[BETA] Delay formatting trimmed path until lint/error is emitted

compiler/rustc_errors/src/diagnostic.rs

@@ -40,6 +40,26 @@ pub trait IntoDiagnosticArg {
     fn into_diagnostic_arg(self) -> DiagnosticArgValue<'static>;
 }
 
+pub struct DiagnosticArgFromDisplay<'a>(pub &'a dyn fmt::Display);
+
+impl IntoDiagnosticArg for DiagnosticArgFromDisplay<'_> {
+    fn into_diagnostic_arg(self) -> DiagnosticArgValue<'static> {
+        self.0.to_string().into_diagnostic_arg()
+    }
+}
+
+impl<'a> From<&'a dyn fmt::Display> for DiagnosticArgFromDisplay<'a> {
+    fn from(t: &'a dyn fmt::Display) -> Self {
+        DiagnosticArgFromDisplay(t)
+    }
+}
+
+impl<'a, T: fmt::Display> From<&'a T> for DiagnosticArgFromDisplay<'a> {
+    fn from(t: &'a T) -> Self {
+        DiagnosticArgFromDisplay(t)
+    }
+}
+
 macro_rules! into_diagnostic_arg_using_display {
     ($( $ty:ty ),+ $(,)?) => {
         $(

compiler/rustc_errors/src/lib.rs

@@ -371,8 +371,8 @@ impl fmt::Display for ExplicitBug {
 impl error::Error for ExplicitBug {}
 
 pub use diagnostic::{
-    AddSubdiagnostic, DecorateLint, Diagnostic, DiagnosticArg, DiagnosticArgValue, DiagnosticId,
-    DiagnosticStyledString, IntoDiagnosticArg, SubDiagnostic,
+    AddSubdiagnostic, DecorateLint, Diagnostic, DiagnosticArg, DiagnosticArgFromDisplay,
+    DiagnosticArgValue, DiagnosticId, DiagnosticStyledString, IntoDiagnosticArg, SubDiagnostic,
 };
 pub use diagnostic_builder::{DiagnosticBuilder, EmissionGuarantee, LintDiagnosticBuilder};
 use std::backtrace::Backtrace;

compiler/rustc_privacy/src/errors.rs

@@ -1,3 +1,4 @@
+use rustc_errors::DiagnosticArgFromDisplay;
 use rustc_macros::{LintDiagnostic, SessionDiagnostic, SessionSubdiagnostic};
 use rustc_span::{Span, Symbol};
 
@@ -35,7 +36,7 @@ pub struct ItemIsPrivate<'a> {
     #[label]
     pub span: Span,
     pub kind: &'a str,
-    pub descr: String,
+    pub descr: DiagnosticArgFromDisplay<'a>,
 }
 
 #[derive(SessionDiagnostic)]
@@ -55,7 +56,7 @@ pub struct InPublicInterfaceTraits<'a> {
     pub span: Span,
     pub vis_descr: &'static str,
     pub kind: &'a str,
-    pub descr: String,
+    pub descr: DiagnosticArgFromDisplay<'a>,
     #[label(privacy::visibility_label)]
     pub vis_span: Span,
 }
@@ -69,7 +70,7 @@ pub struct InPublicInterface<'a> {
     pub span: Span,
     pub vis_descr: &'static str,
     pub kind: &'a str,
-    pub descr: String,
+    pub descr: DiagnosticArgFromDisplay<'a>,
     #[label(privacy::visibility_label)]
     pub vis_span: Span,
 }
@@ -78,7 +79,7 @@ pub struct InPublicInterface<'a> {
 #[lint(privacy::from_private_dep_in_public_interface)]
 pub struct FromPrivateDependencyInPublicInterface<'a> {
     pub kind: &'a str,
-    pub descr: String,
+    pub descr: DiagnosticArgFromDisplay<'a>,
     pub krate: Symbol,
 }
 
@@ -87,5 +88,5 @@ pub struct FromPrivateDependencyInPublicInterface<'a> {
 pub struct PrivateInPublicLint<'a> {
     pub vis_descr: &'static str,
     pub kind: &'a str,
-    pub descr: String,
+    pub descr: DiagnosticArgFromDisplay<'a>,
 }

compiler/rustc_privacy/src/lib.rs

@@ -1079,11 +1079,7 @@ impl<'tcx> TypePrivacyVisitor<'tcx> {
     fn check_def_id(&mut self, def_id: DefId, kind: &str, descr: &dyn fmt::Display) -> bool {
         let is_error = !self.item_is_accessible(def_id);
         if is_error {
-            self.tcx.sess.emit_err(ItemIsPrivate {
-                span: self.span,
-                kind,
-                descr: descr.to_string(),
-            });
+            self.tcx.sess.emit_err(ItemIsPrivate { span: self.span, kind, descr: descr.into() });
         }
         is_error
     }
@@ -1255,7 +1251,9 @@ impl<'tcx> Visitor<'tcx> for TypePrivacyVisitor<'tcx> {
                 };
                 let kind = kind.descr(def_id);
                 let _ = match name {
-                    Some(name) => sess.emit_err(ItemIsPrivate { span, kind, descr: name }),
+                    Some(name) => {
+                        sess.emit_err(ItemIsPrivate { span, kind, descr: (&name).into() })
+                    }
                     None => sess.emit_err(UnnamedItemIsPrivate { span, kind }),
                 };
                 return;
@@ -1723,7 +1721,7 @@ impl SearchInterfaceForPrivateItemsVisitor<'_> {
                 self.tcx.def_span(self.item_def_id.to_def_id()),
                 FromPrivateDependencyInPublicInterface {
                     kind,
-                    descr: descr.to_string(),
+                    descr: descr.into(),
                     krate: self.tcx.crate_name(def_id.krate),
                 },
             );
@@ -1750,7 +1748,6 @@ impl SearchInterfaceForPrivateItemsVisitor<'_> {
                 }
             };
             let span = self.tcx.def_span(self.item_def_id.to_def_id());
-            let descr = descr.to_string();
             if self.has_old_errors
                 || self.in_assoc_ty
                 || self.tcx.resolutions(()).has_pub_restricted
@@ -1761,15 +1758,15 @@ impl SearchInterfaceForPrivateItemsVisitor<'_> {
                         span,
                         vis_descr,
                         kind,
-                        descr,
+                        descr: descr.into(),
                         vis_span,
                     });
                 } else {
                     self.tcx.sess.emit_err(InPublicInterface {
                         span,
                         vis_descr,
                         kind,
-                        descr,
+                        descr: descr.into(),
                         vis_span,
                     });
                 }
@@ -1778,7 +1775,7 @@ impl SearchInterfaceForPrivateItemsVisitor<'_> {
                     lint::builtin::PRIVATE_IN_PUBLIC,
                     hir_id,
                     span,
-                    PrivateInPublicLint { vis_descr, kind, descr },
+                    PrivateInPublicLint { vis_descr, kind, descr: descr.into() },
                 );
             }
         }

src/test/ui/lint/issue-99387.rs

@@ -0,0 +1,24 @@
+// check-pass
+
+#![feature(type_alias_impl_trait)]
+#![allow(private_in_public)]
+
+pub type Successors<'a> = impl Iterator<Item = &'a ()>;
+
+pub fn f<'a>() -> Successors<'a> {
+    None.into_iter()
+}
+
+trait Tr {
+    type Item;
+}
+
+impl<'a> Tr for &'a () {
+    type Item = Successors<'a>;
+}
+
+pub fn ohno<'a>() -> <&'a () as Tr>::Item {
+    None.into_iter()
+}
+
+fn main() {}