[Bug c++/121575] New: ICE on structured binding to a parameter inside the body of expansion statements

[cooky.ykooc922 at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=121575

            Bug ID: 121575
           Summary: ICE on structured binding to a parameter inside the
                    body of expansion statements
           Product: gcc
           Version: 16.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: cooky.ykooc922 at gmail dot com
  Target Milestone: ---

This testcase ICEs on the following:

struct Point {
    int x, y;
};

void foo() {
    Point p {1, 3};
    template for (auto _ : {}) { // ok
        auto [x, y] = p;
    }
    template for (auto _ : {0}) { // ok
        auto [x, y] = p;
    }
}

void bar(Point p) {
    template for (auto _ : {}) { // ok
        auto [x, y] = p;
    }
    template for (auto _ : {0}) { // ICE
        auto [x, y] = p;
    }
}

The ICE triggers when the structured binding binds to a destructurable
parameter inside the expansion statement that expands at least once (won't ICE
if it is the expansion is empty).

Here is the error output from godbolt:
<source>: In instantiation of 'template for' iteration 1:
required from here
<source>:20:24:   
   20 |     template for (auto _ : {0}) {
      |                        ^
<source>:21:23: internal compiler error: in tsubst_expr, at cp/pt.cc:22327
   21 |         auto [x, y] = p;
      |                       ^
0x28a0855 diagnostics::context::diagnostic_impl(rich_location*,
diagnostics::metadata const*, diagnostics::option_id, char const*,
__va_list_tag (*) [1], diagnostics::kind)
        ???:0
0x2895e76 internal_error(char const*, ...)
        ???:0
0xafad16 fancy_abort(char const*, int, char const*)
        ???:0
0xd8bbd8 finish_expansion_stmt(tree_node*, tree_node*, int, tree_node*)
        ???:0
0xd2db73 c_parse_file()
        ???:0
0xe9d0a9 c_common_parse_file()
        ???:0

Godbolt link: https://godbolt.org/z/zP8YecaK4