Add simple async drop glue generation

Explainer: https://zetanumbers.github.io/book/async-drop-design.html

#121801

Author: zetanumbers

compiler/rustc_codegen_ssa/src/back/symbol_export.rs

@@ -363,6 +363,24 @@ fn exported_symbols_provider_local(
                         },
                     ));
                 }
+                MonoItem::Fn(Instance {
+                    def: InstanceDef::AsyncDropGlueCtorShim(def_id, ty),
+                    args,
+                }) => {
+                    // A little sanity-check
+                    debug_assert_eq!(
+                        args.non_erasable_generics(tcx, def_id).skip(1).next(),
+                        Some(GenericArgKind::Type(ty))
+                    );
+                    symbols.push((
+                        ExportedSymbol::AsyncDropGlueCtorShim(ty),
+                        SymbolExportInfo {
+                            level: SymbolExportLevel::Rust,
+                            kind: SymbolExportKind::Text,
+                            used: false,
+                        },
+                    ));
+                }
                 _ => {
                     // Any other symbols don't qualify for sharing
                 }
@@ -385,6 +403,7 @@ fn upstream_monomorphizations_provider(
     let mut instances: DefIdMap<UnordMap<_, _>> = Default::default();
 
     let drop_in_place_fn_def_id = tcx.lang_items().drop_in_place_fn();
+    let async_drop_in_place_fn_def_id = tcx.lang_items().async_drop_in_place_fn();
 
     for &cnum in cnums.iter() {
         for (exported_symbol, _) in tcx.exported_symbols(cnum).iter() {
@@ -399,6 +418,18 @@ fn upstream_monomorphizations_provider(
                         continue;
                     }
                 }
+                ExportedSymbol::AsyncDropGlueCtorShim(ty) => {
+                    if let Some(async_drop_in_place_fn_def_id) = async_drop_in_place_fn_def_id {
+                        (
+                            async_drop_in_place_fn_def_id,
+                            tcx.mk_args(&[tcx.lifetimes.re_erased.into(), ty.into()]),
+                        )
+                    } else {
+                        // `drop_in_place` in place does not exist, don't try
+                        // to use it.
+                        continue;
+                    }
+                }
                 ExportedSymbol::NonGeneric(..)
                 | ExportedSymbol::ThreadLocalShim(..)
                 | ExportedSymbol::NoDefId(..) => {
@@ -534,6 +565,13 @@ pub fn symbol_name_for_instance_in_crate<'tcx>(
             Instance::resolve_drop_in_place(tcx, ty),
             instantiating_crate,
         ),
+        ExportedSymbol::AsyncDropGlueCtorShim(ty) => {
+            rustc_symbol_mangling::symbol_name_for_instance_in_crate(
+                tcx,
+                Instance::resolve_async_drop_in_place(tcx, ty),
+                instantiating_crate,
+            )
+        }
         ExportedSymbol::NoDefId(symbol_name) => symbol_name.to_string(),
     }
 }
@@ -582,6 +620,9 @@ pub fn linking_symbol_name_for_instance_in_crate<'tcx>(
         // DropGlue always use the Rust calling convention and thus follow the target's default
         // symbol decoration scheme.
         ExportedSymbol::DropGlue(..) => None,
+        // AsyncDropGlueCtorShim always use the Rust calling convention and thus follow the
+        // target's default symbol decoration scheme.
+        ExportedSymbol::AsyncDropGlueCtorShim(..) => None,
         // NoDefId always follow the target's default symbol decoration scheme.
         ExportedSymbol::NoDefId(..) => None,
         // ThreadLocalShim always follow the target's default symbol decoration scheme.

compiler/rustc_const_eval/src/interpret/terminator.rs

@@ -558,6 +558,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
             | ty::InstanceDef::CloneShim(..)
             | ty::InstanceDef::FnPtrAddrShim(..)
             | ty::InstanceDef::ThreadLocalShim(..)
+            | ty::InstanceDef::AsyncDropGlueCtorShim(..)
             | ty::InstanceDef::Item(_) => {
                 // We need MIR for this fn
                 let Some((body, instance)) = M::find_mir_or_eval_fn(

compiler/rustc_hir/src/lang_items.rs

@@ -162,6 +162,18 @@ language_item_table! {
     Drop,                    sym::drop,                drop_trait,                 Target::Trait,          GenericRequirement::None;
     Destruct,                sym::destruct,            destruct_trait,             Target::Trait,          GenericRequirement::None;
 
+    AsyncDrop,               sym::async_drop,          async_drop_trait,           Target::Trait,          GenericRequirement::Exact(0);
+    AsyncDestruct,           sym::async_destruct,      async_destruct_trait,       Target::Trait,          GenericRequirement::Exact(0);
+    AsyncDropInPlace,        sym::async_drop_in_place, async_drop_in_place_fn,     Target::Fn,             GenericRequirement::Exact(1);
+    SurfaceAsyncDropInPlace, sym::surface_async_drop_in_place, surface_async_drop_in_place_fn, Target::Fn, GenericRequirement::Exact(1);
+    AsyncDropSurfaceDropInPlace, sym::async_drop_surface_drop_in_place, async_drop_surface_drop_in_place_fn, Target::Fn, GenericRequirement::Exact(1);
+    AsyncDropSlice,          sym::async_drop_slice,    async_drop_slice_fn,        Target::Fn,             GenericRequirement::Exact(1);
+    AsyncDropChain,          sym::async_drop_chain,    async_drop_chain_fn,        Target::Fn,             GenericRequirement::Exact(2);
+    AsyncDropNoop,           sym::async_drop_noop,     async_drop_noop_fn,         Target::Fn,             GenericRequirement::Exact(0);
+    AsyncDropFuse,           sym::async_drop_fuse,     async_drop_fuse_fn,         Target::Fn,             GenericRequirement::Exact(1);
+    AsyncDropDefer,          sym::async_drop_defer,    async_drop_defer_fn,        Target::Fn,             GenericRequirement::Exact(1);
+    AsyncDropEither,         sym::async_drop_either,   async_drop_either_fn,       Target::Fn,             GenericRequirement::Exact(3);
+
     CoerceUnsized,           sym::coerce_unsized,      coerce_unsized_trait,       Target::Trait,          GenericRequirement::Minimum(1);
     DispatchFromDyn,         sym::dispatch_from_dyn,   dispatch_from_dyn_trait,    Target::Trait,          GenericRequirement::Minimum(1);
 
@@ -281,6 +293,7 @@ language_item_table! {
 
     ExchangeMalloc,          sym::exchange_malloc,     exchange_malloc_fn,         Target::Fn,             GenericRequirement::None;
     DropInPlace,             sym::drop_in_place,       drop_in_place_fn,           Target::Fn,             GenericRequirement::Minimum(1);
+    FallbackSurfaceDrop,     sym::fallback_surface_drop, fallback_surface_drop_fn, Target::Fn,             GenericRequirement::None;
     AllocLayout,             sym::alloc_layout,        alloc_layout,               Target::Struct,         GenericRequirement::None;
 
     Start,                   sym::start,               start_fn,                   Target::Fn,             GenericRequirement::Exact(1);

compiler/rustc_hir_typeck/src/callee.rs

@@ -38,8 +38,11 @@ pub fn check_legal_trait_for_method_call(
     receiver: Option<Span>,
     expr_span: Span,
     trait_id: DefId,
+    body_id: DefId,
 ) -> Result<(), ErrorGuaranteed> {
-    if tcx.lang_items().drop_trait() == Some(trait_id) {
+    if tcx.lang_items().drop_trait() == Some(trait_id)
+        && tcx.lang_items().fallback_surface_drop_fn() != Some(body_id)
+    {
         let sugg = if let Some(receiver) = receiver.filter(|s| !s.is_empty()) {
             errors::ExplicitDestructorCallSugg::Snippet {
                 lo: expr_span.shrink_to_lo(),

compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs

@@ -1118,6 +1118,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                             None,
                             span,
                             container_id,
+                            self.body_id.to_def_id(),
                         ) {
                             self.set_tainted_by_errors(e);
                         }

compiler/rustc_hir_typeck/src/method/confirm.rs

@@ -628,6 +628,7 @@ impl<'a, 'tcx> ConfirmContext<'a, 'tcx> {
                 Some(self.self_expr.span),
                 self.call_expr.span,
                 trait_def_id,
+                self.body_id.to_def_id(),
             ) {
                 self.set_tainted_by_errors(e);
             }

compiler/rustc_middle/src/middle/exported_symbols.rs

@@ -43,6 +43,7 @@ pub enum ExportedSymbol<'tcx> {
     NonGeneric(DefId),
     Generic(DefId, GenericArgsRef<'tcx>),
     DropGlue(Ty<'tcx>),
+    AsyncDropGlueCtorShim(Ty<'tcx>),
     ThreadLocalShim(DefId),
     NoDefId(ty::SymbolName<'tcx>),
 }
@@ -59,6 +60,9 @@ impl<'tcx> ExportedSymbol<'tcx> {
             ExportedSymbol::DropGlue(ty) => {
                 tcx.symbol_name(ty::Instance::resolve_drop_in_place(tcx, ty))
             }
+            ExportedSymbol::AsyncDropGlueCtorShim(ty) => {
+                tcx.symbol_name(ty::Instance::resolve_async_drop_in_place(tcx, ty))
+            }
             ExportedSymbol::ThreadLocalShim(def_id) => tcx.symbol_name(ty::Instance {
                 def: ty::InstanceDef::ThreadLocalShim(def_id),
                 args: ty::GenericArgs::empty(),

compiler/rustc_middle/src/mir/mono.rs

@@ -406,7 +406,8 @@ impl<'tcx> CodegenUnit<'tcx> {
                             | InstanceDef::DropGlue(..)
                             | InstanceDef::CloneShim(..)
                             | InstanceDef::ThreadLocalShim(..)
-                            | InstanceDef::FnPtrAddrShim(..) => None,
+                            | InstanceDef::FnPtrAddrShim(..)
+                            | InstanceDef::AsyncDropGlueCtorShim(..) => None,
                         }
                     }
                     MonoItem::Static(def_id) => def_id.as_local().map(Idx::index),

compiler/rustc_middle/src/mir/pretty.rs

@@ -187,6 +187,17 @@ fn dump_path<'tcx>(
             }));
             s
         }
+        ty::InstanceDef::AsyncDropGlueCtorShim(_, ty) => {
+            // Unfortunately, pretty-printed typed are not very filename-friendly.
+            // We dome some filtering.
+            let mut s = ".".to_owned();
+            s.extend(ty.to_string().chars().filter_map(|c| match c {
+                ' ' => None,
+                ':' | '<' | '>' => Some('_'),
+                c => Some(c),
+            }));
+            s
+        }
         _ => String::new(),
     };
 

compiler/rustc_middle/src/mir/visit.rs

@@ -355,7 +355,8 @@ macro_rules! make_mir_visitor {
                         ty::InstanceDef::FnPtrShim(_def_id, ty) |
                         ty::InstanceDef::DropGlue(_def_id, Some(ty)) |
                         ty::InstanceDef::CloneShim(_def_id, ty) |
-                        ty::InstanceDef::FnPtrAddrShim(_def_id, ty) => {
+                        ty::InstanceDef::FnPtrAddrShim(_def_id, ty) |
+                        ty::InstanceDef::AsyncDropGlueCtorShim(_def_id, ty) => {
                             // FIXME(eddyb) use a better `TyContext` here.
                             self.visit_ty($(& $mutability)? *ty, TyContext::Location(location));
                         }