1 use crate::{LateContext, LateLintPass, LintContext};
2 use rustc_errors::{fluent, Applicability};
4 use rustc_hir::def::Res;
5 use rustc_hir::{GenericArg, PathSegment, QPath, TyKind};
7 use rustc_span::symbol::sym;
10 /// The `rustc_pass_by_value` lint marks a type with `#[rustc_pass_by_value]` requiring it to
11 /// always be passed by value. This is usually used for types that are thin wrappers around
12 /// references, so there is no benefit to an extra layer of indirection. (Example: `Ty` which
13 /// is a reference to an `Interned<TyKind>`)
14 pub rustc::PASS_BY_VALUE,
16 "pass by reference of a type flagged as `#[rustc_pass_by_value]`",
17 report_in_external_macro: true
20 declare_lint_pass!(PassByValue => [PASS_BY_VALUE]);
22 impl<'tcx> LateLintPass<'tcx> for PassByValue {
23 fn check_ty(&mut self, cx: &LateContext<'_>, ty: &'tcx hir::Ty<'tcx>) {
25 TyKind::Ref(_, hir::MutTy { ty: inner_ty, mutbl: hir::Mutability::Not }) => {
26 if let Some(impl_did) = cx.tcx.impl_of_method(ty.hir_id.owner.to_def_id()) {
27 if cx.tcx.impl_trait_ref(impl_did).is_some() {
31 if let Some(t) = path_for_pass_by_value(cx, &inner_ty) {
35 fluent::lint_pass_by_value,
37 lint.set_arg("ty", t.clone()).span_suggestion(
41 // Changing type of function argument
42 Applicability::MaybeIncorrect,
53 fn path_for_pass_by_value(cx: &LateContext<'_>, ty: &hir::Ty<'_>) -> Option<String> {
54 if let TyKind::Path(QPath::Resolved(_, path)) = &ty.kind {
56 Res::Def(_, def_id) if cx.tcx.has_attr(def_id, sym::rustc_pass_by_value) => {
57 let name = cx.tcx.item_name(def_id).to_ident_string();
58 let path_segment = path.segments.last().unwrap();
59 return Some(format!("{}{}", name, gen_args(cx, path_segment)));
61 Res::SelfTyAlias { alias_to: did, is_trait_impl: false, .. } => {
62 if let ty::Adt(adt, substs) = cx.tcx.type_of(did).kind() {
63 if cx.tcx.has_attr(adt.did(), sym::rustc_pass_by_value) {
64 return Some(cx.tcx.def_path_str_with_substs(adt.did(), substs));
75 fn gen_args(cx: &LateContext<'_>, segment: &PathSegment<'_>) -> String {
76 if let Some(args) = &segment.args {
80 .map(|arg| match arg {
81 GenericArg::Lifetime(lt) => lt.to_string(),
82 GenericArg::Type(ty) => {
83 cx.tcx.sess.source_map().span_to_snippet(ty.span).unwrap_or_else(|_| "_".into())
85 GenericArg::Const(c) => {
86 cx.tcx.sess.source_map().span_to_snippet(c.span).unwrap_or_else(|_| "_".into())
88 GenericArg::Infer(_) => String::from("_"),
92 if !params.is_empty() {
93 return format!("<{}>", params.join(", "));