A more general implementation of IntoDiagnosticArg for Binder (Also removes DiagArg, as it's no longer necessary)

compiler/rustc_infer/src/errors/mod.rs

@@ -1146,14 +1146,6 @@ pub struct OpaqueCapturesLifetime<'tcx> {
     pub opaque_ty: Ty<'tcx>,
 }
 
-pub struct DiagArg<T>(pub T);
-
-impl<T: ToString> IntoDiagnosticArg for DiagArg<T> {
-    fn into_diagnostic_arg(self) -> rustc_errors::DiagnosticArgValue<'static> {
-        self.0.to_string().into_diagnostic_arg()
-    }
-}
-
 #[derive(Subdiagnostic)]
 pub enum FunctionPointerSuggestion<'a> {
     #[suggestion(
@@ -1221,7 +1213,7 @@ pub enum FunctionPointerSuggestion<'a> {
         fn_name: String,
         #[skip_arg]
         found_sig: Binder<'a, FnSig<'a>>,
-        expected_sig: DiagArg<Binder<'a, FnSig<'a>>>,
+        expected_sig: Binder<'a, FnSig<'a>>,
     },
     #[suggestion(
         infer_fps_cast_both,
@@ -1236,7 +1228,7 @@ pub enum FunctionPointerSuggestion<'a> {
         fn_name: String,
         #[skip_arg]
         found_sig: Binder<'a, FnSig<'a>>,
-        expected_sig: DiagArg<Binder<'a, FnSig<'a>>>,
+        expected_sig: Binder<'a, FnSig<'a>>,
     },
 }
 

compiler/rustc_infer/src/infer/error_reporting/suggest.rs

@@ -13,7 +13,7 @@ use rustc_span::{sym, BytePos, Span};
 use rustc_target::abi::FieldIdx;
 
 use crate::errors::{
-    ConsiderAddingAwait, DiagArg, FnConsiderCasting, FnItemsAreDistinct, FnUniqTypes,
+    ConsiderAddingAwait, FnConsiderCasting, FnItemsAreDistinct, FnUniqTypes,
     FunctionPointerSuggestion, SuggestAccessingField, SuggestAsRefWhereAppropriate,
     SuggestBoxingForReturnImplTrait, SuggestRemoveSemiOrReturnBinding, SuggestTuplePatternMany,
     SuggestTuplePatternOne, TypeErrorAdditionalDiags,
@@ -379,14 +379,14 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                         span,
                         fn_name,
                         found_sig: *found_sig,
-                        expected_sig: DiagArg(*expected_sig),
+                        expected_sig: *expected_sig,
                     }
                 } else {
                     FunctionPointerSuggestion::CastBoth {
                         span,
                         fn_name,
                         found_sig: *found_sig,
-                        expected_sig: DiagArg(*expected_sig),
+                        expected_sig: *expected_sig,
                     }
                 };
 

compiler/rustc_middle/src/ty/sty.rs

@@ -15,6 +15,7 @@ use hir::def::DefKind;
 use polonius_engine::Atom;
 use rustc_data_structures::captures::Captures;
 use rustc_data_structures::intern::Interned;
+use rustc_errors::{DiagnosticArgValue, IntoDiagnosticArg};
 use rustc_hir as hir;
 use rustc_hir::def_id::DefId;
 use rustc_hir::LangItem;
@@ -26,7 +27,7 @@ use rustc_target::abi::{FieldIdx, VariantIdx, FIRST_VARIANT};
 use rustc_target::spec::abi::{self, Abi};
 use std::borrow::Cow;
 use std::cmp::Ordering;
-use std::fmt;
+use std::fmt::{self, Display};
 use std::marker::PhantomData;
 use std::ops::{ControlFlow, Deref, Range};
 use ty::util::IntTypeExt;
@@ -877,12 +878,6 @@ impl<'tcx> PolyTraitRef<'tcx> {
     }
 }
 
-impl rustc_errors::IntoDiagnosticArg for PolyTraitRef<'_> {
-    fn into_diagnostic_arg(self) -> rustc_errors::DiagnosticArgValue<'static> {
-        self.to_string().into_diagnostic_arg()
-    }
-}
-
 /// An existential reference to a trait, where `Self` is erased.
 /// For example, the trait object `Trait<'a, 'b, X, Y>` is:
 /// ```ignore (illustrative)
@@ -939,12 +934,6 @@ impl<'tcx> PolyExistentialTraitRef<'tcx> {
     }
 }
 
-impl rustc_errors::IntoDiagnosticArg for PolyExistentialTraitRef<'_> {
-    fn into_diagnostic_arg(self) -> rustc_errors::DiagnosticArgValue<'static> {
-        self.to_string().into_diagnostic_arg()
-    }
-}
-
 #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Debug, TyEncodable, TyDecodable)]
 #[derive(HashStable)]
 pub enum BoundVariableKind {
@@ -1159,6 +1148,15 @@ impl<'tcx, T: IntoIterator> Binder<'tcx, T> {
     }
 }
 
+impl<'tcx, T> IntoDiagnosticArg for Binder<'tcx, T>
+where
+    Binder<'tcx, T>: Display,
+{
+    fn into_diagnostic_arg(self) -> DiagnosticArgValue<'static> {
+        self.to_string().into_diagnostic_arg()
+    }
+}
+
 struct SkipBindersAt<'tcx> {
     tcx: TyCtxt<'tcx>,
     index: ty::DebruijnIndex,