Assert that ADTs have the right number of args

compiler/rustc_hir_analysis/messages.ftl

@@ -295,6 +295,8 @@ hir_analysis_not_supported_delegation =
     {$descr} is not supported yet
     .label = callee defined here
 
+hir_analysis_only_current_traits_adt = `{$name}` is not defined in the current crate
+
 hir_analysis_only_current_traits_arbitrary = only traits defined in the current crate can be implemented for arbitrary types
 
 hir_analysis_only_current_traits_foreign = this is not defined in the current crate because this is a foreign trait

compiler/rustc_hir_analysis/src/coherence/orphan.rs

@@ -4,7 +4,7 @@
 use crate::errors;
 use rustc_errors::ErrorGuaranteed;
 use rustc_hir as hir;
-use rustc_middle::ty::{self, AliasKind, Ty, TyCtxt, TypeVisitableExt};
+use rustc_middle::ty::{self, AliasKind, TyCtxt, TypeVisitableExt};
 use rustc_span::def_id::LocalDefId;
 use rustc_span::Span;
 use rustc_trait_selection::traits::{self, IsFirstInputType};
@@ -283,8 +283,14 @@ fn emit_orphan_check_error<'tcx>(
     let self_ty = trait_ref.self_ty();
     Err(match err {
         traits::OrphanCheckErr::NonLocalInputType(tys) => {
-            let (mut opaque, mut foreign, mut name, mut pointer, mut ty_diag) =
-                (Vec::new(), Vec::new(), Vec::new(), Vec::new(), Vec::new());
+            // FIXME: Someone needs to just turn these into `Subdiag`s and attach
+            // them to the `Diag` after creating the error.
+            let mut opaque = vec![];
+            let mut foreign = vec![];
+            let mut name = vec![];
+            let mut pointer = vec![];
+            let mut ty_diag = vec![];
+            let mut adt = vec![];
             let mut sugg = None;
             for &(mut ty, is_target_ty) in &tys {
                 let span = if matches!(is_target_ty, IsFirstInputType::Yes) {
@@ -296,15 +302,6 @@ fn emit_orphan_check_error<'tcx>(
                 };
 
                 ty = tcx.erase_regions(ty);
-                ty = match ty.kind() {
-                    // Remove the type arguments from the output, as they are not relevant.
-                    // You can think of this as the reverse of `resolve_vars_if_possible`.
-                    // That way if we had `Vec<MyType>`, we will properly attribute the
-                    // problem to `Vec<T>` and avoid confusing the user if they were to see
-                    // `MyType` in the error.
-                    ty::Adt(def, _) => Ty::new_adt(tcx, *def, ty::List::empty()),
-                    _ => ty,
-                };
 
                 fn push_to_foreign_or_name<'tcx>(
                     is_foreign: bool,
@@ -366,6 +363,10 @@ fn emit_orphan_check_error<'tcx>(
                         }
                         pointer.push(errors::OnlyCurrentTraitsPointer { span, pointer: ty });
                     }
+                    ty::Adt(adt_def, _) => adt.push(errors::OnlyCurrentTraitsAdt {
+                        span,
+                        name: tcx.def_path_str(adt_def.did()),
+                    }),
                     _ => ty_diag.push(errors::OnlyCurrentTraitsTy { span, ty }),
                 }
             }
@@ -379,6 +380,7 @@ fn emit_orphan_check_error<'tcx>(
                     name,
                     pointer,
                     ty: ty_diag,
+                    adt,
                     sugg,
                 },
                 _ if self_ty.is_primitive() => errors::OnlyCurrentTraits::Primitive {
@@ -389,6 +391,7 @@ fn emit_orphan_check_error<'tcx>(
                     name,
                     pointer,
                     ty: ty_diag,
+                    adt,
                     sugg,
                 },
                 _ => errors::OnlyCurrentTraits::Arbitrary {
@@ -399,6 +402,7 @@ fn emit_orphan_check_error<'tcx>(
                     name,
                     pointer,
                     ty: ty_diag,
+                    adt,
                     sugg,
                 },
             };

compiler/rustc_hir_analysis/src/errors.rs

@@ -1395,6 +1395,8 @@ pub enum OnlyCurrentTraits<'a> {
         #[subdiagnostic]
         ty: Vec<OnlyCurrentTraitsTy<'a>>,
         #[subdiagnostic]
+        adt: Vec<OnlyCurrentTraitsAdt>,
+        #[subdiagnostic]
         sugg: Option<OnlyCurrentTraitsPointerSugg<'a>>,
     },
     #[diag(hir_analysis_only_current_traits_primitive, code = E0117)]
@@ -1415,6 +1417,8 @@ pub enum OnlyCurrentTraits<'a> {
         #[subdiagnostic]
         ty: Vec<OnlyCurrentTraitsTy<'a>>,
         #[subdiagnostic]
+        adt: Vec<OnlyCurrentTraitsAdt>,
+        #[subdiagnostic]
         sugg: Option<OnlyCurrentTraitsPointerSugg<'a>>,
     },
     #[diag(hir_analysis_only_current_traits_arbitrary, code = E0117)]
@@ -1435,6 +1439,8 @@ pub enum OnlyCurrentTraits<'a> {
         #[subdiagnostic]
         ty: Vec<OnlyCurrentTraitsTy<'a>>,
         #[subdiagnostic]
+        adt: Vec<OnlyCurrentTraitsAdt>,
+        #[subdiagnostic]
         sugg: Option<OnlyCurrentTraitsPointerSugg<'a>>,
     },
 }
@@ -1445,7 +1451,6 @@ pub struct OnlyCurrentTraitsOpaque {
     #[primary_span]
     pub span: Span,
 }
-
 #[derive(Subdiagnostic)]
 #[label(hir_analysis_only_current_traits_foreign)]
 pub struct OnlyCurrentTraitsForeign {
@@ -1477,6 +1482,14 @@ pub struct OnlyCurrentTraitsTy<'a> {
     pub ty: Ty<'a>,
 }
 
+#[derive(Subdiagnostic)]
+#[label(hir_analysis_only_current_traits_adt)]
+pub struct OnlyCurrentTraitsAdt {
+    #[primary_span]
+    pub span: Span,
+    pub name: String,
+}
+
 #[derive(Subdiagnostic)]
 #[multipart_suggestion(
     hir_analysis_only_current_traits_pointer_sugg,

compiler/rustc_middle/src/ty/sty.rs

@@ -1624,6 +1624,13 @@ impl<'tcx> Ty<'tcx> {
 
     #[inline]
     pub fn new_adt(tcx: TyCtxt<'tcx>, def: AdtDef<'tcx>, args: GenericArgsRef<'tcx>) -> Ty<'tcx> {
+        debug_assert_eq!(
+            tcx.generics_of(def.did()).count(),
+            args.len(),
+            "wrong number of args for ADT: {:#?} vs {:#?}",
+            tcx.generics_of(def.did()).params,
+            args
+        );
         Ty::new(tcx, Adt(def, args))
     }