Auto merge of #17941 - ChayimFriedman2:pre-closure-to-fn, r=Veykril

Preliminary work for #17940

I split the PR as requested, and made small commits.

26 files changed, 815 insertions, 166 deletions

diff --git a/src/tools/rust-analyzer/crates/hir-def/src/lang_item.rs b/src/tools/rust-analyzer/crates/hir-def/src/lang_item.rs
index a09fd658aeb..166c965d14c 100644
--- a/src/tools/rust-analyzer/crates/hir-def/src/lang_item.rs
+++ b/src/tools/rust-analyzer/crates/hir-def/src/lang_item.rs
@@ -74,6 +74,13 @@ impl LangItemTarget {
             _ => None,
         }
     }
+
+    pub fn as_type_alias(self) -> Option<TypeAliasId> {
+        match self {
+            LangItemTarget::TypeAlias(id) => Some(id),
+            _ => None,
+        }
+    }
 }
 
 #[derive(Default, Debug, Clone, PartialEq, Eq)]
@@ -117,11 +124,19 @@ impl LangItems {
                 match def {
                     ModuleDefId::TraitId(trait_) => {
                         lang_items.collect_lang_item(db, trait_, LangItemTarget::Trait);
-                        db.trait_data(trait_).items.iter().for_each(|&(_, assoc_id)| {
-                            if let AssocItemId::FunctionId(f) = assoc_id {
-                                lang_items.collect_lang_item(db, f, LangItemTarget::Function);
-                            }
-                        });
+                        db.trait_data(trait_).items.iter().for_each(
+                            |&(_, assoc_id)| match assoc_id {
+                                AssocItemId::FunctionId(f) => {
+                                    lang_items.collect_lang_item(db, f, LangItemTarget::Function);
+                                }
+                                AssocItemId::TypeAliasId(alias) => lang_items.collect_lang_item(
+                                    db,
+                                    alias,
+                                    LangItemTarget::TypeAlias,
+                                ),
+                                AssocItemId::ConstId(_) => {}
+                            },
+                        );
                     }
                     ModuleDefId::AdtId(AdtId::EnumId(e)) => {
                         lang_items.collect_lang_item(db, e, LangItemTarget::EnumId);
@@ -453,6 +468,7 @@ language_item_table! {
 
     Context,                 sym::Context,             context,                    Target::Struct,         GenericRequirement::None;
     FuturePoll,              sym::poll,                future_poll_fn,             Target::Method(MethodKind::Trait { body: false }), GenericRequirement::None;
+    FutureOutput,            sym::future_output,       future_output,              Target::TypeAlias,      GenericRequirement::None;
 
     Option,                  sym::Option,              option_type,                Target::Enum,           GenericRequirement::None;
     OptionSome,              sym::Some,                option_some_variant,        Target::Variant,        GenericRequirement::None;
@@ -467,6 +483,7 @@ language_item_table! {
     IntoFutureIntoFuture,    sym::into_future,         into_future_fn,             Target::Method(MethodKind::Trait { body: false }), GenericRequirement::None;
     IntoIterIntoIter,        sym::into_iter,           into_iter_fn,               Target::Method(MethodKind::Trait { body: false }), GenericRequirement::None;
     IteratorNext,            sym::next,                next_fn,                    Target::Method(MethodKind::Trait { body: false}), GenericRequirement::None;
+    Iterator,                sym::iterator,            iterator,                   Target::Trait,           GenericRequirement::None;
 
     PinNewUnchecked,         sym::new_unchecked,       new_unchecked_fn,           Target::Method(MethodKind::Inherent), GenericRequirement::None;
 
diff --git a/src/tools/rust-analyzer/crates/hir-ty/src/infer.rs b/src/tools/rust-analyzer/crates/hir-ty/src/infer.rs
index 8b4e98c5500..062ea278151 100644
--- a/src/tools/rust-analyzer/crates/hir-ty/src/infer.rs
+++ b/src/tools/rust-analyzer/crates/hir-ty/src/infer.rs
@@ -59,6 +59,7 @@ use crate::{
     generics::Generics,
     infer::{coerce::CoerceMany, unify::InferenceTable},
     lower::ImplTraitLoweringMode,
+    mir::MirSpan,
     to_assoc_type_id,
     traits::FnTrait,
     utils::{InTypeConstIdMetadata, UnevaluatedConstEvaluatorFolder},
@@ -553,6 +554,12 @@ pub(crate) struct InferenceContext<'a> {
 
     // fields related to closure capture
     current_captures: Vec<CapturedItemWithoutTy>,
+    /// A stack that has an entry for each projection in the current capture.
+    ///
+    /// For example, in `a.b.c`, we capture the spans of `a`, `a.b`, and `a.b.c`.
+    /// We do that because sometimes we truncate projections (when a closure captures
+    /// both `a.b` and `a.b.c`), and we want to provide accurate spans in this case.
+    current_capture_span_stack: Vec<MirSpan>,
     current_closure: Option<ClosureId>,
     /// Stores the list of closure ids that need to be analyzed before this closure. See the
     /// comment on `InferenceContext::sort_closures`
@@ -634,6 +641,7 @@ impl<'a> InferenceContext<'a> {
             breakables: Vec::new(),
             deferred_cast_checks: Vec::new(),
             current_captures: Vec::new(),
+            current_capture_span_stack: Vec::new(),
             current_closure: None,
             deferred_closures: FxHashMap::default(),
             closure_dependencies: FxHashMap::default(),
diff --git a/src/tools/rust-analyzer/crates/hir-ty/src/infer/closure.rs b/src/tools/rust-analyzer/crates/hir-ty/src/infer/closure.rs
index 910e19dc580..68e1a6ee821 100644
--- a/src/tools/rust-analyzer/crates/hir-ty/src/infer/closure.rs
+++ b/src/tools/rust-analyzer/crates/hir-ty/src/infer/closure.rs
@@ -18,7 +18,7 @@ use hir_def::{
 use hir_expand::name::Name;
 use intern::sym;
 use rustc_hash::FxHashMap;
-use smallvec::SmallVec;
+use smallvec::{smallvec, SmallVec};
 use stdx::never;
 
 use crate::{
@@ -236,7 +236,13 @@ pub enum CaptureKind {
 pub struct CapturedItem {
     pub(crate) place: HirPlace,
     pub(crate) kind: CaptureKind,
-    pub(crate) span: MirSpan,
+    /// The inner vec is the stacks; the outer vec is for each capture reference.
+    ///
+    /// Even though we always report only the last span (i.e. the most inclusive span),
+    /// we need to keep them all, since when a closure occurs inside a closure, we
+    /// copy all captures of the inner closure to the outer closure, and then we may
+    /// truncate them, and we want the correct span to be reported.
+    span_stacks: SmallVec<[SmallVec<[MirSpan; 3]>; 3]>,
     pub(crate) ty: Binders<Ty>,
 }
 
@@ -253,6 +259,10 @@ impl CapturedItem {
         self.kind
     }
 
+    pub fn spans(&self) -> SmallVec<[MirSpan; 3]> {
+        self.span_stacks.iter().map(|stack| *stack.last().expect("empty span stack")).collect()
+    }
+
     pub fn display_place(&self, owner: DefWithBodyId, db: &dyn HirDatabase) -> String {
         let body = db.body(owner);
         let krate = owner.krate(db.upcast());
@@ -314,7 +324,8 @@ impl CapturedItem {
 pub(crate) struct CapturedItemWithoutTy {
     pub(crate) place: HirPlace,
     pub(crate) kind: CaptureKind,
-    pub(crate) span: MirSpan,
+    /// The inner vec is the stacks; the outer vec is for each capture reference.
+    pub(crate) span_stacks: SmallVec<[SmallVec<[MirSpan; 3]>; 3]>,
 }
 
 impl CapturedItemWithoutTy {
@@ -333,7 +344,7 @@ impl CapturedItemWithoutTy {
         return CapturedItem {
             place: self.place,
             kind: self.kind,
-            span: self.span,
+            span_stacks: self.span_stacks,
             ty: replace_placeholder_with_binder(ctx, ty),
         };
 
@@ -393,22 +404,26 @@ impl InferenceContext<'_> {
         let r = self.place_of_expr_without_adjust(tgt_expr)?;
         let default = vec![];
         let adjustments = self.result.expr_adjustments.get(&tgt_expr).unwrap_or(&default);
-        apply_adjusts_to_place(r, adjustments)
+        apply_adjusts_to_place(&mut self.current_capture_span_stack, r, adjustments)
     }
 
+    /// Changes `current_capture_span_stack` to contain the stack of spans for this expr.
     fn place_of_expr_without_adjust(&mut self, tgt_expr: ExprId) -> Option<HirPlace> {
+        self.current_capture_span_stack.clear();
         match &self.body[tgt_expr] {
             Expr::Path(p) => {
                 let resolver = resolver_for_expr(self.db.upcast(), self.owner, tgt_expr);
                 if let Some(ResolveValueResult::ValueNs(ValueNs::LocalBinding(b), _)) =
                     resolver.resolve_path_in_value_ns(self.db.upcast(), p)
                 {
+                    self.current_capture_span_stack.push(MirSpan::ExprId(tgt_expr));
                     return Some(HirPlace { local: b, projections: vec![] });
                 }
             }
             Expr::Field { expr, name: _ } => {
                 let mut place = self.place_of_expr(*expr)?;
                 let field = self.result.field_resolution(tgt_expr)?;
+                self.current_capture_span_stack.push(MirSpan::ExprId(tgt_expr));
                 place.projections.push(ProjectionElem::Field(field));
                 return Some(place);
             }
@@ -418,6 +433,7 @@ impl InferenceContext<'_> {
                     TyKind::Ref(..) | TyKind::Raw(..)
                 ) {
                     let mut place = self.place_of_expr(*expr)?;
+                    self.current_capture_span_stack.push(MirSpan::ExprId(tgt_expr));
                     place.projections.push(ProjectionElem::Deref);
                     return Some(place);
                 }
@@ -427,29 +443,65 @@ impl InferenceContext<'_> {
         None
     }
 
-    fn push_capture(&mut self, capture: CapturedItemWithoutTy) {
-        self.current_captures.push(capture);
+    fn push_capture(&mut self, place: HirPlace, kind: CaptureKind) {
+        self.current_captures.push(CapturedItemWithoutTy {
+            place,
+            kind,
+            span_stacks: smallvec![self.current_capture_span_stack.iter().copied().collect()],
+        });
     }
 
-    fn ref_expr(&mut self, expr: ExprId) {
-        if let Some(place) = self.place_of_expr(expr) {
-            self.add_capture(place, CaptureKind::ByRef(BorrowKind::Shared), expr.into());
+    fn is_ref_span(&self, span: MirSpan) -> bool {
+        match span {
+            MirSpan::ExprId(expr) => matches!(self.body[expr], Expr::Ref { .. }),
+            MirSpan::BindingId(_) => true,
+            MirSpan::PatId(_) | MirSpan::SelfParam | MirSpan::Unknown => false,
+        }
+    }
+
+    fn truncate_capture_spans(&self, capture: &mut CapturedItemWithoutTy, mut truncate_to: usize) {
+        // The first span is the identifier, and it must always remain.
+        truncate_to += 1;
+        for span_stack in &mut capture.span_stacks {
+            let mut remained = truncate_to;
+            let mut actual_truncate_to = 0;
+            for &span in &*span_stack {
+                actual_truncate_to += 1;
+                if !self.is_ref_span(span) {
+                    remained -= 1;
+                    if remained == 0 {
+                        break;
+                    }
+                }
+            }
+            if actual_truncate_to < span_stack.len()
+                && self.is_ref_span(span_stack[actual_truncate_to])
+            {
+                // Include the ref operator if there is one, we will fix it later (in `strip_captures_ref_span()`) if it's incorrect.
+                actual_truncate_to += 1;
+            }
+            span_stack.truncate(actual_truncate_to);
+        }
+    }
+
+    fn ref_expr(&mut self, expr: ExprId, place: Option<HirPlace>) {
+        if let Some(place) = place {
+            self.add_capture(place, CaptureKind::ByRef(BorrowKind::Shared));
         }
         self.walk_expr(expr);
     }
 
-    fn add_capture(&mut self, place: HirPlace, kind: CaptureKind, span: MirSpan) {
+    fn add_capture(&mut self, place: HirPlace, kind: CaptureKind) {
         if self.is_upvar(&place) {
-            self.push_capture(CapturedItemWithoutTy { place, kind, span });
+            self.push_capture(place, kind);
         }
     }
 
-    fn mutate_expr(&mut self, expr: ExprId) {
-        if let Some(place) = self.place_of_expr(expr) {
+    fn mutate_expr(&mut self, expr: ExprId, place: Option<HirPlace>) {
+        if let Some(place) = place {
             self.add_capture(
                 place,
                 CaptureKind::ByRef(BorrowKind::Mut { kind: MutBorrowKind::Default }),
-                expr.into(),
             );
         }
         self.walk_expr(expr);
@@ -457,12 +509,12 @@ impl InferenceContext<'_> {
 
     fn consume_expr(&mut self, expr: ExprId) {
         if let Some(place) = self.place_of_expr(expr) {
-            self.consume_place(place, expr.into());
+            self.consume_place(place);
         }
         self.walk_expr(expr);
     }
 
-    fn consume_place(&mut self, place: HirPlace, span: MirSpan) {
+    fn consume_place(&mut self, place: HirPlace) {
         if self.is_upvar(&place) {
             let ty = place.ty(self);
             let kind = if self.is_ty_copy(ty) {
@@ -470,7 +522,7 @@ impl InferenceContext<'_> {
             } else {
                 CaptureKind::ByValue
             };
-            self.push_capture(CapturedItemWithoutTy { place, kind, span });
+            self.push_capture(place, kind);
         }
     }
 
@@ -501,8 +553,10 @@ impl InferenceContext<'_> {
             Mutability::Not => CaptureKind::ByRef(BorrowKind::Shared),
         };
         if let Some(place) = self.place_of_expr_without_adjust(tgt_expr) {
-            if let Some(place) = apply_adjusts_to_place(place, rest) {
-                self.add_capture(place, capture_kind, tgt_expr.into());
+            if let Some(place) =
+                apply_adjusts_to_place(&mut self.current_capture_span_stack, place, rest)
+            {
+                self.add_capture(place, capture_kind);
             }
         }
         self.walk_expr_with_adjust(tgt_expr, rest);
@@ -584,11 +638,7 @@ impl InferenceContext<'_> {
                             self.walk_pat(&mut capture_mode, arm.pat);
                         }
                         if let Some(c) = capture_mode {
-                            self.push_capture(CapturedItemWithoutTy {
-                                place: discr_place,
-                                kind: c,
-                                span: (*expr).into(),
-                            })
+                            self.push_capture(discr_place, c);
                         }
                     }
                 }
@@ -632,10 +682,11 @@ impl InferenceContext<'_> {
                         }
                         false
                     };
+                    let place = self.place_of_expr(*expr);
                     if mutability {
-                        self.mutate_expr(*expr);
+                        self.mutate_expr(*expr, place);
                     } else {
-                        self.ref_expr(*expr);
+                        self.ref_expr(*expr, place);
                     }
                 } else {
                     self.select_from_expr(*expr);
@@ -650,16 +701,22 @@ impl InferenceContext<'_> {
             | Expr::Cast { expr, type_ref: _ } => {
                 self.consume_expr(*expr);
             }
-            Expr::Ref { expr, rawness: _, mutability } => match mutability {
-                hir_def::type_ref::Mutability::Shared => self.ref_expr(*expr),
-                hir_def::type_ref::Mutability::Mut => self.mutate_expr(*expr),
-            },
+            Expr::Ref { expr, rawness: _, mutability } => {
+                // We need to do this before we push the span so the order will be correct.
+                let place = self.place_of_expr(*expr);
+                self.current_capture_span_stack.push(MirSpan::ExprId(tgt_expr));
+                match mutability {
+                    hir_def::type_ref::Mutability::Shared => self.ref_expr(*expr, place),
+                    hir_def::type_ref::Mutability::Mut => self.mutate_expr(*expr, place),
+                }
+            }
             Expr::BinaryOp { lhs, rhs, op } => {
                 let Some(op) = op else {
                     return;
                 };
                 if matches!(op, BinaryOp::Assignment { .. }) {
-                    self.mutate_expr(*lhs);
+                    let place = self.place_of_expr(*lhs);
+                    self.mutate_expr(*lhs, place);
                     self.consume_expr(*rhs);
                     return;
                 }
@@ -690,7 +747,11 @@ impl InferenceContext<'_> {
                     );
                 let mut cc = mem::take(&mut self.current_captures);
                 cc.extend(captures.iter().filter(|it| self.is_upvar(&it.place)).map(|it| {
-                    CapturedItemWithoutTy { place: it.place.clone(), kind: it.kind, span: it.span }
+                    CapturedItemWithoutTy {
+                        place: it.place.clone(),
+                        kind: it.kind,
+                        span_stacks: it.span_stacks.clone(),
+                    }
                 }));
                 self.current_captures = cc;
             }
@@ -812,10 +873,13 @@ impl InferenceContext<'_> {
     }
 
     fn restrict_precision_for_unsafe(&mut self) {
-        for capture in &mut self.current_captures {
+        // FIXME: Borrow checker problems without this.
+        let mut current_captures = std::mem::take(&mut self.current_captures);
+        for capture in &mut current_captures {
             let mut ty = self.table.resolve_completely(self.result[capture.place.local].clone());
             if ty.as_raw_ptr().is_some() || ty.is_union() {
                 capture.kind = CaptureKind::ByRef(BorrowKind::Shared);
+                self.truncate_capture_spans(capture, 0);
                 capture.place.projections.truncate(0);
                 continue;
             }
@@ -830,29 +894,35 @@ impl InferenceContext<'_> {
                 );
                 if ty.as_raw_ptr().is_some() || ty.is_union() {
                     capture.kind = CaptureKind::ByRef(BorrowKind::Shared);
+                    self.truncate_capture_spans(capture, i + 1);
                     capture.place.projections.truncate(i + 1);
                     break;
                 }
             }
         }
+        self.current_captures = current_captures;
     }
 
     fn adjust_for_move_closure(&mut self) {
-        for capture in &mut self.current_captures {
+        // FIXME: Borrow checker won't allow without this.
+        let mut current_captures = std::mem::take(&mut self.current_captures);
+        for capture in &mut current_captures {
             if let Some(first_deref) =
                 capture.place.projections.iter().position(|proj| *proj == ProjectionElem::Deref)
             {
+                self.truncate_capture_spans(capture, first_deref);
                 capture.place.projections.truncate(first_deref);
             }
             capture.kind = CaptureKind::ByValue;
         }
+        self.current_captures = current_captures;
     }
 
     fn minimize_captures(&mut self) {
-        self.current_captures.sort_by_key(|it| it.place.projections.len());
+        self.current_captures.sort_unstable_by_key(|it| it.place.projections.len());
         let mut hash_map = FxHashMap::<HirPlace, usize>::default();
         let result = mem::take(&mut self.current_captures);
-        for item in result {
+        for mut item in result {
             let mut lookup_place = HirPlace { local: item.place.local, projections: vec![] };
             let mut it = item.place.projections.iter();
             let prev_index = loop {
@@ -860,12 +930,17 @@ impl InferenceContext<'_> {
                     break Some(*k);
                 }
                 match it.next() {
-                    Some(it) => lookup_place.projections.push(it.clone()),
+                    Some(it) => {
+                        lookup_place.projections.push(it.clone());
+                    }
                     None => break None,
                 }
             };
             match prev_index {
                 Some(p) => {
+                    let prev_projections_len = self.current_captures[p].place.projections.len();
+                    self.truncate_capture_spans(&mut item, prev_projections_len);
+                    self.current_captures[p].span_stacks.extend(item.span_stacks);
                     let len = self.current_captures[p].place.projections.len();
                     let kind_after_truncate =
                         item.place.capture_kind_of_truncated_place(item.kind, len);
@@ -880,113 +955,128 @@ impl InferenceContext<'_> {
         }
     }
 
-    fn consume_with_pat(&mut self, mut place: HirPlace, pat: PatId) {
-        let cnt = self.result.pat_adjustments.get(&pat).map(|it| it.len()).unwrap_or_default();
-        place.projections = place
-            .projections
-            .iter()
-            .cloned()
-            .chain((0..cnt).map(|_| ProjectionElem::Deref))
-            .collect::<Vec<_>>();
-        match &self.body[pat] {
-            Pat::Missing | Pat::Wild => (),
-            Pat::Tuple { args, ellipsis } => {
-                let (al, ar) = args.split_at(ellipsis.map_or(args.len(), |it| it as usize));
-                let field_count = match self.result[pat].kind(Interner) {
-                    TyKind::Tuple(_, s) => s.len(Interner),
-                    _ => return,
-                };
-                let fields = 0..field_count;
-                let it = al.iter().zip(fields.clone()).chain(ar.iter().rev().zip(fields.rev()));
-                for (arg, i) in it {
-                    let mut p = place.clone();
-                    p.projections.push(ProjectionElem::Field(Either::Right(TupleFieldId {
-                        tuple: TupleId(!0), // dummy this, as its unused anyways
-                        index: i as u32,
-                    })));
-                    self.consume_with_pat(p, *arg);
-                }
-            }
-            Pat::Or(pats) => {
-                for pat in pats.iter() {
-                    self.consume_with_pat(place.clone(), *pat);
+    fn consume_with_pat(&mut self, mut place: HirPlace, tgt_pat: PatId) {
+        let adjustments_count =
+            self.result.pat_adjustments.get(&tgt_pat).map(|it| it.len()).unwrap_or_default();
+        place.projections.extend((0..adjustments_count).map(|_| ProjectionElem::Deref));
+        self.current_capture_span_stack
+            .extend((0..adjustments_count).map(|_| MirSpan::PatId(tgt_pat)));
+        'reset_span_stack: {
+            match &self.body[tgt_pat] {
+                Pat::Missing | Pat::Wild => (),
+                Pat::Tuple { args, ellipsis } => {
+                    let (al, ar) = args.split_at(ellipsis.map_or(args.len(), |it| it as usize));
+                    let field_count = match self.result[tgt_pat].kind(Interner) {
+                        TyKind::Tuple(_, s) => s.len(Interner),
+                        _ => break 'reset_span_stack,
+                    };
+                    let fields = 0..field_count;
+                    let it = al.iter().zip(fields.clone()).chain(ar.iter().rev().zip(fields.rev()));
+                    for (&arg, i) in it {
+                        let mut p = place.clone();
+                        self.current_capture_span_stack.push(MirSpan::PatId(arg));
+                        p.projections.push(ProjectionElem::Field(Either::Right(TupleFieldId {
+                            tuple: TupleId(!0), // dummy this, as its unused anyways
+                            index: i as u32,
+                        })));
+                        self.consume_with_pat(p, arg);
+                        self.current_capture_span_stack.pop();
+                    }
                 }
-            }
-            Pat::Record { args, .. } => {
-                let Some(variant) = self.result.variant_resolution_for_pat(pat) else {
-                    return;
-                };
-                match variant {
-                    VariantId::EnumVariantId(_) | VariantId::UnionId(_) => {
-                        self.consume_place(place, pat.into())
+                Pat::Or(pats) => {
+                    for pat in pats.iter() {
+                        self.consume_with_pat(place.clone(), *pat);
                     }
-                    VariantId::StructId(s) => {
-                        let vd = &*self.db.struct_data(s).variant_data;
-                        for field_pat in args.iter() {
-                            let arg = field_pat.pat;
-                            let Some(local_id) = vd.field(&field_pat.name) else {
-                                continue;
-                            };
-                            let mut p = place.clone();
-                            p.projections.push(ProjectionElem::Field(Either::Left(FieldId {
-                                parent: variant,
-                                local_id,
-                            })));
-                            self.consume_with_pat(p, arg);
+                }
+                Pat::Record { args, .. } => {
+                    let Some(variant) = self.result.variant_resolution_for_pat(tgt_pat) else {
+                        break 'reset_span_stack;
+                    };
+                    match variant {
+                        VariantId::EnumVariantId(_) | VariantId::UnionId(_) => {
+                            self.consume_place(place)
+                        }
+                        VariantId::StructId(s) => {
+                            let vd = &*self.db.struct_data(s).variant_data;
+                            for field_pat in args.iter() {
+                                let arg = field_pat.pat;
+                                let Some(local_id) = vd.field(&field_pat.name) else {
+                                    continue;
+                                };
+                                let mut p = place.clone();
+                                self.current_capture_span_stack.push(MirSpan::PatId(arg));
+                                p.projections.push(ProjectionElem::Field(Either::Left(FieldId {
+                                    parent: variant,
+                                    local_id,
+                                })));
+                                self.consume_with_pat(p, arg);
+                                self.current_capture_span_stack.pop();
+                            }
                         }
                     }
                 }
-            }
-            Pat::Range { .. }
-            | Pat::Slice { .. }
-            | Pat::ConstBlock(_)
-            | Pat::Path(_)
-            | Pat::Lit(_) => self.consume_place(place, pat.into()),
-            Pat::Bind { id: _, subpat: _ } => {
-                let mode = self.result.binding_modes[pat];
-                let capture_kind = match mode {
-                    BindingMode::Move => {
-                        self.consume_place(place, pat.into());
-                        return;
-                    }
-                    BindingMode::Ref(Mutability::Not) => BorrowKind::Shared,
-                    BindingMode::Ref(Mutability::Mut) => {
-                        BorrowKind::Mut { kind: MutBorrowKind::Default }
-                    }
-                };
-                self.add_capture(place, CaptureKind::ByRef(capture_kind), pat.into());
-            }
-            Pat::TupleStruct { path: _, args, ellipsis } => {
-                let Some(variant) = self.result.variant_resolution_for_pat(pat) else {
-                    return;
-                };
-                match variant {
-                    VariantId::EnumVariantId(_) | VariantId::UnionId(_) => {
-                        self.consume_place(place, pat.into())
-                    }
-                    VariantId::StructId(s) => {
-                        let vd = &*self.db.struct_data(s).variant_data;
-                        let (al, ar) = args.split_at(ellipsis.map_or(args.len(), |it| it as usize));
-                        let fields = vd.fields().iter();
-                        let it =
-                            al.iter().zip(fields.clone()).chain(ar.iter().rev().zip(fields.rev()));
-                        for (arg, (i, _)) in it {
-                            let mut p = place.clone();
-                            p.projections.push(ProjectionElem::Field(Either::Left(FieldId {
-                                parent: variant,
-                                local_id: i,
-                            })));
-                            self.consume_with_pat(p, *arg);
+                Pat::Range { .. }
+                | Pat::Slice { .. }
+                | Pat::ConstBlock(_)
+                | Pat::Path(_)
+                | Pat::Lit(_) => self.consume_place(place),
+                &Pat::Bind { id, subpat: _ } => {
+                    let mode = self.result.binding_modes[tgt_pat];
+                    let capture_kind = match mode {
+                        BindingMode::Move => {
+                            self.consume_place(place);
+                            break 'reset_span_stack;
+                        }
+                        BindingMode::Ref(Mutability::Not) => BorrowKind::Shared,
+                        BindingMode::Ref(Mutability::Mut) => {
+                            BorrowKind::Mut { kind: MutBorrowKind::Default }
+                        }
+                    };
+                    self.current_capture_span_stack.push(MirSpan::BindingId(id));
+                    self.add_capture(place, CaptureKind::ByRef(capture_kind));
+                    self.current_capture_span_stack.pop();
+                }
+                Pat::TupleStruct { path: _, args, ellipsis } => {
+                    let Some(variant) = self.result.variant_resolution_for_pat(tgt_pat) else {
+                        break 'reset_span_stack;
+                    };
+                    match variant {
+                        VariantId::EnumVariantId(_) | VariantId::UnionId(_) => {
+                            self.consume_place(place)
+                        }
+                        VariantId::StructId(s) => {
+                            let vd = &*self.db.struct_data(s).variant_data;
+                            let (al, ar) =
+                                args.split_at(ellipsis.map_or(args.len(), |it| it as usize));
+                            let fields = vd.fields().iter();
+                            let it = al
+                                .iter()
+                                .zip(fields.clone())
+                                .chain(ar.iter().rev().zip(fields.rev()));
+                            for (&arg, (i, _)) in it {
+                                let mut p = place.clone();
+                                self.current_capture_span_stack.push(MirSpan::PatId(arg));
+                                p.projections.push(ProjectionElem::Field(Either::Left(FieldId {
+                                    parent: variant,
+                                    local_id: i,
+                                })));
+                                self.consume_with_pat(p, arg);
+                                self.current_capture_span_stack.pop();
+                            }
                         }
                     }
                 }
+                Pat::Ref { pat, mutability: _ } => {
+                    self.current_capture_span_stack.push(MirSpan::PatId(tgt_pat));
+                    place.projections.push(ProjectionElem::Deref);
+                    self.consume_with_pat(place, *pat);
+                    self.current_capture_span_stack.pop();
+                }
+                Pat::Box { .. } => (), // not supported
             }
-            Pat::Ref { pat, mutability: _ } => {
-                place.projections.push(ProjectionElem::Deref);
-                self.consume_with_pat(place, *pat)
-            }
-            Pat::Box { .. } => (), // not supported
         }
+        self.current_capture_span_stack
+            .truncate(self.current_capture_span_stack.len() - adjustments_count);
     }
 
     fn consume_exprs(&mut self, exprs: impl Iterator<Item = ExprId>) {
@@ -1044,12 +1134,28 @@ impl InferenceContext<'_> {
             CaptureBy::Ref => (),
         }
         self.minimize_captures();
+        self.strip_captures_ref_span();
         let result = mem::take(&mut self.current_captures);
         let captures = result.into_iter().map(|it| it.with_ty(self)).collect::<Vec<_>>();
         self.result.closure_info.insert(closure, (captures, closure_kind));
         closure_kind
     }
 
+    fn strip_captures_ref_span(&mut self) {
+        // FIXME: Borrow checker won't allow without this.
+        let mut captures = std::mem::take(&mut self.current_captures);
+        for capture in &mut captures {
+            if matches!(capture.kind, CaptureKind::ByValue) {
+                for span_stack in &mut capture.span_stacks {
+                    if self.is_ref_span(span_stack[span_stack.len() - 1]) {
+                        span_stack.truncate(span_stack.len() - 1);
+                    }
+                }
+            }
+        }
+        self.current_captures = captures;
+    }
+
     pub(crate) fn infer_closures(&mut self) {
         let deferred_closures = self.sort_closures();
         for (closure, exprs) in deferred_closures.into_iter().rev() {
@@ -1110,10 +1216,17 @@ impl InferenceContext<'_> {
     }
 }
 
-fn apply_adjusts_to_place(mut r: HirPlace, adjustments: &[Adjustment]) -> Option<HirPlace> {
+/// Call this only when the last span in the stack isn't a split.
+fn apply_adjusts_to_place(
+    current_capture_span_stack: &mut Vec<MirSpan>,
+    mut r: HirPlace,
+    adjustments: &[Adjustment],
+) -> Option<HirPlace> {
+    let span = *current_capture_span_stack.last().expect("empty capture span stack");
     for adj in adjustments {
         match &adj.kind {
             Adjust::Deref(None) => {
+                current_capture_span_stack.push(span);
                 r.projections.push(ProjectionElem::Deref);
             }
             _ => return None,
diff --git a/src/tools/rust-analyzer/crates/hir-ty/src/mir.rs b/src/tools/rust-analyzer/crates/hir-ty/src/mir.rs
index 9c727cb4ed1..be094b13889 100644
--- a/src/tools/rust-analyzer/crates/hir-ty/src/mir.rs
+++ b/src/tools/rust-analyzer/crates/hir-ty/src/mir.rs
@@ -636,6 +636,7 @@ pub enum TerminatorKind {
     },
 }
 
+// Order of variants in this enum matter: they are used to compare borrow kinds.
 #[derive(Debug, PartialEq, Eq, Clone, Copy, PartialOrd, Ord)]
 pub enum BorrowKind {
     /// Data must be immutable and is aliasable.
@@ -666,15 +667,16 @@ pub enum BorrowKind {
     Mut { kind: MutBorrowKind },
 }
 
+// Order of variants in this enum matter: they are used to compare borrow kinds.
 #[derive(Debug, PartialEq, Eq, Clone, Copy, PartialOrd, Ord)]
 pub enum MutBorrowKind {
+    /// Data must be immutable but not aliasable. This kind of borrow cannot currently
+    /// be expressed by the user and is used only in implicit closure bindings.
+    ClosureCapture,
     Default,
     /// This borrow arose from method-call auto-ref
     /// (i.e., adjustment::Adjust::Borrow).
     TwoPhasedBorrow,
-    /// Data must be immutable but not aliasable. This kind of borrow cannot currently
-    /// be expressed by the user and is used only in implicit closure bindings.
-    ClosureCapture,
 }
 
 impl BorrowKind {
diff --git a/src/tools/rust-analyzer/crates/hir-ty/src/mir/lower.rs b/src/tools/rust-analyzer/crates/hir-ty/src/mir/lower.rs
index 3a0d0c933f9..9e235504519 100644
--- a/src/tools/rust-analyzer/crates/hir-ty/src/mir/lower.rs
+++ b/src/tools/rust-analyzer/crates/hir-ty/src/mir/lower.rs
@@ -1180,8 +1180,15 @@ impl<'ctx> MirLowerCtx<'ctx> {
                             let placeholder_subst = self.placeholder_subst();
                             let tmp_ty =
                                 capture.ty.clone().substitute(Interner, &placeholder_subst);
-                            let tmp: Place = self.temp(tmp_ty, current, capture.span)?.into();
-                            self.push_assignment(current, tmp, Rvalue::Ref(*bk, p), capture.span);
+                            // FIXME: Handle more than one span.
+                            let capture_spans = capture.spans();
+                            let tmp: Place = self.temp(tmp_ty, current, capture_spans[0])?.into();
+                            self.push_assignment(
+                                current,
+                                tmp,
+                                Rvalue::Ref(*bk, p),
+                                capture_spans[0],
+                            );
                             operands.push(Operand::Move(tmp));
                         }
                         CaptureKind::ByValue => operands.push(Operand::Move(p)),
diff --git a/src/tools/rust-analyzer/crates/hir-ty/src/tests.rs b/src/tools/rust-analyzer/crates/hir-ty/src/tests.rs
index efd8546216d..bcf9d5ceff0 100644
--- a/src/tools/rust-analyzer/crates/hir-ty/src/tests.rs
+++ b/src/tools/rust-analyzer/crates/hir-ty/src/tests.rs
@@ -1,3 +1,4 @@
+mod closure_captures;
 mod coercion;
 mod diagnostics;
 mod display_source_code;
diff --git a/src/tools/rust-analyzer/crates/hir-ty/src/tests/closure_captures.rs b/src/tools/rust-analyzer/crates/hir-ty/src/tests/closure_captures.rs
new file mode 100644
index 00000000000..22cef3505bf
--- /dev/null
+++ b/src/tools/rust-analyzer/crates/hir-ty/src/tests/closure_captures.rs
@@ -0,0 +1,433 @@
+use base_db::salsa::InternKey;
+use expect_test::{expect, Expect};
+use hir_def::db::DefDatabase;
+use hir_expand::files::InFileWrapper;
+use itertools::Itertools;
+use span::{HirFileId, TextRange};
+use syntax::{AstNode, AstPtr};
+use test_fixture::WithFixture;
+
+use crate::db::{HirDatabase, InternedClosureId};
+use crate::display::HirDisplay;
+use crate::mir::MirSpan;
+use crate::test_db::TestDB;
+
+use super::visit_module;
+
+fn check_closure_captures(ra_fixture: &str, expect: Expect) {
+    let (db, file_id) = TestDB::with_single_file(ra_fixture);
+    let module = db.module_for_file(file_id);
+    let def_map = module.def_map(&db);
+
+    let mut defs = Vec::new();
+    visit_module(&db, &def_map, module.local_id, &mut |it| defs.push(it));
+
+    let mut captures_info = Vec::new();
+    for def in defs {
+        let infer = db.infer(def);
+        let db = &db;
+        captures_info.extend(infer.closure_info.iter().flat_map(|(closure_id, (captures, _))| {
+            let closure = db.lookup_intern_closure(InternedClosureId::from_intern_id(closure_id.0));
+            let (_, source_map) = db.body_with_source_map(closure.0);
+            let closure_text_range = source_map
+                .expr_syntax(closure.1)
+                .expect("failed to map closure to SyntaxNode")
+                .value
+                .text_range();
+            captures.iter().map(move |capture| {
+                fn text_range<N: AstNode>(
+                    db: &TestDB,
+                    syntax: InFileWrapper<HirFileId, AstPtr<N>>,
+                ) -> TextRange {
+                    let root = syntax.file_syntax(db);
+                    syntax.value.to_node(&root).syntax().text_range()
+                }
+
+                // FIXME: Deduplicate this with hir::Local::sources().
+                let (body, source_map) = db.body_with_source_map(closure.0);
+                let local_text_range = match body.self_param.zip(source_map.self_param_syntax()) {
+                    Some((param, source)) if param == capture.local() => {
+                        format!("{:?}", text_range(db, source))
+                    }
+                    _ => source_map
+                        .patterns_for_binding(capture.local())
+                        .iter()
+                        .map(|&definition| {
+                            text_range(db, source_map.pat_syntax(definition).unwrap())
+                        })
+                        .map(|it| format!("{it:?}"))
+                        .join(", "),
+                };
+                let place = capture.display_place(closure.0, db);
+                let capture_ty = capture.ty.skip_binders().display_test(db).to_string();
+                let spans = capture
+                    .spans()
+                    .iter()
+                    .flat_map(|span| match *span {
+                        MirSpan::ExprId(expr) => {
+                            vec![text_range(db, source_map.expr_syntax(expr).unwrap())]
+                        }
+                        MirSpan::PatId(pat) => {
+                            vec![text_range(db, source_map.pat_syntax(pat).unwrap())]
+                        }
+                        MirSpan::BindingId(binding) => source_map
+                            .patterns_for_binding(binding)
+                            .iter()
+                            .map(|pat| text_range(db, source_map.pat_syntax(*pat).unwrap()))
+                            .collect(),
+                        MirSpan::SelfParam => {
+                            vec![text_range(db, source_map.self_param_syntax().unwrap())]
+                        }
+                        MirSpan::Unknown => Vec::new(),
+                    })
+                    .sorted_by_key(|it| it.start())
+                    .map(|it| format!("{it:?}"))
+                    .join(",");
+
+                (closure_text_range, local_text_range, spans, place, capture_ty, capture.kind())
+            })
+        }));
+    }
+    captures_info.sort_unstable_by_key(|(closure_text_range, local_text_range, ..)| {
+        (closure_text_range.start(), local_text_range.clone())
+    });
+
+    let rendered = captures_info
+        .iter()
+        .map(|(closure_text_range, local_text_range, spans, place, capture_ty, capture_kind)| {
+            format!(
+                "{closure_text_range:?};{local_text_range};{spans} {capture_kind:?} {place} {capture_ty}"
+            )
+        })
+        .join("\n");
+
+    expect.assert_eq(&rendered);
+}
+
+#[test]
+fn deref_in_let() {
+    check_closure_captures(
+        r#"
+//- minicore:copy
+fn main() {
+    let a = &mut true;
+    let closure = || { let b = *a; };
+}
+"#,
+        expect!["53..71;20..21;66..68 ByRef(Shared) *a &'? bool"],
+    );
+}
+
+#[test]
+fn deref_then_ref_pattern() {
+    check_closure_captures(
+        r#"
+//- minicore:copy
+fn main() {
+    let a = &mut true;
+    let closure = || { let &mut ref b = a; };
+}
+"#,
+        expect!["53..79;20..21;67..72 ByRef(Shared) *a &'? bool"],
+    );
+    check_closure_captures(
+        r#"
+//- minicore:copy
+fn main() {
+    let a = &mut true;
+    let closure = || { let &mut ref mut b = a; };
+}
+"#,
+        expect!["53..83;20..21;67..76 ByRef(Mut { kind: Default }) *a &'? mut bool"],
+    );
+}
+
+#[test]
+fn unique_borrow() {
+    check_closure_captures(
+        r#"
+//- minicore:copy
+fn main() {
+    let a = &mut true;
+    let closure = || { *a = false; };
+}
+"#,
+        expect!["53..71;20..21;58..60 ByRef(Mut { kind: Default }) *a &'? mut bool"],
+    );
+}
+
+#[test]
+fn deref_ref_mut() {
+    check_closure_captures(
+        r#"
+//- minicore:copy
+fn main() {
+    let a = &mut true;
+    let closure = || { let ref mut b = *a; };
+}
+"#,
+        expect!["53..79;20..21;62..71 ByRef(Mut { kind: Default }) *a &'? mut bool"],
+    );
+}
+
+#[test]
+fn let_else_not_consuming() {
+    check_closure_captures(
+        r#"
+//- minicore:copy
+fn main() {
+    let a = &mut true;
+    let closure = || { let _ = *a else { return; }; };
+}
+"#,
+        expect!["53..88;20..21;66..68 ByRef(Shared) *a &'? bool"],
+    );
+}
+
+#[test]
+fn consume() {
+    check_closure_captures(
+        r#"
+//- minicore:copy
+struct NonCopy;
+fn main() {
+    let a = NonCopy;
+    let closure = || { let b = a; };
+}
+"#,
+        expect!["67..84;36..37;80..81 ByValue a NonCopy"],
+    );
+}
+
+#[test]
+fn ref_to_upvar() {
+    check_closure_captures(
+        r#"
+//- minicore:copy
+struct NonCopy;
+fn main() {
+    let mut a = NonCopy;
+    let closure = || { let b = &a; };
+    let closure = || { let c = &mut a; };
+}
+"#,
+        expect![[r#"
+            71..89;36..41;84..86 ByRef(Shared) a &'? NonCopy
+            109..131;36..41;122..128 ByRef(Mut { kind: Default }) a &'? mut NonCopy"#]],
+    );
+}
+
+#[test]
+fn field() {
+    check_closure_captures(
+        r#"
+//- minicore:copy
+struct Foo { a: i32, b: i32 }
+fn main() {
+    let a = Foo { a: 0, b: 0 };
+    let closure = || { let b = a.a; };
+}
+"#,
+        expect!["92..111;50..51;105..108 ByRef(Shared) a.a &'? i32"],
+    );
+}
+
+#[test]
+fn fields_different_mode() {
+    check_closure_captures(
+        r#"
+//- minicore:copy
+struct NonCopy;
+struct Foo { a: i32, b: i32, c: NonCopy, d: bool }
+fn main() {
+    let mut a = Foo { a: 0, b: 0 };
+    let closure = || {
+        let b = &a.a;
+        let c = &mut a.b;
+        let d = a.c;
+    };
+}
+"#,
+        expect![[r#"
+            133..212;87..92;154..158 ByRef(Shared) a.a &'? i32
+            133..212;87..92;176..184 ByRef(Mut { kind: Default }) a.b &'? mut i32
+            133..212;87..92;202..205 ByValue a.c NonCopy"#]],
+    );
+}
+
+#[test]
+fn autoref() {
+    check_closure_captures(
+        r#"
+//- minicore:copy
+struct Foo;
+impl Foo {
+    fn imm(&self) {}
+    fn mut_(&mut self) {}
+}
+fn main() {
+    let mut a = Foo;
+    let closure = || a.imm();
+    let closure = || a.mut_();
+}
+"#,
+        expect![[r#"
+            123..133;92..97;126..127 ByRef(Shared) a &'? Foo
+            153..164;92..97;156..157 ByRef(Mut { kind: Default }) a &'? mut Foo"#]],
+    );
+}
+
+#[test]
+fn captures_priority() {
+    check_closure_captures(
+        r#"
+//- minicore:copy
+struct NonCopy;
+fn main() {
+    let mut a = &mut true;
+    // Max ByRef(Mut { kind: Default })
+    let closure = || {
+        *a = false;
+        let b = &mut a;
+    };
+    // Max ByValue
+    let mut a = NonCopy;
+    let closure = || {
+        let b = a;
+        let c = &mut a;
+        let d = &a;
+    };
+}
+"#,
+        expect![[r#"
+            113..167;36..41;127..128,154..160 ByRef(Mut { kind: Default }) a &'? mut &'? mut bool
+            231..304;196..201;252..253,276..277,296..297 ByValue a NonCopy"#]],
+    );
+}
+
+#[test]
+fn let_underscore() {
+    check_closure_captures(
+        r#"
+//- minicore:copy
+fn main() {
+    let mut a = true;
+    let closure = || { let _ = a; };
+}
+"#,
+        expect![""],
+    );
+}
+
+#[test]
+fn match_wildcard() {
+    check_closure_captures(
+        r#"
+//- minicore:copy
+struct NonCopy;
+fn main() {
+    let mut a = NonCopy;
+    let closure = || match a {
+        _ => {}
+    };
+    let closure = || match a {
+        ref b => {}
+    };
+    let closure = || match a {
+        ref mut b => {}
+    };
+}
+"#,
+        expect![[r#"
+            125..163;36..41;134..135 ByRef(Shared) a &'? NonCopy
+            183..225;36..41;192..193 ByRef(Mut { kind: Default }) a &'? mut NonCopy"#]],
+    );
+}
+
+#[test]
+fn multiple_bindings() {
+    check_closure_captures(
+        r#"
+//- minicore:copy
+fn main() {
+    let mut a = false;
+    let mut closure = || { let (b | b) = a; };
+}
+"#,
+        expect!["57..80;20..25;76..77,76..77 ByRef(Shared) a &'? bool"],
+    );
+}
+
+#[test]
+fn multiple_usages() {
+    check_closure_captures(
+        r#"
+//- minicore:copy
+fn main() {
+    let mut a = false;
+    let mut closure = || {
+        let b = &a;
+        let c = &a;
+        let d = &mut a;
+        a = true;
+    };
+}
+"#,
+        expect!["57..149;20..25;78..80,98..100,118..124,134..135 ByRef(Mut { kind: Default }) a &'? mut bool"],
+    );
+}
+
+#[test]
+fn ref_then_deref() {
+    check_closure_captures(
+        r#"
+//- minicore:copy
+fn main() {
+    let mut a = false;
+    let mut closure = || { let b = *&mut a; };
+}
+"#,
+        expect!["57..80;20..25;71..77 ByRef(Mut { kind: Default }) a &'? mut bool"],
+    );
+}
+
+#[test]
+fn ref_of_ref() {
+    check_closure_captures(
+        r#"
+//- minicore:copy
+fn main() {
+    let mut a = &false;
+    let closure = || { let b = &a; };
+    let closure = || { let b = &mut a; };
+    let a = &mut false;
+    let closure = || { let b = &a; };
+    let closure = || { let b = &mut a; };
+}
+"#,
+        expect![[r#"
+            54..72;20..25;67..69 ByRef(Shared) a &'? &'? bool
+            92..114;20..25;105..111 ByRef(Mut { kind: Default }) a &'? mut &'? bool
+            158..176;124..125;171..173 ByRef(Shared) a &'? &'? mut bool
+            196..218;124..125;209..215 ByRef(Mut { kind: Default }) a &'? mut &'? mut bool"#]],
+    );
+}
+
+#[test]
+fn multiple_capture_usages() {
+    check_closure_captures(
+        r#"
+//- minicore:copy
+struct A { a: i32, b: bool }
+fn main() {
+    let mut a = A { a: 123, b: false };
+    let closure = |$0| {
+        let b = a.b;
+        a = A { a: 456, b: true };
+    };
+    closure();
+}
+"#,
+        expect!["99..165;49..54;120..121,133..134 ByRef(Mut { kind: Default }) a &'? mut A"],
+    );
+}
diff --git a/src/tools/rust-analyzer/crates/hir/src/lib.rs b/src/tools/rust-analyzer/crates/hir/src/lib.rs
index 6e26af55af8..2ff5f0d538a 100644
--- a/src/tools/rust-analyzer/crates/hir/src/lib.rs
+++ b/src/tools/rust-analyzer/crates/hir/src/lib.rs
@@ -78,7 +78,7 @@ use hir_ty::{
 use itertools::Itertools;
 use nameres::diagnostics::DefDiagnosticKind;
 use rustc_hash::FxHashSet;
-use span::{Edition, EditionedFileId, FileId, MacroCallId};
+use span::{Edition, EditionedFileId, FileId, MacroCallId, SyntaxContextId};
 use stdx::{impl_from, never};
 use syntax::{
     ast::{self, HasAttrs as _, HasGenericParams, HasName},
@@ -4133,6 +4133,7 @@ impl ClosureCapture {
     }
 }
 
+#[derive(Clone, Copy, PartialEq, Eq)]
 pub enum CaptureKind {
     SharedRef,
     UniqueSharedRef,
@@ -4378,6 +4379,22 @@ impl Type {
         method_resolution::implements_trait(&canonical_ty, db, &self.env, trait_)
     }
 
+    /// This does **not** resolve `IntoFuture`, only `Future`.
+    pub fn future_output(self, db: &dyn HirDatabase) -> Option<Type> {
+        let future_output =
+            db.lang_item(self.env.krate, LangItem::FutureOutput)?.as_type_alias()?;
+        self.normalize_trait_assoc_type(db, &[], future_output.into())
+    }
+
+    /// This does **not** resolve `IntoIterator`, only `Iterator`.
+    pub fn iterator_item(self, db: &dyn HirDatabase) -> Option<Type> {
+        let iterator_trait = db.lang_item(self.env.krate, LangItem::Iterator)?.as_trait()?;
+        let iterator_item = db
+            .trait_data(iterator_trait)
+            .associated_type_by_name(&Name::new_symbol(sym::Item.clone(), SyntaxContextId::ROOT))?;
+        self.normalize_trait_assoc_type(db, &[], iterator_item.into())
+    }
+
     /// Checks that particular type `ty` implements `std::ops::FnOnce`.
     ///
     /// This function can be used to check if a particular type is callable, since FnOnce is a
diff --git a/src/tools/rust-analyzer/crates/ide-assists/src/handlers/extract_function.rs b/src/tools/rust-analyzer/crates/ide-assists/src/handlers/extract_function.rs
index fd379cb88da..fd0b11f6ddf 100644
--- a/src/tools/rust-analyzer/crates/ide-assists/src/handlers/extract_function.rs
+++ b/src/tools/rust-analyzer/crates/ide-assists/src/handlers/extract_function.rs
@@ -1617,6 +1617,7 @@ fn format_function(
         fun.control_flow.is_async,
         fun.mods.is_const,
         fun.control_flow.is_unsafe,
+        false,
     )
 }
 
diff --git a/src/tools/rust-analyzer/crates/ide-assists/src/handlers/generate_delegate_methods.rs b/src/tools/rust-analyzer/crates/ide-assists/src/handlers/generate_delegate_methods.rs
index bbb902f8a2a..081e36b4ff6 100644
--- a/src/tools/rust-analyzer/crates/ide-assists/src/handlers/generate_delegate_methods.rs
+++ b/src/tools/rust-analyzer/crates/ide-assists/src/handlers/generate_delegate_methods.rs
@@ -122,6 +122,7 @@ pub(crate) fn generate_delegate_methods(acc: &mut Assists, ctx: &AssistContext<'
                 let is_async = method_source.async_token().is_some();
                 let is_const = method_source.const_token().is_some();
                 let is_unsafe = method_source.unsafe_token().is_some();
+                let is_gen = method_source.gen_token().is_some();
 
                 let fn_name = make::name(&name);
 
@@ -154,6 +155,7 @@ pub(crate) fn generate_delegate_methods(acc: &mut Assists, ctx: &AssistContext<'
                     is_async,
                     is_const,
                     is_unsafe,
+                    is_gen,
                 )
                 .clone_for_update();
 
diff --git a/src/tools/rust-analyzer/crates/ide-assists/src/handlers/generate_delegate_trait.rs b/src/tools/rust-analyzer/crates/ide-assists/src/handlers/generate_delegate_trait.rs
index 933ab2058ec..bf4ce5c907e 100644
--- a/src/tools/rust-analyzer/crates/ide-assists/src/handlers/generate_delegate_trait.rs
+++ b/src/tools/rust-analyzer/crates/ide-assists/src/handlers/generate_delegate_trait.rs
@@ -740,6 +740,7 @@ fn func_assoc_item(
         item.async_token().is_some(),
         item.const_token().is_some(),
         item.unsafe_token().is_some(),
+        item.gen_token().is_some(),
     )
     .clone_for_update();
 
diff --git a/src/tools/rust-analyzer/crates/ide-assists/src/handlers/generate_function.rs b/src/tools/rust-analyzer/crates/ide-assists/src/handlers/generate_function.rs
index cd29f77f0c9..76a647807cb 100644
--- a/src/tools/rust-analyzer/crates/ide-assists/src/handlers/generate_function.rs
+++ b/src/tools/rust-analyzer/crates/ide-assists/src/handlers/generate_function.rs
@@ -365,6 +365,7 @@ impl FunctionBuilder {
             self.is_async,
             false, // FIXME : const and unsafe are not handled yet.
             false,
+            false,
         )
         .clone_for_update();
 
diff --git a/src/tools/rust-analyzer/crates/ide-assists/src/handlers/generate_getter_or_setter.rs b/src/tools/rust-analyzer/crates/ide-assists/src/handlers/generate_getter_or_setter.rs
index 8e349e84a96..c879a4a3d95 100644
--- a/src/tools/rust-analyzer/crates/ide-assists/src/handlers/generate_getter_or_setter.rs
+++ b/src/tools/rust-analyzer/crates/ide-assists/src/handlers/generate_getter_or_setter.rs
@@ -261,7 +261,19 @@ fn generate_getter_from_info(
     let ret_type = Some(make::ret_type(ty));
     let body = make::block_expr([], Some(body));
 
-    make::fn_(strukt.visibility(), fn_name, None, None, params, body, ret_type, false, false, false)
+    make::fn_(
+        strukt.visibility(),
+        fn_name,
+        None,
+        None,
+        params,
+        body,
+        ret_type,
+        false,
+        false,
+        false,
+        false,
+    )
 }
 
 fn generate_setter_from_info(info: &AssistInfo, record_field_info: &RecordFieldInfo) -> ast::Fn {
@@ -285,7 +297,19 @@ fn generate_setter_from_info(info: &AssistInfo, record_field_info: &RecordFieldI
     let body = make::block_expr([assign_stmt.into()], None);
 
     // Make the setter fn
-    make::fn_(strukt.visibility(), fn_name, None, None, params, body, None, false, false, false)
+    make::fn_(
+        strukt.visibility(),
+        fn_name,
+        None,
+        None,
+        params,
+        body,
+        None,
+        false,
+        false,
+        false,
+        false,
+    )
 }
 
 fn extract_and_parse(
diff --git a/src/tools/rust-analyzer/crates/ide-assists/src/handlers/generate_new.rs b/src/tools/rust-analyzer/crates/ide-assists/src/handlers/generate_new.rs
index b9dede7cbdc..70d14d6b95d 100644
--- a/src/tools/rust-analyzer/crates/ide-assists/src/handlers/generate_new.rs
+++ b/src/tools/rust-analyzer/crates/ide-assists/src/handlers/generate_new.rs
@@ -115,6 +115,7 @@ pub(crate) fn generate_new(acc: &mut Assists, ctx: &AssistContext<'_>) -> Option
             false,
             false,
             false,
+            false,
         )
         .clone_for_update();
         fn_.indent(1.into());
diff --git a/src/tools/rust-analyzer/crates/ide-assists/src/handlers/remove_dbg.rs b/src/tools/rust-analyzer/crates/ide-assists/src/handlers/remove_dbg.rs
index cffa3f55c90..0e9c463e024 100644
--- a/src/tools/rust-analyzer/crates/ide-assists/src/handlers/remove_dbg.rs
+++ b/src/tools/rust-analyzer/crates/ide-assists/src/handlers/remove_dbg.rs
@@ -1,7 +1,7 @@
 use itertools::Itertools;
 use syntax::{
     ast::{self, make, AstNode, AstToken},
-    match_ast, ted, NodeOrToken, SyntaxElement, TextRange, TextSize, T,
+    match_ast, ted, Edition, NodeOrToken, SyntaxElement, TextRange, TextSize, T,
 };
 
 use crate::{AssistContext, AssistId, AssistKind, Assists};
@@ -77,7 +77,7 @@ fn compute_dbg_replacement(macro_expr: ast::MacroExpr) -> Option<(TextRange, Opt
     let input_expressions = input_expressions
         .into_iter()
         .filter_map(|(is_sep, group)| (!is_sep).then_some(group))
-        .map(|mut tokens| syntax::hacks::parse_expr_from_str(&tokens.join("")))
+        .map(|mut tokens| syntax::hacks::parse_expr_from_str(&tokens.join(""), Edition::CURRENT))
         .collect::<Option<Vec<ast::Expr>>>()?;
 
     let parent = macro_expr.syntax().parent()?;
diff --git a/src/tools/rust-analyzer/crates/ide-completion/src/completions/attribute.rs b/src/tools/rust-analyzer/crates/ide-completion/src/completions/attribute.rs
index 75bd327608e..9821fb4a2fa 100644
--- a/src/tools/rust-analyzer/crates/ide-completion/src/completions/attribute.rs
+++ b/src/tools/rust-analyzer/crates/ide-completion/src/completions/attribute.rs
@@ -14,7 +14,7 @@ use ide_db::{
 use itertools::Itertools;
 use syntax::{
     ast::{self, AttrKind},
-    AstNode, SyntaxKind, T,
+    AstNode, Edition, SyntaxKind, T,
 };
 
 use crate::{
@@ -373,7 +373,9 @@ fn parse_comma_sep_expr(input: ast::TokenTree) -> Option<Vec<ast::Expr>> {
         input_expressions
             .into_iter()
             .filter_map(|(is_sep, group)| (!is_sep).then_some(group))
-            .filter_map(|mut tokens| syntax::hacks::parse_expr_from_str(&tokens.join("")))
+            .filter_map(|mut tokens| {
+                syntax::hacks::parse_expr_from_str(&tokens.join(""), Edition::CURRENT)
+            })
             .collect::<Vec<ast::Expr>>(),
     )
 }
diff --git a/src/tools/rust-analyzer/crates/ide-db/src/syntax_helpers/node_ext.rs b/src/tools/rust-analyzer/crates/ide-db/src/syntax_helpers/node_ext.rs
index fa82902a74d..91e0b4495f5 100644
--- a/src/tools/rust-analyzer/crates/ide-db/src/syntax_helpers/node_ext.rs
+++ b/src/tools/rust-analyzer/crates/ide-db/src/syntax_helpers/node_ext.rs
@@ -477,10 +477,12 @@ pub fn parse_tt_as_comma_sep_paths(
         .into_iter()
         .filter_map(|(is_sep, group)| (!is_sep).then_some(group))
         .filter_map(|mut tokens| {
-            syntax::hacks::parse_expr_from_str(&tokens.join("")).and_then(|expr| match expr {
-                ast::Expr::PathExpr(it) => it.path(),
-                _ => None,
-            })
+            syntax::hacks::parse_expr_from_str(&tokens.join(""), Edition::CURRENT).and_then(
+                |expr| match expr {
+                    ast::Expr::PathExpr(it) => it.path(),
+                    _ => None,
+                },
+            )
         })
         .collect();
     Some(paths)
diff --git a/src/tools/rust-analyzer/crates/ide/src/hover/tests.rs b/src/tools/rust-analyzer/crates/ide/src/hover/tests.rs
index fc59307806f..08709d3cc2e 100644
--- a/src/tools/rust-analyzer/crates/ide/src/hover/tests.rs
+++ b/src/tools/rust-analyzer/crates/ide/src/hover/tests.rs
@@ -8465,7 +8465,7 @@ impl Iterator for S {
                                 file_id: FileId(
                                     1,
                                 ),
-                                full_range: 7800..8008,
+                                full_range: 7800..8042,
                                 focus_range: 7865..7871,
                                 name: "Future",
                                 kind: Trait,
@@ -8479,8 +8479,8 @@ impl Iterator for S {
                                 file_id: FileId(
                                     1,
                                 ),
-                                full_range: 8638..9104,
-                                focus_range: 8682..8690,
+                                full_range: 8672..9171,
+                                focus_range: 8749..8757,
                                 name: "Iterator",
                                 kind: Trait,
                                 container_name: "iterator",
diff --git a/src/tools/rust-analyzer/crates/intern/src/symbol/symbols.rs b/src/tools/rust-analyzer/crates/intern/src/symbol/symbols.rs
index 5d05ef3b79b..867d9ea902c 100644
--- a/src/tools/rust-analyzer/crates/intern/src/symbol/symbols.rs
+++ b/src/tools/rust-analyzer/crates/intern/src/symbol/symbols.rs
@@ -240,6 +240,7 @@ define_symbols! {
     fundamental,
     future_trait,
     future,
+    future_output,
     Future,
     ge,
     get_context,
@@ -274,6 +275,7 @@ define_symbols! {
     iter_mut,
     iter,
     Iterator,
+    iterator,
     keyword,
     lang,
     le,
diff --git a/src/tools/rust-analyzer/crates/syntax/rust.ungram b/src/tools/rust-analyzer/crates/syntax/rust.ungram
index ba7d8bacfb2..43375ce6ae0 100644
--- a/src/tools/rust-analyzer/crates/syntax/rust.ungram
+++ b/src/tools/rust-analyzer/crates/syntax/rust.ungram
@@ -190,7 +190,7 @@ UseTreeList =
 
 Fn =
  Attr* Visibility?
- 'default'? 'const'? 'async'? 'unsafe'? Abi?
+ 'default'? 'const'? 'async'? 'gen'? 'unsafe'? Abi?
  'fn' Name GenericParamList? ParamList RetType? WhereClause?
  (body:BlockExpr | ';')
 
diff --git a/src/tools/rust-analyzer/crates/syntax/src/ast/edit.rs b/src/tools/rust-analyzer/crates/syntax/src/ast/edit.rs
index 5bc6b780e47..de40d638be3 100644
--- a/src/tools/rust-analyzer/crates/syntax/src/ast/edit.rs
+++ b/src/tools/rust-analyzer/crates/syntax/src/ast/edit.rs
@@ -8,7 +8,7 @@ use crate::{
     ted, AstToken, NodeOrToken, SyntaxElement, SyntaxNode, SyntaxToken,
 };
 
-#[derive(Debug, Clone, Copy)]
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
 pub struct IndentLevel(pub u8);
 
 impl From<u8> for IndentLevel {
diff --git a/src/tools/rust-analyzer/crates/syntax/src/ast/generated/nodes.rs b/src/tools/rust-analyzer/crates/syntax/src/ast/generated/nodes.rs
index bd8092d7f09..c9b39e9922c 100644
--- a/src/tools/rust-analyzer/crates/syntax/src/ast/generated/nodes.rs
+++ b/src/tools/rust-analyzer/crates/syntax/src/ast/generated/nodes.rs
@@ -486,6 +486,8 @@ impl Fn {
     #[inline]
     pub fn fn_token(&self) -> Option<SyntaxToken> { support::token(&self.syntax, T![fn]) }
     #[inline]
+    pub fn gen_token(&self) -> Option<SyntaxToken> { support::token(&self.syntax, T![gen]) }
+    #[inline]
     pub fn unsafe_token(&self) -> Option<SyntaxToken> { support::token(&self.syntax, T![unsafe]) }
 }
 
diff --git a/src/tools/rust-analyzer/crates/syntax/src/ast/make.rs b/src/tools/rust-analyzer/crates/syntax/src/ast/make.rs
index 00ce5c37cce..abf1a1f3820 100644
--- a/src/tools/rust-analyzer/crates/syntax/src/ast/make.rs
+++ b/src/tools/rust-analyzer/crates/syntax/src/ast/make.rs
@@ -1035,6 +1035,7 @@ pub fn fn_(
     is_async: bool,
     is_const: bool,
     is_unsafe: bool,
+    is_gen: bool,
 ) -> ast::Fn {
     let type_params = match type_params {
         Some(type_params) => format!("{type_params}"),
@@ -1056,9 +1057,10 @@ pub fn fn_(
     let async_literal = if is_async { "async " } else { "" };
     let const_literal = if is_const { "const " } else { "" };
     let unsafe_literal = if is_unsafe { "unsafe " } else { "" };
+    let gen_literal = if is_gen { "gen " } else { "" };
 
     ast_from_text(&format!(
-        "{visibility}{async_literal}{const_literal}{unsafe_literal}fn {fn_name}{type_params}{params} {ret_type}{where_clause}{body}",
+        "{visibility}{const_literal}{async_literal}{gen_literal}{unsafe_literal}fn {fn_name}{type_params}{params} {ret_type}{where_clause}{body}",
     ))
 }
 pub fn struct_(
diff --git a/src/tools/rust-analyzer/crates/syntax/src/ast/node_ext.rs b/src/tools/rust-analyzer/crates/syntax/src/ast/node_ext.rs
index 5447906206c..693bfe330bd 100644
--- a/src/tools/rust-analyzer/crates/syntax/src/ast/node_ext.rs
+++ b/src/tools/rust-analyzer/crates/syntax/src/ast/node_ext.rs
@@ -17,7 +17,7 @@ use crate::{
     ted, NodeOrToken, SmolStr, SyntaxElement, SyntaxToken, TokenText, T,
 };
 
-use super::{RangeItem, RangeOp};
+use super::{GenericParam, RangeItem, RangeOp};
 
 impl ast::Lifetime {
     pub fn text(&self) -> TokenText<'_> {
@@ -822,6 +822,15 @@ pub enum TypeOrConstParam {
     Const(ast::ConstParam),
 }
 
+impl From<TypeOrConstParam> for GenericParam {
+    fn from(value: TypeOrConstParam) -> Self {
+        match value {
+            TypeOrConstParam::Type(it) => GenericParam::TypeParam(it),
+            TypeOrConstParam::Const(it) => GenericParam::ConstParam(it),
+        }
+    }
+}
+
 impl TypeOrConstParam {
     pub fn name(&self) -> Option<ast::Name> {
         match self {
diff --git a/src/tools/rust-analyzer/crates/syntax/src/hacks.rs b/src/tools/rust-analyzer/crates/syntax/src/hacks.rs
index 36615d11d85..9e63448ce96 100644
--- a/src/tools/rust-analyzer/crates/syntax/src/hacks.rs
+++ b/src/tools/rust-analyzer/crates/syntax/src/hacks.rs
@@ -6,9 +6,9 @@ use parser::Edition;
 
 use crate::{ast, AstNode};
 
-pub fn parse_expr_from_str(s: &str) -> Option<ast::Expr> {
+pub fn parse_expr_from_str(s: &str, edition: Edition) -> Option<ast::Expr> {
     let s = s.trim();
-    let file = ast::SourceFile::parse(&format!("const _: () = {s};"), Edition::CURRENT);
+    let file = ast::SourceFile::parse(&format!("const _: () = {s};"), edition);
     let expr = file.syntax_node().descendants().find_map(ast::Expr::cast)?;
     if expr.syntax().text() != s {
         return None;
diff --git a/src/tools/rust-analyzer/crates/test-utils/src/minicore.rs b/src/tools/rust-analyzer/crates/test-utils/src/minicore.rs
index 2e01d199088..754042cf883 100644
--- a/src/tools/rust-analyzer/crates/test-utils/src/minicore.rs
+++ b/src/tools/rust-analyzer/crates/test-utils/src/minicore.rs
@@ -1196,6 +1196,7 @@ pub mod future {
     #[doc(notable_trait)]
     #[lang = "future_trait"]
     pub trait Future {
+        #[lang = "future_output"]
         type Output;
         #[lang = "poll"]
         fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output>;
@@ -1293,6 +1294,7 @@ pub mod iter {
     mod traits {
         mod iterator {
             #[doc(notable_trait)]
+            #[lang = "iterator"]
             pub trait Iterator {
                 type Item;
                 #[lang = "next"]