Minor refactorings

- use `DefWithBodyId::as_generic_def_id()`
- add comments on `InferenceResult` invariant
- move local helper function to bottom to comply with style guide

crates/hir-ty/src/infer.rs

@@ -367,6 +367,10 @@ pub enum PointerCast {
 }
 
 /// The result of type inference: A mapping from expressions and patterns to types.
+///
+/// When you add a field that stores types (including `Substitution` and the like), don't forget
+/// `resolve_completely()`'ing  them in `InferenceContext::resolve_all()`. Inference variables must
+/// not appear in the final inference result.
 #[derive(Clone, PartialEq, Eq, Debug, Default)]
 pub struct InferenceResult {
     /// For each method call expr, records the function it resolves to.
@@ -575,6 +579,8 @@ impl<'a> InferenceContext<'a> {
     // used this function for another workaround, mention it here. If you really need this function and believe that
     // there is no problem in it being `pub(crate)`, remove this comment.
     pub(crate) fn resolve_all(self) -> InferenceResult {
+        // NOTE: `InferenceResult::closure_info` is `resolve_completely()`'d during
+        // `InferenceContext::infer_closures()` (in `HirPlace::ty()` specifically).
         let InferenceContext { mut table, mut result, .. } = self;
 
         table.fallback_if_possible();

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

@@ -236,6 +236,24 @@ pub(crate) struct CapturedItemWithoutTy {
 
 impl CapturedItemWithoutTy {
     fn with_ty(self, ctx: &mut InferenceContext<'_>) -> CapturedItem {
+        let ty = self.place.ty(ctx).clone();
+        let ty = match &self.kind {
+            CaptureKind::ByValue => ty,
+            CaptureKind::ByRef(bk) => {
+                let m = match bk {
+                    BorrowKind::Mut { .. } => Mutability::Mut,
+                    _ => Mutability::Not,
+                };
+                TyKind::Ref(m, static_lifetime(), ty).intern(Interner)
+            }
+        };
+        return CapturedItem {
+            place: self.place,
+            kind: self.kind,
+            span: self.span,
+            ty: replace_placeholder_with_binder(ctx.db, ctx.owner, ty),
+        };
+
         fn replace_placeholder_with_binder(
             db: &dyn HirDatabase,
             owner: DefWithBodyId,
@@ -281,36 +299,13 @@ impl CapturedItemWithoutTy {
                     Ok(BoundVar::new(outer_binder, idx).to_ty(Interner))
                 }
             }
-            let g_def = match owner {
+            let Some(generic_def) = owner.as_generic_def_id() else {
-                DefWithBodyId::FunctionId(f) => Some(f.into()),
-                DefWithBodyId::StaticId(_) => None,
-                DefWithBodyId::ConstId(f) => Some(f.into()),
-                DefWithBodyId::VariantId(f) => Some(f.into()),
-            };
-            let Some(generics) = g_def.map(|g_def| generics(db.upcast(), g_def)) else {
                 return Binders::empty(Interner, ty);
             };
-            let filler = &mut Filler { db, generics };
+            let filler = &mut Filler { db, generics: generics(db.upcast(), generic_def) };
             let result = ty.clone().try_fold_with(filler, DebruijnIndex::INNERMOST).unwrap_or(ty);
             make_binders(db, &filler.generics, result)
         }
-        let ty = self.place.ty(ctx).clone();
-        let ty = match &self.kind {
-            CaptureKind::ByValue => ty,
-            CaptureKind::ByRef(bk) => {
-                let m = match bk {
-                    BorrowKind::Mut { .. } => Mutability::Mut,
-                    _ => Mutability::Not,
-                };
-                TyKind::Ref(m, static_lifetime(), ty).intern(Interner)
-            }
-        };
-        CapturedItem {
-            place: self.place,
-            kind: self.kind,
-            span: self.span,
-            ty: replace_placeholder_with_binder(ctx.db, ctx.owner, ty),
-        }
     }
 }
 

crates/hir-ty/src/mir/monomorphization.rs

@@ -303,13 +303,7 @@ pub fn monomorphized_mir_body_query(
     subst: Substitution,
     trait_env: Arc<crate::TraitEnvironment>,
 ) -> Result<Arc<MirBody>, MirLowerError> {
-    let g_def = match owner {
+    let generics = owner.as_generic_def_id().map(|g_def| generics(db.upcast(), g_def));
-        DefWithBodyId::FunctionId(f) => Some(f.into()),
-        DefWithBodyId::StaticId(_) => None,
-        DefWithBodyId::ConstId(f) => Some(f.into()),
-        DefWithBodyId::VariantId(f) => Some(f.into()),
-    };
-    let generics = g_def.map(|g_def| generics(db.upcast(), g_def));
     let filler = &mut Filler { db, subst: &subst, trait_env, generics, owner };
     let body = db.mir_body(owner)?;
     let mut body = (*body).clone();
@@ -334,13 +328,7 @@ pub fn monomorphized_mir_body_for_closure_query(
     trait_env: Arc<crate::TraitEnvironment>,
 ) -> Result<Arc<MirBody>, MirLowerError> {
     let (owner, _) = db.lookup_intern_closure(closure.into());
-    let g_def = match owner {
+    let generics = owner.as_generic_def_id().map(|g_def| generics(db.upcast(), g_def));
-        DefWithBodyId::FunctionId(f) => Some(f.into()),
-        DefWithBodyId::StaticId(_) => None,
-        DefWithBodyId::ConstId(f) => Some(f.into()),
-        DefWithBodyId::VariantId(f) => Some(f.into()),
-    };
-    let generics = g_def.map(|g_def| generics(db.upcast(), g_def));
     let filler = &mut Filler { db, subst: &subst, trait_env, generics, owner };
     let body = db.mir_body_for_closure(closure)?;
     let mut body = (*body).clone();
@@ -356,13 +344,7 @@ pub fn monomorphize_mir_body_bad(
     trait_env: Arc<crate::TraitEnvironment>,
 ) -> Result<MirBody, MirLowerError> {
     let owner = body.owner;
-    let g_def = match owner {
+    let generics = owner.as_generic_def_id().map(|g_def| generics(db.upcast(), g_def));
-        DefWithBodyId::FunctionId(f) => Some(f.into()),
-        DefWithBodyId::StaticId(_) => None,
-        DefWithBodyId::ConstId(f) => Some(f.into()),
-        DefWithBodyId::VariantId(f) => Some(f.into()),
-    };
-    let generics = g_def.map(|g_def| generics(db.upcast(), g_def));
     let filler = &mut Filler { db, subst: &subst, trait_env, generics, owner };
     filler.fill_body(&mut body)?;
     Ok(body)