improve c++ modules

5 files changed, 84 insertions, 7 deletions

diff --git a/tests/projects/c++/modules/staticlib/xmake.lua b/tests/projects/c++/modules/staticlib/xmake.lua
index 3aa743c64..93045c18f 100644
--- a/tests/projects/c++/modules/staticlib/xmake.lua
+++ b/tests/projects/c++/modules/staticlib/xmake.lua
@@ -1,7 +1,5 @@
 set_languages("c++20")
 
-add_cxxflags("-fmodules-ts")
-
 target("mod")
     set_kind("static")
     add_files("src/mod.mpp", "src/mod.cpp")
diff --git a/xmake/rules/c++/modules/build_modules/clang.lua b/xmake/rules/c++/modules/build_modules/clang.lua
index 06b5aa1db..523c61ad9 100644
--- a/xmake/rules/c++/modules/build_modules/clang.lua
+++ b/xmake/rules/c++/modules/build_modules/clang.lua
@@ -23,6 +23,32 @@ import("core.tool.compiler")
 import("private.action.build.object", {alias = "objectbuilder"})
 import("module_parser")
 
+-- load parent target with modules files
+function load_parent(target, opt)
+    -- get modules flag
+    local modulesflag
+    local compinst = compiler.load("cxx", {target = target})
+    if compinst:has_flags("-fmodules") then
+        modulesflag = "-fmodules"
+    elseif compinst:has_flags("-fmodules-ts") then
+        modulesflag = "-fmodules-ts"
+    end
+    assert(modulesflag, "compiler(clang): does not support c++ module!")
+
+    -- add module flags
+    target:add("cxxflags", modulesflag)
+
+    -- the module cache directory
+    for _, dep in ipairs(target:orderdeps()) do
+        local sourcebatches = dep:sourcebatches()
+        if sourcebatches and sourcebatches["c++.build.modules"] then
+            local cachedir = path.join(dep:autogendir(), "rules", "modules", "cache")
+            target:add("cxxflags", "-fmodules-cache-path=" .. cachedir, {force = true})
+            target:add("cxxflags", "-fimplicit-modules", "-fimplicit-module-maps", "-fprebuilt-module-path=" .. cachedir, {force = true})
+        end
+    end
+end
+
 -- build module files
 function build_with_batchjobs(target, batchjobs, sourcebatch, opt)
 
diff --git a/xmake/rules/c++/modules/build_modules/gcc.lua b/xmake/rules/c++/modules/build_modules/gcc.lua
index 1264f29c2..2abaa4f7f 100644
--- a/xmake/rules/c++/modules/build_modules/gcc.lua
+++ b/xmake/rules/c++/modules/build_modules/gcc.lua
@@ -23,6 +23,20 @@ import("core.tool.compiler")
 import("private.action.build.object", {alias = "objectbuilder"})
 import("module_parser")
 
+-- load parent target with modules files
+function load_parent(target, opt)
+    -- get modules flag
+    local modulesflag
+    local compinst = compiler.load("cxx", {target = target})
+    if compinst:has_flags("-fmodules-ts") then
+        modulesflag = "-fmodules-ts"
+    end
+    assert(modulesflag, "compiler(gcc): does not support c++ module!")
+
+    -- add module flags
+    target:add("cxxflags", modulesflag)
+end
+
 -- build module files
 function build_with_batchjobs(target, batchjobs, sourcebatch, opt)
 
diff --git a/xmake/rules/c++/modules/build_modules/msvc.lua b/xmake/rules/c++/modules/build_modules/msvc.lua
index 4606edb7e..4cc8500ab 100644
--- a/xmake/rules/c++/modules/build_modules/msvc.lua
+++ b/xmake/rules/c++/modules/build_modules/msvc.lua
@@ -23,6 +23,21 @@ import("core.tool.compiler")
 import("private.action.build.object", {alias = "objectbuilder"})
 import("module_parser")
 
+-- load parent target with modules files
+function load_parent(target, opt)
+
+    -- get modules flag
+    local modulesflag
+    local compinst = compiler.load("cxx", {target = target})
+    if compinst:has_flags("/experimental:module", "cxxflags") then
+        modulesflag = "/experimental:module"
+    end
+    assert(modulesflag, "compiler(msvc): does not support c++ module!")
+
+    -- add module flags
+    target:add("cxxflags", modulesflag)
+end
+
 -- build module files
 function build_with_batchjobs(target, batchjobs, sourcebatch, opt)
 
diff --git a/xmake/rules/c++/modules/xmake.lua b/xmake/rules/c++/modules/xmake.lua
index 9018f5e2d..78f754521 100644
--- a/xmake/rules/c++/modules/xmake.lua
+++ b/xmake/rules/c++/modules/xmake.lua
@@ -21,12 +21,36 @@
 -- define rule: c++.build.modules
 rule("c++.build.modules")
     set_extensions(".mpp", ".mxx", ".cppm", ".ixx")
-    before_build_files(function (target, batchjobs, sourcebatch, opt)
+    after_load(function (target)
         -- we disable to build across targets in parallel, because the source files may depend on other target modules
-        -- @note we cannot set it in on_load, because it will affect all c++ projects
-        target:set("policy", "build.across_targets_in_parallel", false)
-
-        -- build module files with batchjobs
+        -- @see https://github.com/xmake-io/xmake/issues/1858
+        local target_with_modules
+        for _, dep in ipairs(target:orderdeps()) do
+            local sourcebatches = dep:sourcebatches()
+            if sourcebatches and sourcebatches["c++.build.modules"] then
+                target_with_modules = true
+                break
+            end
+        end
+        if target_with_modules then
+            -- @note this will cause cross-parallel builds to be disabled for all sub-dependent targets,
+            -- even if some sub-targets do not contain C++ modules.
+            --
+            -- maybe we will have a more fine-grained configuration strategy to disable it in the future.
+            target:set("policy", "build.across_targets_in_parallel", false)
+            local _, toolname = target:tool("cxx")
+            if toolname:find("clang", 1, true) then
+                import("build_modules.clang").load_parent(target, opt)
+            elseif toolname:find("gcc", 1, true) then
+                import("build_modules.gcc").load_parent(target, opt)
+            elseif toolname == "cl" then
+                import("build_modules.msvc").load_parent(target, opt)
+            else
+                raise("compiler(%s): does not support c++ module!", toolname)
+            end
+        end
+    end)
+    before_build_files(function (target, batchjobs, sourcebatch, opt)
         local _, toolname = target:tool("cxx")
         if toolname:find("clang", 1, true) then
             import("build_modules.clang").build_with_batchjobs(target, batchjobs, sourcebatch, opt)