[rbi] Fix demangling of sending results.

The issue here is that the demangler (since we have a postfix mangling) parses
parameters/results/etc and then uses earlier postfix type arguments to attach
the relevant types to the parameters/results/etc. Since the flag for a sending
result was placed in between the parameters and results, we get an off by one
error.

The reason why I originally did it this way is that part of sending was cargo
culted from the autodiff parts of the mangling and parts from the
async/isolated(any) part of the function type mangling. In this case, I followed
the location of the autodiff part of the mangling (which is per parameter)
instead of the async/isolated(any) part of the mangling (which are global flags)
which is what exposed this issue.

The good thing is if we eventually allow for sending to be placed on individual
parameters, we can potentially eliminate seeing this patter in future versions
of the ABI by just placing sending onto the parameters instead. This would
additionally allow for us to eliminate this offset code by checking for the flag
where it is and in such a case, just place it on each parameter as a flag.

rdar://141962865

Author: gottesmm

lib/Demangling/Demangler.cpp

@@ -2431,6 +2431,15 @@ NodePointer Demangler::demangleImplFunctionType() {
     ++NumTypesToAdd;
   }
 
+  // NOTE: Please do not add additional function level flags here besides
+  // ImplSendingResult (which is remaining due to ABI reasons). If one wishes to
+  // place a flag, place it earlier in the mangling so that it is parsed above
+  // near @async (demangles from 'H').
+  //
+  // The reason why is that parameters, results, yields, and errors are
+  // processed backwards as if they are in a contiguous array adding to them the
+  // appropriate set of argument types that are our postfix parameters earlier
+  // in the mangling.
   if (nextIf('T')) {
     type->addChild(createNode(Node::Kind::ImplSendingResult), *this);
   }
@@ -2461,13 +2470,27 @@ NodePointer Demangler::demangleImplFunctionType() {
   if (!nextIf('_'))
     return nullptr;
 
+  // Due to the place that the sending result bit was placed in the mangling and
+  // is expected in the tree (namely before results)... we need to make sure to
+  // skip over it.
+  //
+  // Our methodology is that when we detect the impl sending result, we add 1 to
+  // the node index so that we skip over the value. We subtract since we are
+  // actually updating the children backwards.
+  int implSendingResultIndexAdjustment = 0;
   for (int Idx = 0; Idx < NumTypesToAdd; ++Idx) {
+    int nodeIndex = type->getNumChildren() - Idx - 1;
+    if (type->getChild(nodeIndex)->getKind() == Node::Kind::ImplSendingResult) {
+      implSendingResultIndexAdjustment = 1;
+    }
+    nodeIndex -= implSendingResultIndexAdjustment;
+
     NodePointer ConvTy = popNode(Node::Kind::Type);
     if (!ConvTy)
       return nullptr;
-    type->getChild(type->getNumChildren() - Idx - 1)->addChild(ConvTy, *this);
+    type->getChild(nodeIndex)->addChild(ConvTy, *this);
   }
-  
+
   return createType(type);
 }
 

test/Concurrency/sending_mangling.swift

@@ -1,4 +1,6 @@
-// RUN: %target-swift-frontend %s -emit-silgen -swift-version 6 | swift-demangle | %FileCheck -check-prefix=CHECK %s
+// RUN: %empty-directory(%t)
+// RUN: %target-swift-frontend %s -emit-silgen -swift-version 6 | swift-demangle | %FileCheck %s
+// RUN: %target-swift-frontend %s -emit-silgen -swift-version 6 | %FileCheck -check-prefix=SIL %s
 
 // REQUIRES: concurrency
 // REQUIRES: asserts
@@ -110,3 +112,18 @@ struct ConstructorSharedTest {
   // CHECK: sil hidden [ossa] @sending_mangling.ConstructorSharedTest.functionSuppressed(sending_mangling.NonSendableKlass) -> () : $@convention(method) (@sil_sending @guaranteed NonSendableKlass, ConstructorSharedTest) -> () {
   func functionSuppressed(_ x: __shared sending NonSendableKlass) {}
 }
+
+// Make sure that we produce the appropriate reabstraction thunk.
+func reabstractionThunkTest_takeSendingReturnSending<T>(
+  _ x: sending T) -> sending T { fatalError() }
+func reabstractionThunkTest_reabstractionThunkGenerator<T>(
+  _ x: sending T,
+  _ f: (sending T) -> T) {}
+
+// CHECK: sil shared [transparent] [serialized] [reabstraction_thunk] [ossa] @reabstraction thunk helper from @escaping @callee_guaranteed (@in sending sending_mangling.NonSendableKlass) -> sending (@out sending_mangling.NonSendableKlass) to @escaping @callee_guaranteed (@owned sending sending_mangling.NonSendableKlass) -> sending (@owned sending_mangling.NonSendableKlass) : $@convention(thin) (@sil_sending @owned NonSendableKlass, @guaranteed @callee_guaranteed (@sil_sending @in NonSendableKlass) -> @sil_sending @out NonSendableKlass) -> @owned NonSendableKlass {
+// SIL: sil shared [transparent] [serialized] [reabstraction_thunk] [ossa] @$s16sending_mangling16NonSendableKlassCACIegiTTr_A2CIegxTTo_TR : $@convention(thin) (@sil_sending @owned NonSendableKlass, @guaranteed @callee_guaranteed (@sil_sending @in NonSendableKlass) -> @sil_sending @out NonSendableKlass) -> @owned NonSendableKlass {
+func reabstractionThunkTest() {
+  reabstractionThunkTest_reabstractionThunkGenerator(
+    NonSendableKlass(),
+    reabstractionThunkTest_takeSendingReturnSending)
+}

test/Demangle/Inputs/manglings.txt

@@ -485,3 +485,5 @@ $s4main4SlabVy$1_SiG ---> main.Slab<2, Swift.Int>
 $s$n3_SSBV ---> Builtin.FixedArray<-4, Swift.String>
 $s3red7MyActorC3runyxxyYaKACYcYTXEYaKlFZ ---> static red.MyActor.run<A>(@red.MyActor () async throws -> sending A) async throws -> A
 $s3red7MyActorC3runyxxyYaKYAYTXEYaKlFZ ---> static red.MyActor.run<A>(@isolated(any) () async throws -> sending A) async throws -> A
+$s7ToolKit10TypedValueOACs5Error_pIgHnTTrzo_A2CsAD_pIegHiTrzr_TR ---> {T:} reabstraction thunk helper from @callee_guaranteed @async (@in_guaranteed sending ToolKit.TypedValue) -> sending (@out ToolKit.TypedValue, @error @owned Swift.Error) to @escaping @callee_guaranteed @async (@in sending ToolKit.TypedValue) -> (@out ToolKit.TypedValue, @error @out Swift.Error)
+$s16sending_mangling16NonSendableKlassCACIegiTTr_A2CIegxTTo_TR ---> {T:} reabstraction thunk helper from @callee_guaranteed @async (@in_guaranteed sending ToolKit.TypedValue) -> sending (@out ToolKit.TypedValue, @error @owned Swift.Error) to @escaping @callee_guaranteed @async (@in sending ToolKit.TypedValue) -> (@out ToolKit.TypedValue, @error @out Swift.Error)