[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](#136693 (comment)).
2. Update `lldb_private::formatters::ExtractIndexFromString` to use
`llvm::Expected`. See [this
comment](#136693 (comment)).
3. Create a new class which carries both user and internal errors. See
[this
comment](#136693 (comment)).

Author: charles-zablit

lldb/include/lldb/DataFormatters/TypeSynthetic.h

@@ -51,7 +51,7 @@ class SyntheticChildrenFrontEnd {
 
   virtual lldb::ValueObjectSP GetChildAtIndex(uint32_t idx) = 0;
 
-  virtual size_t GetIndexOfChildWithName(ConstString name) = 0;
+  virtual llvm::Expected<size_t> GetIndexOfChildWithName(ConstString name) = 0;
 
   /// This function is assumed to always succeed and if it fails, the front-end
   /// should know to deal with it in the correct way (most probably, by refusing
@@ -117,8 +117,9 @@ class SyntheticValueProviderFrontEnd : public SyntheticChildrenFrontEnd {
 
   lldb::ValueObjectSP GetChildAtIndex(uint32_t idx) override { return nullptr; }
 
-  size_t GetIndexOfChildWithName(ConstString name) override {
-    return UINT32_MAX;
+  llvm::Expected<size_t> GetIndexOfChildWithName(ConstString name) override {
+    return llvm::createStringError("Type has no child named '%s'",
+                                   name.AsCString());
   }
 
   lldb::ChildCacheState Update() override {
@@ -343,7 +344,7 @@ class TypeFilterImpl : public SyntheticChildren {
 
     bool MightHaveChildren() override { return filter->GetCount() > 0; }
 
-    size_t GetIndexOfChildWithName(ConstString name) override;
+    llvm::Expected<size_t> GetIndexOfChildWithName(ConstString name) override;
 
     typedef std::shared_ptr<SyntheticChildrenFrontEnd> SharedPointer;
 
@@ -442,7 +443,7 @@ class ScriptedSyntheticChildren : public SyntheticChildren {
 
     bool MightHaveChildren() override;
 
-    size_t GetIndexOfChildWithName(ConstString name) override;
+    llvm::Expected<size_t> GetIndexOfChildWithName(ConstString name) override;
 
     lldb::ValueObjectSP GetSyntheticValue() override;
 

lldb/include/lldb/DataFormatters/VectorIterator.h

@@ -30,7 +30,7 @@ class VectorIteratorSyntheticFrontEnd : public SyntheticChildrenFrontEnd {
 
   lldb::ChildCacheState Update() override;
 
-  size_t GetIndexOfChildWithName(ConstString name) override;
+  llvm::Expected<size_t> GetIndexOfChildWithName(ConstString name) override;
 
 private:
   ExecutionContextRef m_exe_ctx_ref;

lldb/include/lldb/Interpreter/ScriptInterpreter.h

@@ -368,10 +368,10 @@ class ScriptInterpreter : public PluginInterface {
     return lldb::ValueObjectSP();
   }
 
-  virtual int
+  virtual llvm::Expected<int>
   GetIndexOfChildWithName(const StructuredData::ObjectSP &implementor,
                           const char *child_name) {
-    return UINT32_MAX;
+    return llvm::createStringError("Type has no child named '%s'", child_name);
   }
 
   virtual bool

lldb/include/lldb/Symbol/CompilerType.h

@@ -444,8 +444,9 @@ class CompilerType {
 
   /// Lookup a child given a name. This function will match base class names and
   /// member member names in "clang_type" only, not descendants.
-  uint32_t GetIndexOfChildWithName(llvm::StringRef name,
-                                   bool omit_empty_base_classes) const;
+  llvm::Expected<uint32_t>
+  GetIndexOfChildWithName(llvm::StringRef name,
+                          bool omit_empty_base_classes) const;
 
   /// Lookup a child member given a name. This function will match member names
   /// only and will descend into "clang_type" children in search for the first

lldb/include/lldb/Symbol/TypeSystem.h

@@ -373,9 +373,12 @@ class TypeSystem : public PluginInterface,
       bool &child_is_base_class, bool &child_is_deref_of_parent,
       ValueObject *valobj, uint64_t &language_flags) = 0;
 
-  virtual uint32_t GetIndexOfChildWithName(lldb::opaque_compiler_type_t type,
-                                           llvm::StringRef name,
-                                           bool omit_empty_base_classes) = 0;
+  // Lookup a child given a name. This function will match base class names and
+  // member member names in "clang_type" only, not descendants.
+  virtual llvm::Expected<uint32_t>
+  GetIndexOfChildWithName(lldb::opaque_compiler_type_t type,
+                          llvm::StringRef name,
+                          bool omit_empty_base_classes) = 0;
 
   virtual size_t GetIndexOfChildMemberWithName(
       lldb::opaque_compiler_type_t type, llvm::StringRef name,

lldb/include/lldb/ValueObject/ValueObject.h

@@ -498,7 +498,7 @@ class ValueObject {
   virtual lldb::ValueObjectSP GetChildMemberWithName(llvm::StringRef name,
                                                      bool can_create = true);
 
-  virtual size_t GetIndexOfChildWithName(llvm::StringRef name);
+  virtual llvm::Expected<size_t> GetIndexOfChildWithName(llvm::StringRef name);
 
   llvm::Expected<uint32_t> GetNumChildren(uint32_t max = UINT32_MAX);
   /// Like \c GetNumChildren but returns 0 on error.  You probably

lldb/include/lldb/ValueObject/ValueObjectRegister.h

@@ -52,7 +52,7 @@ class ValueObjectRegisterSet : public ValueObject {
   lldb::ValueObjectSP GetChildMemberWithName(llvm::StringRef name,
                                              bool can_create = true) override;
 
-  size_t GetIndexOfChildWithName(llvm::StringRef name) override;
+  llvm::Expected<size_t> GetIndexOfChildWithName(llvm::StringRef name) override;
 
 protected:
   bool UpdateValue() override;

lldb/include/lldb/ValueObject/ValueObjectSyntheticFilter.h

@@ -57,7 +57,7 @@ class ValueObjectSynthetic : public ValueObject {
   lldb::ValueObjectSP GetChildMemberWithName(llvm::StringRef name,
                                              bool can_create = true) override;
 
-  size_t GetIndexOfChildWithName(llvm::StringRef name) override;
+  llvm::Expected<size_t> GetIndexOfChildWithName(llvm::StringRef name) override;
 
   lldb::ValueObjectSP
   GetDynamicValue(lldb::DynamicValueType valueType) override;

lldb/source/API/SBValue.cpp

@@ -704,13 +704,15 @@ SBValue SBValue::GetChildAtIndex(uint32_t idx,
 uint32_t SBValue::GetIndexOfChildWithName(const char *name) {
   LLDB_INSTRUMENT_VA(this, name);
 
-  uint32_t idx = UINT32_MAX;
   ValueLocker locker;
   lldb::ValueObjectSP value_sp(GetSP(locker));
   if (value_sp) {
-    idx = value_sp->GetIndexOfChildWithName(name);
+    if (auto idx_or_err = value_sp->GetIndexOfChildWithName(name))
+      return *idx_or_err;
+    else
+      llvm::consumeError(idx_or_err.takeError());
   }
-  return idx;
+  return UINT32_MAX;
 }
 
 SBValue SBValue::GetChildMemberWithName(const char *name) {

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: {