src/tools/clippy/clippy_lints/src/methods/err_expect.rs

   1 use super::ERR_EXPECT;
   2 use clippy_utils::diagnostics::span_lint_and_sugg;
   3 use clippy_utils::ty::implements_trait;
   4 use clippy_utils::{meets_msrv, msrvs, ty::is_type_diagnostic_item};
   5 use rustc_errors::Applicability;
   6 use rustc_lint::LateContext;
   7 use rustc_middle::ty;
   8 use rustc_middle::ty::Ty;
   9 use rustc_semver::RustcVersion;
  10 use rustc_span::{sym, Span};
  11
  12 pub(super) fn check(
  13     cx: &LateContext<'_>,
  14     _expr: &rustc_hir::Expr<'_>,
  15     recv: &rustc_hir::Expr<'_>,
  16     msrv: Option<RustcVersion>,
  17     expect_span: Span,
  18     err_span: Span,
  19 ) {
  20     if_chain! {
  21         if is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(recv), sym::Result);
  22         // Test the version to make sure the lint can be showed (expect_err has been
  23         // introduced in rust 1.17.0 : https://github.com/rust-lang/rust/pull/38982)
  24         if meets_msrv(msrv, msrvs::EXPECT_ERR);
  25
  26         // Grabs the `Result<T, E>` type
  27         let result_type = cx.typeck_results().expr_ty(recv);
  28         // Tests if the T type in a `Result<T, E>` is not None
  29         if let Some(data_type) = get_data_type(cx, result_type);
  30         // Tests if the T type in a `Result<T, E>` implements debug
  31         if has_debug_impl(data_type, cx);
  32
  33         then {
  34             span_lint_and_sugg(
  35                 cx,
  36                 ERR_EXPECT,
  37                 err_span.to(expect_span),
  38                 "called `.err().expect()` on a `Result` value",
  39                 "try",
  40                 "expect_err".to_string(),
  41                 Applicability::MachineApplicable
  42         );
  43         }
  44     };
  45 }
  46
  47 /// Given a `Result<T, E>` type, return its data (`T`).
  48 fn get_data_type<'a>(cx: &LateContext<'_>, ty: Ty<'a>) -> Option<Ty<'a>> {
  49     match ty.kind() {
  50         ty::Adt(_, substs) if is_type_diagnostic_item(cx, ty, sym::Result) => substs.types().next(),
  51         _ => None,
  52     }
  53 }
  54
  55 /// Given a type, very if the Debug trait has been impl'd
  56 fn has_debug_impl<'tcx>(ty: Ty<'tcx>, cx: &LateContext<'tcx>) -> bool {
  57     cx.tcx
  58         .get_diagnostic_item(sym::Debug)
  59         .map_or(false, |debug| implements_trait(cx, ty, debug, &[]))
  60 }