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use clippy_utils::diagnostics::span_lint_and_sugg;
use clippy_utils::last_path_segment;
use clippy_utils::source::snippet;
use rustc_errors::Applicability;
use rustc_hir::{GenericArg, GenericArgsParentheses, Mutability, Ty, TyKind};
use rustc_lint::{LateContext, LateLintPass};
use rustc_session::declare_lint_pass;
use rustc_span::symbol::sym;
declare_clippy_lint! {
/// ### What it does
/// Checks for usage of `&Option<&T>`.
///
/// ### Why is this bad?
/// Since `&` is Copy, it's useless to have a
/// reference on `Option<&T>`.
///
/// ### Known problems
/// It may be irrelevant to use this lint on
/// public API code as it will make a breaking change to apply it.
///
/// ### Example
/// ```rust,ignore
/// let x: &Option<&u32> = &Some(&0u32);
/// ```
/// Use instead:
/// ```rust,ignore
/// let x: Option<&u32> = Some(&0u32);
/// ```
#[clippy::version = "1.49.0"]
pub REF_OPTION_REF,
pedantic,
"use `Option<&T>` instead of `&Option<&T>`"
}
declare_lint_pass!(RefOptionRef => [REF_OPTION_REF]);
impl<'tcx> LateLintPass<'tcx> for RefOptionRef {
fn check_ty(&mut self, cx: &LateContext<'tcx>, ty: &'tcx Ty<'tcx>) {
if let TyKind::Ref(_, ref mut_ty) = ty.kind
&& mut_ty.mutbl == Mutability::Not
&& let TyKind::Path(ref qpath) = &mut_ty.ty.kind
&& let last = last_path_segment(qpath)
&& let Some(def_id) = last.res.opt_def_id()
&& cx.tcx.is_diagnostic_item(sym::Option, def_id)
&& let Some(params) = last_path_segment(qpath).args
&& params.parenthesized == GenericArgsParentheses::No
&& let Some(inner_ty) = params.args.iter().find_map(|arg| match arg {
GenericArg::Type(inner_ty) => Some(inner_ty),
_ => None,
})
&& let TyKind::Ref(_, ref inner_mut_ty) = inner_ty.kind
&& inner_mut_ty.mutbl == Mutability::Not
{
span_lint_and_sugg(
cx,
REF_OPTION_REF,
ty.span,
"since `&` implements the `Copy` trait, `&Option<&T>` can be simplified to `Option<&T>`",
"try",
format!("Option<{}>", &snippet(cx, inner_ty.span, "..")),
Applicability::MaybeIncorrect,
);
}
}
}
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