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use clippy_utils::diagnostics::span_lint_and_help;
use clippy_utils::ty::{implements_trait, is_type_diagnostic_item};
use if_chain::if_chain;
use rustc_hir as hir;
use rustc_lint::LateContext;
use rustc_middle::ty::{self, Ty};
use rustc_span::sym;
use super::OK_EXPECT;
/// lint use of `ok().expect()` for `Result`s
pub(super) fn check(cx: &LateContext<'_>, expr: &hir::Expr<'_>, recv: &hir::Expr<'_>) {
if_chain! {
// lint if the caller of `ok()` is a `Result`
if is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(recv), sym::Result);
let result_type = cx.typeck_results().expr_ty(recv);
if let Some(error_type) = get_error_type(cx, result_type);
if has_debug_impl(error_type, cx);
then {
span_lint_and_help(
cx,
OK_EXPECT,
expr.span,
"called `ok().expect()` on a `Result` value",
None,
"you can call `expect()` directly on the `Result`",
);
}
}
}
/// Given a `Result<T, E>` type, return its error type (`E`).
fn get_error_type<'a>(cx: &LateContext<'_>, ty: Ty<'a>) -> Option<Ty<'a>> {
match ty.kind() {
ty::Adt(_, substs) if is_type_diagnostic_item(cx, ty, sym::Result) => substs.types().nth(1),
_ => None,
}
}
/// This checks whether a given type is known to implement Debug.
fn has_debug_impl<'tcx>(ty: Ty<'tcx>, cx: &LateContext<'tcx>) -> bool {
cx.tcx
.get_diagnostic_item(sym::Debug)
.map_or(false, |debug| implements_trait(cx, ty, debug, &[]))
}
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