Drop tracking: track borrows of projections

Previous efforts to ignore partially consumed values meant we were also
not considering borrows of a projection. This led to cases where we'd
miss borrowed types which MIR expected to be there, leading to ICEs.

Author: eholk

compiler/rustc_typeck/src/check/generator_interior/drop_ranges.rs

@@ -116,6 +116,18 @@ impl TrackedValue {
             TrackedValue::Variable(hir_id) | TrackedValue::Temporary(hir_id) => *hir_id,
         }
     }
+
+    fn from_place_with_projections_allowed(place_with_id: &PlaceWithHirId<'_>) -> Self {
+        match place_with_id.place.base {
+            PlaceBase::Rvalue | PlaceBase::StaticItem => {
+                TrackedValue::Temporary(place_with_id.hir_id)
+            }
+            PlaceBase::Local(hir_id)
+            | PlaceBase::Upvar(ty::UpvarId { var_path: ty::UpvarPath { hir_id }, .. }) => {
+                TrackedValue::Variable(hir_id)
+            }
+        }
+    }
 }
 
 /// Represents a reason why we might not be able to convert a HirId or Place
@@ -142,15 +154,7 @@ impl TryFrom<&PlaceWithHirId<'_>> for TrackedValue {
             return Err(TrackedValueConversionError::PlaceProjectionsNotSupported);
         }
 
-        match place_with_id.place.base {
-            PlaceBase::Rvalue | PlaceBase::StaticItem => {
-                Ok(TrackedValue::Temporary(place_with_id.hir_id))
-            }
-            PlaceBase::Local(hir_id)
-            | PlaceBase::Upvar(ty::UpvarId { var_path: ty::UpvarPath { hir_id }, .. }) => {
-                Ok(TrackedValue::Variable(hir_id))
-            }
-        }
+        Ok(TrackedValue::from_place_with_projections_allowed(place_with_id))
     }
 }
 

compiler/rustc_typeck/src/check/generator_interior/drop_ranges/record_consumed_borrow.rs

@@ -96,9 +96,9 @@ impl<'tcx> expr_use_visitor::Delegate<'tcx> for ExprUseDelegate<'tcx> {
         _diag_expr_id: HirId,
         _bk: rustc_middle::ty::BorrowKind,
     ) {
-        place_with_id
-            .try_into()
-            .map_or(false, |tracked_value| self.places.borrowed.insert(tracked_value));
+        self.places
+            .borrowed
+            .insert(TrackedValue::from_place_with_projections_allowed(place_with_id));
     }
 
     fn mutate(

src/test/ui/async-await/issue-93648.rs

@@ -0,0 +1,12 @@
+// edition:2021
+// build-pass
+// compile-flags: -Zdrop-tracking
+
+fn main() {
+    let _ = async {
+        let mut s = (String::new(),);
+        s.0.push_str("abc");
+        std::mem::drop(s);
+        async {}.await;
+    };
+}