clippy_lints/src/ref_option_ref.rs

   1 use crate::utils::{last_path_segment, snippet, span_lint_and_sugg};
   2 use rustc_hir::{GenericArg, Mutability, Ty, TyKind};
   3 use rustc_lint::{LateContext, LateLintPass};
   4 use rustc_session::{declare_lint_pass, declare_tool_lint};
   5 use rustc_span::symbol::sym;
   6
   7 use if_chain::if_chain;
   8 use rustc_errors::Applicability;
   9
  10 declare_clippy_lint! {
  11     /// **What it does:** Checks for usage of `&Option<&T>`.
  12     ///
  13     /// **Why is this bad?** Since `&` is Copy, it's useless to have a
  14     /// reference on `Option<&T>`.
  15     ///
  16     /// **Known problems:** It may be irrevelent to use this lint on
  17     /// public API code as it will make a breaking change to apply it.
  18     ///
  19     /// **Example:**
  20     ///
  21     /// ```rust,ignore
  22     /// let x: &Option<&u32> = &Some(&0u32);
  23     /// ```
  24     /// Use instead:
  25     /// ```rust,ignore
  26     /// let x: Option<&u32> = Some(&0u32);
  27     /// ```
  28     pub REF_OPTION_REF,
  29     pedantic,
  30     "use `Option<&T>` instead of `&Option<&T>`"
  31 }
  32
  33 declare_lint_pass!(RefOptionRef => [REF_OPTION_REF]);
  34
  35 impl<'tcx> LateLintPass<'tcx> for RefOptionRef {
  36     fn check_ty(&mut self, cx: &LateContext<'tcx>, ty: &'tcx Ty<'tcx>) {
  37         if_chain! {
  38             if let TyKind::Rptr(_, ref mut_ty) = ty.kind;
  39             if mut_ty.mutbl == Mutability::Not;
  40             if let TyKind::Path(ref qpath) = &mut_ty.ty.kind;
  41             let last = last_path_segment(qpath);
  42             if let Some(res) = last.res;
  43             if let Some(def_id) = res.opt_def_id();
  44
  45             if cx.tcx.is_diagnostic_item(sym::option_type, def_id);
  46             if let Some(ref params) = last_path_segment(qpath).args ;
  47             if !params.parenthesized;
  48             if let Some(inner_ty) = params.args.iter().find_map(|arg| match arg {
  49                 GenericArg::Type(inner_ty) => Some(inner_ty),
  50                 _ => None,
  51             });
  52             if let TyKind::Rptr(_, _) = inner_ty.kind;
  53
  54             then {
  55                 span_lint_and_sugg(
  56                     cx,
  57                     REF_OPTION_REF,
  58                     ty.span,
  59                     "since `&` implements the `Copy` trait, `&Option<&T>` can be simplified to `Option<&T>`",
  60                     "try",
  61                     format!("Option<{}>", &snippet(cx, inner_ty.span, "..")),
  62                     Applicability::MaybeIncorrect,
  63                 );
  64             }
  65         }
  66     }
  67 }