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|
use rustc_errors::Diagnostic;
use rustc_hir as hir;
use rustc_lint::{LateContext, LintContext};
use rustc_middle::lint::in_external_macro;
use rustc_middle::ty::{self, Ty};
use rustc_span::{sym, Span};
use clippy_utils::diagnostics::{span_lint_and_help, span_lint_and_then};
use clippy_utils::trait_ref_of_method;
use clippy_utils::ty::{approx_ty_size, is_type_diagnostic_item};
use super::{RESULT_LARGE_ERR, RESULT_UNIT_ERR};
/// The type of the `Err`-variant in a `std::result::Result` returned by the
/// given `FnDecl`
fn result_err_ty<'tcx>(
cx: &LateContext<'tcx>,
decl: &hir::FnDecl<'tcx>,
id: hir::def_id::LocalDefId,
item_span: Span,
) -> Option<(&'tcx hir::Ty<'tcx>, Ty<'tcx>)> {
if !in_external_macro(cx.sess(), item_span)
&& let hir::FnRetTy::Return(hir_ty) = decl.output
&& let ty = cx.tcx.erase_late_bound_regions(cx.tcx.fn_sig(id).output())
&& is_type_diagnostic_item(cx, ty, sym::Result)
&& let ty::Adt(_, substs) = ty.kind()
{
let err_ty = substs.type_at(1);
Some((hir_ty, err_ty))
} else {
None
}
}
pub(super) fn check_item<'tcx>(cx: &LateContext<'tcx>, item: &hir::Item<'tcx>, large_err_threshold: u64) {
if let hir::ItemKind::Fn(ref sig, _generics, _) = item.kind
&& let Some((hir_ty, err_ty)) = result_err_ty(cx, sig.decl, item.def_id, item.span)
{
if cx.access_levels.is_exported(item.def_id) {
let fn_header_span = item.span.with_hi(sig.decl.output.span().hi());
check_result_unit_err(cx, err_ty, fn_header_span);
}
check_result_large_err(cx, err_ty, hir_ty.span, large_err_threshold);
}
}
pub(super) fn check_impl_item<'tcx>(cx: &LateContext<'tcx>, item: &hir::ImplItem<'tcx>, large_err_threshold: u64) {
// Don't lint if method is a trait's implementation, we can't do anything about those
if let hir::ImplItemKind::Fn(ref sig, _) = item.kind
&& let Some((hir_ty, err_ty)) = result_err_ty(cx, sig.decl, item.def_id, item.span)
&& trait_ref_of_method(cx, item.def_id).is_none()
{
if cx.access_levels.is_exported(item.def_id) {
let fn_header_span = item.span.with_hi(sig.decl.output.span().hi());
check_result_unit_err(cx, err_ty, fn_header_span);
}
check_result_large_err(cx, err_ty, hir_ty.span, large_err_threshold);
}
}
pub(super) fn check_trait_item<'tcx>(cx: &LateContext<'tcx>, item: &hir::TraitItem<'tcx>, large_err_threshold: u64) {
if let hir::TraitItemKind::Fn(ref sig, _) = item.kind {
let fn_header_span = item.span.with_hi(sig.decl.output.span().hi());
if let Some((hir_ty, err_ty)) = result_err_ty(cx, sig.decl, item.def_id, item.span) {
if cx.access_levels.is_exported(item.def_id) {
check_result_unit_err(cx, err_ty, fn_header_span);
}
check_result_large_err(cx, err_ty, hir_ty.span, large_err_threshold);
}
}
}
fn check_result_unit_err(cx: &LateContext<'_>, err_ty: Ty<'_>, fn_header_span: Span) {
if err_ty.is_unit() {
span_lint_and_help(
cx,
RESULT_UNIT_ERR,
fn_header_span,
"this returns a `Result<_, ()>`",
None,
"use a custom `Error` type instead",
);
}
}
fn check_result_large_err<'tcx>(cx: &LateContext<'tcx>, err_ty: Ty<'tcx>, hir_ty_span: Span, large_err_threshold: u64) {
let ty_size = approx_ty_size(cx, err_ty);
if ty_size >= large_err_threshold {
span_lint_and_then(
cx,
RESULT_LARGE_ERR,
hir_ty_span,
"the `Err`-variant returned from this function is very large",
|diag: &mut Diagnostic| {
diag.span_label(hir_ty_span, format!("the `Err`-variant is at least {ty_size} bytes"));
diag.help(format!("try reducing the size of `{err_ty}`, for example by boxing large elements or replacing it with `Box<{err_ty}>`"));
},
);
}
}
|
