Rollup merge of #93751 - eholk:issue-93648-drop-tracking-projection, r=tmiasko

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.

This PR also includes the `-Zdrop-tracking` flag from #93313. If that PR lands first, I'll rebase to drop the commit from this one.

Fixes #93648

compiler/rustc_interface/src/tests.rs

@@ -730,6 +730,7 @@ fn test_debugging_options_tracking_hash() {
     tracked!(debug_info_for_profiling, true);
     tracked!(debug_macros, true);
     tracked!(dep_info_omit_d_target, true);
+    tracked!(drop_tracking, true);
     tracked!(dual_proc_macros, true);
     tracked!(fewer_names, Some(true));
     tracked!(force_unstable_if_unmarked, true);

compiler/rustc_session/src/options.rs

@@ -1173,6 +1173,8 @@ options! {
     dont_buffer_diagnostics: bool = (false, parse_bool, [UNTRACKED],
         "emit diagnostics rather than buffering (breaks NLL error downgrading, sorting) \
         (default: no)"),
+    drop_tracking: bool = (false, parse_bool, [TRACKED],
+        "enables drop tracking in generators (default: no)"),
     dual_proc_macros: bool = (false, parse_bool, [TRACKED],
         "load proc macros for both target and host, but only link to the target (default: no)"),
     dump_dep_graph: bool = (false, parse_bool, [UNTRACKED],

compiler/rustc_typeck/src/check/generator_interior.rs

@@ -22,11 +22,6 @@ use tracing::debug;
 
 mod drop_ranges;
 
-// FIXME(eholk): This flag is here to give a quick way to disable drop tracking in case we find
-// unexpected breakages while it's still new. It should be removed before too long. For example,
-// see #93161.
-const ENABLE_DROP_TRACKING: bool = false;
-
 struct InteriorVisitor<'a, 'tcx> {
     fcx: &'a FnCtxt<'a, 'tcx>,
     types: FxIndexSet<ty::GeneratorInteriorTypeCause<'tcx>>,
@@ -82,7 +77,7 @@ impl<'a, 'tcx> InteriorVisitor<'a, 'tcx> {
                                 yield_data.expr_and_pat_count, self.expr_count, source_span
                             );
 
-                            if ENABLE_DROP_TRACKING
+                            if self.fcx.sess().opts.debugging_opts.drop_tracking
                                 && self
                                     .drop_ranges
                                     .is_dropped_at(hir_id, yield_data.expr_and_pat_count)

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

@@ -37,7 +37,7 @@ pub fn compute_drop_ranges<'a, 'tcx>(
     def_id: DefId,
     body: &'tcx Body<'tcx>,
 ) -> DropRanges {
-    if super::ENABLE_DROP_TRACKING {
+    if fcx.sess().opts.debugging_opts.drop_tracking {
         let consumed_borrowed_places = find_consumed_and_borrowed(fcx, def_id, body);
 
         let num_exprs = fcx.tcx.region_scope_tree(def_id).body_expr_count(body.id()).unwrap_or(0);
@@ -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;
+    };
+}