Properly handle lifetimes when checking generic arguments len

And also, prepare for correct lowering of lifetime. We still don't handle most lifetimes correctly, but a bit more of the foundation to lifetime elision is now implemented.

Author: ChayimFriedman2

crates/hir-def/src/hir/type_ref.rs

@@ -106,6 +106,14 @@ pub struct FnType {
     pub abi: Option<Symbol>,
 }
 
+impl FnType {
+    #[inline]
+    pub fn split_params_and_ret(&self) -> (&[(Option<Name>, TypeRefId)], TypeRefId) {
+        let (ret, params) = self.params.split_last().expect("should have at least return type");
+        (params, ret.1)
+    }
+}
+
 #[derive(Clone, PartialEq, Eq, Hash, Debug)]
 pub struct ArrayType {
     pub ty: TypeRefId,

crates/hir-ty/src/chalk_db.rs

@@ -27,6 +27,7 @@ use crate::{
     db::{HirDatabase, InternedCoroutine},
     from_assoc_type_id, from_chalk_trait_id, from_foreign_def_id,
     generics::generics,
+    lower::LifetimeElisionKind,
     make_binders, make_single_type_binders,
     mapping::{ToChalk, TypeAliasAsValue, from_chalk},
     method_resolution::{ALL_FLOAT_FPS, ALL_INT_FPS, TraitImpls, TyFingerprint},
@@ -632,9 +633,14 @@ pub(crate) fn associated_ty_data_query(
     let type_alias_data = db.type_alias_signature(type_alias);
     let generic_params = generics(db, type_alias.into());
     let resolver = hir_def::resolver::HasResolver::resolver(type_alias, db);
-    let mut ctx =
-        crate::TyLoweringContext::new(db, &resolver, &type_alias_data.store, type_alias.into())
-            .with_type_param_mode(crate::lower::ParamLoweringMode::Variable);
+    let mut ctx = crate::TyLoweringContext::new(
+        db,
+        &resolver,
+        &type_alias_data.store,
+        type_alias.into(),
+        LifetimeElisionKind::AnonymousReportError,
+    )
+    .with_type_param_mode(crate::lower::ParamLoweringMode::Variable);
 
     let trait_subst = TyBuilder::subst_for_def(db, trait_, None)
         .fill_with_bound_vars(crate::DebruijnIndex::INNERMOST, 0)

crates/hir-ty/src/infer.rs

@@ -34,8 +34,8 @@ use chalk_ir::{
 };
 use either::Either;
 use hir_def::{
-    AdtId, AssocItemId, DefWithBodyId, FieldId, FunctionId, GenericDefId, GenericParamId, ImplId,
-    ItemContainerId, Lookup, TraitId, TupleFieldId, TupleId, TypeAliasId, VariantId,
+    AdtId, AssocItemId, ConstId, DefWithBodyId, FieldId, FunctionId, GenericDefId, GenericParamId,
+    ImplId, ItemContainerId, Lookup, TraitId, TupleFieldId, TupleId, TypeAliasId, VariantId,
     builtin_type::{BuiltinInt, BuiltinType, BuiltinUint},
     expr_store::{Body, ExpressionStore, HygieneId, path::Path},
     hir::{BindingAnnotation, BindingId, ExprId, ExprOrPatId, LabelId, PatId},
@@ -67,9 +67,9 @@ use crate::{
         expr::ExprIsRead,
         unify::InferenceTable,
     },
-    lower::{GenericArgsPosition, ImplTraitLoweringMode, diagnostics::TyLoweringDiagnostic},
+    lower::{ImplTraitLoweringMode, LifetimeElisionKind, diagnostics::TyLoweringDiagnostic},
     mir::MirSpan,
-    to_assoc_type_id,
+    static_lifetime, to_assoc_type_id,
     traits::FnTrait,
     utils::UnevaluatedConstEvaluatorFolder,
 };
@@ -96,7 +96,7 @@ pub(crate) fn infer_query(db: &dyn HirDatabase, def: DefWithBodyId) -> Arc<Infer
         DefWithBodyId::FunctionId(f) => {
             ctx.collect_fn(f);
         }
-        DefWithBodyId::ConstId(c) => ctx.collect_const(&db.const_signature(c)),
+        DefWithBodyId::ConstId(c) => ctx.collect_const(c, &db.const_signature(c)),
         DefWithBodyId::StaticId(s) => ctx.collect_static(&db.static_signature(s)),
         DefWithBodyId::VariantId(v) => {
             ctx.return_ty = TyBuilder::builtin(
@@ -899,9 +899,13 @@ impl<'a> InferenceContext<'a> {
         result
     }
 
-    fn collect_const(&mut self, data: &ConstSignature) {
-        let return_ty =
-            self.make_ty(data.type_ref, &data.store, InferenceTyDiagnosticSource::Signature);
+    fn collect_const(&mut self, id: ConstId, data: &ConstSignature) {
+        let return_ty = self.make_ty(
+            data.type_ref,
+            &data.store,
+            InferenceTyDiagnosticSource::Signature,
+            LifetimeElisionKind::for_const(id.loc(self.db).container),
+        );
 
         // Constants might be defining usage sites of TAITs.
         self.make_tait_coercion_table(iter::once(&return_ty));
@@ -910,8 +914,12 @@ impl<'a> InferenceContext<'a> {
     }
 
     fn collect_static(&mut self, data: &StaticSignature) {
-        let return_ty =
-            self.make_ty(data.type_ref, &data.store, InferenceTyDiagnosticSource::Signature);
+        let return_ty = self.make_ty(
+            data.type_ref,
+            &data.store,
+            InferenceTyDiagnosticSource::Signature,
+            LifetimeElisionKind::Elided(static_lifetime()),
+        );
 
         // Statics might be defining usage sites of TAITs.
         self.make_tait_coercion_table(iter::once(&return_ty));
@@ -921,12 +929,15 @@ impl<'a> InferenceContext<'a> {
 
     fn collect_fn(&mut self, func: FunctionId) {
         let data = self.db.function_signature(func);
-        let mut param_tys =
-            self.with_ty_lowering(&data.store, InferenceTyDiagnosticSource::Signature, |ctx| {
+        let mut param_tys = self.with_ty_lowering(
+            &data.store,
+            InferenceTyDiagnosticSource::Signature,
+            LifetimeElisionKind::for_fn_params(&data),
+            |ctx| {
                 ctx.type_param_mode(ParamLoweringMode::Placeholder);
-                ctx.in_fn_signature = true;
                 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
@@ -967,10 +978,10 @@ impl<'a> InferenceContext<'a> {
                 let return_ty = self.with_ty_lowering(
                     &data.store,
                     InferenceTyDiagnosticSource::Signature,
+                    LifetimeElisionKind::for_fn_ret(),
                     |ctx| {
                         ctx.type_param_mode(ParamLoweringMode::Placeholder)
                             .impl_trait_mode(ImplTraitLoweringMode::Opaque);
-                        ctx.in_fn_signature = true;
                         ctx.lower_ty(return_ty)
                     },
                 );
@@ -1304,6 +1315,7 @@ impl<'a> InferenceContext<'a> {
         &mut self,
         store: &ExpressionStore,
         types_source: InferenceTyDiagnosticSource,
+        lifetime_elision: LifetimeElisionKind,
         f: impl FnOnce(&mut TyLoweringContext<'_>) -> R,
     ) -> R {
         let mut ctx = TyLoweringContext::new(
@@ -1313,42 +1325,65 @@ impl<'a> InferenceContext<'a> {
             &self.diagnostics,
             types_source,
             self.generic_def,
+            lifetime_elision,
         );
         f(&mut ctx)
     }
 
     fn with_body_ty_lowering<R>(&mut self, f: impl FnOnce(&mut TyLoweringContext<'_>) -> R) -> R {
-        self.with_ty_lowering(self.body, InferenceTyDiagnosticSource::Body, f)
+        self.with_ty_lowering(
+            self.body,
+            InferenceTyDiagnosticSource::Body,
+            LifetimeElisionKind::Infer,
+            f,
+        )
     }
 
     fn make_ty(
         &mut self,
         type_ref: TypeRefId,
         store: &ExpressionStore,
         type_source: InferenceTyDiagnosticSource,
+        lifetime_elision: LifetimeElisionKind,
     ) -> Ty {
-        let ty = self.with_ty_lowering(store, type_source, |ctx| ctx.lower_ty(type_ref));
+        let ty = self
+            .with_ty_lowering(store, type_source, lifetime_elision, |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, InferenceTyDiagnosticSource::Body)
+        self.make_ty(
+            type_ref,
+            self.body,
+            InferenceTyDiagnosticSource::Body,
+            LifetimeElisionKind::Infer,
+        )
     }
 
     fn make_body_const(&mut self, const_ref: ConstRef, ty: Ty) -> Const {
-        let const_ = self.with_ty_lowering(self.body, InferenceTyDiagnosticSource::Body, |ctx| {
-            ctx.type_param_mode = ParamLoweringMode::Placeholder;
-            ctx.lower_const(&const_ref, ty)
-        });
+        let const_ = self.with_ty_lowering(
+            self.body,
+            InferenceTyDiagnosticSource::Body,
+            LifetimeElisionKind::Infer,
+            |ctx| {
+                ctx.type_param_mode = ParamLoweringMode::Placeholder;
+                ctx.lower_const(&const_ref, ty)
+            },
+        );
         self.insert_type_vars(const_)
     }
 
     fn make_path_as_body_const(&mut self, path: &Path, ty: Ty) -> Const {
-        let const_ = self.with_ty_lowering(self.body, InferenceTyDiagnosticSource::Body, |ctx| {
-            ctx.type_param_mode = ParamLoweringMode::Placeholder;
-            ctx.lower_path_as_const(path, ty)
-        });
+        let const_ = self.with_ty_lowering(
+            self.body,
+            InferenceTyDiagnosticSource::Body,
+            LifetimeElisionKind::Infer,
+            |ctx| {
+                ctx.type_param_mode = ParamLoweringMode::Placeholder;
+                ctx.lower_path_as_const(path, ty)
+            },
+        );
         self.insert_type_vars(const_)
     }
 
@@ -1357,9 +1392,12 @@ impl<'a> InferenceContext<'a> {
     }
 
     fn make_body_lifetime(&mut self, lifetime_ref: &LifetimeRef) -> Lifetime {
-        let lt = self.with_ty_lowering(self.body, InferenceTyDiagnosticSource::Body, |ctx| {
-            ctx.lower_lifetime(lifetime_ref)
-        });
+        let lt = self.with_ty_lowering(
+            self.body,
+            InferenceTyDiagnosticSource::Body,
+            LifetimeElisionKind::Infer,
+            |ctx| ctx.lower_lifetime(lifetime_ref),
+        );
         self.insert_type_vars(lt)
     }
 
@@ -1529,23 +1567,24 @@ impl<'a> InferenceContext<'a> {
             &self.diagnostics,
             InferenceTyDiagnosticSource::Body,
             self.generic_def,
+            LifetimeElisionKind::Infer,
         );
-        let mut path_ctx = ctx.at_path(path, node, GenericArgsPosition::Value);
+        let mut path_ctx = ctx.at_path(path, node);
         let (resolution, unresolved) = if value_ns {
             let Some(res) = path_ctx.resolve_path_in_value_ns(HygieneId::ROOT) else {
                 return (self.err_ty(), None);
             };
             match res {
                 ResolveValueResult::ValueNs(value, _) => match value {
                     ValueNs::EnumVariantId(var) => {
-                        let substs = path_ctx.substs_from_path(var.into(), true);
+                        let substs = path_ctx.substs_from_path(var.into(), true, false);
                         drop(ctx);
                         let ty = self.db.ty(var.lookup(self.db).parent.into());
                         let ty = self.insert_type_vars(ty.substitute(Interner, &substs));
                         return (ty, Some(var.into()));
                     }
                     ValueNs::StructId(strukt) => {
-                        let substs = path_ctx.substs_from_path(strukt.into(), true);
+                        let substs = path_ctx.substs_from_path(strukt.into(), true, false);
                         drop(ctx);
                         let ty = self.db.ty(strukt.into());
                         let ty = self.insert_type_vars(ty.substitute(Interner, &substs));
@@ -1567,21 +1606,21 @@ impl<'a> InferenceContext<'a> {
         };
         return match resolution {
             TypeNs::AdtId(AdtId::StructId(strukt)) => {
-                let substs = path_ctx.substs_from_path(strukt.into(), true);
+                let substs = path_ctx.substs_from_path(strukt.into(), true, false);
                 drop(ctx);
                 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 = path_ctx.substs_from_path(u.into(), true);
+                let substs = path_ctx.substs_from_path(u.into(), true, false);
                 drop(ctx);
                 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 = path_ctx.substs_from_path(var.into(), true);
+                let substs = path_ctx.substs_from_path(var.into(), true, false);
                 drop(ctx);
                 let ty = self.db.ty(var.lookup(self.db).parent.into());
                 let ty = self.insert_type_vars(ty.substitute(Interner, &substs));
@@ -1665,7 +1704,7 @@ impl<'a> InferenceContext<'a> {
                     never!("resolver should always resolve lang item paths");
                     return (self.err_ty(), None);
                 };
-                let substs = path_ctx.substs_from_path_segment(it.into(), true, None);
+                let substs = path_ctx.substs_from_path_segment(it.into(), true, None, false);
                 drop(ctx);
                 let ty = self.db.ty(it.into());
                 let ty = self.insert_type_vars(ty.substitute(Interner, &substs));

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

@@ -440,6 +440,8 @@ impl InferenceContext<'_> {
         // collect explicitly written argument types
         for arg_type in arg_types.iter() {
             let arg_ty = match arg_type {
+                // FIXME: I think rustc actually lowers closure params with `LifetimeElisionKind::AnonymousCreateParameter`
+                // (but the return type with infer).
                 Some(type_ref) => self.make_body_ty(*type_ref),
                 None => self.table.new_type_var(),
             };

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

@@ -12,7 +12,7 @@ use hir_def::expr_store::path::Path;
 use hir_def::{hir::ExprOrPatId, resolver::Resolver};
 use la_arena::{Idx, RawIdx};
 
-use crate::lower::GenericArgsPosition;
+use crate::lower::LifetimeElisionKind;
 use crate::{
     InferenceDiagnostic, InferenceTyDiagnosticSource, TyLoweringContext, TyLoweringDiagnostic,
     db::HirDatabase,
@@ -66,16 +66,20 @@ impl<'a> InferenceTyLoweringContext<'a> {
         diagnostics: &'a Diagnostics,
         source: InferenceTyDiagnosticSource,
         generic_def: GenericDefId,
+        lifetime_elision: LifetimeElisionKind,
     ) -> Self {
-        Self { ctx: TyLoweringContext::new(db, resolver, store, generic_def), diagnostics, source }
+        Self {
+            ctx: TyLoweringContext::new(db, resolver, store, generic_def, lifetime_elision),
+            diagnostics,
+            source,
+        }
     }
 
     #[inline]
     pub(super) fn at_path<'b>(
         &'b mut self,
         path: &'b Path,
         node: ExprOrPatId,
-        position: GenericArgsPosition,
     ) -> PathLoweringContext<'b, 'a> {
         let on_diagnostic = PathDiagnosticCallback {
             data: Either::Right(PathDiagnosticCallbackData { diagnostics: self.diagnostics, node }),
@@ -85,14 +89,13 @@ impl<'a> InferenceTyLoweringContext<'a> {
                     .push(InferenceDiagnostic::PathDiagnostic { node: data.node, diag });
             },
         };
-        PathLoweringContext::new(&mut self.ctx, on_diagnostic, path, position)
+        PathLoweringContext::new(&mut self.ctx, on_diagnostic, path)
     }
 
     #[inline]
     pub(super) fn at_path_forget_diagnostics<'b>(
         &'b mut self,
         path: &'b Path,
-        position: GenericArgsPosition,
     ) -> PathLoweringContext<'b, 'a> {
         let on_diagnostic = PathDiagnosticCallback {
             data: Either::Right(PathDiagnosticCallbackData {
@@ -101,7 +104,7 @@ impl<'a> InferenceTyLoweringContext<'a> {
             }),
             callback: |_data, _, _diag| {},
         };
-        PathLoweringContext::new(&mut self.ctx, on_diagnostic, path, position)
+        PathLoweringContext::new(&mut self.ctx, on_diagnostic, path)
     }
 
     #[inline]