1 files changed, 96 insertions, 0 deletions
diff --git a/compiler/rustc_lint/src/pass_by_value.rs b/compiler/rustc_lint/src/pass_by_value.rs
new file mode 100644
index 000000000..af5e5faf1
--- /dev/null
+++ b/compiler/rustc_lint/src/pass_by_value.rs
@@ -0,0 +1,96 @@
+use crate::{LateContext, LateLintPass, LintContext};
+use rustc_errors::{fluent, Applicability};
+use rustc_hir as hir;
+use rustc_hir::def::Res;
+use rustc_hir::{GenericArg, PathSegment, QPath, TyKind};
+use rustc_middle::ty;
+use rustc_span::symbol::sym;
+
+declare_tool_lint! {
+    /// The `rustc_pass_by_value` lint marks a type with `#[rustc_pass_by_value]` requiring it to
+    /// always be passed by value. This is usually used for types that are thin wrappers around
+    /// references, so there is no benefit to an extra layer of indirection. (Example: `Ty` which
+    /// is a reference to an `Interned<TyS>`)
+    pub rustc::PASS_BY_VALUE,
+    Warn,
+    "pass by reference of a type flagged as `#[rustc_pass_by_value]`",
+    report_in_external_macro: true
+}
+
+declare_lint_pass!(PassByValue => [PASS_BY_VALUE]);
+
+impl<'tcx> LateLintPass<'tcx> for PassByValue {
+    fn check_ty(&mut self, cx: &LateContext<'_>, ty: &'tcx hir::Ty<'tcx>) {
+        match &ty.kind {
+            TyKind::Rptr(_, hir::MutTy { ty: inner_ty, mutbl: hir::Mutability::Not }) => {
+                if let Some(impl_did) = cx.tcx.impl_of_method(ty.hir_id.owner.to_def_id()) {
+                    if cx.tcx.impl_trait_ref(impl_did).is_some() {
+                        return;
+                    }
+                }
+                if let Some(t) = path_for_pass_by_value(cx, &inner_ty) {
+                    cx.struct_span_lint(PASS_BY_VALUE, ty.span, |lint| {
+                        lint.build(fluent::lint::pass_by_value)
+                            .set_arg("ty", t.clone())
+                            .span_suggestion(
+                                ty.span,
+                                fluent::lint::suggestion,
+                                t,
+                                // Changing type of function argument
+                                Applicability::MaybeIncorrect,
+                            )
+                            .emit();
+                    })
+                }
+            }
+            _ => {}
+        }
+    }
+}
+
+fn path_for_pass_by_value(cx: &LateContext<'_>, ty: &hir::Ty<'_>) -> Option<String> {
+    if let TyKind::Path(QPath::Resolved(_, path)) = &ty.kind {
+        match path.res {
+            Res::Def(_, def_id) if cx.tcx.has_attr(def_id, sym::rustc_pass_by_value) => {
+                let name = cx.tcx.item_name(def_id).to_ident_string();
+                let path_segment = path.segments.last().unwrap();
+                return Some(format!("{}{}", name, gen_args(cx, path_segment)));
+            }
+            Res::SelfTy { trait_: None, alias_to: Some((did, _)) } => {
+                if let ty::Adt(adt, substs) = cx.tcx.type_of(did).kind() {
+                    if cx.tcx.has_attr(adt.did(), sym::rustc_pass_by_value) {
+                        return Some(cx.tcx.def_path_str_with_substs(adt.did(), substs));
+                    }
+                }
+            }
+            _ => (),
+        }
+    }
+
+    None
+}
+
+fn gen_args(cx: &LateContext<'_>, segment: &PathSegment<'_>) -> String {
+    if let Some(args) = &segment.args {
+        let params = args
+            .args
+            .iter()
+            .map(|arg| match arg {
+                GenericArg::Lifetime(lt) => lt.name.ident().to_string(),
+                GenericArg::Type(ty) => {
+                    cx.tcx.sess.source_map().span_to_snippet(ty.span).unwrap_or_else(|_| "_".into())
+                }
+                GenericArg::Const(c) => {
+                    cx.tcx.sess.source_map().span_to_snippet(c.span).unwrap_or_else(|_| "_".into())
+                }
+                GenericArg::Infer(_) => String::from("_"),
+            })
+            .collect::<Vec<_>>();
+
+        if !params.is_empty() {
+            return format!("<{}>", params.join(", "));
+        }
+    }
+
+    String::new()
+}