Disable variant_issue_55.cpp on clang-cl 32 bit

Call boost::core::lwt_init() in variant_issue_55.cpp, because it doesn't invoke any BOOST_TEST macros and clang-win 32 bit hangs w/ assertion
Disable -Wmaybe-uninitialized false positive. Refs #55 .
2026-01-13 18:56:59 +01:00 · 2026-01-02 12:29:11 +02:00 · 2026-01-02 02:51:46 +02:00 · 2026-01-02 02:21:29 +02:00 · 2026-01-01 22:28:25 +02:00 · 2026-01-01 22:21:34 +02:00
17 changed files with 706 additions and 122 deletions
--- a/.drone.jsonnet
+++ b/.drone.jsonnet
@@ -34,7 +34,6 @@ local linux_pipeline(name, image, environment, packages = "", sources = [], arch
                'set -e',
                'uname -a',
                'echo $DRONE_STAGE_MACHINE',
-                'wget -O - https://apt.llvm.org/llvm-snapshot.gpg.key | apt-key add -',
            ] +
            (if sources != [] then [ ('apt-add-repository "' + source + '"') for source in sources ] else []) +
            (if packages != "" then [ 'apt-get update', 'apt-get -y install ' + packages ] else []) +
@@ -213,6 +212,13 @@ local windows_pipeline(name, image, environment, arch = "amd64") =
        "g++-14-multilib",
    ),

+    linux_pipeline(
+        "Linux 25.04 GCC 15 32/64",
+        "cppalliance/droneubuntu2504:1",
+        { TOOLSET: 'gcc', COMPILER: 'g++-15', CXXSTD: '11,14,17,20,23,2c', ADDRMD: '32,64' },
+        "g++-15-multilib",
+    ),
+
    linux_pipeline(
        "Linux 16.04 Clang 3.5",
        "cppalliance/droneubuntu1604:1",
@@ -340,40 +346,47 @@ local windows_pipeline(name, image, environment, arch = "amd64") =
    ),

    linux_pipeline(
-        "Linux 24.04 Clang 17 UBSAN",
+        "Linux 24.04 Clang 17",
        "cppalliance/droneubuntu2404:1",
-        { TOOLSET: 'clang', COMPILER: 'clang++-17', CXXSTD: '11,14,17,20,2b' } + ubsan,
+        { TOOLSET: 'clang', COMPILER: 'clang++-17', CXXSTD: '11,14,17,20,2b' },
        "clang-17",
    ),

    linux_pipeline(
-        "Linux 24.04 Clang 17 ASAN",
+        "Linux 24.04 Clang 18",
        "cppalliance/droneubuntu2404:1",
-        { TOOLSET: 'clang', COMPILER: 'clang++-17', CXXSTD: '11,14,17,20,2b' } + asan,
-        "clang-17",
-    ),
-
-    linux_pipeline(
-        "Linux 24.04 Clang 18 UBSAN",
-        "cppalliance/droneubuntu2404:1",
-        { TOOLSET: 'clang', COMPILER: 'clang++-18', CXXSTD: '11,14,17,20,2b' } + ubsan,
+        { TOOLSET: 'clang', COMPILER: 'clang++-18', CXXSTD: '11,14,17,20,2b' },
        "clang-18",
    ),

    linux_pipeline(
-        "Linux 24.04 Clang 18 ASAN",
+        "Linux 24.04 Clang 19",
        "cppalliance/droneubuntu2404:1",
-        { TOOLSET: 'clang', COMPILER: 'clang++-18', CXXSTD: '11,14,17,20,2b' } + asan,
-        "clang-18",
-    ),
-
-    linux_pipeline(
-        "Linux 24.10 Clang 19",
-        "cppalliance/droneubuntu2410:1",
-        { TOOLSET: 'clang', COMPILER: 'clang++-19', CXXSTD: '11,14,17,20,2b' } + asan,
+        { TOOLSET: 'clang', COMPILER: 'clang++-19', CXXSTD: '11,14,17,20,2b' },
        "clang-19",
    ),

+    linux_pipeline(
+        "Linux 24.04 Clang 20 UBSAN",
+        "cppalliance/droneubuntu2404:1",
+        { TOOLSET: 'clang', COMPILER: 'clang++-20', CXXSTD: '11,14,17,20,23,2c' } + ubsan,
+        "clang-20",
+    ),
+
+    linux_pipeline(
+        "Linux 24.04 Clang 20 ASAN",
+        "cppalliance/droneubuntu2404:1",
+        { TOOLSET: 'clang', COMPILER: 'clang++-20', CXXSTD: '11,14,17,20,23,2c' } + asan,
+        "clang-20",
+    ),
+
+    linux_pipeline(
+        "Linux 25.10 Clang 21",
+        "cppalliance/droneubuntu2510:1",
+        { TOOLSET: 'clang', COMPILER: 'clang++-21', CXXSTD: '11,14,17,20,23,2c' },
+        "clang-21",
+    ),
+
    macos_pipeline(
        "MacOS 10.15 Xcode 12.2 UBSAN",
        { TOOLSET: 'clang', COMPILER: 'clang++', CXXSTD: '11,14,1z' } + ubsan,
@@ -437,4 +450,16 @@ local windows_pipeline(name, image, environment, arch = "amd64") =
        "cppalliance/dronevs2022:1",
        { TOOLSET: 'msvc-14.3', CXXSTD: '14,17', CXXFLAGS: '/permissive-' },
    ),
+
+    windows_pipeline(
+        "Windows VS2026 msvc-14.5",
+        "cppalliance/dronevs2026:1",
+        { TOOLSET: 'msvc-14.5', CXXSTD: '14,17,20,latest' },
+    ),
+
+    windows_pipeline(
+        "Windows VS2026 msvc-14.5 permissive-",
+        "cppalliance/dronevs2026:1",
+        { TOOLSET: 'msvc-14.5', CXXSTD: '14,17', CXXFLAGS: '/permissive-' },
+    ),
 ]
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -43,22 +43,27 @@ jobs:
            os: ubuntu-latest
          - toolset: gcc-8
            cxxstd: "11,14,17,2a"
-            os: ubuntu-20.04
+            container: ubuntu:20.04
+            os: ubuntu-latest
            install: g++-8
          - toolset: gcc-9
            cxxstd: "11,14,17,2a"
-            os: ubuntu-20.04
+            container: ubuntu:20.04
+            os: ubuntu-latest
          - toolset: gcc-10
            cxxstd: "11,14,17,2a"
-            os: ubuntu-22.04
+            container: ubuntu:22.04
+            os: ubuntu-latest
            install: g++-10
          - toolset: gcc-11
            cxxstd: "11,14,17,2a"
-            os: ubuntu-22.04
+            container: ubuntu:22.04
+            os: ubuntu-latest
            install: g++-11
          - toolset: gcc-12
            cxxstd: "11,14,17,20,2b"
-            os: ubuntu-22.04
+            container: ubuntu:22.04
+            os: ubuntu-latest
            install: g++-12
          - toolset: gcc-13
            cxxstd: "11,14,17,20,2b"
@@ -70,6 +75,11 @@ jobs:
            container: ubuntu:24.04
            os: ubuntu-latest
            install: g++-14
+          - toolset: gcc-15
+            cxxstd: "11,14,17,20,23,2c"
+            container: ubuntu:25.04
+            os: ubuntu-latest
+            install: g++-15
          - toolset: clang
            compiler: clang++-3.9
            cxxstd: "11,14"
@@ -91,37 +101,44 @@ jobs:
          - toolset: clang
            compiler: clang++-6.0
            cxxstd: "11,14,17"
-            os: ubuntu-20.04
+            container: ubuntu:20.04
+            os: ubuntu-latest
            install: clang-6.0
          - toolset: clang
            compiler: clang++-7
            cxxstd: "11,14,17"
-            os: ubuntu-20.04
+            container: ubuntu:20.04
+            os: ubuntu-latest
            install: clang-7
          - toolset: clang
            compiler: clang++-8
            cxxstd: "11,14,17"
-            os: ubuntu-20.04
+            container: ubuntu:20.04
+            os: ubuntu-latest
            install: clang-8
          - toolset: clang
            compiler: clang++-9
            cxxstd: "11,14,17,2a"
-            os: ubuntu-20.04
+            container: ubuntu:20.04
+            os: ubuntu-latest
            install: clang-9
          - toolset: clang
            compiler: clang++-10
            cxxstd: "11,14,17,2a"
-            os: ubuntu-20.04
+            container: ubuntu:20.04
+            os: ubuntu-latest
            install: clang-10
          - toolset: clang
            compiler: clang++-11
            cxxstd: "11,14,17,2a"
-            os: ubuntu-20.04
+            container: ubuntu:20.04
+            os: ubuntu-latest
            install: clang-11
          - toolset: clang
            compiler: clang++-12
            cxxstd: "11,14,17,2a"
-            os: ubuntu-20.04
+            container: ubuntu:20.04
+            os: ubuntu-latest
            install: clang-12
          - toolset: clang
            compiler: clang++-13
@@ -162,18 +179,30 @@ jobs:
          - toolset: clang
            compiler: clang++-19
            cxxstd: "11,14,17,20,2b"
-            container: ubuntu:24.10
+            container: ubuntu:24.04
            os: ubuntu-latest
            install: clang-19
          - toolset: clang
-            cxxstd: "11,14,17,20,2b"
-            os: macos-13
+            compiler: clang++-20
+            cxxstd: "11,14,17,20,23,2c"
+            container: ubuntu:24.04
+            os: ubuntu-latest
+            install: clang-20
+          - toolset: clang
+            compiler: clang++-21
+            cxxstd: "11,14,17,20,23,2c"
+            container: ubuntu:25.10
+            os: ubuntu-latest
+            install: clang-21
          - toolset: clang
            cxxstd: "11,14,17,20,2b"
            os: macos-14
          - toolset: clang
-            cxxstd: "11,14,17,20,2b"
+            cxxstd: "11,14,17,20,23,2c"
            os: macos-15
+          - toolset: clang
+            cxxstd: "11,14,17,20,23,2c"
+            os: macos-26

    runs-on: ${{matrix.os}}

@@ -246,14 +275,6 @@ jobs:
      fail-fast: false
      matrix:
        include:
-          - toolset: msvc-14.0
-            cxxstd: "14,latest"
-            addrmd: 32,64
-            os: windows-2019
-          - toolset: msvc-14.2
-            cxxstd: "14,17,20,latest"
-            addrmd: 32,64
-            os: windows-2019
          - toolset: msvc-14.3
            cxxstd: "14,17,20,latest"
            addrmd: 32,64
@@ -265,7 +286,7 @@ jobs:
          - toolset: gcc
            cxxstd: "11,14,17,2a"
            addrmd: 64
-            os: windows-2019
+            os: windows-2022

    runs-on: ${{matrix.os}}

@@ -305,12 +326,11 @@ jobs:
      fail-fast: false
      matrix:
        include:
-          - os: ubuntu-20.04
          - os: ubuntu-22.04
          - os: ubuntu-24.04
-          - os: macos-13
          - os: macos-14
          - os: macos-15
+          - os: macos-26

    runs-on: ${{matrix.os}}

@@ -354,12 +374,11 @@ jobs:
      fail-fast: false
      matrix:
        include:
-          - os: ubuntu-20.04
          - os: ubuntu-22.04
          - os: ubuntu-24.04
-          - os: macos-13
          - os: macos-14
          - os: macos-15
+          - os: macos-26

    runs-on: ${{matrix.os}}

@@ -413,12 +432,11 @@ jobs:
      fail-fast: false
      matrix:
        include:
-          - os: ubuntu-20.04
          - os: ubuntu-22.04
          - os: ubuntu-24.04
-          - os: macos-13
          - os: macos-14
          - os: macos-15
+          - os: macos-26

    runs-on: ${{matrix.os}}

@@ -470,8 +488,7 @@ jobs:
      fail-fast: false
      matrix:
        include:
-          - os: windows-2019
-          - os: windows-2022
+          - os: windows-latest

    runs-on: ${{matrix.os}}

@@ -519,8 +536,7 @@ jobs:
      fail-fast: false
      matrix:
        include:
-          - os: windows-2019
-          - os: windows-2022
+          - os: windows-latest

    runs-on: ${{matrix.os}}

@@ -586,8 +602,7 @@ jobs:
      fail-fast: false
      matrix:
        include:
-          - os: windows-2019
-          - os: windows-2022
+          - os: windows-latest

    runs-on: ${{matrix.os}}

--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -19,7 +19,7 @@ target_link_libraries(boost_variant2
    Boost::mp11
 )

-if(CMAKE_VERSION VERSION_GREATER 3.18 AND CMAKE_GENERATOR MATCHES "Visual Studio")
+if(NOT CMAKE_VERSION VERSION_LESS 3.19 AND CMAKE_GENERATOR MATCHES "Visual Studio")

  file(GLOB_RECURSE boost_variant2_IDEFILES CONFIGURE_DEPENDS include/*.hpp)
  source_group(TREE ${PROJECT_SOURCE_DIR}/include FILES ${boost_variant2_IDEFILES} PREFIX "Header Files")
--- a/doc/variant2/changelog.adoc
+++ b/doc/variant2/changelog.adoc
@@ -1,5 +1,5 @@
 ////
-Copyright 2019-2022 Peter Dimov
+Copyright 2019-2025 Peter Dimov
 Distributed under the Boost Software License, Version 1.0.
 https://www.boost.org/LICENSE_1_0.txt
 ////
@@ -8,6 +8,15 @@ https://www.boost.org/LICENSE_1_0.txt
 # Revision History
 :idprefix: changelog_

+## Changes in 1.90.0
+
+* More functions have been marked as `constexpr`, including `~variant`.
+  This didn't matter before {cpp}20, but does now.
+
+## Changes in 1.88.0
+
+* Use the smallest appropriate unsigned type for the index.
+
 ## Changes in 1.83.0

 * Added `uses_double_storage()`.
--- a/include/boost/variant2/variant.hpp
+++ b/include/boost/variant2/variant.hpp
@@ -30,6 +30,15 @@

 //

+// constexpr destructors
+#if defined(__cpp_constexpr_dynamic_alloc) && __cpp_constexpr_dynamic_alloc >= 201907L
+# define BOOST_VARIANT2_CXX20_CONSTEXPR constexpr
+#else
+# define BOOST_VARIANT2_CXX20_CONSTEXPR
+#endif
+
+//
+
 namespace boost
 {

@@ -84,7 +93,7 @@ struct monostate
 {
 };

-#if !BOOST_WORKAROUND(BOOST_MSVC, < 1950)
+#if !BOOST_WORKAROUND(BOOST_MSVC, < 1960)

 constexpr bool operator<(monostate, monostate) noexcept { return false; }
 constexpr bool operator>(monostate, monostate) noexcept { return false; }
@@ -549,24 +558,34 @@ template<class T1, class... T> union variant_storage_impl<mp11::mp_false, T1, T.
    T1 first_;
    variant_storage<T...> rest_;

+#if defined(BOOST_GCC) && (__GNUC__ >= 12)
+// false positive, see https://github.com/boostorg/variant2/issues/55
+# pragma GCC diagnostic push
+# pragma GCC diagnostic ignored "-Wmaybe-uninitialized"
+#endif
+
    template<class... A> constexpr variant_storage_impl( mp11::mp_size_t<0>, A&&... a ): first_( std::forward<A>(a)... )
    {
    }

+#if defined(BOOST_GCC) && (__GNUC__ >= 12)
+# pragma GCC diagnostic pop
+#endif
+
    template<std::size_t I, class... A> constexpr variant_storage_impl( mp11::mp_size_t<I>, A&&... a ): rest_( mp11::mp_size_t<I-1>(), std::forward<A>(a)... )
    {
    }

-    ~variant_storage_impl()
+    BOOST_VARIANT2_CXX20_CONSTEXPR ~variant_storage_impl()
    {
    }

-    template<class... A> void emplace( mp11::mp_size_t<0>, A&&... a )
+    template<class... A> BOOST_CXX14_CONSTEXPR void emplace( mp11::mp_size_t<0>, A&&... a )
    {
        ::new( &first_ ) T1( std::forward<A>(a)... );
    }

-    template<std::size_t I, class... A> void emplace( mp11::mp_size_t<I>, A&&... a )
+    template<std::size_t I, class... A> BOOST_CXX14_CONSTEXPR void emplace( mp11::mp_size_t<I>, A&&... a )
    {
        rest_.emplace( mp11::mp_size_t<I-1>(), std::forward<A>(a)... );
    }
@@ -606,22 +625,22 @@ template<class T0, class T1, class T2, class T3, class T4, class T5, class T6, c

    template<std::size_t I, class... A> constexpr variant_storage_impl( mp11::mp_size_t<I>, A&&... a ): rest_( mp11::mp_size_t<I-10>(), std::forward<A>(a)... ) {}

-    ~variant_storage_impl()
+    BOOST_VARIANT2_CXX20_CONSTEXPR ~variant_storage_impl()
    {
    }

-    template<class... A> void emplace( mp11::mp_size_t<0>, A&&... a ) { ::new( &t0_ ) T0( std::forward<A>(a)... ); }
-    template<class... A> void emplace( mp11::mp_size_t<1>, A&&... a ) { ::new( &t1_ ) T1( std::forward<A>(a)... ); }
-    template<class... A> void emplace( mp11::mp_size_t<2>, A&&... a ) { ::new( &t2_ ) T2( std::forward<A>(a)... ); }
-    template<class... A> void emplace( mp11::mp_size_t<3>, A&&... a ) { ::new( &t3_ ) T3( std::forward<A>(a)... ); }
-    template<class... A> void emplace( mp11::mp_size_t<4>, A&&... a ) { ::new( &t4_ ) T4( std::forward<A>(a)... ); }
-    template<class... A> void emplace( mp11::mp_size_t<5>, A&&... a ) { ::new( &t5_ ) T5( std::forward<A>(a)... ); }
-    template<class... A> void emplace( mp11::mp_size_t<6>, A&&... a ) { ::new( &t6_ ) T6( std::forward<A>(a)... ); }
-    template<class... A> void emplace( mp11::mp_size_t<7>, A&&... a ) { ::new( &t7_ ) T7( std::forward<A>(a)... ); }
-    template<class... A> void emplace( mp11::mp_size_t<8>, A&&... a ) { ::new( &t8_ ) T8( std::forward<A>(a)... ); }
-    template<class... A> void emplace( mp11::mp_size_t<9>, A&&... a ) { ::new( &t9_ ) T9( std::forward<A>(a)... ); }
+    template<class... A> BOOST_CXX14_CONSTEXPR void emplace( mp11::mp_size_t<0>, A&&... a ) { ::new( &t0_ ) T0( std::forward<A>(a)... ); }
+    template<class... A> BOOST_CXX14_CONSTEXPR void emplace( mp11::mp_size_t<1>, A&&... a ) { ::new( &t1_ ) T1( std::forward<A>(a)... ); }
+    template<class... A> BOOST_CXX14_CONSTEXPR void emplace( mp11::mp_size_t<2>, A&&... a ) { ::new( &t2_ ) T2( std::forward<A>(a)... ); }
+    template<class... A> BOOST_CXX14_CONSTEXPR void emplace( mp11::mp_size_t<3>, A&&... a ) { ::new( &t3_ ) T3( std::forward<A>(a)... ); }
+    template<class... A> BOOST_CXX14_CONSTEXPR void emplace( mp11::mp_size_t<4>, A&&... a ) { ::new( &t4_ ) T4( std::forward<A>(a)... ); }
+    template<class... A> BOOST_CXX14_CONSTEXPR void emplace( mp11::mp_size_t<5>, A&&... a ) { ::new( &t5_ ) T5( std::forward<A>(a)... ); }
+    template<class... A> BOOST_CXX14_CONSTEXPR void emplace( mp11::mp_size_t<6>, A&&... a ) { ::new( &t6_ ) T6( std::forward<A>(a)... ); }
+    template<class... A> BOOST_CXX14_CONSTEXPR void emplace( mp11::mp_size_t<7>, A&&... a ) { ::new( &t7_ ) T7( std::forward<A>(a)... ); }
+    template<class... A> BOOST_CXX14_CONSTEXPR void emplace( mp11::mp_size_t<8>, A&&... a ) { ::new( &t8_ ) T8( std::forward<A>(a)... ); }
+    template<class... A> BOOST_CXX14_CONSTEXPR void emplace( mp11::mp_size_t<9>, A&&... a ) { ::new( &t9_ ) T9( std::forward<A>(a)... ); }

-    template<std::size_t I, class... A> void emplace( mp11::mp_size_t<I>, A&&... a )
+    template<std::size_t I, class... A> BOOST_CXX14_CONSTEXPR void emplace( mp11::mp_size_t<I>, A&&... a )
    {
        rest_.emplace( mp11::mp_size_t<I-10>(), std::forward<A>(a)... );
    }
@@ -674,7 +693,7 @@ template<class T1, class... T> union variant_storage_impl<mp11::mp_true, T1, T..
    {
    }

-    template<class... A> void emplace_impl( mp11::mp_false, mp11::mp_size_t<0>, A&&... a )
+    template<class... A> BOOST_CXX14_CONSTEXPR void emplace_impl( mp11::mp_false, mp11::mp_size_t<0>, A&&... a )
    {
        ::new( &first_ ) T1( std::forward<A>(a)... );
    }
@@ -695,6 +714,7 @@ template<class T1, class... T> union variant_storage_impl<mp11::mp_true, T1, T..
 # pragma GCC diagnostic ignored "-Wuninitialized"
 #endif
 #endif
+
        *this = variant_storage_impl( mp11::mp_size_t<I>(), std::forward<A>(a)... );

 #if defined(BOOST_GCC) && (__GNUC__ >= 7)
@@ -742,16 +762,16 @@ template<class T0, class T1, class T2, class T3, class T4, class T5, class T6, c

    template<std::size_t I, class... A> constexpr variant_storage_impl( mp11::mp_size_t<I>, A&&... a ): rest_( mp11::mp_size_t<I-10>(), std::forward<A>(a)... ) {}

-    template<class... A> void emplace_impl( mp11::mp_false, mp11::mp_size_t<0>, A&&... a ) { ::new( &t0_ ) T0( std::forward<A>(a)... ); }
-    template<class... A> void emplace_impl( mp11::mp_false, mp11::mp_size_t<1>, A&&... a ) { ::new( &t1_ ) T1( std::forward<A>(a)... ); }
-    template<class... A> void emplace_impl( mp11::mp_false, mp11::mp_size_t<2>, A&&... a ) { ::new( &t2_ ) T2( std::forward<A>(a)... ); }
-    template<class... A> void emplace_impl( mp11::mp_false, mp11::mp_size_t<3>, A&&... a ) { ::new( &t3_ ) T3( std::forward<A>(a)... ); }
-    template<class... A> void emplace_impl( mp11::mp_false, mp11::mp_size_t<4>, A&&... a ) { ::new( &t4_ ) T4( std::forward<A>(a)... ); }
-    template<class... A> void emplace_impl( mp11::mp_false, mp11::mp_size_t<5>, A&&... a ) { ::new( &t5_ ) T5( std::forward<A>(a)... ); }
-    template<class... A> void emplace_impl( mp11::mp_false, mp11::mp_size_t<6>, A&&... a ) { ::new( &t6_ ) T6( std::forward<A>(a)... ); }
-    template<class... A> void emplace_impl( mp11::mp_false, mp11::mp_size_t<7>, A&&... a ) { ::new( &t7_ ) T7( std::forward<A>(a)... ); }
-    template<class... A> void emplace_impl( mp11::mp_false, mp11::mp_size_t<8>, A&&... a ) { ::new( &t8_ ) T8( std::forward<A>(a)... ); }
-    template<class... A> void emplace_impl( mp11::mp_false, mp11::mp_size_t<9>, A&&... a ) { ::new( &t9_ ) T9( std::forward<A>(a)... ); }
+    template<class... A> BOOST_CXX14_CONSTEXPR void emplace_impl( mp11::mp_false, mp11::mp_size_t<0>, A&&... a ) { ::new( &t0_ ) T0( std::forward<A>(a)... ); }
+    template<class... A> BOOST_CXX14_CONSTEXPR void emplace_impl( mp11::mp_false, mp11::mp_size_t<1>, A&&... a ) { ::new( &t1_ ) T1( std::forward<A>(a)... ); }
+    template<class... A> BOOST_CXX14_CONSTEXPR void emplace_impl( mp11::mp_false, mp11::mp_size_t<2>, A&&... a ) { ::new( &t2_ ) T2( std::forward<A>(a)... ); }
+    template<class... A> BOOST_CXX14_CONSTEXPR void emplace_impl( mp11::mp_false, mp11::mp_size_t<3>, A&&... a ) { ::new( &t3_ ) T3( std::forward<A>(a)... ); }
+    template<class... A> BOOST_CXX14_CONSTEXPR void emplace_impl( mp11::mp_false, mp11::mp_size_t<4>, A&&... a ) { ::new( &t4_ ) T4( std::forward<A>(a)... ); }
+    template<class... A> BOOST_CXX14_CONSTEXPR void emplace_impl( mp11::mp_false, mp11::mp_size_t<5>, A&&... a ) { ::new( &t5_ ) T5( std::forward<A>(a)... ); }
+    template<class... A> BOOST_CXX14_CONSTEXPR void emplace_impl( mp11::mp_false, mp11::mp_size_t<6>, A&&... a ) { ::new( &t6_ ) T6( std::forward<A>(a)... ); }
+    template<class... A> BOOST_CXX14_CONSTEXPR void emplace_impl( mp11::mp_false, mp11::mp_size_t<7>, A&&... a ) { ::new( &t7_ ) T7( std::forward<A>(a)... ); }
+    template<class... A> BOOST_CXX14_CONSTEXPR void emplace_impl( mp11::mp_false, mp11::mp_size_t<8>, A&&... a ) { ::new( &t8_ ) T8( std::forward<A>(a)... ); }
+    template<class... A> BOOST_CXX14_CONSTEXPR void emplace_impl( mp11::mp_false, mp11::mp_size_t<9>, A&&... a ) { ::new( &t9_ ) T9( std::forward<A>(a)... ); }

    template<std::size_t I, class... A> BOOST_CXX14_CONSTEXPR void emplace_impl( mp11::mp_false, mp11::mp_size_t<I>, A&&... a )
    {
@@ -890,7 +910,7 @@ template<class... T> struct variant_base_impl<true, true, T...>
    }

    // requires: ix_ == 0
-    template<class I, class... A> void _replace( I, A&&... a )
+    template<class I, class... A> BOOST_CXX14_CONSTEXPR void _replace( I, A&&... a )
    {
        ::new( &st_ ) variant_storage<none, T...>( mp11::mp_size_t<I::value + 1>(), std::forward<A>(a)... );

@@ -974,7 +994,7 @@ template<class... T> struct variant_base_impl<true, false, T...>
    }

    // requires: ix_ == 0
-    template<class I, class... A> void _replace( I, A&&... a )
+    template<class I, class... A> BOOST_CXX14_CONSTEXPR void _replace( I, A&&... a )
    {
        ::new( &st_[ 0 ] ) variant_storage<none, T...>( mp11::mp_size_t<I::value + 1>(), std::forward<A>(a)... );

@@ -1042,7 +1062,7 @@ template<class... T> struct variant_base_impl<false, true, T...>
    }

    // requires: ix_ == 0
-    template<class I, class... A> void _replace( I, A&&... a )
+    template<class I, class... A> BOOST_CXX14_CONSTEXPR void _replace( I, A&&... a )
    {
        ::new( &st_ ) variant_storage<none, T...>( mp11::mp_size_t<I::value + 1>(), std::forward<A>(a)... );

@@ -1059,14 +1079,25 @@ template<class... T> struct variant_base_impl<false, true, T...>
    {
        variant_base_impl * this_;

-        template<class I> void operator()( I ) const noexcept
+        template<class I> BOOST_CXX14_CONSTEXPR void operator()( I ) const noexcept
        {
            using U = mp11::mp_at<mp11::mp_list<none, T...>, I>;
+
+#if defined(BOOST_GCC) && (__GNUC__ >= 12)
+// false positive, see https://github.com/boostorg/variant2/issues/55
+# pragma GCC diagnostic push
+# pragma GCC diagnostic ignored "-Wmaybe-uninitialized"
+#endif
+
            this_->st_.get( I() ).~U();
+
+#if defined(BOOST_GCC) && (__GNUC__ >= 12)
+# pragma GCC diagnostic pop
+#endif
        }
    };

-    void _destroy() noexcept
+    BOOST_CXX14_CONSTEXPR void _destroy() noexcept
    {
        if( ix_ > 0 )
        {
@@ -1074,7 +1105,7 @@ template<class... T> struct variant_base_impl<false, true, T...>
        }
    }

-    ~variant_base_impl() noexcept
+    BOOST_VARIANT2_CXX20_CONSTEXPR ~variant_base_impl() noexcept
    {
        _destroy();
    }
@@ -1102,7 +1133,7 @@ template<class... T> struct variant_base_impl<false, true, T...>
        return st_.get( mp11::mp_size_t<I+1>() );
    }

-    template<std::size_t I, class... A> void emplace( A&&... a )
+    template<std::size_t I, class... A> BOOST_CXX14_CONSTEXPR void emplace( A&&... a )
    {
        std::size_t const J = I+1;

@@ -1110,8 +1141,18 @@ template<class... T> struct variant_base_impl<false, true, T...>

        static_assert( std::is_nothrow_move_constructible<U>::value, "Logic error: U must be nothrow move constructible" );

+#if defined(BOOST_GCC) && (__GNUC__ >= 12)
+// false positive, see https://github.com/boostorg/variant2/issues/55
+# pragma GCC diagnostic push
+# pragma GCC diagnostic ignored "-Wmaybe-uninitialized"
+#endif
+
        U tmp( std::forward<A>(a)... );

+#if defined(BOOST_GCC) && (__GNUC__ >= 12)
+# pragma GCC diagnostic pop
+#endif
+
        _destroy();

        st_.emplace( mp11::mp_size_t<J>(), std::move(tmp) );
@@ -1182,7 +1223,7 @@ template<class... T> struct variant_base_impl<false, false, T...>
 #endif

    // requires: ix_ == 0
-    template<class I, class... A> void _replace( I, A&&... a )
+    template<class I, class... A> BOOST_CXX14_CONSTEXPR void _replace( I, A&&... a )
    {
        ::new( &storage( 0 ) ) variant_storage<none, T...>( mp11::mp_size_t<I::value + 1>(), std::forward<A>(a)... );

@@ -1200,19 +1241,19 @@ template<class... T> struct variant_base_impl<false, false, T...>
        variant_base_impl * this_;
        unsigned i2_;

-        template<class I> void operator()( I ) const noexcept
+        template<class I> BOOST_CXX14_CONSTEXPR void operator()( I ) const noexcept
        {
            using U = mp11::mp_at<mp11::mp_list<none, T...>, I>;
            this_->storage( i2_ ).get( I() ).~U();
        }
    };

-    void _destroy() noexcept
+    BOOST_CXX14_CONSTEXPR void _destroy() noexcept
    {
        mp11::mp_with_index<1 + sizeof...(T)>( ix_ / 2, _destroy_L1{ this, static_cast<unsigned>( ix_ & 1 ) } );
    }

-    ~variant_base_impl() noexcept
+    BOOST_VARIANT2_CXX20_CONSTEXPR ~variant_base_impl() noexcept
    {
        _destroy();
    }
@@ -1242,7 +1283,7 @@ template<class... T> struct variant_base_impl<false, false, T...>
        return storage( ix_ & 1 ).get( mp11::mp_size_t<I+1>() );
    }

-    template<std::size_t I, class... A> void emplace( A&&... a )
+    template<std::size_t I, class... A> BOOST_CXX14_CONSTEXPR void emplace( A&&... a )
    {
        std::size_t const J = I+1;

@@ -1403,7 +1444,7 @@ private:
        variant_base * this_;
        variant_base const & r;

-        template<class I> void operator()( I i ) const
+        template<class I> BOOST_CXX14_CONSTEXPR void operator()( I i ) const
        {
            this_->_replace( i, r._get_impl( i ) );
        }
@@ -1411,7 +1452,7 @@ private:

 public:

-    variant_cc_base_impl( variant_cc_base_impl const& r )
+    BOOST_CXX14_CONSTEXPR variant_cc_base_impl( variant_cc_base_impl const& r )
        noexcept( mp11::mp_all<std::is_nothrow_copy_constructible<T>...>::value )
        : variant_base()
    {
@@ -1483,7 +1524,7 @@ private:
        variant_base * this_;
        variant_base const & r;

-        template<class I> void operator()( I i ) const
+        template<class I> BOOST_CXX14_CONSTEXPR void operator()( I i ) const
        {
            this_->template emplace<I::value>( r._get_impl( i ) );
        }
@@ -1557,7 +1598,7 @@ private:
        variant_base * this_;
        variant_base & r;

-        template<class I> void operator()( I i ) const
+        template<class I> BOOST_CXX14_CONSTEXPR void operator()( I i ) const
        {
            this_->_replace( i, std::move( r._get_impl( i ) ) );
        }
@@ -1565,7 +1606,7 @@ private:

 public:

-    variant_mc_base_impl( variant_mc_base_impl && r )
+    BOOST_CXX14_CONSTEXPR variant_mc_base_impl( variant_mc_base_impl && r )
        noexcept( mp11::mp_all<std::is_nothrow_move_constructible<T>...>::value )
    {
        mp11::mp_with_index<sizeof...(T)>( r.index(), L2{ this, r } );
@@ -1636,7 +1677,7 @@ private:
        variant_base * this_;
        variant_base & r;

-        template<class I> void operator()( I i ) const
+        template<class I> BOOST_CXX14_CONSTEXPR void operator()( I i ) const
        {
            this_->template emplace<I::value>( std::move( r._get_impl( i ) ) );
        }
@@ -1644,7 +1685,7 @@ private:

 public:

-    variant_ma_base_impl& operator=( variant_ma_base_impl && r )
+    BOOST_CXX14_CONSTEXPR variant_ma_base_impl& operator=( variant_ma_base_impl && r )
        noexcept( mp11::mp_all<std::is_nothrow_move_constructible<T>...>::value )
    {
        mp11::mp_with_index<sizeof...(T)>( r.index(), L4{ this, r } );
@@ -1680,7 +1721,7 @@ public:
        class Ud = typename std::decay<U>::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,

-#if BOOST_WORKAROUND(BOOST_MSVC, < 1950)
+#if BOOST_WORKAROUND(BOOST_MSVC, < 1960)

        class V = mp11::mp_apply_q< mp11::mp_bind_front<detail::resolve_overload_type, U&&>, variant >,

@@ -1790,7 +1831,7 @@ private:
        variant * this_;
        variant & r;

-        template<class I> void operator()( I i ) const
+        template<class I> BOOST_CXX14_CONSTEXPR void operator()( I i ) const
        {
            using std::swap;
            swap( this_->_get_impl( i ), r._get_impl( i ) );
@@ -1799,7 +1840,7 @@ private:

 public:

-    void swap( variant& r ) noexcept( mp11::mp_all<std::is_nothrow_move_constructible<T>..., detail::is_nothrow_swappable<T>...>::value )
+    BOOST_CXX14_CONSTEXPR void swap( variant& r ) noexcept( mp11::mp_all<std::is_nothrow_move_constructible<T>..., detail::is_nothrow_swappable<T>...>::value )
    {
        if( index() == r.index() )
        {
@@ -1826,7 +1867,7 @@ private:
        variant_base * this_;
        variant<U...> const & r;

-        template<class I> void operator()( I i ) const
+        template<class I> BOOST_CXX14_CONSTEXPR void operator()( I i ) const
        {
            using J = mp11::mp_find<mp11::mp_list<T...>, mp11::mp_at<mp11::mp_list<U...>, I>>;
            this_->_replace( J{}, r._get_impl( i ) );
@@ -1837,7 +1878,7 @@ public:

    template<class... U,
        class E2 = mp11::mp_if<mp11::mp_all<std::is_copy_constructible<U>..., mp11::mp_contains<mp11::mp_list<T...>, U>...>, void> >
-    variant( variant<U...> const& r )
+    BOOST_CXX14_CONSTEXPR variant( variant<U...> const& r )
        noexcept( mp11::mp_all<std::is_nothrow_copy_constructible<U>...>::value )
    {
        mp11::mp_with_index<sizeof...(U)>( r.index(), L6<U...>{ this, r } );
@@ -1850,7 +1891,7 @@ private:
        variant_base * this_;
        variant<U...> & r;

-        template<class I> void operator()( I i ) const
+        template<class I> BOOST_CXX14_CONSTEXPR void operator()( I i ) const
        {
            using J = mp11::mp_find<mp11::mp_list<T...>, mp11::mp_at<mp11::mp_list<U...>, I>>;
            this_->_replace( J{}, std::move( r._get_impl( i ) ) );
@@ -1861,7 +1902,7 @@ public:

    template<class... U,
        class E2 = mp11::mp_if<mp11::mp_all<std::is_move_constructible<U>..., mp11::mp_contains<mp11::mp_list<T...>, U>...>, void> >
-    variant( variant<U...> && r )
+    BOOST_CXX14_CONSTEXPR variant( variant<U...> && r )
        noexcept( mp11::mp_all<std::is_nothrow_move_constructible<U>...>::value )
    {
        mp11::mp_with_index<sizeof...(U)>( r.index(), L7<U...>{ this, r } );
@@ -1887,7 +1928,7 @@ private:
    {
        variant * this_;

-        template<class I> variant<U...> operator()( I i ) const
+        template<class I> BOOST_CXX14_CONSTEXPR variant<U...> operator()( I i ) const
        {
            using J = mp11::mp_find<mp11::mp_list<U...>, mp11::mp_at<mp11::mp_list<T...>, I>>;
            return this_->_subset_impl<U...>( J{}, this_->_get_impl( i ) );
@@ -1909,7 +1950,7 @@ private:
    {
        variant const * this_;

-        template<class I> variant<U...> operator()( I i ) const
+        template<class I> BOOST_CXX14_CONSTEXPR variant<U...> operator()( I i ) const
        {
            using J = mp11::mp_find<mp11::mp_list<U...>, mp11::mp_at<mp11::mp_list<T...>, I>>;
            return this_->_subset_impl<U...>( J{}, this_->_get_impl( i ) );
@@ -1931,7 +1972,7 @@ private:
    {
        variant * this_;

-        template<class I> variant<U...> operator()( I i ) const
+        template<class I> BOOST_CXX14_CONSTEXPR variant<U...> operator()( I i ) const
        {
            using J = mp11::mp_find<mp11::mp_list<U...>, mp11::mp_at<mp11::mp_list<T...>, I>>;
            return this_->_subset_impl<U...>( J{}, std::move( this_->_get_impl( i ) ) );
@@ -1957,7 +1998,7 @@ private:
    {
        variant const * this_;

-        template<class I> variant<U...> operator()( I i ) const
+        template<class I> BOOST_CXX14_CONSTEXPR variant<U...> operator()( I i ) const
        {
            using J = mp11::mp_find<mp11::mp_list<U...>, mp11::mp_at<mp11::mp_list<T...>, I>>;
            return this_->_subset_impl<U...>( J{}, std::move( this_->_get_impl( i ) ) );
@@ -2293,7 +2334,7 @@ template<class R = detail::deduced, class F, class V1, class V2, class... V> con
 // specialized algorithms
 template<class... T,
    class E = typename std::enable_if<mp11::mp_all<std::is_move_constructible<T>..., detail::is_swappable<T>...>::value>::type>
-void swap( variant<T...> & v, variant<T...> & w )
+BOOST_CXX14_CONSTEXPR void swap( variant<T...> & v, variant<T...> & w )
    noexcept( noexcept(v.swap(w)) )
 {
    v.swap( w );
--- a/test/CMakeLists.txt
+++ b/test/CMakeLists.txt
@@ -6,6 +6,6 @@ include(BoostTestJamfile OPTIONAL RESULT_VARIABLE HAVE_BOOST_TEST)

 if(HAVE_BOOST_TEST)

-boost_test_jamfile(FILE Jamfile LINK_LIBRARIES Boost::variant2 Boost::core Boost::container_hash)
+boost_test_jamfile(FILE Jamfile LINK_LIBRARIES Boost::variant2 Boost::core Boost::container_hash Boost::system)

 endif()
--- a/test/Jamfile
+++ b/test/Jamfile
@@ -131,7 +131,13 @@ run variant_visit_by_index.cpp ;
 run variant_ostream_insert.cpp ;
 run is_output_streamable.cpp ;

-local JSON = <library>/boost/json//boost_json/<warnings>off "<toolset>msvc-14.0:<build>no" "<toolset>msvc-14.2:<cxxflags>-wd5104" "<undefined-sanitizer>norecover:<link>static" ;
+local JSON =
+    <library>/boost/json//boost_json/<warnings>off
+    "<toolset>msvc-14.0:<build>no"
+    "<toolset>msvc-14.2:<cxxflags>-wd5104"
+    "<undefined-sanitizer>norecover:<link>static"
+    "<toolset>gcc-4.9:<build>no"
+    ;

 run variant_json_value_from.cpp : : : $(JSON) ;
 run variant_json_value_to.cpp : : : $(JSON) ;
@@ -157,3 +163,21 @@ for local list-size in $(list-sizes)
 {
    run variant_index_type.cpp : : : $(index-type-reqs) <define>LIST_SIZE=$(list-size) : variant_index_type_$(list-size) ;
 }
+
+compile variant_default_construct_cx_2.cpp ;
+compile variant_default_construct_cx_3.cpp ;
+compile variant_default_construct_cx_4.cpp ;
+compile variant_default_construct_cx_5.cpp ;
+
+compile variant_value_construct_cx_2.cpp ;
+compile variant_value_construct_cx_3.cpp ;
+compile variant_value_construct_cx_4.cpp ;
+
+# GCC 12+ false positive -Wmaybe-uninitialized with non-trivially-copyable types
+run variant_issue_55.cpp
+  : : :
+    <library>/boost/system//boost_system
+
+    # clang-cl 32 bit fails with an assertion in mp_with_index, likely due to a codegen bug
+    "<toolset>clang-win,<address-model>32:<build>no"
+  ;
--- a/test/variant_copy_assign_throw.cpp
+++ b/test/variant_copy_assign_throw.cpp
@@ -45,7 +45,7 @@ void test()
    variant<Y1, Y2> v1( in_place_type_t<Y1>{} );
    variant<Y1, Y2> v2( in_place_type_t<Y2>{} );

-    BOOST_TEST_THROWS( v1 = v2, std::runtime_error )
+    BOOST_TEST_THROWS( v1 = v2, std::runtime_error );
 }

 int main()
--- a/test/variant_default_construct_cx_2.cpp
+++ b/test/variant_default_construct_cx_2.cpp
@@ -0,0 +1,32 @@
+// Copyright 2025 Peter Dimov
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/variant2/variant.hpp>
+#include <boost/config/pragma_message.hpp>
+
+#if !defined(__cpp_constexpr_dynamic_alloc) || __cpp_constexpr_dynamic_alloc < 201907L
+
+BOOST_PRAGMA_MESSAGE("Skipping constexpr destructor test because __cpp_constexpr_dynamic_alloc < 201907L")
+int main() {}
+
+#else
+
+using namespace boost::variant2;
+
+#define STATIC_ASSERT(...) static_assert(__VA_ARGS__, #__VA_ARGS__)
+
+struct X
+{
+    constexpr ~X() {}
+};
+
+int main()
+{
+    constexpr variant<int, X> v;
+
+    STATIC_ASSERT( v.index() == 0 );
+    STATIC_ASSERT( get<0>(v) == 0 );
+}
+
+#endif
--- a/test/variant_default_construct_cx_3.cpp
+++ b/test/variant_default_construct_cx_3.cpp
@@ -0,0 +1,37 @@
+// Copyright 2025 Peter Dimov
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/variant2/variant.hpp>
+#include <boost/config/pragma_message.hpp>
+
+#if !defined(__cpp_constexpr_dynamic_alloc) || __cpp_constexpr_dynamic_alloc < 201907L
+
+BOOST_PRAGMA_MESSAGE("Skipping constexpr destructor test because __cpp_constexpr_dynamic_alloc < 201907L")
+int main() {}
+
+#elif defined(BOOST_CLANG) && BOOST_CLANG_VERSION < 180000
+
+BOOST_PRAGMA_MESSAGE("Skipping constexpr destructor test because BOOST_CLANG_VERSION < 180000")
+int main() {}
+
+#else
+
+using namespace boost::variant2;
+
+#define STATIC_ASSERT(...) static_assert(__VA_ARGS__, #__VA_ARGS__)
+
+struct X
+{
+	~X() {}
+};
+
+int main()
+{
+    constexpr variant<int, X> v;
+
+    STATIC_ASSERT( v.index() == 0 );
+    STATIC_ASSERT( get<0>(v) == 0 );
+}
+
+#endif
--- a/test/variant_default_construct_cx_4.cpp
+++ b/test/variant_default_construct_cx_4.cpp
@@ -0,0 +1,33 @@
+// Copyright 2025 Peter Dimov
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/variant2/variant.hpp>
+#include <boost/config/pragma_message.hpp>
+#include <string>
+
+#if !defined(__cpp_constexpr_dynamic_alloc) || __cpp_constexpr_dynamic_alloc < 201907L
+
+BOOST_PRAGMA_MESSAGE("Skipping constexpr destructor test because __cpp_constexpr_dynamic_alloc < 201907L")
+int main() {}
+
+#elif defined(BOOST_CLANG) && BOOST_CLANG_VERSION < 180000
+
+BOOST_PRAGMA_MESSAGE("Skipping constexpr destructor test because BOOST_CLANG_VERSION < 180000")
+int main() {}
+
+#else
+
+using namespace boost::variant2;
+
+#define STATIC_ASSERT(...) static_assert(__VA_ARGS__, #__VA_ARGS__)
+
+int main()
+{
+    constexpr variant<int, std::string> v;
+
+    STATIC_ASSERT( v.index() == 0 );
+    STATIC_ASSERT( get<0>(v) == 0 );
+}
+
+#endif
--- a/test/variant_default_construct_cx_5.cpp
+++ b/test/variant_default_construct_cx_5.cpp
@@ -0,0 +1,49 @@
+// Copyright 2025 Peter Dimov
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/variant2/variant.hpp>
+#include <boost/config/pragma_message.hpp>
+
+#if !defined(__cpp_constexpr_dynamic_alloc) || __cpp_constexpr_dynamic_alloc < 201907L
+
+BOOST_PRAGMA_MESSAGE("Skipping constexpr destructor test because __cpp_constexpr_dynamic_alloc < 201907L")
+int main() {}
+
+#elif defined(BOOST_MSVC) && BOOST_MSVC < 1960
+
+BOOST_PRAGMA_MESSAGE("Skipping constexpr destructor test because BOOST_MSVC < 1960")
+int main() {}
+
+#elif defined(BOOST_CLANG) && BOOST_CLANG_VERSION < 180000
+
+BOOST_PRAGMA_MESSAGE("Skipping constexpr destructor test because BOOST_CLANG_VERSION < 180000")
+int main() {}
+
+#else
+
+using namespace boost::variant2;
+
+#define STATIC_ASSERT(...) static_assert(__VA_ARGS__, #__VA_ARGS__)
+
+struct X
+{
+};
+
+struct Y
+{
+    constexpr ~Y() {}
+};
+
+struct Z
+{
+    ~Z() {}
+};
+
+int main()
+{
+    constexpr variant<X, Y, Z> v;
+    STATIC_ASSERT( v.index() == 0 );
+}
+
+#endif
--- a/test/variant_issue_55.cpp
+++ b/test/variant_issue_55.cpp
@@ -0,0 +1,194 @@
+// Copyright 2025 Peter Dimov
+// Copyright 2025 Vinnie Falco
+//
+// Distributed under the Boost Software License, Version 1.0.
+//
+// See accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt
+
+// GCC 12+ -Wmaybe-uninitialized false positive tests
+// https://github.com/boostorg/variant2/issues/55
+//
+// GCC 12+'s improved dataflow analysis sees code paths for all alternatives
+// in mp_with_index and warns that members may be uninitialized, even though
+// the variant's discriminator guarantees only initialized alternatives are
+// accessed.
+
+#include <boost/system/result.hpp>
+#include <boost/core/lightweight_test.hpp>
+#include <boost/config.hpp>
+#include <exception>
+#include <string>
+
+// Check for C++17 std::optional support
+#if BOOST_CXX_VERSION >= 201703L
+# include <optional>
+# define BOOST_VARIANT2_TEST_HAS_OPTIONAL 1
+#endif
+
+// Check for C++20 coroutine support
+#if defined(__cpp_impl_coroutine) && __cpp_impl_coroutine >= 201902L
+# include <coroutine>
+# define BOOST_VARIANT2_TEST_HAS_CORO 1
+#endif
+
+using result_void = boost::system::result<void, std::exception_ptr>;
+using result_string = boost::system::result<std::string, std::exception_ptr>;
+
+void testGccUninitialized()
+{
+    // Test 1: Simple copy construction
+    {
+        result_void r1;
+        result_void r2(r1);
+        (void)r2;
+    }
+
+    // Test 2: Copy assignment
+    {
+        result_void r1;
+        result_void r2;
+        r2 = r1;
+        (void)r2;
+    }
+
+#ifdef BOOST_VARIANT2_TEST_HAS_OPTIONAL
+    // Test 3: std::optional assignment (matches spawn pattern)
+    {
+        std::optional<result_void> opt;
+        opt = result_void{};
+        (void)opt;
+    }
+#endif
+
+    // Test 4: Pass to function via copy
+    {
+        auto fn = [](result_void r) { (void)r; };
+        fn(result_void{});
+    }
+
+#ifdef BOOST_VARIANT2_TEST_HAS_OPTIONAL
+    // Test 5: Lambda capture + optional (closest to spawn)
+    {
+        auto fn = [](result_void r) {
+            std::optional<result_void> opt;
+            opt = r;
+            return opt.has_value();
+        };
+        (void)fn(result_void{});
+    }
+#endif
+
+    // Test 6: Non-void result with string (triggers string warning)
+    {
+        result_string r1;
+        result_string r2(r1);
+        (void)r2;
+    }
+
+    // Test 7: Assign exception to result holding value
+    {
+        result_string r1{"hello"};
+        r1 = std::make_exception_ptr(std::runtime_error("test"));
+        (void)r1;
+    }
+
+#ifdef BOOST_VARIANT2_TEST_HAS_OPTIONAL
+    // Test 8: Optional with string result
+    {
+        std::optional<result_string> opt;
+        opt = result_string{};
+        (void)opt;
+    }
+#endif
+
+#ifdef BOOST_VARIANT2_TEST_HAS_CORO
+    // Minimal fire-and-forget coroutine for testing
+    struct fire_and_forget
+    {
+        struct promise_type
+        {
+            fire_and_forget get_return_object() { return {}; }
+            std::suspend_never initial_suspend() noexcept { return {}; }
+            std::suspend_never final_suspend() noexcept { return {}; }
+            void return_void() {}
+            void unhandled_exception() { std::terminate(); }
+        };
+    };
+
+    // Test 9: Coroutine returning result (mimics spawn)
+    {
+        auto coro = []() -> fire_and_forget {
+            result_void r{};
+            (void)r;
+            co_return;
+        };
+        coro();
+    }
+
+    // Test 10: Coroutine with handler call (closest to actual spawn)
+    {
+        std::optional<result_void> received;
+        auto handler = [&](result_void r) {
+            received = r;
+        };
+        auto coro = [&]() -> fire_and_forget {
+            handler(result_void{});
+            co_return;
+        };
+        coro();
+        (void)received;
+    }
+
+    // Test 11: Coroutine with try/catch like spawn
+    {
+        std::optional<result_void> received;
+        auto handler = [&](result_void r) {
+            received = r;
+        };
+        auto coro = [&]() -> fire_and_forget {
+            try
+            {
+                handler(result_void{});
+            }
+            catch (...)
+            {
+                handler(result_void{std::current_exception()});
+            }
+            co_return;
+        };
+        coro();
+        (void)received;
+    }
+
+    // Test 12: Coroutine with string result
+    {
+        std::optional<result_string> received;
+        auto handler = [&](result_string r) {
+            received = r;
+        };
+        auto coro = [&]() -> fire_and_forget {
+            try
+            {
+                handler(result_string{"test"});
+            }
+            catch (...)
+            {
+                handler(result_string{std::current_exception()});
+            }
+            co_return;
+        };
+        coro();
+        (void)received;
+    }
+#endif
+}
+
+int main()
+{
+    boost::core::lwt_init();
+
+    testGccUninitialized();
+
+    return boost::report_errors();
+}
--- a/test/variant_move_assign_throw.cpp
+++ b/test/variant_move_assign_throw.cpp
@@ -45,7 +45,7 @@ void test()
    variant<Y1, Y2> v1( in_place_type_t<Y1>{} );
    variant<Y1, Y2> v2( in_place_type_t<Y2>{} );

-    BOOST_TEST_THROWS( v1 = std::move( v2 ), std::runtime_error )
+    BOOST_TEST_THROWS( v1 = std::move( v2 ), std::runtime_error );
 }

 int main()
--- a/test/variant_value_construct_cx_2.cpp
+++ b/test/variant_value_construct_cx_2.cpp
@@ -0,0 +1,32 @@
+// Copyright 2025 Peter Dimov
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/variant2/variant.hpp>
+#include <boost/config/pragma_message.hpp>
+
+#if !defined(__cpp_constexpr_dynamic_alloc) || __cpp_constexpr_dynamic_alloc < 201907L
+
+BOOST_PRAGMA_MESSAGE("Skipping test because __cpp_constexpr_dynamic_alloc < 201907L")
+int main() {}
+
+#else
+
+using namespace boost::variant2;
+
+#define STATIC_ASSERT(...) static_assert(__VA_ARGS__, #__VA_ARGS__)
+
+struct X
+{
+    constexpr ~X() {}
+};
+
+int main()
+{
+    constexpr variant<X, int> v( 5 );
+
+    STATIC_ASSERT( v.index() == 1 );
+    STATIC_ASSERT( get<1>(v) == 5 );
+}
+
+#endif
--- a/test/variant_value_construct_cx_3.cpp
+++ b/test/variant_value_construct_cx_3.cpp
@@ -0,0 +1,37 @@
+// Copyright 2025 Peter Dimov
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/variant2/variant.hpp>
+#include <boost/config/pragma_message.hpp>
+
+#if !defined(__cpp_constexpr_dynamic_alloc) || __cpp_constexpr_dynamic_alloc < 201907L
+
+BOOST_PRAGMA_MESSAGE("Skipping test because __cpp_constexpr_dynamic_alloc < 201907L")
+int main() {}
+
+#elif defined(BOOST_CLANG) && BOOST_CLANG_VERSION < 180000
+
+BOOST_PRAGMA_MESSAGE("Skipping test because BOOST_CLANG_VERSION < 180000")
+int main() {}
+
+#else
+
+using namespace boost::variant2;
+
+#define STATIC_ASSERT(...) static_assert(__VA_ARGS__, #__VA_ARGS__)
+
+struct X
+{
+	~X() {}
+};
+
+int main()
+{
+    constexpr variant<X, int> v( 5 );
+
+    STATIC_ASSERT( v.index() == 1 );
+    STATIC_ASSERT( get<1>(v) == 5 );
+}
+
+#endif
--- a/test/variant_value_construct_cx_4.cpp
+++ b/test/variant_value_construct_cx_4.cpp
@@ -0,0 +1,56 @@
+// Copyright 2025 Peter Dimov
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/variant2/variant.hpp>
+#include <boost/config/pragma_message.hpp>
+
+#if !defined(__cpp_constexpr_dynamic_alloc) || __cpp_constexpr_dynamic_alloc < 201907L
+
+BOOST_PRAGMA_MESSAGE("Skipping test because __cpp_constexpr_dynamic_alloc < 201907L")
+int main() {}
+
+#elif defined(BOOST_MSVC) && BOOST_MSVC < 1960
+
+BOOST_PRAGMA_MESSAGE("Skipping test because BOOST_MSVC < 1960")
+int main() {}
+
+#elif defined(BOOST_CLANG) && BOOST_CLANG_VERSION < 180000
+
+BOOST_PRAGMA_MESSAGE("Skipping test because BOOST_CLANG_VERSION < 180000")
+int main() {}
+
+#else
+
+using namespace boost::variant2;
+
+#define STATIC_ASSERT(...) static_assert(__VA_ARGS__, #__VA_ARGS__)
+
+struct X
+{
+};
+
+struct Y
+{
+    constexpr ~Y() {}
+};
+
+struct Z
+{
+    ~Z() {}
+};
+
+int main()
+{
+    {
+        constexpr variant<X, Y, Z> v( X{} );
+        STATIC_ASSERT( v.index() == 0 );
+    }
+
+    {
+        constexpr variant<X, Y, Z> v( Y{} );
+        STATIC_ASSERT( v.index() == 1 );
+    }
+}
+
+#endif
Author	SHA1	Message	Date
Peter Dimov	155ed414ab	Disable variant_issue_55.cpp on clang-cl 32 bit	2026-01-02 12:29:11 +02:00
Peter Dimov	e6b336ec68	Call boost::core::lwt_init() in variant_issue_55.cpp, because it doesn't invoke any BOOST_TEST macros and clang-win 32 bit hangs w/ assertion	2026-01-02 02:51:46 +02:00
Peter Dimov	799a69eccc	Disable -Wmaybe-uninitialized false positive. Refs #55 .	2026-01-02 02:21:29 +02:00
Peter Dimov	74f6f0cd96	Fix issue link; fix __cplusplus check	2026-01-01 22:28:25 +02:00
Peter Dimov	fc786d39b3	Rename variant_gcc_false_positive.cpp	2026-01-01 22:21:34 +02:00
Vinnie Falco	382cf33824	Add test for GCC 12+ -Wmaybe-uninitialized false positive Add variant_gcc_false_positive.cpp to reproduce GCC 12+ spurious -Wmaybe-uninitialized warnings when copying/moving variant containing non-trivially-copyable types like std::exception_ptr and std::string. Tests use boost::system::result which internally uses variant2, and include coroutine-based tests when C++20 coroutine support is available. The test uses -O3 optimization to trigger the aggressive inlining that exposes the false positive where GCC's dataflow analysis cannot prove the discriminator ensures only initialized alternatives are accessed. See https://github.com/boostorg/variant2/issues/33	2026-01-01 22:16:48 +02:00
Peter Dimov	4632862a4b	msvc-14.5 still needs two more workarounds	2026-01-01 20:04:58 +02:00
Peter Dimov	48ed0a243f	Update .drone.jsonnet	2026-01-01 18:45:22 +02:00
Peter Dimov	936a1a95b5	msvc-14.5 still needs the workarounds. sad!	2026-01-01 18:15:20 +02:00
Peter Dimov	fcdaadb0f5	Update .drone.jsonnet	2026-01-01 18:05:28 +02:00
Peter Dimov	540354878c	Disable Boost.JSON tests on gcc-4.9	2026-01-01 17:28:41 +02:00
Peter Dimov	2a5aa1c7ad	Update ci.yml	2026-01-01 15:52:54 +02:00
Peter Dimov	f267609ad6	Update revision history	2025-10-22 21:03:21 +03:00
Peter Dimov	edf1c7925b	Correct CMake version check; VERSION_GREATER 3.18 is true for 3.18.1	2025-10-19 21:07:20 +03:00
Peter Dimov	b9d0499a8f	BOOST_TEST_THROWS requires a semicolon after https://github.com/boostorg/core/pull/205	2025-10-18 20:23:49 +03:00
Peter Dimov	a63b03286e	Add test/variant_value_construct_cx_2, 3, 4. Refs #53 .	2025-10-18 08:24:39 +03:00
Peter Dimov	5661f2ba15	Disable variant_default_construct_cx_4, _5 on Clang < 18 as well	2025-10-18 03:12:52 +03:00
Peter Dimov	9d913eb1a0	Disable variant_default_construct_cx_3 on Clang < 18; earlier versions complain that the type isn't literal.	2025-10-18 03:01:19 +03:00
Peter Dimov	43377dcada	Add test/variant_default_construct_cx_5. Refs #53 .	2025-10-18 02:49:29 +03:00
Peter Dimov	2af2d02fce	Add test/variant_default_construct_cx_4. Refs #53 .	2025-10-18 02:41:28 +03:00
Peter Dimov	b2109dee2a	Add test/variant_default_construct_cx_3. Refs #53 .	2025-10-18 02:37:21 +03:00
Peter Dimov	df001efb54	Add test/variant_default_construct_cx_2. Refs #53 .	2025-10-18 02:29:52 +03:00
Peter Dimov	e708866c65	Add more constexpr. Refs #53 .	2025-10-17 22:24:26 +03:00
Peter Dimov	28d23c14f6	Update ci.yml	2025-10-17 21:21:02 +03:00
Peter Dimov	8caa1a3484	Update revision history	2025-01-15 19:44:18 +02:00