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

5 files changed, 55 insertions, 13 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;
           }
diff --git a/build2/cc/lexer.cxx b/build2/cc/lexer.cxx
index faf73c8..ba6ea18 100644
--- a/build2/cc/lexer.cxx
+++ b/build2/cc/lexer.cxx
@@ -330,6 +330,13 @@ namespace build2
 
             if (alpha (c) || c == '_')
             {
+              // This smells a little: we know skip_spaces() did not peek at
+              // the next character because this is not '/'. Which means the
+              // position in the stream must be of this character + 1.
+              //
+              if (buf_ != nullptr)
+                t.position = buf_->tellg () - 1;
+
               string& id (t.value);
               id.clear ();
 
diff --git a/build2/cc/lexer.hxx b/build2/cc/lexer.hxx
index c74a0a9..65e9012 100644
--- a/build2/cc/lexer.hxx
+++ b/build2/cc/lexer.hxx
@@ -50,22 +50,19 @@ namespace build2
 
     struct token
     {
-      token_type type;
+      token_type type = token_type::eos;
       string     value;
 
+      // Logical position.
+      //
       path     file;
-      uint64_t line;
-      uint64_t column;
-
-    public:
-      token ()
-          : token (token_type::eos, 0, 0) {}
+      uint64_t line   = 0;
+      uint64_t column = 0;
 
-      token (token_type t, uint64_t l, uint64_t c)
-          : token (t, string (), l, c) {}
-
-      token (token_type t, string v, uint64_t l, uint64_t c)
-          : type (t), value (move (v)), line (l), column (c) {}
+      // Physical position in the stream, currently only for identifiers and
+      // only if the stream is ifdstream.
+      //
+      uint64_t position = 0;
     };
 
     // Output the token value in a format suitable for diagnostics.
diff --git a/build2/cc/parser.cxx b/build2/cc/parser.cxx
index aae49dc..df2e257 100644
--- a/build2/cc/parser.cxx
+++ b/build2/cc/parser.cxx
@@ -82,13 +82,18 @@ namespace build2
               }
               else if (id == "export")
               {
+                uint64_t pos (t.position);
+
                 switch (l_->next (t))
                 {
                 case type::lcbrace:    ++bb; ex = true; break;
                 case type::identifier:
                   {
                     if      (id == "module")
+                    {
+                      export_pos = pos;
                       parse_module (t, true);
+                    }
                     else if (id == "import")
                       parse_import (t, true);
                     else
diff --git a/build2/cc/parser.hxx b/build2/cc/parser.hxx
index 8f327cd..d542d57 100644
--- a/build2/cc/parser.hxx
+++ b/build2/cc/parser.hxx
@@ -37,6 +37,9 @@ namespace build2
       string
       parse_module_name (token&);
 
+    public:
+      uint64_t export_pos; // Temporary hack, see parse_unit().
+
     private:
       lexer* l_;
       translation_unit* u_;