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-rw-r--r--build2/cxx/init.cxx14
1 files changed, 10 insertions, 4 deletions
diff --git a/build2/cxx/init.cxx b/build2/cxx/init.cxx
index 8c4249c..2c59f2c 100644
--- a/build2/cxx/init.cxx
+++ b/build2/cxx/init.cxx
@@ -126,7 +126,12 @@ namespace build2
if (*v == "experimental")
{
- // Unless disabled by the user, try to enable C++ modules.
+ // Unless disabled by the user, try to enable C++ modules. Here
+ // we use a tri-state:
+ //
+ // - false - disabled
+ // - unspecified - enabled if practically usable
+ // - true - enabled even if practically unusable
//
lookup l;
if (!(l = rs[v_m]) || cast<bool> (l))
@@ -140,7 +145,7 @@ namespace build2
// makes them pretty much unusable. This has been fixed in
// VC15u3 (19.11)
//
- if (mj > 19 || (mj == 19 && mi >= 11))
+ if (mj > 19 || (mj == 19 && mi >= (l ? 10 : 11)))
{
r.push_back ("/D__cpp_modules=201703"); // n4647
r.push_back ("/experimental:module");
@@ -153,7 +158,8 @@ namespace build2
// Enable starting with GCC 8.0.0 (currently the c++-modules
// branch).
//
- if (mj >= 8 &&
+ if (l && // Barely usable at the moment.
+ mj >= 8 &&
ci.version.build.find ("cxx-modules") != string::npos)
{
r.push_back ("-fmodules");
@@ -168,7 +174,7 @@ namespace build2
// Note that we are using Apple to vanilla Clang version re-
// map from above so may need to update things there as well.
//
- // Note: see Clang modules support hack in cc::compile.
+ // Also see Clang modules support hack in cc::compile.
//
if (mj >= 5)
{