add a policy to toggle C++23 std module

4 files changed, 43 insertions, 39 deletions

diff --git a/xmake/core/project/policy.lua b/xmake/core/project/policy.lua
index e7212189e..916ce9677 100644
--- a/xmake/core/project/policy.lua
+++ b/xmake/core/project/policy.lua
@@ -64,8 +64,8 @@ function policy.policies()
             ["build.sanitizer.undefined"]         = {description = "Enable undefined sanitizer for c/c++ building.", type = "boolean"},
             -- Enable C++ modules for C++ building, even if no .mpp is involved in the compilation
             ["build.c++.modules"]                 = {description = "Enable C++ modules for C++ building.", type = "boolean"},
-            -- Enable clang std modulemap
-            ["build.c++.clang.stdmodules"]        = {description = "Enable clang std modulemap.", default = false, type = "boolean"},
+            -- Enable std module
+            ["build.c++.modules.std"]        = {description = "Enable std modules.", default = true, type = "boolean"},
             -- Force C++ modules fallback dependency scanner for clang
             ["build.c++.clang.fallbackscanner"]   = {description = "Force clang fallback module dependency scanner.", default = false, type = "boolean"},
             -- Force C++ modules fallback dependency scanner for msvc
diff --git a/xmake/rules/c++/modules/modules_support/clang/compiler_support.lua b/xmake/rules/c++/modules/modules_support/clang/compiler_support.lua
index ea2301859..a1f10b5ae 100644
--- a/xmake/rules/c++/modules/modules_support/clang/compiler_support.lua
+++ b/xmake/rules/c++/modules/modules_support/clang/compiler_support.lua
@@ -74,11 +74,6 @@ function load(target)
         target:add("cxxflags", modulestsflag)
     end
 
-    -- enable clang modules to emulate std modules
-    if target:policy("build.c++.clang.stdmodules") then
-       target:add("cxxflags", clangmodulesflag)
-    end
-
     -- fix default visibility for functions and variables [-fvisibility] differs in PCH file vs. current file
     -- module.pcm cannot be loaded due to a configuration mismatch with the current compilation.
     --
@@ -211,28 +206,31 @@ end
 
 -- not supported atm
 function get_stdmodules(target)
-    if _use_stdlib(target, "libc++") then
-        -- TODO support libc++ std module file when https://github.com/xmake-io/xmake/pull/4630
-        return {}
-    elseif _use_stdlib(target, "libstdc++") then
-        -- libstdc++ doesn't have a std module file atm
-        return {}
-    elseif _use_stdlib(target, "msstl") then
-        -- msstl std module file is not compatible with llvm <= 18
-        -- local toolchain = target:toolchain("clang")
-        -- local msvc = import("core.tool.toolchain", {anonymous = true}).load("msvc", {plat = toolchain:plat(), arch = toolchain:arch()})
-        -- if msvc then
-        --     local vcvars = msvc:config("vcvars")
-        --     if vcvars.VCInstallDir and vcvars.VCToolsVersion then
-        --         modules = {}
-        --
-        --         local stdmodulesdir = path.join(vcvars.VCInstallDir, "Tools", "MSVC", vcvars.VCToolsVersion, "modules")
-        --         assert(stdmodulesdir, "Can't enable C++23 std modules, directory missing !")
-        --
-        --         return {path.join(stdmodulesdir, "std.ixx"), path.join(stdmodulesdir, "std.compat.ixx")}
-        --     end
-        -- end
+    if target:policy("build.c++.modules.std") then
+        if _use_stdlib(target, "libc++") then
+            -- TODO support libc++ std module file when https://github.com/xmake-io/xmake/pull/4630
+            return {}
+        elseif _use_stdlib(target, "libstdc++") then
+            -- libstdc++ doesn't have a std module file atm
+        elseif _use_stdlib(target, "msstl") then
+            -- msstl std module file is not compatible with llvm <= 18
+            -- local toolchain = target:toolchain("clang")
+            -- local msvc = import("core.tool.toolchain", {anonymous = true}).load("msvc", {plat = toolchain:plat(), arch = toolchain:arch()})
+            -- if msvc then
+            --     local vcvars = msvc:config("vcvars")
+            --     if vcvars.VCInstallDir and vcvars.VCToolsVersion then
+            --         modules = {}
+            --
+            --         local stdmodulesdir = path.join(vcvars.VCInstallDir, "Tools", "MSVC", vcvars.VCToolsVersion, "modules")
+            --         assert(stdmodulesdir, "Can't enable C++23 std modules, directory missing !")
+            --
+            --         return {path.join(stdmodulesdir, "std.ixx"), path.join(stdmodulesdir, "std.compat.ixx")}
+            --     end
+            -- end
+        end
     end
+
+    return {}
 end
 
 function get_bmi_extension()
diff --git a/xmake/rules/c++/modules/modules_support/gcc/compiler_support.lua b/xmake/rules/c++/modules/modules_support/gcc/compiler_support.lua
index 147c8eeb1..7dab1f4da 100644
--- a/xmake/rules/c++/modules/modules_support/gcc/compiler_support.lua
+++ b/xmake/rules/c++/modules/modules_support/gcc/compiler_support.lua
@@ -101,6 +101,8 @@ end
 
 -- not supported atm
 function get_stdmodules(_)
+    if target:policy("build.c++.modules.std") then
+    end
     return {}
 end
 
diff --git a/xmake/rules/c++/modules/modules_support/msvc/compiler_support.lua b/xmake/rules/c++/modules/modules_support/msvc/compiler_support.lua
index 3b6aafb9a..3f67e0291 100644
--- a/xmake/rules/c++/modules/modules_support/msvc/compiler_support.lua
+++ b/xmake/rules/c++/modules/modules_support/msvc/compiler_support.lua
@@ -31,7 +31,7 @@ function load(target)
     local vcvars = msvc:config("vcvars")
 
     -- enable std modules if c++23 by defaults
-    if target:data("c++.msvc.enable_std_import") == nil then
+    if target:data("c++.msvc.enable_std_import") == nil and target:policy("build.c++.modules.std") then
         local languages = target:get("languages")
         local isatleastcpp23 = false
         for _, language in ipairs(languages) do
@@ -70,22 +70,26 @@ function toolchain_includedirs(target)
     raise("msvc toolchain includedirs not found!")
 end
 
+-- build c++23 standard modules if needed
 function get_stdmodules(target)
-    -- build c++23 standard modules if needed
-    if target:data("c++.msvc.enable_std_import") then
-        local msvc = target:toolchain("msvc")
-        if msvc then
-            local vcvars = msvc:config("vcvars")
-            if vcvars.VCInstallDir and vcvars.VCToolsVersion then
-                modules = {}
+    if target:policy("build.c++.modules.std") then
+        if target:data("c++.msvc.enable_std_import") then
+            local msvc = target:toolchain("msvc")
+            if msvc then
+                local vcvars = msvc:config("vcvars")
+                if vcvars.VCInstallDir and vcvars.VCToolsVersion then
+                    modules = {}
 
-                local stdmodulesdir = path.join(vcvars.VCInstallDir, "Tools", "MSVC", vcvars.VCToolsVersion, "modules")
-                assert(stdmodulesdir, "Can't enable C++23 std modules, directory missing !")
+                    local stdmodulesdir = path.join(vcvars.VCInstallDir, "Tools", "MSVC", vcvars.VCToolsVersion, "modules")
+                    assert(stdmodulesdir, "Can't enable C++23 std modules, directory missing !")
 
-                return {path.join(stdmodulesdir, "std.ixx"), path.join(stdmodulesdir, "std.compat.ixx")}
+                    return {path.join(stdmodulesdir, "std.ixx"), path.join(stdmodulesdir, "std.compat.ixx")}
+                end
             end
         end
     end
+
+    return {}
 end
 
 function get_bmi_extension()