[Lldb-commits] [lldb] b6a56c4 - [lldb] Call SetSyntheticChildrenGenerated on GetSyntheticChildAtOffset (#198859)

[via lldb-commits]

Author: Dave Lee
Date: 2026-05-21T20:49:25Z
New Revision: b6a56c4665936ea28c2d4739c92714a725c2c174

URL: https://github.com/llvm/llvm-project/commit/b6a56c4665936ea28c2d4739c92714a725c2c174
DIFF: https://github.com/llvm/llvm-project/commit/b6a56c4665936ea28c2d4739c92714a725c2c174.diff

LOG: [lldb] Call SetSyntheticChildrenGenerated on GetSyntheticChildAtOffset (#198859)

Follow up to #197311 and based on the feedback on that PR.

One way a Python synthetic formatter can construct a child is with
`SBValue::GetSyntheticChildAtOffset`. However those values were are not
marked as having been generated by `SyntheticChildren`. This means the
previous PR (#197311) did not apply to them as would be expected. The
fix is to call `SetSyntheticChildrenGenerated(true)` on the child values
created in `GetSyntheticChildAtOffset`.

Assisted-by: claude (tests and review)

Added: 
    lldb/test/API/python_api/sbvalue_get_parent/MyContainer_synthetic.py

Modified: 
    lldb/source/ValueObject/ValueObject.cpp
    lldb/test/API/python_api/sbvalue_get_parent/TestSBValueGetParent.py
    lldb/test/API/python_api/sbvalue_get_parent/main.cpp

Removed: 
    


################################################################################
diff  --git a/lldb/source/ValueObject/ValueObject.cpp b/lldb/source/ValueObject/ValueObject.cpp
index 806073db8c6fb..bffa3d30b00a3 100644
--- a/lldb/source/ValueObject/ValueObject.cpp
+++ b/lldb/source/ValueObject/ValueObject.cpp
@@ -1954,6 +1954,7 @@ ValueObjectSP ValueObject::GetSyntheticChildAtOffset(
     synthetic_child_sp = synthetic_child->GetSP();
     synthetic_child_sp->SetName(name_const_str);
     synthetic_child_sp->m_flags.m_is_child_at_offset = true;
+    synthetic_child_sp->SetSyntheticChildrenGenerated(true);
   }
   return synthetic_child_sp;
 }

diff  --git a/lldb/test/API/python_api/sbvalue_get_parent/MyContainer_synthetic.py b/lldb/test/API/python_api/sbvalue_get_parent/MyContainer_synthetic.py
new file mode 100644
index 0000000000000..b22c5373eb5e4
--- /dev/null
+++ b/lldb/test/API/python_api/sbvalue_get_parent/MyContainer_synthetic.py
@@ -0,0 +1,29 @@
+import lldb
+
+
+ at lldb.synthetic("MyContainer")
+class MyContainerSynthetic:
+    """Formatter that mimicks libstdc++ std::vector use of CreateChildAtOffset."""
+
+    valobj: lldb.SBValue
+
+    def __init__(self, valobj: lldb.SBValue, _) -> None:
+        self.valobj = valobj
+
+    def update(self) -> bool:
+        self.data = self.valobj.GetChildMemberWithName("data")
+        self.element_type = self.data.GetType().GetPointeeType()
+        self.element_size = self.element_type.GetByteSize()
+        self.count = self.valobj.GetChildMemberWithName("count").GetValueAsUnsigned(0)
+        return True
+
+    def num_children(self) -> int:
+        return self.count
+
+    def get_child_at_index(self, index: int) -> lldb.SBValue:
+        if 0 <= index < self.count:
+            offset = index * self.element_size
+            return self.data.CreateChildAtOffset(
+                f"[{index}]", offset, self.element_type
+            )
+        return lldb.SBValue()

diff  --git a/lldb/test/API/python_api/sbvalue_get_parent/TestSBValueGetParent.py b/lldb/test/API/python_api/sbvalue_get_parent/TestSBValueGetParent.py
index 50a6b95009208..7fe05aa9f1e43 100644
--- a/lldb/test/API/python_api/sbvalue_get_parent/TestSBValueGetParent.py
+++ b/lldb/test/API/python_api/sbvalue_get_parent/TestSBValueGetParent.py
@@ -19,6 +19,10 @@ def test(self):
         self._do_test(frame, "parent", "child")
         self._do_test(frame, "vec", 0)
 
+        # Test Python synthetic formatters using CreateChildAtOffset.
+        self.runCmd("command script import MyContainer_synthetic.py")
+        self._do_test(frame, "container", 0)
+
     def _do_test(
         self, frame: lldb.SBFrame, parent_name: str, child_key: Union[str, int]
     ):
@@ -32,7 +36,7 @@ def _do_test(
             child = parent.GetChildMemberWithName(child_key)
         self.assertTrue(child.IsValid())
 
-        # GetParent of child should be the parent struct.
+        # GetParent of child should be the original parent.
         child_parent = child.GetParent()
         self.assertTrue(child_parent.IsValid())
         self.assertEqual(child_parent.name, parent_name)

diff  --git a/lldb/test/API/python_api/sbvalue_get_parent/main.cpp b/lldb/test/API/python_api/sbvalue_get_parent/main.cpp
index cfb3452a70eb5..57e9c1a06b302 100644
--- a/lldb/test/API/python_api/sbvalue_get_parent/main.cpp
+++ b/lldb/test/API/python_api/sbvalue_get_parent/main.cpp
@@ -8,8 +8,15 @@ struct Parent {
   Child child;
 };
 
+struct MyContainer {
+  int *data;
+  unsigned count;
+};
+
 int main() {
   Parent parent = {{1}};
   std::vector<int> vec = {10, 20, 30};
+  int arr[] = {100, 200, 300};
+  MyContainer container = {arr, 3};
   return 0; // break here
 }