Compiler crashes with SIGSEGV when appending to ArrayList(*const T) with the comptime_allocator from #25198

[tristanpemble]

Zig Version

0.15.1

Steps to Reproduce and Observed Behavior

Related to discussions about comptime allocators in #1291 and #25198. I was able to reproduce this with any pointer, which is why the repro has *const void; it seems to have nothing to do with the fact that it was a function pointer like I thought in #25198.

https://zigbin.io/a142dd

or

const std = @import("std");
const Allocator = std.mem.Allocator;
const Alignment = std.mem.Alignment;

pub const comptime_allocator: Allocator = .{
    .ptr = undefined,
    .vtable = &.{
        .alloc = &comptimeAlloc,
        .resize = &comptimeResize,
        .remap = &comptimeRemap,
        .free = &Allocator.noFree,
    },
};

fn comptimeAlloc(_: *anyopaque, len: usize, alignment: Alignment, ra: usize) ?[*]u8 {
    _ = ra;
    var buf: [len]u8 align(alignment.toByteUnits()) = undefined;
    return &buf;
}

fn comptimeResize(_: *anyopaque, mem: []u8, alignment: Alignment, new_len: usize, ra: usize) bool {
    _ = alignment;
    _ = ra;
    return new_len <= mem.len; // allow shrinking in-place
}

fn comptimeRemap(_: *anyopaque, mem: []u8, alignment: Alignment, new_len: usize, ra: usize) ?[*]u8 {
    _ = alignment;
    _ = ra;
    return if (new_len <= mem.len) mem.ptr else null; // allow shrinking in-place
}

comptime {
    var fns: std.ArrayList(*const void) = .empty;
    fns.append(comptime_allocator, &{});
}

Expected Behavior

Either it compiles successfully or fails with a compiler error