[lldb] Provide default impl for MightHaveChildren (NFC) (llvm#119977)

The vast majority of `SyntheticChildrenFrontEnd` subclasses provide
children, and as such implement `MightHaveChildren` with a constant
value of `true`. This change makes `true` the default value. With this
change, `MightHaveChildren` only needs to be implemented by synthetic
providers that can return `false`, which is only 3 subclasses.

Author: kastiglione

lldb/include/lldb/DataFormatters/TypeSynthetic.h

@@ -68,7 +68,7 @@ class SyntheticChildrenFrontEnd {
   // a false return value from this call if it returns true, then
   // CalculateNumChildren() can return any number >= 0 (0 being valid) it
   // should if at all possible be more efficient than CalculateNumChildren()
-  virtual bool MightHaveChildren() = 0;
+  virtual bool MightHaveChildren() { return true; }
 
   // if this function returns a non-null ValueObject, then the returned
   // ValueObject will stand for this ValueObject whenever a "value" request is

lldb/include/lldb/DataFormatters/VectorIterator.h

@@ -30,8 +30,6 @@ class VectorIteratorSyntheticFrontEnd : public SyntheticChildrenFrontEnd {
 
   lldb::ChildCacheState Update() override;
 
-  bool MightHaveChildren() override;
-
   size_t GetIndexOfChildWithName(ConstString name) override;
 
 private:

lldb/source/DataFormatters/VectorType.cpp

@@ -268,8 +268,6 @@ class VectorTypeSyntheticFrontEnd : public SyntheticChildrenFrontEnd {
     return lldb::ChildCacheState::eRefetch;
   }
 
-  bool MightHaveChildren() override { return true; }
-
   size_t GetIndexOfChildWithName(ConstString name) override {
     const char *item_name = name.GetCString();
     uint32_t idx = ExtractIndexFromString(item_name);

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

@@ -144,9 +144,6 @@ class BlockPointerSyntheticFrontEnd : public SyntheticChildrenFrontEnd {
     return lldb::ChildCacheState::eRefetch;
   }
 
-  // maybe return false if the block pointer is, say, null
-  bool MightHaveChildren() override { return true; }
-
   size_t GetIndexOfChildWithName(ConstString name) override {
     if (!m_block_struct_type.IsValid())
       return UINT32_MAX;

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

@@ -199,11 +199,6 @@ lldb_private::formatters::StdlibCoroutineHandleSyntheticFrontEnd::Update() {
   return lldb::ChildCacheState::eRefetch;
 }
 
-bool lldb_private::formatters::StdlibCoroutineHandleSyntheticFrontEnd::
-    MightHaveChildren() {
-  return true;
-}
-
 size_t StdlibCoroutineHandleSyntheticFrontEnd::GetIndexOfChildWithName(
     ConstString name) {
   if (!m_resume_ptr_sp || !m_destroy_ptr_sp)

lldb/source/Plugins/Language/CPlusPlus/Coroutines.h

@@ -40,8 +40,6 @@ class StdlibCoroutineHandleSyntheticFrontEnd
 
   lldb::ChildCacheState Update() override;
 
-  bool MightHaveChildren() override;
-
   size_t GetIndexOfChildWithName(ConstString name) override;
 
 private:

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

@@ -32,7 +32,6 @@ class GenericBitsetFrontEnd : public SyntheticChildrenFrontEnd {
     return formatters::ExtractIndexFromString(name.GetCString());
   }
 
-  bool MightHaveChildren() override { return true; }
   lldb::ChildCacheState Update() override;
   llvm::Expected<uint32_t> CalculateNumChildren() override {
     return m_elements.size();

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

@@ -42,7 +42,6 @@ class GenericOptionalFrontend : public SyntheticChildrenFrontEnd {
     return formatters::ExtractIndexFromString(name.GetCString());
   }
 
-  bool MightHaveChildren() override { return true; }
   llvm::Expected<uint32_t> CalculateNumChildren() override {
     return m_has_value ? 1U : 0U;
   }

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

@@ -309,11 +309,6 @@ lldb_private::formatters::LibcxxSharedPtrSyntheticFrontEnd::Update() {
   return lldb::ChildCacheState::eRefetch;
 }
 
-bool lldb_private::formatters::LibcxxSharedPtrSyntheticFrontEnd::
-    MightHaveChildren() {
-  return true;
-}
-
 size_t lldb_private::formatters::LibcxxSharedPtrSyntheticFrontEnd::
     GetIndexOfChildWithName(ConstString name) {
   if (name == "__ptr_")
@@ -412,11 +407,6 @@ lldb_private::formatters::LibcxxUniquePtrSyntheticFrontEnd::Update() {
   return lldb::ChildCacheState::eRefetch;
 }
 
-bool lldb_private::formatters::LibcxxUniquePtrSyntheticFrontEnd::
-    MightHaveChildren() {
-  return true;
-}
-
 size_t lldb_private::formatters::LibcxxUniquePtrSyntheticFrontEnd::
     GetIndexOfChildWithName(ConstString name) {
   if (name == "pointer")

lldb/source/Plugins/Language/CPlusPlus/LibCxx.h

@@ -102,8 +102,6 @@ class LibcxxSharedPtrSyntheticFrontEnd : public SyntheticChildrenFrontEnd {
 
   lldb::ChildCacheState Update() override;
 
-  bool MightHaveChildren() override;
-
   size_t GetIndexOfChildWithName(ConstString name) override;
 
   ~LibcxxSharedPtrSyntheticFrontEnd() override;
@@ -122,8 +120,6 @@ class LibcxxUniquePtrSyntheticFrontEnd : public SyntheticChildrenFrontEnd {
 
   lldb::ChildCacheState Update() override;
 
-  bool MightHaveChildren() override;
-
   size_t GetIndexOfChildWithName(ConstString name) override;
 
   ~LibcxxUniquePtrSyntheticFrontEnd() override;