[lldb] Upgrade `GetIndexOfChildWithName` to use `llvm::Expected` (#136693)

This patch replaces the use of `UINT32_MAX` as the error return value of
`GetIndexOfChildWithName` with `llvm::Expected`.


# Tasks to do in another PR

1. Replace `CalculateNumChildrenIgnoringErrors` with
`CalculateNumChildren`. See [this
comment](https://github.com/llvm/llvm-project/pull/136693#discussion_r2056319358).
2. Update `lldb_private::formatters::ExtractIndexFromString` to use
`llvm::Expected`. See [this
comment](https://github.com/llvm/llvm-project/pull/136693#discussion_r2054217536).
3. Create a new class which carries both user and internal errors. See
[this
comment](https://github.com/llvm/llvm-project/pull/136693#discussion_r2056439608).

1 files changed, 5 insertions, 1 deletions

diff --git a/lldb/source/DataFormatters/FormatterBytecode.cpp b/lldb/source/DataFormatters/FormatterBytecode.cpp
index 7f3dbe0dba37..714de74abcb3 100644
--- a/lldb/source/DataFormatters/FormatterBytecode.cpp
+++ b/lldb/source/DataFormatters/FormatterBytecode.cpp
@@ -9,6 +9,7 @@
 #include "FormatterBytecode.h"
 #include "lldb/Utility/LLDBLog.h"
 #include "lldb/ValueObject/ValueObject.h"
+#include "lldb/ValueObject/ValueObjectConstResult.h"
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/Support/DataExtractor.h"
 #include "llvm/Support/Format.h"
@@ -489,7 +490,10 @@ llvm::Error Interpret(std::vector<ControlStackElement> &control,
         TYPE_CHECK(Object, String);
         auto name = data.Pop<std::string>();
         POP_VALOBJ(valobj);
-        data.Push((uint64_t)valobj->GetIndexOfChildWithName(name));
+        if (auto index_or_err = valobj->GetIndexOfChildWithName(name))
+          data.Push((uint64_t)*index_or_err);
+        else
+          return index_or_err.takeError();
         break;
       }
       case sel_get_type: {