[ABI] Emit associated conformance descriptors for inherited protocols.

Start emitting associated conformance requirement descriptors for
inherited protocols, so we have a symbol to reference from resilient
witness tables and mangled names in the future.

Author: DougGregor

docs/ABI/Mangling.rst

@@ -200,6 +200,7 @@ types where the metadata itself has unknown layout.)
   global ::= assoc-type-name 'Tl'        // associated type descriptor
   global ::= assoc-type-name 'TM'        // default associated type witness accessor (HISTORICAL)
   global ::= type assoc-type-list protocol 'Tn' // associated conformance descriptor
+  global ::= type type protocol 'Tn' // inherited protocol witness descriptor
   global ::= type assoc-type-list protocol 'TN' // default associated conformance witness accessor
 
   REABSTRACT-THUNK-TYPE ::= 'R'          // reabstraction thunk helper function

include/swift/Demangling/Demangler.h

@@ -455,6 +455,7 @@ class Demangler : public NodeFactory {
 
   NodePointer popAssocTypeName();
   NodePointer popAssocTypePath();
+  NodePointer popSelfOrAssocTypePath();
   NodePointer getDependentGenericParamType(int depth, int index);
   NodePointer demangleGenericParamIndex();
   NodePointer popProtocolConformance();

lib/Demangling/Demangler.cpp

@@ -1875,6 +1875,20 @@ NodePointer Demangler::popAssocTypePath() {
   return AssocTypePath;
 }
 
+NodePointer Demangler::popSelfOrAssocTypePath() {
+  if (auto Type = popNode(Node::Kind::Type)) {
+    if (Type->getChild(0) &&
+        Type->getChild(0)->getKind() ==
+        Node::Kind::DependentGenericParamType) {
+      return Type;
+    }
+
+    pushNode(Type);
+  }
+
+  return popAssocTypePath();
+}
+
 NodePointer Demangler::getDependentGenericParamType(int depth, int index) {
   if (depth < 0 || index < 0)
     return nullptr;
@@ -2048,15 +2062,15 @@ NodePointer Demangler::demangleThunkOrSpecialization() {
 
     case 'n': {
       NodePointer requirementTy = popProtocol();
-      auto assocTypePath = popAssocTypePath();
+      NodePointer conformingType = popSelfOrAssocTypePath();
       NodePointer protoTy = popNode(Node::Kind::Type);
       return createWithChildren(Node::Kind::AssociatedConformanceDescriptor,
-                                protoTy, assocTypePath, requirementTy);
+                                protoTy, conformingType, requirementTy);
     }
 
     case 'N': {
       NodePointer requirementTy = popProtocol();
-      auto assocTypePath = popAssocTypePath();
+      auto assocTypePath = popSelfOrAssocTypePath();
       NodePointer protoTy = popNode(Node::Kind::Type);
       return createWithChildren(
                             Node::Kind::DefaultAssociatedConformanceAccessor,
@@ -2437,19 +2451,7 @@ NodePointer Demangler::demangleWitness() {
     }
     case 'T': {
       NodePointer ProtoTy = popNode(Node::Kind::Type);
-      NodePointer ConformingType = nullptr;
-      if (auto Type = popNode(Node::Kind::Type)) {
-        if (Type->getChild(0) &&
-            Type->getChild(0)->getKind() ==
-            Node::Kind::DependentGenericParamType) {
-          ConformingType = Type;
-        } else {
-          pushNode(Type);
-        }
-      }
-
-      if (!ConformingType)
-        ConformingType = popAssocTypePath();
+      NodePointer ConformingType = popSelfOrAssocTypePath();
       NodePointer Conf = popProtocolConformance();
       return createWithChildren(Node::Kind::AssociatedTypeWitnessTableAccessor,
                                 Conf, ConformingType, ProtoTy);

lib/IRGen/GenMeta.cpp

@@ -729,6 +729,20 @@ namespace {
               B.getAddrOfCurrentPosition(IGM.ProtocolRequirementStructTy));
         }
 
+        if (entry.isBase()) {
+          // Define the associated conformance descriptor to point to the
+          // current position in the protocol descriptor, which is an
+          // out-of-line base protocol.
+          AssociatedConformance conformance(
+                                  Proto,
+                                  Proto->getProtocolSelfType()
+                                    ->getCanonicalType(),
+                                  entry.getBase());
+          IGM.defineAssociatedConformanceDescriptor(
+              conformance,
+              B.getAddrOfCurrentPosition(IGM.ProtocolRequirementStructTy));
+        }
+
         auto reqt = B.beginStruct(IGM.ProtocolRequirementStructTy);
 
         auto info = getRequirementInfo(entry);

lib/IRGen/IRGenMangler.h

@@ -197,8 +197,12 @@ class IRGenMangler : public Mangle::ASTMangler {
       const ProtocolDecl *requirement) {
     beginMangling();
     appendAnyGenericType(proto);
-    bool isFirstAssociatedTypeIdentifier = true;
-    appendAssociatedTypePath(subject, isFirstAssociatedTypeIdentifier);
+    if (isa<GenericTypeParamType>(subject)) {
+      appendType(subject);
+    } else {
+      bool isFirstAssociatedTypeIdentifier = true;
+      appendAssociatedTypePath(subject, isFirstAssociatedTypeIdentifier);
+    }
     appendProtocolName(requirement);
     appendOperator("Tn");
     return finalize();

lib/IRGen/Linking.cpp

@@ -880,8 +880,10 @@ bool LinkEntity::isWeakImported(ModuleDecl *module) const {
     // their declaration, but are weak linked if the associated
     // type stored in extra storage area is weak linked.
     auto assocConformance = getAssociatedConformance();
-    auto *depMemTy = assocConformance.first->castTo<DependentMemberType>();
-    return depMemTy->getAssocType()->isWeakImported(module);
+    if (auto *depMemTy = assocConformance.first->getAs<DependentMemberType>())
+      return depMemTy->getAssocType()->isWeakImported(module);
+
+    return cast<ProtocolDecl>(getDecl())->isWeakImported(module);
   }
 
   case Kind::TypeMetadata:

lib/TBDGen/TBDGen.cpp

@@ -431,10 +431,6 @@ void TBDGenVisitor::visitProtocolDecl(ProtocolDecl *PD) {
       if (req.getKind() != RequirementKind::Conformance)
         continue;
 
-      // Skip inherited requirements.
-      if (req.getFirstType()->isEqual(PD->getSelfInterfaceType()))
-        continue;
-
       AssociatedConformance conformance(
         PD,
         req.getFirstType()->getCanonicalType(),

test/Demangle/Inputs/manglings.txt

@@ -335,3 +335,4 @@ $S1t1PP10AssocType2_AA1QTN ---> default associated conformance accessor for t.P.
 $sSD5IndexVy__GD ---> $sSD5IndexVy__GD
 $s4test3StrCACycfC ---> {T:$s4test3StrCACycfc} test.Str.__allocating_init() -> test.Str
 $s18keypaths_inlinable13KeypathStructV8computedSSvpACTKq  ---> key path getter for keypaths_inlinable.KeypathStruct.computed : Swift.String : keypaths_inlinable.KeypathStruct, serialized
+$s18resilient_protocol24ResilientDerivedProtocolPxAA0c4BaseE0Tn --> associated conformance descriptor for resilient_protocol.ResilientDerivedProtocol.A: resilient_protocol.ResilientBaseProtocol

test/IRGen/protocol_resilience_descriptors.swift

@@ -29,6 +29,9 @@
 // Protocol requirements base descriptor
 // CHECK-DEFINITION: @"$s18resilient_protocol21ResilientBaseProtocolTL" ={{( dllexport)?}}{{( protected)?}} alias %swift.protocol_requirement, getelementptr (%swift.protocol_requirement, %swift.protocol_requirement* getelementptr inbounds (<{ i32, i32, i32, i32, i32, i32, %swift.protocol_requirement }>, <{ i32, i32, i32, i32, i32, i32, %swift.protocol_requirement }>* @"$s18resilient_protocol21ResilientBaseProtocolMp", i32 0, i32 6), i32 -1)
 
+// Associated conformance descriptor for inherited protocol
+// CHECK-DEFINITION-LABEL: s18resilient_protocol24ResilientDerivedProtocolPxAA0c4BaseE0Tn" = alias 
+
 // Associated type and conformance
 
 // CHECK-DEFINITION: @"$s1T18resilient_protocol24ProtocolWithRequirementsPTl" ={{( dllexport)?}}{{( protected)?}} alias