Lazy generics

crates/hir-ty/src/consteval.rs

@@ -71,12 +71,12 @@ impl From<MirEvalError> for ConstEvalError {
     }
 }
 
-pub(crate) fn path_to_const(
+pub(crate) fn path_to_const<'g>(
     db: &dyn HirDatabase,
     resolver: &Resolver,
     path: &Path,
     mode: ParamLoweringMode,
-    args: impl FnOnce() -> Option<Generics>,
+    args: impl FnOnce() -> Option<&'g Generics>,
     debruijn: DebruijnIndex,
     expected_ty: Ty,
 ) -> Option<Const> {
@@ -89,7 +89,7 @@ pub(crate) fn path_to_const(
                 }
                 ParamLoweringMode::Variable => {
                     let args = args();
-                    match args.as_ref().and_then(|args| args.type_or_const_param_idx(p.into())) {
+                    match args.and_then(|args| args.type_or_const_param_idx(p.into())) {
                         Some(it) => ConstValue::BoundVar(BoundVar::new(debruijn, it)),
                         None => {
                             never!(

crates/hir-ty/src/infer.rs

@@ -49,6 +49,7 @@ use hir_def::{
 use hir_expand::name::{name, Name};
 use indexmap::IndexSet;
 use la_arena::{ArenaMap, Entry};
+use once_cell::unsync::OnceCell;
 use rustc_hash::{FxHashMap, FxHashSet};
 use stdx::{always, never};
 use triomphe::Arc;
@@ -527,6 +528,7 @@ pub(crate) struct InferenceContext<'a> {
     pub(crate) owner: DefWithBodyId,
     pub(crate) body: &'a Body,
     pub(crate) resolver: Resolver,
+    generics: OnceCell<Option<Generics>>,
     table: unify::InferenceTable<'a>,
     /// The traits in scope, disregarding block modules. This is used for caching purposes.
     traits_in_scope: FxHashSet<TraitId>,
@@ -612,6 +614,7 @@ impl<'a> InferenceContext<'a> {
     ) -> Self {
         let trait_env = db.trait_environment_for_body(owner);
         InferenceContext {
+            generics: OnceCell::new(),
             result: InferenceResult::default(),
             table: unify::InferenceTable::new(db, trait_env),
             tuple_field_accesses_rev: Default::default(),
@@ -633,8 +636,14 @@ impl<'a> InferenceContext<'a> {
         }
     }
 
-    pub(crate) fn generics(&self) -> Option<Generics> {
-        Some(crate::generics::generics(self.db.upcast(), self.resolver.generic_def()?))
+    pub(crate) fn generics(&self) -> Option<&Generics> {
+        self.generics
+            .get_or_init(|| {
+                self.resolver
+                    .generic_def()
+                    .map(|def| crate::generics::generics(self.db.upcast(), def))
+            })
+            .as_ref()
     }
 
     // FIXME: This function should be private in module. It is currently only used in the consteval, since we need

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

@@ -339,7 +339,7 @@ impl CapturedItemWithoutTy {
         fn replace_placeholder_with_binder(ctx: &mut InferenceContext<'_>, ty: Ty) -> Binders<Ty> {
             struct Filler<'a> {
                 db: &'a dyn HirDatabase,
-                generics: Generics,
+                generics: &'a Generics,
             }
             impl FallibleTypeFolder<Interner> for Filler<'_> {
                 type Error = ();
@@ -382,7 +382,7 @@ impl CapturedItemWithoutTy {
             };
             let filler = &mut Filler { db: ctx.db, generics };
             let result = ty.clone().try_fold_with(filler, DebruijnIndex::INNERMOST).unwrap_or(ty);
-            make_binders(ctx.db, &filler.generics, result)
+            make_binders(ctx.db, filler.generics, result)
         }
     }
 }

crates/hir-ty/src/lower.rs

@@ -45,6 +45,7 @@ use hir_def::{
 use hir_expand::{name::Name, ExpandResult};
 use intern::Interned;
 use la_arena::{Arena, ArenaMap};
+use once_cell::unsync::OnceCell;
 use rustc_hash::FxHashSet;
 use smallvec::SmallVec;
 use stdx::{impl_from, never};
@@ -122,6 +123,7 @@ impl ImplTraitLoweringState {
 pub struct TyLoweringContext<'a> {
     pub db: &'a dyn HirDatabase,
     resolver: &'a Resolver,
+    generics: OnceCell<Option<Generics>>,
     in_binders: DebruijnIndex,
     // FIXME: Should not be an `Option` but `Resolver` currently does not return owners in all cases
     // where expected
@@ -153,6 +155,7 @@ impl<'a> TyLoweringContext<'a> {
         Self {
             db,
             resolver,
+            generics: OnceCell::new(),
             owner,
             in_binders,
             impl_trait_mode,
@@ -175,6 +178,7 @@ impl<'a> TyLoweringContext<'a> {
             impl_trait_mode,
             expander: RefCell::new(expander),
             unsized_types: RefCell::new(unsized_types),
+            generics: self.generics.clone(),
             ..*self
         };
         let result = f(&new_ctx);
@@ -246,8 +250,10 @@ impl<'a> TyLoweringContext<'a> {
         )
     }
 
-    fn generics(&self) -> Option<Generics> {
-        Some(generics(self.db.upcast(), self.resolver.generic_def()?))
+    fn generics(&self) -> Option<&Generics> {
+        self.generics
+            .get_or_init(|| self.resolver.generic_def().map(|def| generics(self.db.upcast(), def)))
+            .as_ref()
     }
 
     pub fn lower_ty_ext(&self, type_ref: &TypeRef) -> (Ty, Option<TypeNs>) {
@@ -2207,14 +2213,14 @@ pub(crate) fn generic_arg_to_chalk<'a, T>(
     }
 }
 
-pub(crate) fn const_or_path_to_chalk(
+pub(crate) fn const_or_path_to_chalk<'g>(
     db: &dyn HirDatabase,
     resolver: &Resolver,
     owner: TypeOwnerId,
     expected_ty: Ty,
     value: &ConstRef,
     mode: ParamLoweringMode,
-    args: impl FnOnce() -> Option<Generics>,
+    args: impl FnOnce() -> Option<&'g Generics>,
     debruijn: DebruijnIndex,
 ) -> Const {
     match value {