[Bug ada/83935] New: DWARF for a variant part is incorrect

[tromey at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83935

            Bug ID: 83935
           Summary: DWARF for a variant part is incorrect
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: ada
          Assignee: unassigned at gcc dot gnu.org
          Reporter: tromey at gcc dot gnu.org
  Target Milestone: ---

Joel Brobecker sent me an Ada test case so that I could see a real-life
example of the use of DW_TAG_variant_part (in support of some Rust
stuff I'm doing elsewhere).

For this test case, GCC emits this DWARF:

 <1><7c0>: Abbrev Number: 4 (DW_TAG_structure_type)
    <7c1>   DW_AT_name        : (indirect string, offset: 0xb26): pck__rec
    <7c5>   DW_AT_byte_size   : 13 byte block: 97 94 1 99 95 0 0 0 23 7 9 fc 1a 
    <7d3>   DW_AT_decl_file   : 2
    <7d4>   DW_AT_decl_line   : 15
    <7d5>   DW_AT_sibling     : <0x817>
 <2><7d9>: Abbrev Number: 5 (DW_TAG_member)
    <7da>   DW_AT_name        : (indirect string, offset: 0xaf8): discr
    <7de>   DW_AT_decl_file   : 2
    <7df>   DW_AT_decl_line   : 15
    <7e0>   DW_AT_type        : <0x7af>
    <7e4>   DW_AT_data_member_location: 0
 <2><7e5>: Abbrev Number: 6 (DW_TAG_variant_part)
    <7e6>   DW_AT_discr       : <0x7d9>
 <3><7ea>: Abbrev Number: 7 (DW_TAG_variant)
    <7eb>   DW_AT_discr_value : 1
    <7ec>   DW_AT_sibling     : <0x7fd>


However, the DWARF standard says:

> If the variant part has a discriminant, the discriminant is represented
> by a separate debugging information entry which is a child of the variant part entry.

So, I think that, according to the DWARF standard, that "discr" member must be
a child (not a sibling) of the DW_TAG_variant_part.