Make VC compatible with 'export module M;' by fixing up preprocessed output

1 files changed, 31 insertions, 1 deletions

diff --git a/build2/cc/compile.cxx b/build2/cc/compile.cxx
index eddd465..9b8f31b 100644
--- a/build2/cc/compile.cxx
+++ b/build2/cc/compile.cxx
@@ -2398,7 +2398,37 @@ namespace build2
             // implementation units.
             //
             if (cid == compiler_id::msvc && src.is_a (*x_mod))
-              tu.mod.iface = true;
+            {
+              // It's quite painful to guard the export with an #if/#endif so
+              // if it is present, "fixup" the (temporary) preprocessed output
+              // by getting rid of the keyword.
+              //
+              // Note: when removing this also remember to remove the test.
+              //
+              if (tu.mod.iface)
+              {
+                // We can only fixup a temporary file.
+                //
+                if (!ps)
+                  fail (relative (src)) << "fixup requires preprocessor";
+
+                // Stomp out the export keyword with spaces. We are using
+                // std::fstream since our fdstream does not yet support
+                // seeking.
+                //
+                fstream os (psrc.path ().string (),
+                            fstream::out | fstream::in);
+
+                auto pos (static_cast<fstream::pos_type> (p.export_pos));
+
+                if (!os.is_open ()  ||
+                    !os.seekp (pos) ||
+                    !os.write ("      ", 6))
+                  fail << "unable to overwrite preprocessor output";
+              }
+              else
+                tu.mod.iface = true;
+            }
 
             return tu;
           }