CMake: Support upcoming C++26 language level

Help/prop_gbl/CMAKE_CUDA_KNOWN_FEATURES.rst

@@ -36,4 +36,9 @@ The features known to this version of CMake are:
 
   Compiler mode is at least CUDA/C++ 23.
 
+``cuda_std_26``
+  .. versionadded:: 3.25
+
+  Compiler mode is at least CUDA/C++ 26.
+
 .. include:: CMAKE_LANG_STD_FLAGS.txt

Help/prop_gbl/CMAKE_CXX_KNOWN_FEATURES.rst

@@ -46,6 +46,11 @@ but it does not necessarily imply complete conformance to that standard.
 
   Compiler mode is at least C++ 23.
 
+``cxx_std_26``
+  .. versionadded:: 3.25
+
+  Compiler mode is at least C++ 26.
+
 .. include:: CMAKE_LANG_STD_FLAGS.txt
 
 Low level individual compile features

Help/prop_tgt/CUDA_STANDARD.rst

@@ -39,6 +39,12 @@ Supported values are:
 
   CUDA C++23
 
+``26``
+  .. versionadded:: 3.25
+
+  CUDA C++26. CMake 3.25 and later *recognize* ``26`` as a valid value,
+  no version has support for any compiler.
+
 If the value requested does not result in a compile flag being added for
 the compiler in use, a previous standard flag will be added instead.  This
 means that using:

Help/prop_tgt/CXX_STANDARD.rst

@@ -37,6 +37,12 @@ Supported values are:
 
   C++23
 
+``26``
+  .. versionadded:: 3.25
+
+  C++26. CMake 3.25 and later *recognize* ``26`` as a valid value,
+  no version has support for any compiler.
+
 If the value requested does not result in a compile flag being added for
 the compiler in use, a previous standard flag will be added instead.  This
 means that using:

Help/prop_tgt/HIP_STANDARD.rst

@@ -25,6 +25,12 @@ Supported values are:
 ``23``
   HIP C++23
 
+``26``
+  .. versionadded:: 3.25
+
+  HIP C++26. CMake 3.25 and later *recognize* ``26`` as a valid value,
+  no version has support for any compiler.
+
 If the value requested does not result in a compile flag being added for
 the compiler in use, a previous standard flag will be added instead.  This
 means that using:

Help/prop_tgt/OBJCXX_STANDARD.rst

@@ -31,6 +31,12 @@ Supported values are:
 
   Objective C++23
 
+``26``
+  .. versionadded:: 3.25
+
+  Objective C++26. CMake 3.25 and later *recognize* ``26`` as a valid value,
+  no version has support for any compiler.
+
 If the value requested does not result in a compile flag being added for
 the compiler in use, a previous standard flag will be added instead.  This
 means that using:

Help/release/dev/cxx_std_26.rst

@@ -0,0 +1,8 @@
+cxx_std_26
+----------
+
+* C++26 compiler modes may now be specified via the :prop_tgt:`CXX_STANDARD`,
+  :prop_tgt:`CUDA_STANDARD`, :prop_tgt:`HIP_STANDARD`, or
+  :prop_tgt:`OBJCXX_STANDARD` target properties,
+  or via the :manual:`Compile Features <cmake-compile-features(7)>`
+  functionality's ``cxx_std_26`` meta-feature.

Modules/CMakeDetermineCompileFeatures.cmake

@@ -63,6 +63,7 @@ function(cmake_determine_compile_features lang)
     set(CMAKE_CXX17_COMPILE_FEATURES)
     set(CMAKE_CXX20_COMPILE_FEATURES)
     set(CMAKE_CXX23_COMPILE_FEATURES)
+    set(CMAKE_CXX26_COMPILE_FEATURES)
 
     include("${CMAKE_ROOT}/Modules/Internal/FeatureTesting.cmake")
 
@@ -73,6 +74,9 @@ function(cmake_determine_compile_features lang)
       return()
     endif()
 
+    if (CMAKE_CXX23_COMPILE_FEATURES AND CMAKE_CXX26_COMPILE_FEATURES)
+      list(REMOVE_ITEM CMAKE_CXX26_COMPILE_FEATURES ${CMAKE_CXX23_COMPILE_FEATURES})
+    endif()
     if (CMAKE_CXX20_COMPILE_FEATURES AND CMAKE_CXX23_COMPILE_FEATURES)
       list(REMOVE_ITEM CMAKE_CXX23_COMPILE_FEATURES ${CMAKE_CXX20_COMPILE_FEATURES})
     endif()
@@ -97,6 +101,7 @@ function(cmake_determine_compile_features lang)
         ${CMAKE_CXX17_COMPILE_FEATURES}
         ${CMAKE_CXX20_COMPILE_FEATURES}
         ${CMAKE_CXX23_COMPILE_FEATURES}
+        ${CMAKE_CXX26_COMPILE_FEATURES}
       )
     endif()
 
@@ -107,6 +112,7 @@ function(cmake_determine_compile_features lang)
     set(CMAKE_CXX17_COMPILE_FEATURES ${CMAKE_CXX17_COMPILE_FEATURES} PARENT_SCOPE)
     set(CMAKE_CXX20_COMPILE_FEATURES ${CMAKE_CXX20_COMPILE_FEATURES} PARENT_SCOPE)
     set(CMAKE_CXX23_COMPILE_FEATURES ${CMAKE_CXX23_COMPILE_FEATURES} PARENT_SCOPE)
+    set(CMAKE_CXX26_COMPILE_FEATURES ${CMAKE_CXX26_COMPILE_FEATURES} PARENT_SCOPE)
 
     message(CHECK_PASS "done")
 
@@ -119,6 +125,7 @@ function(cmake_determine_compile_features lang)
     set(CMAKE_CUDA17_COMPILE_FEATURES)
     set(CMAKE_CUDA20_COMPILE_FEATURES)
     set(CMAKE_CUDA23_COMPILE_FEATURES)
+    set(CMAKE_CUDA26_COMPILE_FEATURES)
 
     include("${CMAKE_ROOT}/Modules/Internal/FeatureTesting.cmake")
 
@@ -129,6 +136,9 @@ function(cmake_determine_compile_features lang)
       return()
     endif()
 
+    if (CMAKE_CUDA23_COMPILE_FEATURES AND CMAKE_CUDA26_COMPILE_FEATURES)
+      list(REMOVE_ITEM CMAKE_CUDA26_COMPILE_FEATURES ${CMAKE_CUDA23_COMPILE_FEATURES})
+    endif()
     if (CMAKE_CUDA20_COMPILE_FEATURES AND CMAKE_CUDA23_COMPILE_FEATURES)
       list(REMOVE_ITEM CMAKE_CUDA23_COMPILE_FEATURES ${CMAKE_CUDA20_COMPILE_FEATURES})
     endif()
@@ -153,6 +163,7 @@ function(cmake_determine_compile_features lang)
         ${CMAKE_CUDA17_COMPILE_FEATURES}
         ${CMAKE_CUDA20_COMPILE_FEATURES}
         ${CMAKE_CUDA23_COMPILE_FEATURES}
+        ${CMAKE_CUDA26_COMPILE_FEATURES}
       )
     endif()
 
@@ -163,6 +174,7 @@ function(cmake_determine_compile_features lang)
     set(CMAKE_CUDA17_COMPILE_FEATURES ${CMAKE_CUDA17_COMPILE_FEATURES} PARENT_SCOPE)
     set(CMAKE_CUDA20_COMPILE_FEATURES ${CMAKE_CUDA20_COMPILE_FEATURES} PARENT_SCOPE)
     set(CMAKE_CUDA23_COMPILE_FEATURES ${CMAKE_CUDA23_COMPILE_FEATURES} PARENT_SCOPE)
+    set(CMAKE_CUDA26_COMPILE_FEATURES ${CMAKE_CUDA26_COMPILE_FEATURES} PARENT_SCOPE)
 
     message(CHECK_PASS "done")
 
@@ -175,6 +187,8 @@ function(cmake_determine_compile_features lang)
     set(CMAKE_HIP17_COMPILE_FEATURES)
     set(CMAKE_HIP20_COMPILE_FEATURES)
     set(CMAKE_HIP23_COMPILE_FEATURES)
+    set(CMAKE_HIP26_COMPILE_FEATURES)
+
 
     include("${CMAKE_ROOT}/Modules/Internal/FeatureTesting.cmake")
 
@@ -185,6 +199,9 @@ function(cmake_determine_compile_features lang)
       return()
     endif()
 
+    if (CMAKE_HIP23_COMPILE_FEATURES AND CMAKE_HIP26_COMPILE_FEATURES)
+      list(REMOVE_ITEM CMAKE_HIP26_COMPILE_FEATURES ${CMAKE_HIP23_COMPILE_FEATURES})
+    endif()
     if (CMAKE_HIP20_COMPILE_FEATURES AND CMAKE_HIP23_COMPILE_FEATURES)
       list(REMOVE_ITEM CMAKE_HIP23_COMPILE_FEATURES ${CMAKE_HIP20_COMPILE_FEATURES})
     endif()
@@ -209,6 +226,7 @@ function(cmake_determine_compile_features lang)
         ${CMAKE_HIP17_COMPILE_FEATURES}
         ${CMAKE_HIP20_COMPILE_FEATURES}
         ${CMAKE_HIP23_COMPILE_FEATURES}
+        ${CMAKE_HIP26_COMPILE_FEATURES}
       )
     endif()
 
@@ -219,6 +237,7 @@ function(cmake_determine_compile_features lang)
     set(CMAKE_HIP17_COMPILE_FEATURES ${CMAKE_HIP17_COMPILE_FEATURES} PARENT_SCOPE)
     set(CMAKE_HIP20_COMPILE_FEATURES ${CMAKE_HIP20_COMPILE_FEATURES} PARENT_SCOPE)
     set(CMAKE_HIP23_COMPILE_FEATURES ${CMAKE_HIP23_COMPILE_FEATURES} PARENT_SCOPE)
+    set(CMAKE_HIP26_COMPILE_FEATURES ${CMAKE_HIP26_COMPILE_FEATURES} PARENT_SCOPE)
 
     message(CHECK_PASS "done")
 

Modules/Compiler/Clang.cmake

@@ -255,6 +255,7 @@ macro(__compiler_clang_cxx_standards lang)
         cxx_std_17
         cxx_std_20
         cxx_std_23
+        cxx_std_26
         )
       _record_compiler_features(${lang} "" CMAKE_${lang}_COMPILE_FEATURES)
     endmacro()

Modules/Compiler/MSVC-CXX.cmake

@@ -72,6 +72,7 @@ elseif (CMAKE_CXX_COMPILER_VERSION VERSION_GREATER_EQUAL 16.0)
       cxx_std_17
       cxx_std_20
       cxx_std_23
+      cxx_std_26
       )
     _record_compiler_features(CXX "" CMAKE_CXX_COMPILE_FEATURES)
   endmacro()

Source/cmStandardLevelResolver.cxx

@@ -378,25 +378,29 @@ std::unordered_map<std::string, StandardLevelComputer>
         "C", std::vector<int>{ 90, 99, 11, 17, 23 },
         std::vector<std::string>{ "90", "99", "11", "17", "23" } } },
     { "CXX",
-      StandardLevelComputer{
-        "CXX", std::vector<int>{ 98, 11, 14, 17, 20, 23 },
-        std::vector<std::string>{ "98", "11", "14", "17", "20", "23" } } },
+      StandardLevelComputer{ "CXX",
+                             std::vector<int>{ 98, 11, 14, 17, 20, 23, 26 },
+                             std::vector<std::string>{ "98", "11", "14", "17",
+                                                       "20", "23", "26" } } },
     { "CUDA",
-      StandardLevelComputer{
-        "CUDA", std::vector<int>{ 03, 11, 14, 17, 20, 23 },
-        std::vector<std::string>{ "03", "11", "14", "17", "20", "23" } } },
+      StandardLevelComputer{ "CUDA",
+                             std::vector<int>{ 03, 11, 14, 17, 20, 23, 26 },
+                             std::vector<std::string>{ "03", "11", "14", "17",
+                                                       "20", "23", "26" } } },
     { "OBJC",
       StandardLevelComputer{
         "OBJC", std::vector<int>{ 90, 99, 11, 17, 23 },
         std::vector<std::string>{ "90", "99", "11", "17", "23" } } },
     { "OBJCXX",
-      StandardLevelComputer{
-        "OBJCXX", std::vector<int>{ 98, 11, 14, 17, 20, 23 },
-        std::vector<std::string>{ "98", "11", "14", "17", "20", "23" } } },
+      StandardLevelComputer{ "OBJCXX",
+                             std::vector<int>{ 98, 11, 14, 17, 20, 23, 26 },
+                             std::vector<std::string>{ "98", "11", "14", "17",
+                                                       "20", "23", "26" } } },
     { "HIP",
-      StandardLevelComputer{
-        "HIP", std::vector<int>{ 98, 11, 14, 17, 20, 23 },
-        std::vector<std::string>{ "98", "11", "14", "17", "20", "23" } } }
+      StandardLevelComputer{ "HIP",
+                             std::vector<int>{ 98, 11, 14, 17, 20, 23, 26 },
+                             std::vector<std::string>{ "98", "11", "14", "17",
+                                                       "20", "23", "26" } } }
   };
 }
 

Source/cmake.h

@@ -861,6 +861,7 @@ private:
   F(cxx_std_17)                                                               \
   F(cxx_std_20)                                                               \
   F(cxx_std_23)                                                               \
+  F(cxx_std_26)                                                               \
   FOR_EACH_CXX98_FEATURE(F)                                                   \
   FOR_EACH_CXX11_FEATURE(F)                                                   \
   FOR_EACH_CXX14_FEATURE(F)
@@ -871,7 +872,8 @@ private:
   F(cuda_std_14)                                                              \
   F(cuda_std_17)                                                              \
   F(cuda_std_20)                                                              \
-  F(cuda_std_23)
+  F(cuda_std_23)                                                              \
+  F(cuda_std_26)
 
 #define FOR_EACH_HIP_FEATURE(F)                                               \
   F(hip_std_98)                                                               \
@@ -879,4 +881,5 @@ private:
   F(hip_std_14)                                                               \
   F(hip_std_17)                                                               \
   F(hip_std_20)                                                               \
-  F(hip_std_23)
+  F(hip_std_23)                                                               \
+  F(hip_std_26)

Tests/CompileFeatures/CMakeLists.txt

@@ -356,6 +356,7 @@ else()
       HAVE_CXX_STD_17=$<COMPILE_FEATURES:cxx_std_17>
       HAVE_CXX_STD_20=$<COMPILE_FEATURES:cxx_std_20>
       HAVE_CXX_STD_23=$<COMPILE_FEATURES:cxx_std_23>
+      HAVE_CXX_STD_26=$<COMPILE_FEATURES:cxx_std_26>
     )
   endif()
 

Tests/CompileFeatures/genex_test.cpp

@@ -27,6 +27,9 @@
 #  if HAVE_CXX_STD_23 && !defined(ALLOW_LATER_STANDARDS)
 #    error HAVE_CXX_STD_23 is true with CXX_STANDARD == 11
 #  endif
+#  if HAVE_CXX_STD_26 && !defined(ALLOW_LATER_STANDARDS)
+#    error HAVE_CXX_STD_26 is true with CXX_STANDARD == 11
+#  endif
 #endif
 
 #if !HAVE_OVERRIDE_CONTROL