Async drop source info fix for proxy-drop-coroutine - fixes crash at debug info generation

Author: azhogin

compiler/rustc_middle/src/ty/mod.rs

@@ -1929,13 +1929,17 @@ impl<'tcx> TyCtxt<'tcx> {
             if arg_cor_ty.is_coroutine() {
                 let span = self.def_span(def_id);
                 let source_info = SourceInfo::outermost(span);
+                // Even minimal, empty coroutine has 3 states (RESERVED_VARIANTS),
+                // so variant_fields and variant_source_info should have 3 elements.
                 let variant_fields: IndexVec<VariantIdx, IndexVec<FieldIdx, CoroutineSavedLocal>> =
                     iter::repeat(IndexVec::new()).take(CoroutineArgs::RESERVED_VARIANTS).collect();
+                let variant_source_info: IndexVec<VariantIdx, SourceInfo> =
+                    iter::repeat(source_info).take(CoroutineArgs::RESERVED_VARIANTS).collect();
                 let proxy_layout = CoroutineLayout {
                     field_tys: [].into(),
                     field_names: [].into(),
                     variant_fields,
-                    variant_source_info: [source_info].into(),
+                    variant_source_info,
                     storage_conflicts: BitMatrix::new(0, 0),
                 };
                 return Some(self.arena.alloc(proxy_layout));