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

   1 use clippy_utils::diagnostics::span_lint_and_sugg;
   2 use clippy_utils::source::snippet_opt;
   3 use clippy_utils::ty::is_type_diagnostic_item;
   4 use rustc_errors::Applicability;
   5 use rustc_hir::{Expr, ExprKind};
   6 use rustc_lint::{LateContext, LateLintPass};
   7 use rustc_session::{declare_lint_pass, declare_tool_lint};
   8 use rustc_span::symbol::sym;
   9
  10 declare_clippy_lint! {
  11     /// ### What it does
  12     /// Checks for no-op uses of Option::{as_deref,as_deref_mut},
  13     /// for example, `Option<&T>::as_deref()` returns the same type.
  14     ///
  15     /// ### Why is this bad?
  16     /// Redundant code and improving readability.
  17     ///
  18     /// ### Example
  19     /// ```rust
  20     /// let a = Some(&1);
  21     /// let b = a.as_deref(); // goes from Option<&i32> to Option<&i32>
  22     /// ```
  23     /// Could be written as:
  24     /// ```rust
  25     /// let a = Some(&1);
  26     /// let b = a;
  27     /// ```
  28     #[clippy::version = "1.57.0"]
  29     pub NEEDLESS_OPTION_AS_DEREF,
  30     complexity,
  31     "no-op use of `deref` or `deref_mut` method to `Option`."
  32 }
  33
  34 declare_lint_pass!(OptionNeedlessDeref=> [
  35     NEEDLESS_OPTION_AS_DEREF,
  36 ]);
  37
  38 impl<'tcx> LateLintPass<'tcx> for OptionNeedlessDeref {
  39     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
  40         if expr.span.from_expansion() {
  41             return;
  42         }
  43         let typeck = cx.typeck_results();
  44         let outer_ty = typeck.expr_ty(expr);
  45
  46         if_chain! {
  47             if is_type_diagnostic_item(cx,outer_ty,sym::Option);
  48             if let ExprKind::MethodCall(path, [sub_expr], _) = expr.kind;
  49             let symbol = path.ident.as_str();
  50             if symbol == "as_deref" || symbol == "as_deref_mut";
  51             if outer_ty == typeck.expr_ty(sub_expr);
  52             then{
  53                 span_lint_and_sugg(
  54                     cx,
  55                     NEEDLESS_OPTION_AS_DEREF,
  56                     expr.span,
  57                     "derefed type is same as origin",
  58                     "try this",
  59                     snippet_opt(cx,sub_expr.span).unwrap(),
  60                     Applicability::MachineApplicable
  61                 );
  62             }
  63         }
  64     }
  65 }