Auto merge of #68804 - ecstatic-morse:qualif-cursor-lazy, r=estebank

Always use lazy qualif getters during const-checking

`has_mut_interior_eager_seek` was needed to work around an overly restrictive bound on the `per_local` argument to the `Qualif` trait. This PR makes that bound `FnMut` instead of `Fn` so we can seek cursors inside of it, resolving a FIXME in the const-checking code.

Author: bors

src/librustc_mir/transform/check_consts/qualifs.rs

@@ -34,7 +34,7 @@ pub trait Qualif {
 
     fn in_projection_structurally(
         cx: &ConstCx<'_, 'tcx>,
-        per_local: &impl Fn(Local) -> bool,
+        per_local: &mut impl FnMut(Local) -> bool,
         place: PlaceRef<'_, 'tcx>,
     ) -> bool {
         if let [proj_base @ .., elem] = place.projection {
@@ -66,15 +66,15 @@ pub trait Qualif {
 
     fn in_projection(
         cx: &ConstCx<'_, 'tcx>,
-        per_local: &impl Fn(Local) -> bool,
+        per_local: &mut impl FnMut(Local) -> bool,
         place: PlaceRef<'_, 'tcx>,
     ) -> bool {
         Self::in_projection_structurally(cx, per_local, place)
     }
 
     fn in_place(
         cx: &ConstCx<'_, 'tcx>,
-        per_local: &impl Fn(Local) -> bool,
+        per_local: &mut impl FnMut(Local) -> bool,
         place: PlaceRef<'_, 'tcx>,
     ) -> bool {
         match place {
@@ -85,7 +85,7 @@ pub trait Qualif {
 
     fn in_operand(
         cx: &ConstCx<'_, 'tcx>,
-        per_local: &impl Fn(Local) -> bool,
+        per_local: &mut impl FnMut(Local) -> bool,
         operand: &Operand<'tcx>,
     ) -> bool {
         match *operand {
@@ -126,7 +126,7 @@ pub trait Qualif {
 
     fn in_rvalue_structurally(
         cx: &ConstCx<'_, 'tcx>,
-        per_local: &impl Fn(Local) -> bool,
+        per_local: &mut impl FnMut(Local) -> bool,
         rvalue: &Rvalue<'tcx>,
     ) -> bool {
         match *rvalue {
@@ -170,15 +170,15 @@ pub trait Qualif {
 
     fn in_rvalue(
         cx: &ConstCx<'_, 'tcx>,
-        per_local: &impl Fn(Local) -> bool,
+        per_local: &mut impl FnMut(Local) -> bool,
         rvalue: &Rvalue<'tcx>,
     ) -> bool {
         Self::in_rvalue_structurally(cx, per_local, rvalue)
     }
 
     fn in_call(
         cx: &ConstCx<'_, 'tcx>,
-        _per_local: &impl Fn(Local) -> bool,
+        _per_local: &mut impl FnMut(Local) -> bool,
         _callee: &Operand<'tcx>,
         _args: &[Operand<'tcx>],
         return_ty: Ty<'tcx>,
@@ -208,7 +208,7 @@ impl Qualif for HasMutInterior {
 
     fn in_rvalue(
         cx: &ConstCx<'_, 'tcx>,
-        per_local: &impl Fn(Local) -> bool,
+        per_local: &mut impl FnMut(Local) -> bool,
         rvalue: &Rvalue<'tcx>,
     ) -> bool {
         match *rvalue {
@@ -249,7 +249,7 @@ impl Qualif for NeedsDrop {
 
     fn in_rvalue(
         cx: &ConstCx<'_, 'tcx>,
-        per_local: &impl Fn(Local) -> bool,
+        per_local: &mut impl FnMut(Local) -> bool,
         rvalue: &Rvalue<'tcx>,
     ) -> bool {
         if let Rvalue::Aggregate(ref kind, _) = *rvalue {

src/librustc_mir/transform/check_consts/resolver.rs

@@ -71,8 +71,13 @@ where
         return_place: &mir::Place<'tcx>,
     ) {
         let return_ty = return_place.ty(*self.item.body, self.item.tcx).ty;
-        let qualif =
-            Q::in_call(self.item, &|l| self.qualifs_per_local.contains(l), func, args, return_ty);
+        let qualif = Q::in_call(
+            self.item,
+            &mut |l| self.qualifs_per_local.contains(l),
+            func,
+            args,
+            return_ty,
+        );
         if !return_place.is_indirect() {
             self.assign_qualif_direct(return_place, qualif);
         }
@@ -105,7 +110,7 @@ where
         rvalue: &mir::Rvalue<'tcx>,
         location: Location,
     ) {
-        let qualif = Q::in_rvalue(self.item, &|l| self.qualifs_per_local.contains(l), rvalue);
+        let qualif = Q::in_rvalue(self.item, &mut |l| self.qualifs_per_local.contains(l), rvalue);
         if !place.is_indirect() {
             self.assign_qualif_direct(place, qualif);
         }
@@ -120,7 +125,8 @@ where
         // here; that occurs in `apply_call_return_effect`.
 
         if let mir::TerminatorKind::DropAndReplace { value, location: dest, .. } = kind {
-            let qualif = Q::in_operand(self.item, &|l| self.qualifs_per_local.contains(l), value);
+            let qualif =
+                Q::in_operand(self.item, &mut |l| self.qualifs_per_local.contains(l), value);
             if !dest.is_indirect() {
                 self.assign_qualif_direct(dest, qualif);
             }

src/librustc_mir/transform/check_consts/validation.rs

@@ -64,7 +64,7 @@ impl Qualifs<'a, 'mir, 'tcx> {
     /// Returns `true` if `local` is `NeedsDrop` at the given `Location`.
     ///
     /// Only updates the cursor if absolutely necessary
-    fn needs_drop_lazy_seek(&mut self, local: Local, location: Location) -> bool {
+    fn needs_drop(&mut self, local: Local, location: Location) -> bool {
         if !self.needs_drop.in_any_value_of_ty.contains(local) {
             return false;
         }
@@ -76,7 +76,7 @@ impl Qualifs<'a, 'mir, 'tcx> {
     /// Returns `true` if `local` is `HasMutInterior` at the given `Location`.
     ///
     /// Only updates the cursor if absolutely necessary.
-    fn has_mut_interior_lazy_seek(&mut self, local: Local, location: Location) -> bool {
+    fn has_mut_interior(&mut self, local: Local, location: Location) -> bool {
         if !self.has_mut_interior.in_any_value_of_ty.contains(local) {
             return false;
         }
@@ -86,17 +86,6 @@ impl Qualifs<'a, 'mir, 'tcx> {
             || self.indirectly_mutable(local, location)
     }
 
-    /// Returns `true` if `local` is `HasMutInterior`, but requires the `has_mut_interior` and
-    /// `indirectly_mutable` cursors to be updated beforehand.
-    fn has_mut_interior_eager_seek(&self, local: Local) -> bool {
-        if !self.has_mut_interior.in_any_value_of_ty.contains(local) {
-            return false;
-        }
-
-        self.has_mut_interior.cursor.get().contains(local)
-            || self.indirectly_mutable.get().contains(local)
-    }
-
     fn in_return_place(&mut self, item: &Item<'_, 'tcx>) -> ConstQualifs {
         // Find the `Return` terminator if one exists.
         //
@@ -120,8 +109,8 @@ impl Qualifs<'a, 'mir, 'tcx> {
         let return_loc = item.body.terminator_loc(return_block);
 
         ConstQualifs {
-            needs_drop: self.needs_drop_lazy_seek(RETURN_PLACE, return_loc),
-            has_mut_interior: self.has_mut_interior_lazy_seek(RETURN_PLACE, return_loc),
+            needs_drop: self.needs_drop(RETURN_PLACE, return_loc),
+            has_mut_interior: self.has_mut_interior(RETURN_PLACE, return_loc),
         }
     }
 }
@@ -244,23 +233,6 @@ impl Validator<'a, 'mir, 'tcx> {
             self.check_op_spanned(ops::StaticAccess, span)
         }
     }
-
-    fn check_immutable_borrow_like(&mut self, location: Location, place: &Place<'tcx>) {
-        // FIXME: Change the `in_*` methods to take a `FnMut` so we don't have to manually
-        // seek the cursors beforehand.
-        self.qualifs.has_mut_interior.cursor.seek_before(location);
-        self.qualifs.indirectly_mutable.seek(location);
-
-        let borrowed_place_has_mut_interior = HasMutInterior::in_place(
-            &self.item,
-            &|local| self.qualifs.has_mut_interior_eager_seek(local),
-            place.as_ref(),
-        );
-
-        if borrowed_place_has_mut_interior {
-            self.check_op(ops::CellBorrow);
-        }
-    }
 }
 
 impl Visitor<'tcx> for Validator<'_, 'mir, 'tcx> {
@@ -366,12 +338,17 @@ impl Visitor<'tcx> for Validator<'_, 'mir, 'tcx> {
             Rvalue::AddressOf(Mutability::Mut, _) => self.check_op(ops::MutAddressOf),
 
             Rvalue::Ref(_, BorrowKind::Shared, ref place)
-            | Rvalue::Ref(_, BorrowKind::Shallow, ref place) => {
-                self.check_immutable_borrow_like(location, place)
-            }
-
-            Rvalue::AddressOf(Mutability::Not, ref place) => {
-                self.check_immutable_borrow_like(location, place)
+            | Rvalue::Ref(_, BorrowKind::Shallow, ref place)
+            | Rvalue::AddressOf(Mutability::Not, ref place) => {
+                let borrowed_place_has_mut_interior = HasMutInterior::in_place(
+                    &self.item,
+                    &mut |local| self.qualifs.has_mut_interior(local, location),
+                    place.as_ref(),
+                );
+
+                if borrowed_place_has_mut_interior {
+                    self.check_op(ops::CellBorrow);
+                }
             }
 
             Rvalue::Cast(CastKind::Misc, ref operand, cast_ty) => {
@@ -571,7 +548,7 @@ impl Visitor<'tcx> for Validator<'_, 'mir, 'tcx> {
                 let needs_drop = if let Some(local) = dropped_place.as_local() {
                     // Use the span where the local was declared as the span of the drop error.
                     err_span = self.body.local_decls[local].source_info.span;
-                    self.qualifs.needs_drop_lazy_seek(local, location)
+                    self.qualifs.needs_drop(local, location)
                 } else {
                     true
                 };

src/librustc_mir/transform/promote_consts.rs

@@ -407,7 +407,7 @@ impl<'tcx> Validator<'_, 'tcx> {
 
     // FIXME(eddyb) maybe cache this?
     fn qualif_local<Q: qualifs::Qualif>(&self, local: Local) -> bool {
-        let per_local = &|l| self.qualif_local::<Q>(l);
+        let per_local = &mut |l| self.qualif_local::<Q>(l);
 
         if let TempState::Defined { location: loc, .. } = self.temps[local] {
             let num_stmts = self.body[loc.block].statements.len();