From 2bebee6b37f9d6f3361999b6164bf15492bc675b Mon Sep 17 00:00:00 2001
From: Radoslaw Zarzynski <rzarzyns@redhat.com>
Date: Tue, 30 Nov 2021 13:49:04 +0000
Subject: [PATCH] crimson/os: fix FTBFS on recent versions of Seastar.

Seastar since c4516f564197da409c1e5a012bd24c35457a9a40 provides
two variants of `seastar::with_lock`:
  - generic, friendly towards throwing move constructors of
    the passed callable,
  - specialized for `noexcept`.

Unfortunately, the former has a limitation: the return value of
callable must be compatible with `current_exception_as_future()`
which boils down to returning `seastar::future<void>`. Therefore
we need to use the latter. The obstacle is `boost::intrusive_ptr`
we use for `CollectionRef` as it has the move constructor defined
without `noexcept`:

```cpp
emplate<class T> class intrusive_ptr
{
    //
    BOOST_CONSTEXPR intrusive_ptr() BOOST_SP_NOEXCEPT : px( 0 )
    {
    }

    // ...

    template<class U>

    intrusive_ptr( intrusive_ptr<U> const & rhs, typename boost::detail::sp_enable_if_convertible<U,T>::type = boost::detail::sp_empty() )

    intrusive_ptr( intrusive_ptr<U> const & rhs )

    : px( rhs.get() )
    {
        if( px != 0 ) intrusive_ptr_add_ref( px );
    }

    // ...

    intrusive_ptr(intrusive_ptr && rhs) BOOST_SP_NOEXCEPT : px( rhs.px )
    {
        rhs.px = 0;
    }

    intrusive_ptr & operator=(intrusive_ptr && rhs) BOOST_SP_NOEXCEPT
    {
        this_type( static_cast< intrusive_ptr && >( rhs ) ).swap(*this);
        return *this;
    }

```

Signed-off-by: Radoslaw Zarzynski <rzarzyns@redhat.com>
---
 src/crimson/os/alienstore/alien_collection.h | 7 +++++++
 src/crimson/os/alienstore/alien_store.cc     | 3 ++-
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/src/crimson/os/alienstore/alien_collection.h b/src/crimson/os/alienstore/alien_collection.h
index 538db3dae66..17a930e77a9 100644
--- a/src/crimson/os/alienstore/alien_collection.h
+++ b/src/crimson/os/alienstore/alien_collection.h
@@ -21,6 +21,13 @@ public:
 
   template <typename Func, typename Result = std::invoke_result_t<Func>>
   seastar::futurize_t<Result> with_lock(Func&& func) {
+    // newer versions of Seastar provide two variants of `with_lock`
+    //   - generic, friendly towards throwing move constructors of Func,
+    //   - specialized for `noexcept`.
+    // unfortunately, the former has a limitation: the return value
+    // of `Func` must be compatible with `current_exception_as_future()`
+    // which boils down to returning `seastar::future<void>`.
+    static_assert(std::is_nothrow_move_constructible_v<Func>);
     return seastar::with_lock(mutex, std::forward<Func>(func));
   }
 
diff --git a/src/crimson/os/alienstore/alien_store.cc b/src/crimson/os/alienstore/alien_store.cc
index 43ff8d35415..c9c3116f81e 100644
--- a/src/crimson/os/alienstore/alien_store.cc
+++ b/src/crimson/os/alienstore/alien_store.cc
@@ -429,7 +429,8 @@ seastar::future<> AlienStore::do_transaction(CollectionRef ch,
     [this, ch, id] (auto &txn, auto &done) {
       return seastar::with_gate(transaction_gate, [this, ch, id, &txn, &done] {
 	AlienCollection* alien_coll = static_cast<AlienCollection*>(ch.get());
-	return alien_coll->with_lock([this, ch, id, &txn, &done] {
+        // moving the `ch` is crucial for buildability on newer S* versions.
+	return alien_coll->with_lock([this, ch=std::move(ch), id, &txn, &done] {
 	  Context *crimson_wrapper =
 	    ceph::os::Transaction::collect_all_contexts(txn);
 	  assert(tp);
-- 
2.39.5