(ty_qpath, ty.hir_id);
if let Some(def_id) = res.opt_def_id();
if Some(def_id) == cx.tcx.lang_items().owned_box();
// At this point, we know ty is Box<T>, now get T
if let Some(last) = last_path_segment(ty_qpath).args;
if let Some(boxed_ty) = last.args.iter().find_map(|arg| match arg {
GenericArg::Type(ty) => Some(ty),
_ => None,
});
let ty_ty = hir_ty_to_ty(cx.tcx, boxed_ty);
if !ty_ty.has_escaping_bound_vars();
if ty_ty.is_sized(cx.tcx, cx.param_env);
if let Ok(ty_ty_size) = cx.layout_of(ty_ty).map(|l| l.size.bytes());
if ty_ty_size < box_size_threshold;
then {
span_lint_and_sugg(
cx,
VEC_BOX,
hir_ty.span,
"`Vec<T>` is already on the heap, the boxing is unnecessary",
"try",
format!("Vec<{}>", snippet(cx, boxed_ty.span, "..")),
Applicability::MachineApplicable,
);
true
} else {
false
}
}
} else {
false
}
}
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