[AST] Reinstate "Fix excessive deserialization in GenericSignatureBuilder"

include/swift/AST/Decl.h

@@ -2854,8 +2854,8 @@ class NominalTypeDecl : public GenericTypeDecl, public IterableDeclContext {
   ///
   /// \param ignoreNewExtensions Whether to avoid loading any new extension.
   /// Used by the module loader to break recursion.
-  ArrayRef<ValueDecl *> lookupDirect(DeclName name,
-                                     bool ignoreNewExtensions = false);
+  TinyPtrVector<ValueDecl *> lookupDirect(DeclName name,
+                                          bool ignoreNewExtensions = false);
 
   /// Collect the set of protocols to which this type should implicitly
   /// conform, such as AnyObject (for classes).

lib/AST/GenericSignatureBuilder.cpp

@@ -554,7 +554,16 @@ auto GenericSignatureBuilder::PotentialArchetype::getNestedType(
   SmallVector<std::pair<ProtocolDecl *, RequirementSource>, 4>
     conformsTo(rep->ConformsTo.begin(), rep->ConformsTo.end());
   for (auto &conforms : conformsTo) {
-    for (auto member : conforms.first->lookupDirect(nestedName)) {
+    // Make sure we don't trigger deserialization of extensions,
+    // since they can refer back to a protocol we're currently
+    // type checking.
+    //
+    // Note that typealiases in extensions won't matter here,
+    // because a typealias is never going to be a representative
+    // PA.
+    auto members = conforms.first->lookupDirect(nestedName,
+                                                /*ignoreNewExtensions=*/true);
+    for (auto member : members) {
       PotentialArchetype *pa;
 
       if (auto assocType = dyn_cast<AssociatedTypeDecl>(member)) {

lib/AST/NameLookup.cpp

@@ -1183,8 +1183,9 @@ void NominalTypeDecl::makeMemberVisible(ValueDecl *member) {
   LookupTable.getPointer()->addMember(member);
 }
 
-ArrayRef<ValueDecl *> NominalTypeDecl::lookupDirect(DeclName name,
-                                                    bool ignoreNewExtensions) {
+TinyPtrVector<ValueDecl *> NominalTypeDecl::lookupDirect(
+                                                  DeclName name,
+                                                  bool ignoreNewExtensions) {
   // Make sure we have the complete list of members (in this nominal and in all
   // extensions).
   if (!ignoreNewExtensions) {
@@ -1202,7 +1203,7 @@ ArrayRef<ValueDecl *> NominalTypeDecl::lookupDirect(DeclName name,
     return { };
 
   // We found something; return it.
-  return { known->second.begin(), known->second.size() };
+  return known->second;
 }
 
 void ClassDecl::createObjCMethodLookup() {

lib/Sema/TypeCheckDecl.cpp

@@ -867,21 +867,20 @@ static void checkRedeclaration(TypeChecker &tc, ValueDecl *current) {
     isCascading = (current->getFormalAccess() > Accessibility::FilePrivate);
 
   // Find other potential definitions.
-  SmallVector<ValueDecl *, 4> otherDefinitionsVec;
-  ArrayRef<ValueDecl *> otherDefinitions;
+  SmallVector<ValueDecl *, 4> otherDefinitions;
   if (currentDC->isTypeContext()) {
     // Look within a type context.
     if (auto nominal = currentDC->getAsNominalTypeOrNominalTypeExtensionContext()) {
-      otherDefinitions = nominal->lookupDirect(current->getBaseName());
+      auto found = nominal->lookupDirect(current->getBaseName());
+      otherDefinitions.append(found.begin(), found.end());
       if (tracker)
         tracker->addUsedMember({nominal, current->getName()}, isCascading);
     }
   } else {
     // Look within a module context.
     currentFile->getParentModule()->lookupValue({ }, current->getBaseName(),
                                                 NLKind::QualifiedLookup,
-                                                otherDefinitionsVec);
-    otherDefinitions = otherDefinitionsVec;
+                                                otherDefinitions);
     if (tracker)
       tracker->addTopLevelName(current->getName(), isCascading);
   }

test/Serialization/Inputs/circular-associated-type/a.swift

@@ -0,0 +1,3 @@
+public protocol A {
+  associatedtype T : B
+}

test/Serialization/Inputs/circular-associated-type/b.swift

@@ -0,0 +1,7 @@
+public protocol BB {
+  associatedtype T
+}
+
+public protocol B {
+  associatedtype T : BB
+}

test/Serialization/Inputs/circular-associated-type/c.swift

@@ -0,0 +1,5 @@
+extension B {
+  public init?<T : A>(_: T) where T.T == Self {
+    return nil
+  }
+}

test/Serialization/multi-file-associated-type-circularity.swift

@@ -0,0 +1,8 @@
+// RUN: rm -rf %t && mkdir -p %t
+
+// RUN: %target-swift-frontend -emit-module -module-name Multi -o %t/a.swiftmodule -primary-file %S/Inputs/circular-associated-type/a.swift %S/Inputs/circular-associated-type/b.swift %S/Inputs/circular-associated-type/c.swift
+// RUN: %target-swift-frontend -emit-module -module-name Multi -o %t/b.swiftmodule -primary-file %S/Inputs/circular-associated-type/b.swift %S/Inputs/circular-associated-type/a.swift %S/Inputs/circular-associated-type/c.swift
+// RUN: %target-swift-frontend -emit-module -module-name Multi -o %t/c.swiftmodule -primary-file %S/Inputs/circular-associated-type/c.swift %S/Inputs/circular-associated-type/a.swift %S/Inputs/circular-associated-type/b.swift
+
+// RUN: %target-swift-frontend -parse-as-library -emit-module -module-name Multi %t/a.swiftmodule %t/b.swiftmodule %t/c.swiftmodule -o %t
+