[Swift] lldb: Adjust code after result type change in lldb_private::TypeSystem::GetIndexOfChildWithName

See llvm#136693.

(cherry picked from commit 61cac61)

Author: AnthonyLatsis

lldb/source/Plugins/LanguageRuntime/Swift/SwiftLanguageRuntime.cpp

@@ -1612,13 +1612,14 @@ class ProjectionSyntheticChildren : public SyntheticChildren {
       return nullptr;
     }
 
-    size_t GetIndexOfChildWithName(ConstString name) override {
+    llvm::Expected<size_t> GetIndexOfChildWithName(ConstString name) override {
       for (size_t idx = 0; idx < m_projection->field_projections.size();
            idx++) {
         if (m_projection->field_projections.at(idx).name == name)
           return idx;
       }
-      return UINT32_MAX;
+      return llvm::createStringError("Type has no child named '%s'",
+                                     name.AsCString());
     }
 
     lldb::ChildCacheState Update() override {

lldb/source/Plugins/TypeSystem/Swift/TypeSystemSwift.cpp

@@ -154,13 +154,19 @@ bool TypeSystemSwift::ShouldTreatScalarValueAsAddress(
       .AnySet(eTypeInstanceIsPointer | eTypeIsReference);
 }
 
-uint32_t TypeSystemSwift::GetIndexOfChildWithName(
+llvm::Expected<uint32_t> TypeSystemSwift::GetIndexOfChildWithName(
     opaque_compiler_type_t type, llvm::StringRef name,
     ExecutionContext *exe_ctx, bool omit_empty_base_classes) {
   std::vector<uint32_t> child_indexes;
   size_t num_child_indexes = GetIndexOfChildMemberWithName(
       type, name, exe_ctx, omit_empty_base_classes, child_indexes);
-  return num_child_indexes == 1 ? child_indexes.front() : UINT32_MAX;
+
+  if (num_child_indexes == 1) {
+    return child_indexes.front();
+  }
+
+  return llvm::createStringError("Type has no child named '%s'",
+                                 name.str().c_str());
 }
 
 lldb::Format TypeSystemSwift::GetFormat(opaque_compiler_type_t type) {

lldb/source/Plugins/TypeSystem/Swift/TypeSystemSwift.h

@@ -327,10 +327,10 @@ class TypeSystemSwift : public TypeSystem {
 
   /// Lookup a child given a name. This function will match base class names
   /// and member names in \p type only, not descendants.
-  uint32_t GetIndexOfChildWithName(lldb::opaque_compiler_type_t type,
-                                   llvm::StringRef name,
-                                   ExecutionContext *exe_ctx,
-                                   bool omit_empty_base_classes) override;
+  llvm::Expected<uint32_t>
+  GetIndexOfChildWithName(lldb::opaque_compiler_type_t type,
+                          llvm::StringRef name, ExecutionContext *exe_ctx,
+                          bool omit_empty_base_classes) override;
 
   CompilerType
   GetLValueReferenceType(lldb::opaque_compiler_type_t type) override {