[SymbolGraphGen] only recurse public-private type aliases from Clang

lib/SymbolGraphGen/SymbolGraphASTWalker.cpp

@@ -335,15 +335,28 @@ bool SymbolGraphASTWalker::walkToDeclPre(Decl *D, CharSourceRange Range) {
     }
   }
 
+  // If this is a Clang typedef of an underlying type that is being hidden (e.g. `typedef struct
+  // _MyStruct { ... } MyStruct`) then copy in the child symbols from the underlying type to the
+  // type alias.
   if (const auto *TD = dyn_cast_or_null<TypeAliasDecl>(VD)) {
     const auto InnerType = TD->getUnderlyingType();
     if (NominalTypeDecl *NTD = InnerType->getAnyNominal()) {
       // Only fold typedefs together if the inner type is from our module and it
       // otherwise isn't being shown
       if (isOurModule(NTD->getModuleContext()) &&
           !SG->canIncludeDeclAsNode(NTD)) {
-        PublicPrivateTypeAliases.insert_or_assign(NTD, TD);
-        synthesizeChildSymbols(NTD, TD);
+        // We specifically only want to look for underlying types that are "embedded" in the typedef
+        // definition, so let's pull out the Clang decl and check for that
+        if (NTD->hasClangNode()) {
+          if (const auto *ClangDecl = NTD->getClangNode().getAsDecl()) {
+            if (const auto *ClangTagDecl = dyn_cast<clang::TagDecl>(ClangDecl)) {
+              if (ClangTagDecl->isEmbeddedInDeclarator()) {
+                PublicPrivateTypeAliases.insert_or_assign(NTD, TD);
+                synthesizeChildSymbols(NTD, TD);
+              }
+            }
+          }
+        }
       }
     }
   }

test/SymbolGraph/Relationships/Synthesized/HiddenTypeAlias.swift

@@ -10,21 +10,7 @@
 // _InnerType's type name should only appear in quotes like this once, in the declaration for OuterType
 // INNER-COUNT-1: "_InnerType"
 
-// _InnerType.someFunc() as synthesized on OuterType
-// CHECK-DAG: "precise": "s:15HiddenTypeAlias06_InnerB0C8someFuncyyF::SYNTHESIZED::s:15HiddenTypeAlias05OuterB0a"
-
-// someFunc is a member of OuterType
-// CHECK-DAG: "kind": "memberOf",{{[[:space:]]*}}"source": "s:15HiddenTypeAlias06_InnerB0C8someFuncyyF::SYNTHESIZED::s:15HiddenTypeAlias05OuterB0a",{{[[:space:]]*}}"target": "s:15HiddenTypeAlias05OuterB0a"
-
-// OuterType conforms to SomeProtocol
-// CHECK-DAG: "kind": "conformsTo",{{[[:space:]]*}}"source": "s:15HiddenTypeAlias05OuterB0a",{{[[:space:]]*}}"target": "s:15HiddenTypeAlias12SomeProtocolP"
-
-// OuterType "inherits from" BaseType
-// CHECK-DAG: "kind": "inheritsFrom",{{[[:space:]]*}}"source": "s:15HiddenTypeAlias05OuterB0a",{{[[:space:]]*}}"target": "s:15HiddenTypeAlias04BaseB0C"
-
-// bonusFunc as a synthesized member of OuterType
-// CHECK-DAG: "precise": "s:15HiddenTypeAlias12SomeProtocolPAAE9bonusFuncyyF::SYNTHESIZED::s:15HiddenTypeAlias05OuterB0a",
-// CHECK-DAG: "kind": "memberOf",{{[[:space:]]*}}"source": "s:15HiddenTypeAlias12SomeProtocolPAAE9bonusFuncyyF::SYNTHESIZED::s:15HiddenTypeAlias05OuterB0a",{{[[:space:]]*}}"target": "s:15HiddenTypeAlias05OuterB0a",
+// CHECK-NOT: someFunc
 
 public protocol SomeProtocol {}
 

test/SymbolGraph/Relationships/Synthesized/HiddenTypeAliasRecursive.swift

@@ -0,0 +1,28 @@
+// RUN: %empty-directory(%t)
+// RUN: %target-build-swift %s -module-name HiddenTypeAliasRecursive -emit-module -emit-module-path %t/
+// RUN: %target-swift-symbolgraph-extract -module-name HiddenTypeAliasRecursive -I %t -pretty-print -output-dir %t -v
+// RUN: %FileCheck %s --input-file %t/HiddenTypeAliasRecursive.symbols.json
+
+// Ensure that mutually-recursive public-private type aliases don't cause infinite recursion in
+// SymbolGraphGen when generating symbol graphs. (rdar://145980187)
+
+// HiddenClassB is not referenced by any public symbol, so it shouldn't appear in any symbol graph
+// CHECK-NOT: HiddenClassB
+
+// HiddenClassA should only appear one time: in the declaration for PublicAlias
+// CHECK-COUNT-1: HiddenClassA
+// CHECK-NOT: HiddenClassA
+
+@_documentation(visibility: private)
+public class HiddenClassA {
+    public typealias ProblematicA = HiddenClassB
+    public func funcA() {}
+}
+
+@_documentation(visibility: private)
+public class HiddenClassB {
+    public typealias ProblematicB = HiddenClassA
+    public func funcB() {}
+}
+
+public typealias PublicAlias = HiddenClassA