improve pch for std modules

2 files changed, 18 insertions, 1 deletions

diff --git a/xmake/modules/core/tools/gcc.lua b/xmake/modules/core/tools/gcc.lua
index 3bd9aefef..9172dd2ed 100644
--- a/xmake/modules/core/tools/gcc.lua
+++ b/xmake/modules/core/tools/gcc.lua
@@ -974,7 +974,8 @@ function compargv(self, sourcefile, objectfile, flags, opt)
     local extension = path.extension(sourcefile)
     if toolchain_utils.is_cxx_headerext(extension) then
         flags = _translate_flags_for_pch(self, flags)
-    elseif support.has_module_extension(sourcefile, {extension = extension}) then
+    elseif support.has_module_extension(sourcefile, {extension = extension})
+        or support.is_stdmodule_file(opt.target, sourcefile) then
         flags = _translate_flags_for_mpp(self, flags)
     end
 
diff --git a/xmake/rules/c++/modules/support.lua b/xmake/rules/c++/modules/support.lua
index 1dd7625bb..126e25c61 100644
--- a/xmake/rules/c++/modules/support.lua
+++ b/xmake/rules/c++/modules/support.lua
@@ -201,6 +201,22 @@ function has_module_extension(sourcefile, opt)
     return modulexts:has(extension:lower())
 end
 
+-- is std module file?
+-- e.g. libstdc++'s bits/std.cc and bits/std.compat.cc, which use the .cc extension
+-- and therefore are not detected by has_module_extension.
+-- @see https://github.com/xmake-io/xmake/issues/4051
+-- @see https://github.com/xmake-io/xmake/issues/7560
+function is_stdmodule_file(target, sourcefile)
+    if not target or not target.policy then
+        return false
+    end
+    if not target:policy("build.c++.modules.std") then
+        return false
+    end
+    local _, stdmodules_set = get_stdmodules(target)
+    return stdmodules_set and stdmodules_set:has(sourcefile) or false
+end
+
 -- this target contains module files?
 function contains_modules(target)
     -- we can not use `"c++.build.modules.builder"`, because it contains sourcekind/cxx.