Repository: rust
Issue: rust-lldb: cannot get backtrace on macOS
Labels: O-macos,A-debuginfo,T-compiler,C-bug

I have a breakpoint set on `rust_panic`, but when I hit this and then do `bt`, I get:

```
error: need to add support for DW_TAG_base_type '()' encoded with DW_ATE = 0x7, bit_size = 0
Traceback (most recent call last):
  File "/Users/alex/Software/rust-devel/src/etc/lldb_rust_formatters.py", line 89, in print_val
    is_tuple_like = False)
  File "/Users/alex/Software/rust-devel/src/etc/lldb_rust_formatters.py", line 210, in print_struct_val
    body = separator.join([render_child(idx) for idx in range(field_start_index, len(fields))])
  File "/Users/alex/Software/rust-devel/src/etc/lldb_rust_formatters.py", line 203, in render_child
    return this + print_val(field_val.get_wrapped_value(), internal_dict)
  File "/Users/alex/Software/rust-devel/src/etc/lldb_rust_formatters.py", line 89, in print_val
    is_tuple_like = False)
  File "/Users/alex/Software/rust-devel/src/etc/lldb_rust_formatters.py", line 210, in print_struct_val
    body = separator.join([render_child(idx) for idx in range(field_start_index, len(fields))])
  File "/Users/alex/Software/rust-devel/src/etc/lldb_rust_formatters.py", line 203, in render_child
    return this + print_val(field_val.get_wrapped_value(), internal_dict)
  File "/Users/alex/Software/rust-devel/src/etc/lldb_rust_formatters.py", line 89, in print_val
    is_tuple_like = False)
  File "/Users/alex/Software/rust-devel/src/etc/lldb_rust_formatters.py", line 210, in print_struct_val
    body = separator.join([render_child(idx) for idx in range(field_start_index, len(fields))])
  File "/Users/alex/Software/rust-devel/src/etc/lldb_rust_formatters.py", line 203, in render_child
    return this + print_val(field_val.get_wrapped_value(), internal_dict)
  File "/Users/alex/Software/rust-devel/src/etc/lldb_rust_formatters.py", line 89, in print_val
    is_tuple_like = False)
  File "/Users/alex/Software/rust-devel/src/etc/lldb_rust_formatters.py", line 210, in print_struct_val
    body = separator.join([render_child(idx) for idx in range(field_start_index, len(fields))])
  File "/Users/alex/Software/rust-devel/src/etc/lldb_rust_formatters.py", line 203, in render_child
    return this + print_val(field_val.get_wrapped_value(), internal_dict)
  File "/Users/alex/Software/rust-devel/src/etc/lldb_rust_formatters.py", line 89, in print_val
    is_tuple_like = False)
  File "/Users/alex/Software/rust-devel/src/etc/lldb_rust_formatters.py", line 210, in print_struct_val
    body = separator.join([render_child(idx) for idx in range(field_start_index, len(fields))])
  File "/Users/alex/Software/rust-devel/src/etc/lldb_rust_formatters.py", line 203, in render_child
    return this + print_val(field_val.get_wrapped_value(), internal_dict)
  File "/Users/alex/Software/rust-devel/src/etc/lldb_rust_formatters.py", line 89, in print_val
    is_tuple_like = False)
  File "/Users/alex/Software/rust-devel/src/etc/lldb_rust_formatters.py", line 210, in print_struct_val
    body = separator.join([render_child(idx) for idx in range(field_start_index, len(fields))])
  File "/Users/alex/Software/rust-devel/src/etc/lldb_rust_formatters.py", line 203, in render_child
    return this + print_val(field_val.get_wrapped_value(), internal_dict)
  File "/Users/alex/Software/rust-devel/src/etc/lldb_rust_formatters.py", line 89, in print_val
    is_tuple_like = False)
  File "/Users/alex/Software/rust-devel/src/etc/lldb_rust_formatters.py", line 210, in print_struct_val
    body = separator.join([render_child(idx) for idx in range(field_start_index, len(fields))])
  File "/Users/alex/Software/rust-devel/src/etc/lldb_rust_formatters.py", line 203, in render_child
    return this + print_val(field_val.get_wrapped_value(), internal_dict)
  File "/Users/alex/Software/rust-devel/src/etc/lldb_rust_formatters.py", line 89, in print_val
    is_tuple_like = False)
  File "/Users/alex/Software/rust-devel/src/etc/lldb_rust_formatters.py", line 210, in print_struct_val
    body = separator.join([render_child(idx) for idx in range(field_start_index, len(fields))])
  File "/Users/alex/Software/rust-devel/src/etc/lldb_rust_formatters.py", line 203, in render_child
    return this + print_val(field_val.get_wrapped_value(), internal_dict)
  File "/Users/alex/Software/rust-devel/src/etc/lldb_rust_formatters.py", line 105, in print_val
    return print_std_vec_val(val, internal_dict)
  File "/Users/alex/Software/rust-devel/src/etc/lldb_rust_formatters.py", line 254, in print_std_vec_val
    internal_dict)
  File "/Users/alex/Software/rust-devel/src/etc/lldb_rust_formatters.py", line 289, in print_array_of_values
    return ', '.join([render_element(i) for i in range(length)])
  File "/Users/alex/Software/rust-devel/src/etc/lldb_rust_formatters.py", line 287, in render_element
    return print_val(element_val, internal_dict)
  File "/Users/alex/Software/rust-devel/src/etc/lldb_rust_formatters.py", line 89, in print_val
    is_tuple_like = False)
  File "/Users/alex/Software/rust-devel/src/etc/lldb_rust_formatters.py", line 210, in print_struct_val
    body = separator.join([render_child(idx) for idx in range(field_start_index, len(fields))])
  File "/Users/alex/Software/rust-devel/src/etc/lldb_rust_formatters.py", line 203, in render_child
    return this + print_val(field_val.get_wrapped_value(), internal_dict)
TypeError: cannot concatenate 'str' and 'NoneType' objects
error: librustc_driver-f561ecb0e4be7b67.dylib DWARF DIE at 0x076fab13 (class closure) has a member variable 0x076fab1a (__0) whose type is a forward declaration, not a complete definition.
Try compiling the source file with -fstandalone-debug
Illegal instruction: 4
```