src/tools/clippy/clippy_lints/src/needless_option_as_deref.rs

   1 use clippy_utils::diagnostics::span_lint_and_sugg;
   2 use clippy_utils::in_macro;
   3 use clippy_utils::source::snippet_opt;
   4 use clippy_utils::ty::is_type_diagnostic_item;
   5 use rustc_errors::Applicability;
   6 use rustc_hir::{Expr, ExprKind};
   7 use rustc_lint::{LateContext, LateLintPass};
   8 use rustc_middle::ty::TyS;
   9 use rustc_session::{declare_lint_pass, declare_tool_lint};
  10 use rustc_span::symbol::sym;
  11
  12 declare_clippy_lint! {
  13     /// ### What it does
  14     /// Checks for no-op uses of Option::{as_deref,as_deref_mut},
  15     /// for example, `Option<&T>::as_deref()` returns the same type.
  16     ///
  17     /// ### Why is this bad?
  18     /// Redundant code and improving readability.
  19     ///
  20     /// ### Example
  21     /// ```rust
  22     /// let a = Some(&1);
  23     /// let b = a.as_deref(); // goes from Option<&i32> to Option<&i32>
  24     /// ```
  25     /// Could be written as:
  26     /// ```rust
  27     /// let a = Some(&1);
  28     /// let b = a;
  29     /// ```
  30     pub NEEDLESS_OPTION_AS_DEREF,
  31     complexity,
  32     "no-op use of `deref` or `deref_mut` method to `Option`."
  33 }
  34
  35 declare_lint_pass!(OptionNeedlessDeref=> [
  36     NEEDLESS_OPTION_AS_DEREF,
  37 ]);
  38
  39 impl<'tcx> LateLintPass<'tcx> for OptionNeedlessDeref {
  40     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
  41         if expr.span.from_expansion() || in_macro(expr.span) {
  42             return;
  43         }
  44         let typeck = cx.typeck_results();
  45         let outer_ty = typeck.expr_ty(expr);
  46
  47         if_chain! {
  48             if is_type_diagnostic_item(cx,outer_ty,sym::Option);
  49             if let ExprKind::MethodCall(path, _, [sub_expr], _) = expr.kind;
  50             let symbol = path.ident.as_str();
  51             if symbol=="as_deref" || symbol=="as_deref_mut";
  52             if TyS::same_type( outer_ty, typeck.expr_ty(sub_expr) );
  53             then{
  54                 span_lint_and_sugg(
  55                     cx,
  56                     NEEDLESS_OPTION_AS_DEREF,
  57                     expr.span,
  58                     "derefed type is same as origin",
  59                     "try this",
  60                     snippet_opt(cx,sub_expr.span).unwrap(),
  61                     Applicability::MachineApplicable
  62                 );
  63             }
  64         }
  65     }
  66 }