Compilation error with GCC 10/11 due to coroutine + template function

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When compiling async_simple with GCC 10 or GCC 11, code that uses coroutines inside function templates triggers a spurious static_assert failure in Lazy.h, even though the usage is valid.This is a known compiler bug in GCC 10/11 related to how the promise type is deduced in coroutine functions under specific template patterns. The issue does not occur in GCC 12+, or Clang.

🔗 Minimal ReproductionGodbolt link: https://godbolt.org/z/oar1hbxTb

📄 Repro Code

#include "async_simple/coro/Lazy.h"

async_simple::coro::Lazy<void> foo();

// ✅ OK: template with type parameter

async_simple::coro::Lazy<void> bar_ok() {
    co_await foo();
}
async_simple::coro::Lazy<void> test_ok() {
    co_await bar_ok();
}

// ❌ FAILS on GCC 10/11: template with ONLY non-type parameter
template <int io>
async_simple::coro::Lazy<void> bar_err() {
    co_await foo();
}
async_simple::coro::Lazy<void> test_err() {
    co_await bar_err<0>();
}

❌ Error Message

.../async_simple/coro/Lazy.h:345:70: error: static assertion failed: 
'co_await Lazy' is only allowed to be called by Lazy or DetachedCoroutine
  345 |                 std::is_base_of<LazyPromiseBase, PromiseType>::value ||
      |                                                                ~~~~~~^~
  346 |                     std::is_same_v<detail::DetachedCoroutine::promise_type,
  347 |                                    PromiseType>,

The PromiseType is incorrectly inferred (or mangled) by GCC 10/11 due to GCC Bug #100673, causing the static_assert to fail even when the caller is a valid Lazy coroutine.
✅ Workarounds

1. Remove template functions to normal functions on GCC 10/11.
2. Upgrade to GCC ≥12 or use Clang;

💡 Suggested Improvement To improve user experience

Consider enhancing the static_assert message in Lazy.h for GCC 10/11 to include a hint about this known compiler issue, e.g.:'co_await Lazy' failed due to potential GCC 10/11 coroutine bug (see https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100673). Workaround: Remove template parameter, or upgrade to Clang/GCC 12+.
This would help users quickly identify and resolve the issue without deep debugging.