[lldb] Change interface of StructuredData::Array::GetItemAtIndexAsDictionary (#71961)

Similar to my previous patch (#71613) where I changed
`GetItemAtIndexAsString`, this patch makes the same change to
`GetItemAtIndexAsDictionary`.

`GetItemAtIndexAsDictionary` now returns a std::optional that is either
`std::nullopt` or is a valid pointer. Therefore, if the optional is
populated, we consider the pointer to always be valid (i.e. no need to
check pointer validity).

6 files changed, 37 insertions, 18 deletions

diff --git a/lldb/include/lldb/Utility/StructuredData.h b/lldb/include/lldb/Utility/StructuredData.h
index 6e39bcf..8d0ae37 100644
--- a/lldb/include/lldb/Utility/StructuredData.h
+++ b/lldb/include/lldb/Utility/StructuredData.h
@@ -256,14 +256,24 @@ public:
       return {};
     }
 
-    bool GetItemAtIndexAsDictionary(size_t idx, Dictionary *&result) const {
-      result = nullptr;
-      ObjectSP value_sp = GetItemAtIndex(idx);
-      if (value_sp.get()) {
-        result = value_sp->GetAsDictionary();
-        return (result != nullptr);
+    /// Retrieves the element at index \a idx from a StructuredData::Array if it
+    /// is a Dictionary.
+    ///
+    /// \param[in] idx
+    ///   The index of the element to retrieve.
+    ///
+    /// \return
+    ///   If the element at index \a idx is a Dictionary, this method returns a
+    ///   valid pointer to the Dictionary wrapped in a std::optional. If the
+    ///   element is not a Dictionary or the index is invalid, this returns
+    ///   std::nullopt. Note that the underlying Dictionary pointer is never
+    ///   nullptr.
+    std::optional<Dictionary *> GetItemAtIndexAsDictionary(size_t idx) const {
+      if (auto item_sp = GetItemAtIndex(idx)) {
+        if (auto *dict = item_sp->GetAsDictionary())
+          return dict;
       }
-      return false;
+      return {};
     }
 
     bool GetItemAtIndexAsArray(size_t idx, Array *&result) const {
diff --git a/lldb/source/Plugins/ObjectFile/Mach-O/ObjectFileMachO.cpp b/lldb/source/Plugins/ObjectFile/Mach-O/ObjectFileMachO.cpp
index 3714e37..1ea4f64 100644
--- a/lldb/source/Plugins/ObjectFile/Mach-O/ObjectFileMachO.cpp
+++ b/lldb/source/Plugins/ObjectFile/Mach-O/ObjectFileMachO.cpp
@@ -5688,14 +5688,16 @@ bool ObjectFileMachO::GetCorefileThreadExtraInfos(std::vector<tid_t> &tids) {
       }
       const size_t num_threads = threads->GetSize();
       for (size_t i = 0; i < num_threads; i++) {
-        StructuredData::Dictionary *thread;
-        if (!threads->GetItemAtIndexAsDictionary(i, thread) || !thread) {
+        std::optional<StructuredData::Dictionary *> maybe_thread =
+            threads->GetItemAtIndexAsDictionary(i);
+        if (!maybe_thread) {
           LLDB_LOGF(log,
                     "Unable to read 'process metadata' LC_NOTE, threads "
                     "array does not have a dictionary at index %zu.",
                     i);
           return false;
         }
+        StructuredData::Dictionary *thread = *maybe_thread;
         tid_t tid = LLDB_INVALID_THREAD_ID;
         if (thread->GetValueForKeyAsInteger<tid_t>("thread_id", tid))
           if (tid == 0)
diff --git a/lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunicationClient.cpp b/lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunicationClient.cpp
index 04d98b9..2cf8c29 100644
--- a/lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunicationClient.cpp
+++ b/lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunicationClient.cpp
@@ -2649,10 +2649,12 @@ size_t GDBRemoteCommunicationClient::QueryGDBServer(
     return 0;
 
   for (size_t i = 0, count = array->GetSize(); i < count; ++i) {
-    StructuredData::Dictionary *element = nullptr;
-    if (!array->GetItemAtIndexAsDictionary(i, element))
+    std::optional<StructuredData::Dictionary *> maybe_element =
+        array->GetItemAtIndexAsDictionary(i);
+    if (!maybe_element)
       continue;
 
+    StructuredData::Dictionary *element = *maybe_element;
     uint16_t port = 0;
     if (StructuredData::ObjectSP port_osp =
             element->GetValueForKey(llvm::StringRef("port")))
diff --git a/lldb/source/Plugins/Process/scripted/ScriptedThread.cpp b/lldb/source/Plugins/Process/scripted/ScriptedThread.cpp
index aa2796d..88a4ca3 100644
--- a/lldb/source/Plugins/Process/scripted/ScriptedThread.cpp
+++ b/lldb/source/Plugins/Process/scripted/ScriptedThread.cpp
@@ -176,8 +176,9 @@ bool ScriptedThread::LoadArtificialStackFrames() {
   StackFrameListSP frames = GetStackFrameList();
 
   for (size_t idx = 0; idx < arr_size; idx++) {
-    StructuredData::Dictionary *dict;
-    if (!arr_sp->GetItemAtIndexAsDictionary(idx, dict) || !dict)
+    std::optional<StructuredData::Dictionary *> maybe_dict =
+        arr_sp->GetItemAtIndexAsDictionary(idx);
+    if (!maybe_dict)
       return ScriptedInterface::ErrorWithMessage<bool>(
           LLVM_PRETTY_FUNCTION,
           llvm::Twine(
@@ -185,6 +186,7 @@ bool ScriptedThread::LoadArtificialStackFrames() {
               llvm::Twine(idx) + llvm::Twine(") from stackframe array."))
               .str(),
           error, LLDBLog::Thread);
+    StructuredData::Dictionary *dict = *maybe_dict;
 
     lldb::addr_t pc;
     if (!dict->GetValueForKeyAsInteger("pc", pc))
diff --git a/lldb/source/Target/DynamicRegisterInfo.cpp b/lldb/source/Target/DynamicRegisterInfo.cpp
index cc2df5b..7469c1d 100644
--- a/lldb/source/Target/DynamicRegisterInfo.cpp
+++ b/lldb/source/Target/DynamicRegisterInfo.cpp
@@ -231,13 +231,15 @@ DynamicRegisterInfo::SetRegisterInfo(const StructuredData::Dictionary &dict,
   //        InvalidateNameMap;
   //        InvalidateNameMap invalidate_map;
   for (uint32_t i = 0; i < num_regs; ++i) {
-    StructuredData::Dictionary *reg_info_dict = nullptr;
-    if (!regs->GetItemAtIndexAsDictionary(i, reg_info_dict)) {
+    std::optional<StructuredData::Dictionary *> maybe_reg_info_dict =
+        regs->GetItemAtIndexAsDictionary(i);
+    if (!maybe_reg_info_dict) {
       Clear();
       printf("error: items in the 'registers' array must be dictionaries\n");
       regs->DumpToStdout();
       return 0;
     }
+    StructuredData::Dictionary *reg_info_dict = *maybe_reg_info_dict;
 
     // { 'name':'rcx'       , 'bitsize' :  64, 'offset' :  16,
     // 'encoding':'uint' , 'format':'hex'         , 'set': 0, 'ehframe' : 2,
diff --git a/lldb/unittests/tools/lldb-server/tests/MessageObjects.cpp b/lldb/unittests/tools/lldb-server/tests/MessageObjects.cpp
index ed1c8b9..3283392 100644
--- a/lldb/unittests/tools/lldb-server/tests/MessageObjects.cpp
+++ b/lldb/unittests/tools/lldb-server/tests/MessageObjects.cpp
@@ -106,11 +106,12 @@ Expected<JThreadsInfo> JThreadsInfo::create(StringRef Response,
     return make_parsing_error("JThreadsInfo: JSON array");
 
   for (size_t i = 0; i < array->GetSize(); i++) {
-    StructuredData::Dictionary *thread_info;
-    array->GetItemAtIndexAsDictionary(i, thread_info);
-    if (!thread_info)
+    std::optional<StructuredData::Dictionary *> maybe_thread_info =
+        array->GetItemAtIndexAsDictionary(i);
+    if (!maybe_thread_info)
       return make_parsing_error("JThreadsInfo: JSON obj at {0}", i);
 
+    StructuredData::Dictionary *thread_info = *maybe_thread_info;
     StringRef name, reason;
     thread_info->GetValueForKeyAsString("name", name);
     thread_info->GetValueForKeyAsString("reason", reason);