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