make sure the library builds with C++17 and C++20, in addition to C++14

.github/workflows/linux.yml

@@ -25,7 +25,7 @@ jobs:
 
    build:
       name: build
-      runs-on: ubuntu-20.04
+      runs-on: ubuntu-22.04
       continue-on-error: true
 
       strategy:
@@ -52,7 +52,7 @@ jobs:
 
       - name: install boost
         run: |
-          sudo apt install libboost-tools-dev libboost-dev libboost-system-dev
+          sudo apt install libboost-python-dev libboost-tools-dev libboost-dev libboost-system-dev python3
           echo "using gcc ;" >>~/user-config.jam
 
       - name: install gcrypt
@@ -61,18 +61,23 @@ jobs:
 
       - name: build library
         run: |
-          b2 ${{ matrix.config }} cxxstd=14
+          b2 ${{ matrix.config }} cxxstd=14,17,20 warnings-as-errors=on
 
       - name: build examples
         run: |
           cd examples
-          b2 ${{ matrix.config }}
+          b2 ${{ matrix.config }} cxxstd=14,17,20 warnings-as-errors=on
 
       - name: build tools
         run: |
           cd tools
-          b2 ${{ matrix.config }} warnings-as-errors=on
+          b2 ${{ matrix.config }} cxxstd=14,17,20 warnings-as-errors=on
 
+      - name: build python bindings
+        run: |
+          cd bindings/python
+          echo "using python ;" >>~/user-config.jam
+          BOOST_ROOT="" b2 ${{ matrix.config }} cxxstd=14,17,20 warnings-as-errors=on
 
 
    fuzzers:

bindings/python/src/entry.cpp

@@ -20,7 +20,7 @@ struct entry_to_python
             result.append(*i);
         }
 
-        return std::move(result);
+        return TORRENT_RVO(result);
     }
 
     static object convert(entry::dictionary_type const& d)
@@ -30,7 +30,7 @@ struct entry_to_python
         for (entry::dictionary_type::const_iterator i(d.begin()), e(d.end()); i != e; ++i)
             result[bytes(i->first)] = i->second;
 
-        return std::move(result);
+        return TORRENT_RVO(result);
     }
 
     static object convert0(entry const& e)

include/libtorrent/config.hpp

@@ -616,6 +616,12 @@ POSSIBILITY OF SUCH DAMAGE.
 #define __has_builtin(x) 0  // for non-clang compilers
 #endif
 
+#if __cplusplus >= 202002L
+#define TORRENT_RVO(x) x
+#else
+#define TORRENT_RVO(x) std::move(x)
+#endif
+
 #if (TORRENT_HAS_SSE && defined __GNUC__)
 #	define TORRENT_HAS_BUILTIN_CLZ 1
 #elif (TORRENT_HAS_ARM && defined __GNUC__ && !defined __clang__)

src/alert.cpp

@@ -2579,7 +2579,7 @@ namespace {
 		for (int i = 0; i < m_v6_num_peers; i++)
 			peers.push_back(aux::read_v6_endpoint<tcp::endpoint>(v6_ptr));
 
-		return std::move(peers);
+		return TORRENT_RVO(peers);
 	}
 
 	dht_direct_response_alert::dht_direct_response_alert(
@@ -2819,7 +2819,7 @@ namespace {
 			nodes.emplace_back(ih, aux::read_v6_endpoint<udp::endpoint>(v6_ptr));
 		}
 
-		return std::move(nodes);
+		return TORRENT_RVO(nodes);
 	}
 	}
 
@@ -2931,7 +2931,7 @@ namespace {
 		char const* ptr = m_alloc.get().ptr(m_samples_idx);
 		std::memcpy(samples.data(), ptr, samples.size() * 20);
 
-		return std::move(samples);
+		return TORRENT_RVO(samples);
 	}
 
 	int dht_sample_infohashes_alert::num_nodes() const

src/session_stats.cpp

@@ -584,7 +584,7 @@ namespace {
 			stats[i].type = metrics[i].value_index >= counters::num_stats_counters
 				? metric_type_t::gauge : metric_type_t::counter;
 		}
-		return std::move(stats);
+		return TORRENT_RVO(stats);
 	}
 
 	int find_metric_idx(string_view name)

src/torrent_handle.cpp

@@ -484,7 +484,7 @@ namespace libtorrent {
 	{
 		aux::vector<std::int64_t, file_index_t> ret;
 		sync_call(&torrent::file_progress, std::ref(ret), flags);
-		return std::move(ret);
+		return TORRENT_RVO(ret);
 	}
 
 	void torrent_handle::post_file_progress(file_progress_flags_t const flags) const
@@ -542,7 +542,7 @@ namespace libtorrent {
 		aux::vector<download_priority_t, piece_index_t> ret;
 		auto retp = &ret;
 		sync_call(&torrent::piece_priorities, retp);
-		return std::move(ret);
+		return TORRENT_RVO(ret);
 	}
 
 #if TORRENT_ABI_VERSION == 1
@@ -598,7 +598,7 @@ namespace libtorrent {
 		aux::vector<download_priority_t, file_index_t> ret;
 		auto retp = &ret;
 		sync_call(&torrent::file_priorities, retp);
-		return std::move(ret);
+		return TORRENT_RVO(ret);
 	}
 
 #if TORRENT_ABI_VERSION == 1