[lldb] Show more children of top level values

lldb/include/lldb/Target/Target.h

@@ -186,7 +186,7 @@ class TargetProperties : public Properties {
 
   uint32_t GetMaxZeroPaddingInFloatFormat() const;
 
-  uint32_t GetMaximumNumberOfChildrenToDisplay() const;
+  std::pair<uint32_t, bool> GetMaximumNumberOfChildrenToDisplay() const;
 
   /// Get the max depth value, augmented with a bool to indicate whether the
   /// depth is the default.

lldb/source/API/SBTarget.cpp

@@ -1648,7 +1648,7 @@ uint32_t SBTarget::GetMaximumNumberOfChildrenToDisplay() const {
   LLDB_INSTRUMENT_VA(this);
 
   if (TargetSP target_sp = GetSP())
-    return target_sp->GetMaximumNumberOfChildrenToDisplay();
+    return target_sp->GetMaximumNumberOfChildrenToDisplay().first;
   return 0;
 }
 

lldb/source/Core/FormatEntity.cpp

@@ -1027,7 +1027,7 @@ static bool DumpValue(Stream &s, const SymbolContext *sc,
     if (index_higher < 0)
       index_higher = valobj->GetNumChildrenIgnoringErrors() - 1;
 
-    uint32_t max_num_children =
+    auto [max_num_children, _] =
         target->GetTargetSP()->GetMaximumNumberOfChildrenToDisplay();
 
     bool success = true;

lldb/source/DataFormatters/FormatManager.cpp

@@ -466,7 +466,7 @@ bool FormatManager::ShouldPrintAsOneLiner(ValueObject &valobj) {
   if (valobj.GetSummaryFormat().get() != nullptr)
     return valobj.GetSummaryFormat()->IsOneLiner();
 
-  const size_t max_num_children =
+  const auto [max_num_children, _] =
       (target_sp ? *target_sp : Target::GetGlobalProperties())
           .GetMaximumNumberOfChildrenToDisplay();
   auto num_children = valobj.GetNumChildren(max_num_children);

lldb/source/DataFormatters/ValueObjectPrinter.cpp

@@ -633,6 +633,27 @@ void ValueObjectPrinter::PrintChild(
   }
 }
 
+static uint32_t determineMaxChildren(bool ignore_cap, uint32_t cur_depth,
+                                     TargetSP target_sp) {
+  if (ignore_cap)
+    return UINT32_MAX;
+
+  const auto [max_num_children, max_is_default] =
+      target_sp->GetMaximumNumberOfChildrenToDisplay();
+
+  // Special handling for printing values at the top level (such as variables).
+  // The original default value for target.max-children-count was 256. The
+  // default has since been reduced, to avoid printing too much data. However,
+  // users will naturally have expectations that all children are shown for top
+  // level values. The following code keeps 256 as the max count for top level
+  // values (unless customized).
+  const uint32_t top_level_max_num_childen = 256;
+  if (cur_depth == 0 && max_is_default)
+    return top_level_max_num_childen;
+
+  return max_num_children;
+}
+
 llvm::Expected<uint32_t>
 ValueObjectPrinter::GetMaxNumChildrenToPrint(bool &print_dotdotdot) {
   ValueObject &synth_valobj = GetValueObjectForChildrenGeneration();
@@ -641,10 +662,8 @@ ValueObjectPrinter::GetMaxNumChildrenToPrint(bool &print_dotdotdot) {
     return m_options.m_pointer_as_array.m_element_count;
 
   const uint32_t max_num_children =
-      m_options.m_ignore_cap ? UINT32_MAX
-                             : GetMostSpecializedValue()
-                                   .GetTargetSP()
-                                   ->GetMaximumNumberOfChildrenToDisplay();
+      determineMaxChildren(m_options.m_ignore_cap, m_curr_depth,
+                           GetMostSpecializedValue().GetTargetSP());
   // Ask for one more child than the maximum to see if we should print "...".
   auto num_children_or_err = synth_valobj.GetNumChildren(
       llvm::SaturatingAdd(max_num_children, uint32_t(1)));

lldb/source/Plugins/Language/CPlusPlus/LibCxxList.cpp

@@ -176,7 +176,7 @@ lldb::ChildCacheState AbstractListFrontEnd::Update() {
 
   if (m_backend.GetTargetSP())
     m_list_capping_size =
-        m_backend.GetTargetSP()->GetMaximumNumberOfChildrenToDisplay();
+        m_backend.GetTargetSP()->GetMaximumNumberOfChildrenToDisplay().first;
   if (m_list_capping_size == 0)
     m_list_capping_size = 255;
 

lldb/source/Target/Target.cpp

@@ -4814,10 +4814,13 @@ uint32_t TargetProperties::GetMaxZeroPaddingInFloatFormat() const {
       idx, g_target_properties[idx].default_uint_value);
 }
 
-uint32_t TargetProperties::GetMaximumNumberOfChildrenToDisplay() const {
+std::pair<uint32_t, bool>
+TargetProperties::GetMaximumNumberOfChildrenToDisplay() const {
   const uint32_t idx = ePropertyMaxChildrenCount;
-  return GetPropertyAtIndexAs<uint64_t>(
-      idx, g_target_properties[idx].default_uint_value);
+  auto *option_value =
+      m_collection_sp->GetPropertyAtIndexAsOptionValueUInt64(idx);
+  bool is_default = !option_value->OptionWasSet();
+  return {option_value->GetCurrentValue(), is_default};
 }
 
 std::pair<uint32_t, bool>

lldb/source/Target/TargetProperties.td

@@ -97,7 +97,7 @@ let Definition = "target" in {
     Desc<"The maximum number of zeroes to insert when displaying a very small float before falling back to scientific notation.">;
   def MaxChildrenCount: Property<"max-children-count", "UInt64">,
     DefaultUnsignedValue<24>,
-    Desc<"Maximum number of children to expand in any level of depth.">;
+    Desc<"Maximum number of children to show. Note: The default behavior will show 256 children for top-level values, and 24 children for any nested value. A custom count applies to all values, at any nesting.">;
   def MaxChildrenDepth: Property<"max-children-depth", "UInt64">,
     DefaultUnsignedValue<0xFFFFFFFF>,
     Desc<"Maximum depth to expand children.">;