[Bug c++/114911] New: Anonymous unions can cause ICE when the name of their type escapes

[Bug c++/114911] New: Anonymous unions can cause ICE when the name of their type escapes

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114911

            Bug ID: 114911
           Summary: Anonymous unions can cause ICE when the name of their
                    type escapes
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Keywords: ice-checking, ice-on-valid-code
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: pinskia at gcc dot gnu.org
  Target Milestone: ---

Take:
```
void g();

template<typename T>
struct Capture;

template<typename T>
struct Capture<T*>  {
    friend void g() {
        &T::a;
    }
};

struct X;

void f() {
    union {
        int a = sizeof(Capture<decltype(this)>);
    };
    g();
}
```

GCC ICEs with:
```
<source>: In instantiation of 'void g()':
<source>:19:6:   required from here
   19 |     g();
      |     ~^~
<source>:9:9: internal compiler error: tree check: expected class 'type', have
'declaration' (function_decl) in build_offset_type, at tree.cc:7718
    9 |         &T::a;
      |         ^~~~~
0x267adac internal_error(char const*, ...)
        ???:0
0x966cd9 tree_class_check_failed(tree_node const*, tree_code_class, char
const*, int, char const*)
        ???:0
0xd20f91 build_x_unary_op(unsigned int, tree_code, cp_expr, tree_node*, int)
        ???:0
0xc95413 instantiate_decl(tree_node*, bool, bool)
        ???:0
0xcbeb3b instantiate_pending_templates(int)
        ???:0
0xb59819 c_parse_final_cleanups()
        ???:0
0xdb2668 c_common_parse_file()
        ???:0
Please submit a full bug report, with preprocessed source (by using
-freport-bug).
Please include the complete backtrace with any bug report.
See <https://gcc.gnu.org/bugs/> for instructions.

```

Note this is the same testcase as the clang bug:
https://github.com/llvm/llvm-project/issues/90751 just that GCC ICEs too.

Note also this seems not to ICE with release checking .

[Bug c++/114911] Anonymous unions can cause ICE when the name of their type escapes

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114911

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to fail|                            |4.7.1
           Keywords|ice-checking                |

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Not changing `&T::a` to be a full definition:

int T::*b = &T::a;

or
auto b = &T::a;

Gives an ICE all the way back to GCC 4.7.