[index] Fix infinite loop while looking at superclasses

include/swift/AST/Decl.h

@@ -3647,6 +3647,19 @@ class ClassDecl final : public NominalTypeDecl {
     Bits.ClassDecl.Circularity = static_cast<unsigned>(circularity);
   }
 
+  /// Walk this class and all of the superclasses of this class, transitively,
+  /// invoking the callback function for each class.
+  ///
+  /// \param fn The callback function that will be invoked for each superclass.
+  /// It can return \c Continue to continue the traversal. Returning
+  /// \c SkipChildren halts the search and returns \c false, while returning
+  /// \c Stop halts the search and returns \c true.
+  ///
+  /// \returns \c true if \c fn returned \c Stop for any class, \c false
+  /// otherwise.
+  bool walkSuperclasses(
+      llvm::function_ref<TypeWalker::Action(ClassDecl *)> fn) const;
+
   //// Whether this class requires all of its stored properties to
   //// have initializers in the class definition.
   bool requiresStoredPropertyInits() const { 
@@ -3975,8 +3988,8 @@ class ProtocolDecl final : public NominalTypeDecl {
   /// a protocol having nested types (ObjC protocols).
   llvm::TinyPtrVector<AssociatedTypeDecl *> getAssociatedTypeMembers() const;
 
-  /// Walk all of the protocols inherited by this protocol, transitively,
-  /// invoking the callback function for each protocol.
+  /// Walk this protocol and all of the protocols inherited by this protocol,
+  /// transitively, invoking the callback function for each protocol.
   ///
   /// \param fn The callback function that will be invoked for each inherited
   /// protocol. It can return \c Continue to continue the traversal,

lib/AST/Decl.cpp

@@ -3794,6 +3794,27 @@ ClassDecl::findImplementingMethod(const AbstractFunctionDecl *Method) const {
   return nullptr;
 }
 
+bool ClassDecl::walkSuperclasses(
+    llvm::function_ref<TypeWalker::Action(ClassDecl *)> fn) const {
+
+  SmallPtrSet<ClassDecl *, 8> seen;
+  auto *cls = const_cast<ClassDecl *>(this);
+
+  while (cls && seen.insert(cls).second) {
+    switch (fn(cls)) {
+    case TypeWalker::Action::Stop:
+      return true;
+    case TypeWalker::Action::SkipChildren:
+      return false;
+    case TypeWalker::Action::Continue:
+      cls = cls->getSuperclassDecl();
+      continue;
+    }
+  }
+
+  return false;
+}
+
 EnumCaseDecl *EnumCaseDecl::create(SourceLoc CaseLoc,
                                    ArrayRef<EnumElementDecl *> Elements,
                                    DeclContext *DC) {

lib/Index/IndexSymbol.cpp

@@ -28,12 +28,13 @@ static NominalTypeDecl *getNominalParent(const ValueDecl *D) {
 static bool isUnitTestCase(const ClassDecl *D) {
   if (!D)
     return false;
-  while (auto *SuperD = D->getSuperclassDecl()) {
-    if (SuperD->getNameStr() == "XCTestCase")
-      return true;
-    D = SuperD;
-  }
-  return false;
+
+  return D->walkSuperclasses([D](ClassDecl *SuperD) {
+    if (SuperD != D && // Do not treate XCTestCase itself as a test.
+        SuperD->getNameStr() == "XCTestCase")
+      return TypeWalker::Action::Stop; // Found test; stop and return true.
+    return TypeWalker::Action::Continue;
+  });
 }
 
 static bool isUnitTest(const ValueDecl *D) {

test/Index/circular.swift

@@ -0,0 +1,66 @@
+// RUN: %target-swift-ide-test -print-indexed-symbols -source-filename %s | %FileCheck %s
+
+class SelfCycle : SelfCycle {}
+// CHECK: [[@LINE-1]]:7 | class/Swift | SelfCycle | {{[^ ]*}} | Def | rel: 0
+// CHECK: [[@LINE-2]]:19 | class/Swift | SelfCycle | {{[^ ]*}} | Ref,RelBase | rel: 1
+// CHECK:   RelBase | class/Swift | SelfCycle | {{\W*}}
+
+class Cycle1_A: Cycle1_B {}
+// CHECK: [[@LINE-1]]:7 | class/Swift | Cycle1_A | {{[^ ]*}} | Def | rel: 0
+// CHECK: [[@LINE-2]]:17 | class/Swift | Cycle1_B | {{[^ ]*}} | Ref,RelBase | rel: 1
+// CHECK:   RelBase | class/Swift | Cycle1_A | {{[^ ]*}}
+class Cycle1_B: Cycle1_A {}
+// CHECK: [[@LINE-1]]:7 | class/Swift | Cycle1_B | {{[^ ]*}} | Def | rel: 0
+// CHECK: [[@LINE-2]]:17 | class/Swift | Cycle1_A | {{[^ ]*}} | Ref,RelBase | rel: 1
+// CHECK:   RelBase | class/Swift | Cycle1_B | {{[^ ]*}}
+
+class Cycle2_A: Cycle2_C {}
+// CHECK: [[@LINE-1]]:7 | class/Swift | Cycle2_A | {{[^ ]*}} | Def | rel: 0
+// CHECK: [[@LINE-2]]:17 | class/Swift | Cycle2_C | {{[^ ]*}} | Ref,RelBase | rel: 1
+// CHECK:   RelBase | class/Swift | Cycle2_A | {{[^ ]*}}
+class Cycle2_B: Cycle2_A {}
+// CHECK: [[@LINE-1]]:7 | class/Swift | Cycle2_B | {{[^ ]*}} | Def | rel: 0
+// CHECK: [[@LINE-2]]:17 | class/Swift | Cycle2_A | {{[^ ]*}} | Ref,RelBase | rel: 1
+// CHECK:   RelBase | class/Swift | Cycle2_B | {{[^ ]*}}
+class Cycle2_C: Cycle2_B {}
+// CHECK: [[@LINE-1]]:7 | class/Swift | Cycle2_C | {{[^ ]*}} | Def | rel: 0
+// CHECK: [[@LINE-2]]:17 | class/Swift | Cycle2_B | {{[^ ]*}} | Ref,RelBase | rel: 1
+// CHECK:   RelBase | class/Swift | Cycle2_C | {{[^ ]*}}
+
+class TestCase1: XCTestCase {}
+// CHECK: [[@LINE-1]]:7 | class(test)/Swift | TestCase1 | {{[^ ]*}} | Def | rel: 0
+// CHECK: [[@LINE-2]]:18 | class/Swift | XCTestCase | {{[^ ]*}} | Ref,RelBase | rel: 1
+// CHECK:   RelBase | class(test)/Swift | TestCase1 | {{[^ ]*}}
+class XCTestCase: TestCase1 {}
+// CHECK: [[@LINE-1]]:7 | class/Swift | XCTestCase | {{[^ ]*}} | Def | rel: 0
+// CHECK: [[@LINE-2]]:19 | class(test)/Swift | TestCase1 | {{[^ ]*}} | Ref,RelBase | rel: 1
+// CHECK:   RelBase | class/Swift | XCTestCase | {{[^ ]*}}
+class TestCase2: TestCase1 {}
+// CHECK: [[@LINE-1]]:7 | class(test)/Swift | TestCase2 | {{[^ ]*}} | Def | rel: 0
+// CHECK: [[@LINE-2]]:18 | class(test)/Swift | TestCase1 | {{[^ ]*}} | Ref,RelBase | rel: 1
+// CHECK:   RelBase | class(test)/Swift | TestCase2 | {{[^ ]*}}
+
+protocol SelfCycleP: SelfCycleP {}
+// CHECK: [[@LINE-1]]:10 | protocol/Swift | SelfCycleP | {{[^ ]*}} | Def | rel: 0
+// CHECK: [[@LINE-2]]:22 | protocol/Swift | SelfCycleP | {{[^ ]*}} | Ref,RelBase | rel: 1
+// CHECK:   RelBase | protocol/Swift | SelfCycleP | {{[^ ]*}}
+protocol Cycle1P_A: Cycle1P_B {}
+// CHECK: [[@LINE-1]]:10 | protocol/Swift | Cycle1P_A | {{[^ ]*}} | Def | rel: 0
+// CHECK: [[@LINE-2]]:21 | protocol/Swift | Cycle1P_B | {{[^ ]*}} | Ref,RelBase | rel: 1
+// CHECK:   RelBase | protocol/Swift | Cycle1P_A | {{[^ ]*}}
+protocol Cycle1P_B: Cycle1P_A {}
+// CHECK: [[@LINE-1]]:10 | protocol/Swift | Cycle1P_B | {{[^ ]*}} | Def | rel: 0
+// CHECK: [[@LINE-2]]:21 | protocol/Swift | Cycle1P_A | {{[^ ]*}} | Ref,RelBase | rel: 1
+// CHECK:   RelBase | protocol/Swift | Cycle1P_B | {{[^ ]*}}
+protocol Cycle2P_A: Cycle2P_C {}
+// CHECK: [[@LINE-1]]:10 | protocol/Swift | Cycle2P_A | {{[^ ]*}} | Def | rel: 0
+// CHECK: [[@LINE-2]]:21 | protocol/Swift | Cycle2P_C | {{[^ ]*}} | Ref,RelBase | rel: 1
+// CHECK:   RelBase | protocol/Swift | Cycle2P_A | {{[^ ]*}}
+protocol Cycle2P_B: Cycle2P_A {}
+// CHECK: [[@LINE-1]]:10 | protocol/Swift | Cycle2P_B | {{[^ ]*}} | Def | rel: 0
+// CHECK: [[@LINE-2]]:21 | protocol/Swift | Cycle2P_A | {{[^ ]*}} | Ref,RelBase | rel: 1
+// CHECK:   RelBase | protocol/Swift | Cycle2P_B | {{[^ ]*}}
+protocol Cycle2P_C: Cycle2P_B {}
+// CHECK: [[@LINE-1]]:10 | protocol/Swift | Cycle2P_C | {{[^ ]*}} | Def | rel: 0
+// CHECK: [[@LINE-2]]:21 | protocol/Swift | Cycle2P_B | {{[^ ]*}} | Ref,RelBase | rel: 1
+// CHECK:   RelBase | protocol/Swift | Cycle2P_C | {{[^ ]*}}