[ABI] Mangling for default associated conformance accessors.

Default associated conformance accessors will be used in default
witness tables to fill in associated conformances for defaulted
associated types. Add (de|re|)mangling support for them and make them
linking entities in IRGen.

Author: DougGregor

docs/ABI/Mangling.rst

@@ -141,7 +141,8 @@ types where the metadata itself has unknown layout.)
   global ::= protocol 'TL'               // protocol requirements base descriptor
   global ::= assoc-type-name 'Tl'        // associated type descriptor
   global ::= assoc-type-name 'TM'        // default associated type witness accessor
-  global ::= type assoc-type-path protocol  // associated conformance descriptor
+  global ::= type assoc-type-path protocol 'Tn' // associated conformance descriptor
+  global ::= type assoc-type-path protocol 'TN' // default associated conformance witness accessor
 
   REABSTRACT-THUNK-TYPE ::= 'R'          // reabstraction thunk helper function
   REABSTRACT-THUNK-TYPE ::= 'r'          // reabstraction thunk

include/swift/Demangling/DemangleNodes.def

@@ -211,6 +211,7 @@ NODE(DispatchThunk)
 NODE(MethodDescriptor)
 NODE(ProtocolRequirementsBaseDescriptor)
 NODE(AssociatedConformanceDescriptor)
+NODE(DefaultAssociatedConformanceAccessor)
 NODE(AssociatedTypeDescriptor)
 NODE(ThrowsAnnotation)
 NODE(EmptyList)

include/swift/IRGen/Linking.h

@@ -213,6 +213,11 @@ class LinkEntity {
     /// is stored in the data.
     AssociatedConformanceDescriptor,
 
+    /// A default accessor for an associated conformance of a protocol.
+    /// The pointer is a ProtocolDecl*; the index of the associated conformance
+    /// is stored in the data.
+    DefaultAssociatedConformanceAccessor,
+
     /// A function which returns the default type metadata for the associated
     /// type of a protocol.  The secondary pointer is a ProtocolDecl*.
     /// The index of the associated type declaration is stored in the data.
@@ -834,6 +839,17 @@ class LinkEntity {
     return entity;
   }
 
+  static LinkEntity
+  forDefaultAssociatedConformanceAccessor(AssociatedConformance conformance) {
+    LinkEntity entity;
+    entity.setForProtocolAndAssociatedConformance(
+        Kind::DefaultAssociatedConformanceAccessor,
+        conformance.getSourceProtocol(),
+        conformance.getAssociation(),
+        conformance.getAssociatedRequirement());
+    return entity;
+  }
+
   static LinkEntity forReflectionBuiltinDescriptor(CanType type) {
     LinkEntity entity;
     entity.setForType(Kind::ReflectionBuiltinDescriptor, type);
@@ -924,7 +940,8 @@ class LinkEntity {
                        LINKENTITY_GET_FIELD(Data, AssociatedConformanceIndex));
     }
 
-    assert(getKind() == Kind::AssociatedConformanceDescriptor);
+    assert(getKind() == Kind::AssociatedConformanceDescriptor ||
+           getKind() == Kind::DefaultAssociatedConformanceAccessor);
     return getAssociatedConformanceByIndex(
              cast<ProtocolDecl>(getDecl()),
              LINKENTITY_GET_FIELD(Data, AssociatedConformanceIndex));

lib/Demangling/Demangler.cpp

@@ -1835,6 +1835,15 @@ NodePointer Demangler::demangleThunkOrSpecialization() {
                                 protoTy, assocTypePath, requirementTy);
     }
 
+    case 'N': {
+      NodePointer requirementTy = popProtocol();
+      auto assocTypePath = popAssocTypePath();
+      NodePointer protoTy = popNode(Node::Kind::Type);
+      return createWithChildren(
+                            Node::Kind::DefaultAssociatedConformanceAccessor,
+                            protoTy, assocTypePath, requirementTy);
+    }
+
     case 'H':
     case 'h': {
       auto nodeKind = c == 'H' ? Node::Kind::KeyPathEqualsThunkHelper

lib/Demangling/NodePrinter.cpp

@@ -323,6 +323,7 @@ class NodePrinter {
     case Node::Kind::DeclContext:
     case Node::Kind::DefaultArgumentInitializer:
     case Node::Kind::DefaultAssociatedTypeMetadataAccessor:
+    case Node::Kind::DefaultAssociatedConformanceAccessor:
     case Node::Kind::DependentAssociatedTypeRef:
     case Node::Kind::DependentGenericSignature:
     case Node::Kind::DependentGenericParamCount:
@@ -1564,6 +1565,14 @@ NodePointer NodePrinter::print(NodePointer Node, bool asPrefixContext) {
     Printer << ": ";
     print(Node->getChild(2));
     return nullptr;
+  case Node::Kind::DefaultAssociatedConformanceAccessor:
+    Printer << "default associated conformance accessor for ";
+    print(Node->getChild(0));
+    Printer << ".";
+    print(Node->getChild(1));
+    Printer << ": ";
+    print(Node->getChild(2));
+    return nullptr;
   case Node::Kind::AssociatedTypeDescriptor:
     Printer << "associated type descriptor for ";
     print(Node->getChild(0));

lib/Demangling/OldRemangler.cpp

@@ -888,6 +888,10 @@ void Remangler::mangleAssociatedConformanceDescriptor(Node *node) {
   Out << "<associated-conformance-descriptor>";
 }
 
+void Remangler::mangleDefaultAssociatedConformanceAccessor(Node *node) {
+  Out << "<default-associated-conformance-descriptor>";
+}
+
 void Remangler::mangleAssociatedTypeMetadataAccessor(Node *node) {
   Out << "Wt";
   mangleChildNodes(node); // protocol conformance, identifier

lib/Demangling/Remangler.cpp

@@ -579,6 +579,11 @@ void Remangler::mangleAssociatedConformanceDescriptor(Node *node) {
   Buffer << "Tn";
 }
 
+void Remangler::mangleDefaultAssociatedConformanceAccessor(Node *node) {
+  mangleChildNodes(node);
+  Buffer << "TN";
+}
+
 void Remangler::mangleAssociatedTypeMetadataAccessor(Node *node) {
   mangleChildNodes(node); // protocol conformance, identifier
   Buffer << "Wt";

lib/IRGen/IRGenMangler.h

@@ -197,6 +197,19 @@ class IRGenMangler : public Mangle::ASTMangler {
     return finalize();
   }
 
+  std::string mangleDefaultAssociatedConformanceAccessor(
+      const ProtocolDecl *proto,
+      CanType subject,
+      const ProtocolDecl *requirement) {
+    beginMangling();
+    appendAnyGenericType(proto);
+    bool isFirstAssociatedTypeIdentifier = true;
+    appendAssociatedTypePath(subject, isFirstAssociatedTypeIdentifier);
+    appendProtocolName(requirement);
+    appendOperator("TN");
+    return finalize();
+  }
+
   std::string mangleProtocolConformanceDescriptor(
                                  const ProtocolConformance *Conformance) {
     beginMangling();

lib/IRGen/Linking.cpp

@@ -187,6 +187,14 @@ std::string LinkEntity::mangleAsString() const {
              assocConformance.second);
   }
 
+  case Kind::DefaultAssociatedConformanceAccessor: {
+    auto assocConformance = getAssociatedConformance();
+    return mangler.mangleDefaultAssociatedConformanceAccessor(
+             cast<ProtocolDecl>(getDecl()),
+             assocConformance.first,
+             assocConformance.second);
+  }
+
   case Kind::ProtocolConformanceDescriptor:
     return mangler.mangleProtocolConformanceDescriptor(
                    cast<NormalProtocolConformance>(getProtocolConformance()));
@@ -498,6 +506,7 @@ SILLinkage LinkEntity::getLinkage(ForDefinition_t forDefinition) const {
   case Kind::AssociatedTypeMetadataAccessFunction:
   case Kind::DefaultAssociatedTypeMetadataAccessFunction:
   case Kind::AssociatedTypeWitnessTableAccessFunction:
+  case Kind::DefaultAssociatedConformanceAccessor:
   case Kind::GenericProtocolWitnessTableCache:
   case Kind::GenericProtocolWitnessTableInstantiationFunction:
     return SILLinkage::Private;
@@ -629,6 +638,7 @@ bool LinkEntity::isAvailableExternally(IRGenModule &IGM) const {
   case Kind::TypeMetadataCompletionFunction:
   case Kind::TypeMetadataPattern:
   case Kind::DefaultAssociatedTypeMetadataAccessFunction:
+  case Kind::DefaultAssociatedConformanceAccessor:
     return false;
 
   case Kind::ValueWitness:

test/Demangle/Inputs/manglings.txt

@@ -332,3 +332,4 @@ A.h<A>(A) -> ()inlined generic function <(A, A1)> of
 $S1T19protocol_resilience17ResilientProtocolPTl --> associated type descriptor for T
 $S18resilient_protocol21ResilientBaseProtocolTL --> protocol requirements base descriptor for resilient_protocol.ResilientBaseProtocol
 $S1t1PP10AssocType2_AA1QTn --> associated conformance descriptor for t.P.AssocType2: t.Q
+$S1t1PP10AssocType2_AA1QTN --> default associated conformance accessor for t.P.AssocType2: t.Q