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use clippy_utils::diagnostics::span_lint_and_sugg;
use clippy_utils::source::snippet_with_applicability;
use clippy_utils::ty::is_type_diagnostic_item;
use clippy_utils::{get_parent_expr, is_lang_ctor, match_def_path, paths};
use if_chain::if_chain;
use rustc_errors::Applicability;
use rustc_hir::LangItem::ResultErr;
use rustc_hir::{Expr, ExprKind, LangItem, MatchSource, QPath};
use rustc_lint::LateContext;
use rustc_middle::ty::{self, Ty};
use rustc_span::{hygiene, sym};
use super::TRY_ERR;
pub(super) fn check<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, scrutinee: &'tcx Expr<'_>) {
// Looks for a structure like this:
// match ::std::ops::Try::into_result(Err(5)) {
// ::std::result::Result::Err(err) =>
// #[allow(unreachable_code)]
// return ::std::ops::Try::from_error(::std::convert::From::from(err)),
// ::std::result::Result::Ok(val) =>
// #[allow(unreachable_code)]
// val,
// };
if_chain! {
if let ExprKind::Call(match_fun, [try_arg, ..]) = scrutinee.kind;
if let ExprKind::Path(ref match_fun_path) = match_fun.kind;
if matches!(match_fun_path, QPath::LangItem(LangItem::TryTraitBranch, ..));
if let ExprKind::Call(err_fun, [err_arg, ..]) = try_arg.kind;
if let ExprKind::Path(ref err_fun_path) = err_fun.kind;
if is_lang_ctor(cx, err_fun_path, ResultErr);
if let Some(return_ty) = find_return_type(cx, &expr.kind);
then {
let prefix;
let suffix;
let err_ty;
if let Some(ty) = result_error_type(cx, return_ty) {
prefix = "Err(";
suffix = ")";
err_ty = ty;
} else if let Some(ty) = poll_result_error_type(cx, return_ty) {
prefix = "Poll::Ready(Err(";
suffix = "))";
err_ty = ty;
} else if let Some(ty) = poll_option_result_error_type(cx, return_ty) {
prefix = "Poll::Ready(Some(Err(";
suffix = ")))";
err_ty = ty;
} else {
return;
};
let expr_err_ty = cx.typeck_results().expr_ty(err_arg);
let span = hygiene::walk_chain(err_arg.span, try_arg.span.ctxt());
let mut applicability = Applicability::MachineApplicable;
let origin_snippet = snippet_with_applicability(cx, span, "_", &mut applicability);
let ret_prefix = if get_parent_expr(cx, expr).map_or(false, |e| matches!(e.kind, ExprKind::Ret(_))) {
"" // already returns
} else {
"return "
};
let suggestion = if err_ty == expr_err_ty {
format!("{}{}{}{}", ret_prefix, prefix, origin_snippet, suffix)
} else {
format!("{}{}{}.into(){}", ret_prefix, prefix, origin_snippet, suffix)
};
span_lint_and_sugg(
cx,
TRY_ERR,
expr.span,
"returning an `Err(_)` with the `?` operator",
"try this",
suggestion,
applicability,
);
}
}
}
/// Finds function return type by examining return expressions in match arms.
fn find_return_type<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx ExprKind<'_>) -> Option<Ty<'tcx>> {
if let ExprKind::Match(_, arms, MatchSource::TryDesugar) = expr {
for arm in arms.iter() {
if let ExprKind::Ret(Some(ret)) = arm.body.kind {
return Some(cx.typeck_results().expr_ty(ret));
}
}
}
None
}
/// Extracts the error type from Result<T, E>.
fn result_error_type<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> Option<Ty<'tcx>> {
if_chain! {
if let ty::Adt(_, subst) = ty.kind();
if is_type_diagnostic_item(cx, ty, sym::Result);
then {
Some(subst.type_at(1))
} else {
None
}
}
}
/// Extracts the error type from Poll<Result<T, E>>.
fn poll_result_error_type<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> Option<Ty<'tcx>> {
if_chain! {
if let ty::Adt(def, subst) = ty.kind();
if match_def_path(cx, def.did(), &paths::POLL);
let ready_ty = subst.type_at(0);
if let ty::Adt(ready_def, ready_subst) = ready_ty.kind();
if cx.tcx.is_diagnostic_item(sym::Result, ready_def.did());
then {
Some(ready_subst.type_at(1))
} else {
None
}
}
}
/// Extracts the error type from Poll<Option<Result<T, E>>>.
fn poll_option_result_error_type<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> Option<Ty<'tcx>> {
if_chain! {
if let ty::Adt(def, subst) = ty.kind();
if match_def_path(cx, def.did(), &paths::POLL);
let ready_ty = subst.type_at(0);
if let ty::Adt(ready_def, ready_subst) = ready_ty.kind();
if cx.tcx.is_diagnostic_item(sym::Option, ready_def.did());
let some_ty = ready_subst.type_at(0);
if let ty::Adt(some_def, some_subst) = some_ty.kind();
if cx.tcx.is_diagnostic_item(sym::Result, some_def.did());
then {
Some(some_subst.type_at(1))
} else {
None
}
}
}
|
