[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, 15 insertions, 10 deletions

diff --git a/lldb/source/Plugins/Language/CPlusPlus/LibStdcpp.cpp b/lldb/source/Plugins/Language/CPlusPlus/LibStdcpp.cpp
index a97264f..02113ba 100644
--- a/lldb/source/Plugins/Language/CPlusPlus/LibStdcpp.cpp
+++ b/lldb/source/Plugins/Language/CPlusPlus/LibStdcpp.cpp
@@ -49,7 +49,7 @@ public:
 
   lldb::ChildCacheState Update() override;
 
-  size_t GetIndexOfChildWithName(ConstString name) override;
+  llvm::Expected<size_t> GetIndexOfChildWithName(ConstString name) override;
 
 private:
   ExecutionContextRef m_exe_ctx_ref;
@@ -68,7 +68,8 @@ public:
 
   lldb::ChildCacheState Update() override;
 
-  size_t GetIndexOfChildWithName(ConstString name) override;
+  llvm::Expected<size_t> GetIndexOfChildWithName(ConstString name) override;
+
 private:
 
   // The lifetime of a ValueObject and all its derivative ValueObjects
@@ -145,13 +146,15 @@ LibstdcppMapIteratorSyntheticFrontEnd::GetChildAtIndex(uint32_t idx) {
   return lldb::ValueObjectSP();
 }
 
-size_t LibstdcppMapIteratorSyntheticFrontEnd::GetIndexOfChildWithName(
+llvm::Expected<size_t>
+LibstdcppMapIteratorSyntheticFrontEnd::GetIndexOfChildWithName(
     ConstString name) {
   if (name == "first")
     return 0;
   if (name == "second")
     return 1;
-  return UINT32_MAX;
+  return llvm::createStringError("Type has no child named '%s'",
+                                 name.AsCString());
 }
 
 SyntheticChildrenFrontEnd *
@@ -226,11 +229,12 @@ VectorIteratorSyntheticFrontEnd::GetChildAtIndex(uint32_t idx) {
   return lldb::ValueObjectSP();
 }
 
-size_t VectorIteratorSyntheticFrontEnd::GetIndexOfChildWithName(
-    ConstString name) {
+llvm::Expected<size_t>
+VectorIteratorSyntheticFrontEnd::GetIndexOfChildWithName(ConstString name) {
   if (name == "item")
     return 0;
-  return UINT32_MAX;
+  return llvm::createStringError("Type has no child named '%s'",
+                                 name.AsCString());
 }
 
 bool lldb_private::formatters::LibStdcppStringSummaryProvider(
@@ -409,13 +413,14 @@ lldb::ChildCacheState LibStdcppSharedPtrSyntheticFrontEnd::Update() {
   return lldb::ChildCacheState::eRefetch;
 }
 
-size_t LibStdcppSharedPtrSyntheticFrontEnd::GetIndexOfChildWithName(
-    ConstString name) {
+llvm::Expected<size_t>
+LibStdcppSharedPtrSyntheticFrontEnd::GetIndexOfChildWithName(ConstString name) {
   if (name == "pointer")
     return 0;
   if (name == "object" || name == "$$dereference$$")
     return 1;
-  return UINT32_MAX;
+  return llvm::createStringError("Type has no child named '%s'",
+                                 name.AsCString());
 }
 
 SyntheticChildrenFrontEnd *