rust-lang/rust · error · Exception

Cannot bless invalid SBTypeMember object

Error message

Cannot bless invalid SBTypeMember object

What it means

Raised by from_lldb.field_from_lldb during a bless run when an lldb.SBTypeMember (a struct/enum field) fails IsValid(). Blessing records reference data, so recording an invalid field would corrupt the golden file; the guard refuses to do so.

Source

Thrown at src/etc/lldb_batchmode/from_lldb.py:181

def get_summary_or_value(valobj: lldb.SBValue) -> Optional[str]:
    """`SBValue.GetSummary` only prints summaries from summary providers. It returns `None` if there
    is no summary provider, rather than printing the default representation of the value. Often we
    want any printable representation at all, so this function falls back to `SBValue.GetValue`.
    That covers things like primitives and flat enums that typically don't have summary providers.
    """

    summary = valobj.GetSummary()
    if summary is None:
        return valobj.GetValue()

    return summary


def field_from_lldb(field: lldb.SBTypeMember) -> Field:
    if BLESS and not field.IsValid():
        raise Exception("Cannot bless invalid SBTypeMember object")

    return Field(field.GetName(), field.GetType().GetName(), field.GetOffsetInBytes())


def get_generics(ty: lldb.SBType, sbtarget: lldb.SBTarget) -> list[lldb.SBType]:
    """Platform-agnostic equivalent to `SBType.template_args`. `SBType`'s template functions do not
    work correctly with PDB debug info because PDB has no way to represent template parameters.

    Due to the DWARF spec using
    C++-centric terminology (e.g. `DW_TAG_template_type_parameter`), the following terms are
    interchangable:

    * template type param/arg <-> generic param
    * template value param/arg <-> const generic param

    The difference between "param" and "arg" is largely irrelevant for our purposes.
    Pre-parameterized types (e.g. `Vec<T>`, which could be parameterized to `Vec<u8>`, LLDB calls
    this "template specialization") are not reflected in the DWARF data at all, and are largely an

View on GitHub (pinned to 7088e4b63a)

Solutions

1. Recompile the test crate with full debug info (-C debuginfo=2) and minimal optimization.
2. Inspect the SBType in LLDB interactively (type lookup) to confirm the field exists and is valid before blessing.
3. Update or fix the synthetic provider/DWARF so GetFieldAtIndex returns a valid member.

Example fix

# before
rustc -C opt-level=2 test.rs
# after
rustc -C opt-level=0 -C debuginfo=2 test.rs

def field_from_lldb(field):
    if BLESS and not field.IsValid():
        raise Exception("Cannot bless invalid SBTypeMember object")
    ...

def is_valid_field(field: lldb.SBTypeMember) -> bool:
    return field.IsValid()

When it happens

Trigger: Calling field_from_lldb while BLESS is True with an SBTypeMember returned by SBType.GetFieldAtIndex(i) where LLDB could not resolve the field (e.g. incomplete debug info, optimized-out field, PDB/DWARF mismatch).

Common situations: Debug info for the type is incomplete because the crate was compiled without -g or with too much optimization; the type is a forward declaration; a clang/LLDB version change makes a previously-resolvable field invalid.

Related errors

• Invalid input data path: '{path}'\nIf test data has not been
• Cannot bless invalid SBType object
• Cannot bless invalid child
• Cannot bless invalid SBValue object
• <bless error: Cannot find variable {var_name}>

AI-assisted analysis of rust-lang/rust@7088e4b63a (2026-08-10). Data as JSON: /api/errors/1eff736da477cd11. Report an issue: GitHub.