Update .github/workflows

.github/workflows/ci.yml

@@ -38,6 +38,7 @@ jobs:
           - toolset: gcc-8
             cxxstd: "03,11,14,17,2a"
             os: ubuntu-18.04
+            install: g++-8
           - toolset: gcc-9
             cxxstd: "03,11,14,17,2a"
             os: ubuntu-18.04
@@ -83,6 +84,7 @@ jobs:
             compiler: clang++-6.0
             cxxstd: "03,11,14,17"
             os: ubuntu-18.04
+            install: clang-6.0
           - toolset: clang
             compiler: clang++-7
             cxxstd: "03,11,14,17"
@@ -92,6 +94,7 @@ jobs:
             compiler: clang++-8
             cxxstd: "03,11,14,17,2a"
             os: ubuntu-20.04
+            install: clang-8
           - toolset: clang
             compiler: clang++-9
             cxxstd: "03,11,14,17,2a"
@@ -100,6 +103,10 @@ jobs:
             compiler: clang++-10
             cxxstd: "03,11,14,17,2a"
             os: ubuntu-20.04
+          - toolset: clang
+            compiler: clang++-11
+            cxxstd: "03,11,14,17,2a"
+            os: ubuntu-20.04
           - toolset: clang
             cxxstd: "03,11,14,17,2a"
             os: macos-10.15

.travis.yml

@@ -288,7 +288,7 @@ matrix:
       env: CMAKE_TEST=1
       script:
         - mkdir __build__ && cd __build__
-        - cmake -DBOOST_ENABLE_CMAKE=1 -DBoost_VERBOSE=1 -DBOOST_INCLUDE_LIBRARIES=variant2 ..
+        - cmake -DBOOST_ENABLE_CMAKE=1 -DBUILD_TESTING=ON -DBoost_VERBOSE=1 -DBOOST_INCLUDE_LIBRARIES=variant2 ..
         - ctest --output-on-failure -R boost_variant2
 
     - os: linux

include/boost/variant2/variant.hpp

@@ -1584,7 +1584,7 @@ public:
 
     template<class U,
         class Ud = typename std::decay<U>::type,
-        class E1 = typename std::enable_if< !std::is_same<Ud, variant>::value && !detail::is_in_place_index<Ud>::value && !detail::is_in_place_type<Ud>::value >::type,
+        class E1 = typename std::enable_if< !std::is_same<Ud, variant>::value && !std::is_base_of<variant, Ud>::value && !detail::is_in_place_index<Ud>::value && !detail::is_in_place_type<Ud>::value >::type,
         class V = detail::resolve_overload_type<U&&, T...>,
         class E2 = typename std::enable_if<std::is_constructible<V, U&&>::value>::type
         >

test/Jamfile

@@ -119,3 +119,5 @@ run variant_visit_r.cpp : : :
     <toolset>gcc,<target-os>windows:<variant>release
     <toolset>gcc,<target-os>cygwin:<variant>release
     ;
+
+compile variant_derived_construct.cpp ;

test/variant_derived_construct.cpp

@@ -0,0 +1,33 @@
+// Copyright 2021 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/variant2/variant.hpp>
+
+using namespace boost::variant2;
+
+template<class... T> class X: variant<T...>
+{
+    using base = variant<T...>;
+    using base::base;
+};
+
+struct Y
+{
+    Y( Y const& rhs ) = default;
+
+    template<class T> Y( T const& t )
+    {
+        t.bar();
+    }
+};
+
+int main()
+{
+    using W = X<int, double, Y>;
+
+    W a( 1 );
+    W b( a );
+
+    (void)b;
+}