From 4e7f1fa14fe54c20eb583dbf40efe3284d48a3b0 Mon Sep 17 00:00:00 2001 From: Ralf Jung Date: Sun, 21 Mar 2021 18:09:53 +0100 Subject: [PATCH] post-drop-elab check-const: explain why we still check qualifs --- .../src/transform/check_consts/post_drop_elaboration.rs | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/compiler/rustc_mir/src/transform/check_consts/post_drop_elaboration.rs b/compiler/rustc_mir/src/transform/check_consts/post_drop_elaboration.rs index 1a2d932ba1905..057092b8ef574 100644 --- a/compiler/rustc_mir/src/transform/check_consts/post_drop_elaboration.rs +++ b/compiler/rustc_mir/src/transform/check_consts/post_drop_elaboration.rs @@ -79,7 +79,9 @@ impl Visitor<'tcx> for CheckLiveDrops<'mir, 'tcx> { mir::TerminatorKind::Drop { place: dropped_place, .. } => { let dropped_ty = dropped_place.ty(self.body, self.tcx).ty; if !NeedsDrop::in_any_value_of_ty(self.ccx, dropped_ty) { - return; + bug!( + "Drop elaboration left behind a Drop for a type that does not need dropping" + ); } if dropped_place.is_indirect() { @@ -87,6 +89,10 @@ impl Visitor<'tcx> for CheckLiveDrops<'mir, 'tcx> { return; } + // Drop elaboration is not precise enough to accept code like + // `src/test/ui/consts/control-flow/drop-pass.rs`; e.g., when an `Option>` is + // initialized with `None` and never changed, it still emits drop glue. + // Hence we additionally check the qualifs here to allow more code to pass. if self.qualifs.needs_drop(self.ccx, dropped_place.local, location) { // Use the span where the dropped local was declared for the error. let span = self.body.local_decls[dropped_place.local].source_info.span;