Lay the foundation for diagnostics in ty lowering, and implement a first diagnostic

The diagnostic implemented is a simple one (E0109). It serves as a test for the new foundation.

This commit only implements diagnostics for type in bodies and body-carrying signatures; the next commit will include diagnostics in the rest of the things.

Also fix one weird bug that was detected when implementing this that caused `Fn::(A, B) -> C` (which is a valid, if bizarre, alternative syntax to `Fn(A, B) -> C` to lower incorrectly.

And also fix a maybe-bug where parentheses were sneaked into a code string needlessly; this was not detected until now because the parentheses were removed (by the make-AST family API), but with a change in this commit they are now inserted. So fix that too.

crates/hir-ty/src/infer.rs

@@ -58,7 +58,7 @@ use crate::{
     fold_tys,
     generics::Generics,
     infer::{coerce::CoerceMany, expr::ExprIsRead, unify::InferenceTable},
-    lower::ImplTraitLoweringMode,
+    lower::{ImplTraitLoweringMode, TyLoweringDiagnostic},
     mir::MirSpan,
     to_assoc_type_id,
     traits::FnTrait,
@@ -191,6 +191,14 @@ impl<T> InferOk<T> {
     }
 }
 
+#[derive(Debug, PartialEq, Eq, Clone, Copy)]
+pub enum InferenceTyDiagnosticSource {
+    /// Diagnostics that come from types in the body.
+    Body,
+    /// Diagnostics that come from types in fn parameters/return type, or static & const types.
+    Signature,
+}
+
 #[derive(Debug)]
 pub(crate) struct TypeError;
 pub(crate) type InferResult<T> = Result<InferOk<T>, TypeError>;
@@ -264,6 +272,10 @@ pub enum InferenceDiagnostic {
         expr_ty: Ty,
         cast_ty: Ty,
     },
+    TyDiagnostic {
+        source: InferenceTyDiagnosticSource,
+        diag: TyLoweringDiagnostic,
+    },
 }
 
 /// A mismatch between an expected and an inferred type.
@@ -858,7 +870,8 @@ impl<'a> InferenceContext<'a> {
     }
 
     fn collect_const(&mut self, data: &ConstData) {
-        let return_ty = self.make_ty(data.type_ref, &data.types_map);
+        let return_ty =
+            self.make_ty(data.type_ref, &data.types_map, InferenceTyDiagnosticSource::Signature);
 
         // Constants might be defining usage sites of TAITs.
         self.make_tait_coercion_table(iter::once(&return_ty));
@@ -867,7 +880,8 @@ impl<'a> InferenceContext<'a> {
     }
 
     fn collect_static(&mut self, data: &StaticData) {
-        let return_ty = self.make_ty(data.type_ref, &data.types_map);
+        let return_ty =
+            self.make_ty(data.type_ref, &data.types_map, InferenceTyDiagnosticSource::Signature);
 
         // Statics might be defining usage sites of TAITs.
         self.make_tait_coercion_table(iter::once(&return_ty));
@@ -877,11 +891,12 @@ impl<'a> InferenceContext<'a> {
 
     fn collect_fn(&mut self, func: FunctionId) {
         let data = self.db.function_data(func);
-        let mut param_tys = self.with_ty_lowering(&data.types_map, |ctx| {
-            ctx.type_param_mode(ParamLoweringMode::Placeholder)
-                .impl_trait_mode(ImplTraitLoweringMode::Param);
-            data.params.iter().map(|&type_ref| ctx.lower_ty(type_ref)).collect::<Vec<_>>()
-        });
+        let mut param_tys =
+            self.with_ty_lowering(&data.types_map, InferenceTyDiagnosticSource::Signature, |ctx| {
+                ctx.type_param_mode(ParamLoweringMode::Placeholder)
+                    .impl_trait_mode(ImplTraitLoweringMode::Param);
+                data.params.iter().map(|&type_ref| ctx.lower_ty(type_ref)).collect::<Vec<_>>()
+            });
         // Check if function contains a va_list, if it does then we append it to the parameter types
         // that are collected from the function data
         if data.is_varargs() {
@@ -918,11 +933,12 @@ impl<'a> InferenceContext<'a> {
         }
         let return_ty = data.ret_type;
 
-        let return_ty = self.with_ty_lowering(&data.types_map, |ctx| {
-            ctx.type_param_mode(ParamLoweringMode::Placeholder)
-                .impl_trait_mode(ImplTraitLoweringMode::Opaque)
-                .lower_ty(return_ty)
-        });
+        let return_ty =
+            self.with_ty_lowering(&data.types_map, InferenceTyDiagnosticSource::Signature, |ctx| {
+                ctx.type_param_mode(ParamLoweringMode::Placeholder)
+                    .impl_trait_mode(ImplTraitLoweringMode::Opaque)
+                    .lower_ty(return_ty)
+            });
         let return_ty = self.insert_type_vars(return_ty);
 
         let return_ty = if let Some(rpits) = self.db.return_type_impl_traits(func) {
@@ -1226,9 +1242,20 @@ impl<'a> InferenceContext<'a> {
         self.result.diagnostics.push(diagnostic);
     }
 
+    fn push_ty_diagnostics(
+        &mut self,
+        source: InferenceTyDiagnosticSource,
+        diagnostics: Vec<TyLoweringDiagnostic>,
+    ) {
+        self.result.diagnostics.extend(
+            diagnostics.into_iter().map(|diag| InferenceDiagnostic::TyDiagnostic { source, diag }),
+        );
+    }
+
     fn with_ty_lowering<R>(
-        &self,
+        &mut self,
         types_map: &TypesMap,
+        types_source: InferenceTyDiagnosticSource,
         f: impl FnOnce(&mut crate::lower::TyLoweringContext<'_>) -> R,
     ) -> R {
         let mut ctx = crate::lower::TyLoweringContext::new(
@@ -1237,32 +1264,41 @@ impl<'a> InferenceContext<'a> {
             types_map,
             self.owner.into(),
         );
-        f(&mut ctx)
+        let result = f(&mut ctx);
+        self.push_ty_diagnostics(types_source, ctx.diagnostics);
+        result
     }
 
     fn with_body_ty_lowering<R>(
-        &self,
+        &mut self,
         f: impl FnOnce(&mut crate::lower::TyLoweringContext<'_>) -> R,
     ) -> R {
-        self.with_ty_lowering(&self.body.types, f)
+        self.with_ty_lowering(&self.body.types, InferenceTyDiagnosticSource::Body, f)
     }
 
-    fn make_ty(&mut self, type_ref: TypeRefId, types_map: &TypesMap) -> Ty {
-        let ty = self.with_ty_lowering(types_map, |ctx| ctx.lower_ty(type_ref));
+    fn make_ty(
+        &mut self,
+        type_ref: TypeRefId,
+        types_map: &TypesMap,
+        type_source: InferenceTyDiagnosticSource,
+    ) -> Ty {
+        let ty = self.with_ty_lowering(types_map, type_source, |ctx| ctx.lower_ty(type_ref));
         let ty = self.insert_type_vars(ty);
         self.normalize_associated_types_in(ty)
     }
 
     fn make_body_ty(&mut self, type_ref: TypeRefId) -> Ty {
-        self.make_ty(type_ref, &self.body.types)
+        self.make_ty(type_ref, &self.body.types, InferenceTyDiagnosticSource::Body)
     }
 
     fn err_ty(&self) -> Ty {
         self.result.standard_types.unknown.clone()
     }
 
-    fn make_lifetime(&mut self, lifetime_ref: &LifetimeRef) -> Lifetime {
-        let lt = self.with_ty_lowering(TypesMap::EMPTY, |ctx| ctx.lower_lifetime(lifetime_ref));
+    fn make_body_lifetime(&mut self, lifetime_ref: &LifetimeRef) -> Lifetime {
+        let lt = self.with_ty_lowering(TypesMap::EMPTY, InferenceTyDiagnosticSource::Body, |ctx| {
+            ctx.lower_lifetime(lifetime_ref)
+        });
         self.insert_type_vars(lt)
     }
 
@@ -1431,12 +1467,20 @@ impl<'a> InferenceContext<'a> {
                 Some(ResolveValueResult::ValueNs(value, _)) => match value {
                     ValueNs::EnumVariantId(var) => {
                         let substs = ctx.substs_from_path(path, var.into(), true);
+                        self.push_ty_diagnostics(
+                            InferenceTyDiagnosticSource::Body,
+                            ctx.diagnostics,
+                        );
                         let ty = self.db.ty(var.lookup(self.db.upcast()).parent.into());
                         let ty = self.insert_type_vars(ty.substitute(Interner, &substs));
                         return (ty, Some(var.into()));
                     }
                     ValueNs::StructId(strukt) => {
                         let substs = ctx.substs_from_path(path, strukt.into(), true);
+                        self.push_ty_diagnostics(
+                            InferenceTyDiagnosticSource::Body,
+                            ctx.diagnostics,
+                        );
                         let ty = self.db.ty(strukt.into());
                         let ty = self.insert_type_vars(ty.substitute(Interner, &substs));
                         return (ty, Some(strukt.into()));
@@ -1462,18 +1506,21 @@ impl<'a> InferenceContext<'a> {
         return match resolution {
             TypeNs::AdtId(AdtId::StructId(strukt)) => {
                 let substs = ctx.substs_from_path(path, strukt.into(), true);
+                self.push_ty_diagnostics(InferenceTyDiagnosticSource::Body, ctx.diagnostics);
                 let ty = self.db.ty(strukt.into());
                 let ty = self.insert_type_vars(ty.substitute(Interner, &substs));
                 forbid_unresolved_segments((ty, Some(strukt.into())), unresolved)
             }
             TypeNs::AdtId(AdtId::UnionId(u)) => {
                 let substs = ctx.substs_from_path(path, u.into(), true);
+                self.push_ty_diagnostics(InferenceTyDiagnosticSource::Body, ctx.diagnostics);
                 let ty = self.db.ty(u.into());
                 let ty = self.insert_type_vars(ty.substitute(Interner, &substs));
                 forbid_unresolved_segments((ty, Some(u.into())), unresolved)
             }
             TypeNs::EnumVariantId(var) => {
                 let substs = ctx.substs_from_path(path, var.into(), true);
+                self.push_ty_diagnostics(InferenceTyDiagnosticSource::Body, ctx.diagnostics);
                 let ty = self.db.ty(var.lookup(self.db.upcast()).parent.into());
                 let ty = self.insert_type_vars(ty.substitute(Interner, &substs));
                 forbid_unresolved_segments((ty, Some(var.into())), unresolved)
@@ -1519,6 +1566,9 @@ impl<'a> InferenceContext<'a> {
                         resolved_segment,
                         current_segment,
                         false,
+                        &mut |_, _reason| {
+                            // FIXME: Report an error.
+                        },
                     );
 
                     ty = self.table.insert_type_vars(ty);
@@ -1532,6 +1582,7 @@ impl<'a> InferenceContext<'a> {
                     remaining_idx += 1;
                     remaining_segments = remaining_segments.skip(1);
                 }
+                self.push_ty_diagnostics(InferenceTyDiagnosticSource::Body, ctx.diagnostics);
 
                 let variant = ty.as_adt().and_then(|(id, _)| match id {
                     AdtId::StructId(s) => Some(VariantId::StructId(s)),
@@ -1550,6 +1601,7 @@ impl<'a> InferenceContext<'a> {
                 };
                 let substs =
                     ctx.substs_from_path_segment(resolved_seg, Some(it.into()), true, None);
+                self.push_ty_diagnostics(InferenceTyDiagnosticSource::Body, ctx.diagnostics);
                 let ty = self.db.ty(it.into());
                 let ty = self.insert_type_vars(ty.substitute(Interner, &substs));
 

crates/hir-ty/src/infer/expr.rs

@@ -2155,7 +2155,7 @@ impl InferenceContext<'_> {
                                 DebruijnIndex::INNERMOST,
                             )
                         },
-                        |this, lt_ref| this.make_lifetime(lt_ref),
+                        |this, lt_ref| this.make_body_lifetime(lt_ref),
                     ),
                 };
 

crates/hir-ty/src/infer/path.rs

@@ -19,7 +19,7 @@ use crate::{
     TyBuilder, TyExt, TyKind, ValueTyDefId,
 };
 
-use super::{ExprOrPatId, InferenceContext};
+use super::{ExprOrPatId, InferenceContext, InferenceTyDiagnosticSource};
 
 impl InferenceContext<'_> {
     pub(super) fn infer_path(&mut self, path: &Path, id: ExprOrPatId) -> Option<Ty> {
@@ -163,6 +163,7 @@ impl InferenceContext<'_> {
 
             let remaining_segments_for_ty = path.segments().take(path.segments().len() - 1);
             let (ty, _) = ctx.lower_ty_relative_path(ty, orig_ns, remaining_segments_for_ty);
+            self.push_ty_diagnostics(InferenceTyDiagnosticSource::Body, ctx.diagnostics);
             let ty = self.table.insert_type_vars(ty);
             let ty = self.table.normalize_associated_types_in(ty);
             self.resolve_ty_assoc_item(ty, last.name, id).map(|(it, substs)| (it, Some(substs)))?
@@ -265,6 +266,9 @@ impl InferenceContext<'_> {
                         resolved_segment,
                         remaining_segments_for_ty,
                         true,
+                        &mut |_, _reason| {
+                            // FIXME: Report an error.
+                        },
                     )
                 });
                 if ty.is_unknown() {

crates/hir-ty/src/lib.rs

@@ -84,12 +84,13 @@ pub use infer::{
     cast::CastError,
     closure::{CaptureKind, CapturedItem},
     could_coerce, could_unify, could_unify_deeply, Adjust, Adjustment, AutoBorrow, BindingMode,
-    InferenceDiagnostic, InferenceResult, OverloadedDeref, PointerCast,
+    InferenceDiagnostic, InferenceResult, InferenceTyDiagnosticSource, OverloadedDeref,
+    PointerCast,
 };
 pub use interner::Interner;
 pub use lower::{
-    associated_type_shorthand_candidates, ImplTraitLoweringMode, ParamLoweringMode, TyDefId,
-    TyLoweringContext, ValueTyDefId,
+    associated_type_shorthand_candidates, GenericArgsProhibitedReason, ImplTraitLoweringMode,
+    ParamLoweringMode, TyDefId, TyLoweringContext, TyLoweringDiagnosticKind, ValueTyDefId,
 };
 pub use mapping::{
     from_assoc_type_id, from_chalk_trait_id, from_foreign_def_id, from_placeholder_idx,

crates/hir-ty/src/lower.rs

@@ -102,6 +102,31 @@ impl ImplTraitLoweringState {
     }
 }
 
+type TypeSource = Either<TypeRefId, hir_def::type_ref::TypeSource>;
+
+#[derive(Debug, PartialEq, Eq, Clone)]
+pub struct TyLoweringDiagnostic {
+    pub source: TypeSource,
+    pub kind: TyLoweringDiagnosticKind,
+}
+
+#[derive(Debug, PartialEq, Eq, Clone)]
+pub enum TyLoweringDiagnosticKind {
+    GenericArgsProhibited { segment: u32, reason: GenericArgsProhibitedReason },
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum GenericArgsProhibitedReason {
+    Module,
+    TyParam,
+    SelfTy,
+    PrimitiveTy,
+    /// When there is a generic enum, within the expression `Enum::Variant`,
+    /// either `Enum` or `Variant` are allowed to have generic arguments, but not both.
+    // FIXME: This is not used now but it should be.
+    EnumVariant,
+}
+
 #[derive(Debug)]
 pub struct TyLoweringContext<'a> {
     pub db: &'a dyn HirDatabase,
@@ -125,6 +150,7 @@ pub struct TyLoweringContext<'a> {
     expander: Option<Expander>,
     /// Tracks types with explicit `?Sized` bounds.
     pub(crate) unsized_types: FxHashSet<Ty>,
+    pub(crate) diagnostics: Vec<TyLoweringDiagnostic>,
 }
 
 impl<'a> TyLoweringContext<'a> {
@@ -159,6 +185,7 @@ impl<'a> TyLoweringContext<'a> {
             type_param_mode,
             expander: None,
             unsized_types: FxHashSet::default(),
+            diagnostics: Vec::new(),
         }
     }
 
@@ -198,6 +225,20 @@ impl<'a> TyLoweringContext<'a> {
         self.type_param_mode = type_param_mode;
         self
     }
+
+    pub fn push_diagnostic(&mut self, type_ref: TypeRefId, kind: TyLoweringDiagnosticKind) {
+        let source = match self.types_source_map {
+            Some(source_map) => {
+                let Ok(source) = source_map.type_syntax(type_ref) else {
+                    stdx::never!("error in synthetic type");
+                    return;
+                };
+                Either::Right(source)
+            }
+            None => Either::Left(type_ref),
+        };
+        self.diagnostics.push(TyLoweringDiagnostic { source, kind });
+    }
 }
 
 #[derive(Copy, Clone, Debug, PartialEq, Eq, Default)]
@@ -464,6 +505,7 @@ impl<'a> TyLoweringContext<'a> {
                                 impl_trait_mode: mem::take(&mut self.impl_trait_mode),
                                 expander: self.expander.take(),
                                 unsized_types: mem::take(&mut self.unsized_types),
+                                diagnostics: mem::take(&mut self.diagnostics),
                             };
 
                             let ty = inner_ctx.lower_ty(type_ref);
@@ -471,6 +513,7 @@ impl<'a> TyLoweringContext<'a> {
                             self.impl_trait_mode = inner_ctx.impl_trait_mode;
                             self.expander = inner_ctx.expander;
                             self.unsized_types = inner_ctx.unsized_types;
+                            self.diagnostics = inner_ctx.diagnostics;
 
                             self.expander.as_mut().unwrap().exit(mark);
                             Some(ty)
@@ -542,6 +585,10 @@ impl<'a> TyLoweringContext<'a> {
         resolved_segment: PathSegment<'_>,
         remaining_segments: PathSegments<'_>,
         infer_args: bool,
+        on_prohibited_generics_for_resolved_segment: &mut dyn FnMut(
+            &mut Self,
+            GenericArgsProhibitedReason,
+        ),
     ) -> (Ty, Option<TypeNs>) {
         let ty = match resolution {
             TypeNs::TraitId(trait_) => {
@@ -608,28 +655,44 @@ impl<'a> TyLoweringContext<'a> {
                 // FIXME(trait_alias): Implement trait alias.
                 return (TyKind::Error.intern(Interner), None);
             }
-            TypeNs::GenericParam(param_id) => match self.type_param_mode {
-                ParamLoweringMode::Placeholder => {
-                    TyKind::Placeholder(to_placeholder_idx(self.db, param_id.into()))
+            TypeNs::GenericParam(param_id) => {
+                if resolved_segment.args_and_bindings.is_some() {
+                    on_prohibited_generics_for_resolved_segment(
+                        self,
+                        GenericArgsProhibitedReason::TyParam,
+                    );
                 }
-                ParamLoweringMode::Variable => {
-                    let idx = match self
-                        .generics()
-                        .expect("generics in scope")
-                        .type_or_const_param_idx(param_id.into())
-                    {
-                        None => {
-                            never!("no matching generics");
-                            return (TyKind::Error.intern(Interner), None);
-                        }
-                        Some(idx) => idx,
-                    };
 
-                    TyKind::BoundVar(BoundVar::new(self.in_binders, idx))
+                match self.type_param_mode {
+                    ParamLoweringMode::Placeholder => {
+                        TyKind::Placeholder(to_placeholder_idx(self.db, param_id.into()))
+                    }
+                    ParamLoweringMode::Variable => {
+                        let idx = match self
+                            .generics()
+                            .expect("generics in scope")
+                            .type_or_const_param_idx(param_id.into())
+                        {
+                            None => {
+                                never!("no matching generics");
+                                return (TyKind::Error.intern(Interner), None);
+                            }
+                            Some(idx) => idx,
+                        };
+
+                        TyKind::BoundVar(BoundVar::new(self.in_binders, idx))
+                    }
                 }
+                .intern(Interner)
             }
-            .intern(Interner),
             TypeNs::SelfType(impl_id) => {
+                if resolved_segment.args_and_bindings.is_some() {
+                    on_prohibited_generics_for_resolved_segment(
+                        self,
+                        GenericArgsProhibitedReason::SelfTy,
+                    );
+                }
+
                 let generics = self.generics().expect("impl should have generic param scope");
 
                 match self.type_param_mode {
@@ -655,6 +718,13 @@ impl<'a> TyLoweringContext<'a> {
                 }
             }
             TypeNs::AdtSelfType(adt) => {
+                if resolved_segment.args_and_bindings.is_some() {
+                    on_prohibited_generics_for_resolved_segment(
+                        self,
+                        GenericArgsProhibitedReason::SelfTy,
+                    );
+                }
+
                 let generics = generics(self.db.upcast(), adt.into());
                 let substs = match self.type_param_mode {
                     ParamLoweringMode::Placeholder => generics.placeholder_subst(self.db),
@@ -667,6 +737,12 @@ impl<'a> TyLoweringContext<'a> {
 
             TypeNs::AdtId(it) => self.lower_path_inner(resolved_segment, it.into(), infer_args),
             TypeNs::BuiltinType(it) => {
+                if resolved_segment.args_and_bindings.is_some() {
+                    on_prohibited_generics_for_resolved_segment(
+                        self,
+                        GenericArgsProhibitedReason::PrimitiveTy,
+                    );
+                }
                 self.lower_path_inner(resolved_segment, it.into(), infer_args)
             }
             TypeNs::TypeAliasId(it) => {
@@ -698,14 +774,39 @@ impl<'a> TyLoweringContext<'a> {
             return (ty, None);
         }
 
-        let (resolved_segment, remaining_segments) = match remaining_index {
-            None => (
-                path.segments().last().expect("resolved path has at least one element"),
-                PathSegments::EMPTY,
-            ),
-            Some(i) => (path.segments().get(i - 1).unwrap(), path.segments().skip(i)),
-        };
-        self.lower_partly_resolved_path(resolution, resolved_segment, remaining_segments, false)
+        let (module_segments, resolved_segment_idx, resolved_segment, remaining_segments) =
+            match remaining_index {
+                None => (
+                    path.segments().strip_last(),
+                    path.segments().len() - 1,
+                    path.segments().last().expect("resolved path has at least one element"),
+                    PathSegments::EMPTY,
+                ),
+                Some(i) => (
+                    path.segments().take(i - 1),
+                    i - 1,
+                    path.segments().get(i - 1).unwrap(),
+                    path.segments().skip(i),
+                ),
+            };
+
+        self.prohibit_generics(path_id, 0, module_segments, GenericArgsProhibitedReason::Module);
+
+        self.lower_partly_resolved_path(
+            resolution,
+            resolved_segment,
+            remaining_segments,
+            false,
+            &mut |this, reason| {
+                this.push_diagnostic(
+                    path_id.type_ref(),
+                    TyLoweringDiagnosticKind::GenericArgsProhibited {
+                        segment: resolved_segment_idx as u32,
+                        reason,
+                    },
+                )
+            },
+        )
     }
 
     fn select_associated_type(&mut self, res: Option<TypeNs>, segment: PathSegment<'_>) -> Ty {
@@ -742,12 +843,8 @@ impl<'a> TyLoweringContext<'a> {
                 // generic params. It's inefficient to splice the `Substitution`s, so we may want
                 // that method to optionally take parent `Substitution` as we already know them at
                 // this point (`t.substitution`).
-                let substs = self.substs_from_path_segment(
-                    segment.clone(),
-                    Some(associated_ty.into()),
-                    false,
-                    None,
-                );
+                let substs =
+                    self.substs_from_path_segment(segment, Some(associated_ty.into()), false, None);
 
                 let len_self =
                     crate::generics::generics(self.db.upcast(), associated_ty.into()).len_self();
@@ -999,6 +1096,23 @@ impl<'a> TyLoweringContext<'a> {
         TraitRef { trait_id: to_chalk_trait_id(resolved), substitution: substs }
     }
 
+    fn prohibit_generics(
+        &mut self,
+        path_id: PathId,
+        idx: u32,
+        segments: PathSegments<'_>,
+        reason: GenericArgsProhibitedReason,
+    ) {
+        segments.iter().zip(idx..).for_each(|(segment, idx)| {
+            if segment.args_and_bindings.is_some() {
+                self.push_diagnostic(
+                    path_id.type_ref(),
+                    TyLoweringDiagnosticKind::GenericArgsProhibited { segment: idx, reason },
+                );
+            }
+        });
+    }
+
     fn lower_trait_ref_from_path(
         &mut self,
         path_id: PathId,
@@ -1010,6 +1124,13 @@ impl<'a> TyLoweringContext<'a> {
             TypeNs::TraitId(tr) => tr,
             _ => return None,
         };
+        // Do this after we verify it's indeed a trait to not confuse the user if they're not modules.
+        self.prohibit_generics(
+            path_id,
+            0,
+            path.segments().strip_last(),
+            GenericArgsProhibitedReason::Module,
+        );
         let segment = path.segments().last().expect("path should have at least one segment");
         Some(self.lower_trait_ref_from_resolved_path(resolved, segment, explicit_self_ty))
     }
@@ -1233,7 +1354,9 @@ impl<'a> TyLoweringContext<'a> {
                                     }
                                     _ => unreachable!(),
                                 }
-                                ext.lower_ty(type_ref)
+                                let ty = ext.lower_ty(type_ref);
+                                self.diagnostics.extend(ext.diagnostics);
+                                ty
                             } else {
                                 self.lower_ty(type_ref)
                             };