1 use clippy_utils::diagnostics::span_lint_and_sugg; 2 use clippy_utils::last_path_segment; 3 use clippy_utils::source::snippet; 4 use if_chain::if_chain; 5 use rustc_errors::Applicability; 6 use rustc_hir::{GenericArg, GenericArgsParentheses, Mutability, Ty, TyKind}; 7 use rustc_lint::{LateContext, LateLintPass}; 8 use rustc_session::{declare_lint_pass, declare_tool_lint}; 9 use rustc_span::symbol::sym; 10 11 declare_clippy_lint! { 12 /// ### What it does 13 /// Checks for usage of `&Option<&T>`. 14 /// 15 /// ### Why is this bad? 16 /// Since `&` is Copy, it's useless to have a 17 /// reference on `Option<&T>`. 18 /// 19 /// ### Known problems 20 /// It may be irrelevant to use this lint on 21 /// public API code as it will make a breaking change to apply it. 22 /// 23 /// ### Example 24 /// ```rust,ignore 25 /// let x: &Option<&u32> = &Some(&0u32); 26 /// ``` 27 /// Use instead: 28 /// ```rust,ignore 29 /// let x: Option<&u32> = Some(&0u32); 30 /// ``` 31 #[clippy::version = "1.49.0"] 32 pub REF_OPTION_REF, 33 pedantic, 34 "use `Option<&T>` instead of `&Option<&T>`" 35 } 36 37 declare_lint_pass!(RefOptionRef => [REF_OPTION_REF]); 38 39 impl<'tcx> LateLintPass<'tcx> for RefOptionRef { check_ty(&mut self, cx: &LateContext<'tcx>, ty: &'tcx Ty<'tcx>)40 fn check_ty(&mut self, cx: &LateContext<'tcx>, ty: &'tcx Ty<'tcx>) { 41 if_chain! { 42 if let TyKind::Ref(_, ref mut_ty) = ty.kind; 43 if mut_ty.mutbl == Mutability::Not; 44 if let TyKind::Path(ref qpath) = &mut_ty.ty.kind; 45 let last = last_path_segment(qpath); 46 if let Some(def_id) = last.res.opt_def_id(); 47 48 if cx.tcx.is_diagnostic_item(sym::Option, def_id); 49 if let Some(params) = last_path_segment(qpath).args ; 50 if params.parenthesized == GenericArgsParentheses::No; 51 if let Some(inner_ty) = params.args.iter().find_map(|arg| match arg { 52 GenericArg::Type(inner_ty) => Some(inner_ty), 53 _ => None, 54 }); 55 if let TyKind::Ref(_, ref inner_mut_ty) = inner_ty.kind; 56 if inner_mut_ty.mutbl == Mutability::Not; 57 58 then { 59 span_lint_and_sugg( 60 cx, 61 REF_OPTION_REF, 62 ty.span, 63 "since `&` implements the `Copy` trait, `&Option<&T>` can be simplified to `Option<&T>`", 64 "try", 65 format!("Option<{}>", &snippet(cx, inner_ty.span, "..")), 66 Applicability::MaybeIncorrect, 67 ); 68 } 69 } 70 } 71 } 72