slint-ui/slint · error · RuntimeError

unsupported NonNull layout in Slice

Error message

unsupported NonNull layout in Slice

What it means

Slice._data_pointer() unwraps the slice's NonNull to reach the data pointer for GDB pretty-printing. It recognizes the common Rust pointer field layouts (pointer, __0, tuple field 0); this error sentinel is yielded when the NonNull's type has none of those field names, i.e. a std layout change or an exotic NonNull representation the printer doesn't know. The input at fault is the GDB type of the ptr field, and the result is a '<error>' pseudo-child in the debugger view rather than a crash.

Solutions

1. Update the pretty printer's _data_pointer to handle the new NonNull layout by checking candidate.type.code == gdb.TYPE_CODE_PTR before use and adding the new wrapper field name to the accepted list
2. Print nn.type and its fields with 'info type' / ptype in GDB to identify the actual wrapper field and add it to ("pointer", "__0", "0")
3. Fall back to the raw address: use nn.reinterpret_cast(elem_type.pointer()) when no recognized pointer field is found
4. Verify the Rust std version; NonNull/Slice internal layouts changed across releases, so pin the debugger script expectations to the std version in use

When it happens

Trigger: Thrown at internal/core/gdb_pretty_printers.py:112 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of slint-ui/slint@bb937076de (2026-09-16). Data as JSON: /api/errors/7723dfa97e781c4b. Report an issue: GitHub.

Appendix: source

Thrown at internal/core/gdb_pretty_printers.py:112

            elem_type = data_ptr.type.target()
            for i in range(length):
                yield f"[{i}]", (data_ptr + i).dereference()
        except Exception as e:
            yield "<error>", f"error reading elements: {e}"

    def display_hint(self):
        return "array"

    def _data_pointer(self):
        nn = self.val["ptr"]
        if nn.type.code == gdb.TYPE_CODE_PTR:
            return nn
        for field in nn.type.fields():
            if field.name in ("pointer", "__0", "0"):
                candidate = nn[field]
                if candidate.type.code == gdb.TYPE_CODE_PTR:
                    return candidate
        raise RuntimeError("unsupported NonNull layout in Slice")


class SliceSubPrinter(gdb.printing.SubPrettyPrinter):
    def __init__(self):
        super().__init__("Slice")

    def __call__(self, val):
        if not self.enabled:
            return None
        t = val.type.strip_typedefs()
        if t.code == gdb.TYPE_CODE_PTR:  # also support reference to Slice
            try:
                val = val.dereference()
                t = val.type.strip_typedefs()
            except gdb.error:
                return None
        if (
            t.code == gdb.TYPE_CODE_STRUCT

View on GitHub (pinned to bb937076de)