VS: Fix WINDOWS_EXPORT_ALL_SYMBOLS for object libraries

Teach Visual Studio generators to include object files from object
libraries in the list of objects whose symbols are to be exported.
The Makefile and Ninja generators already did this.  Update the
test to cover this case.

Reported-by: Bertrand Bellenot <Bertrand.Bellenot@cern.ch>

Source/cmGlobalVisualStudioGenerator.cxx

@@ -827,6 +827,7 @@ void cmGlobalVisualStudioGenerator::AddSymbolExportCommand(
     cmSystemTools::Error("could not open ", objs_file.c_str());
     return;
   }
+  std::vector<std::string> objs;
   for (std::vector<cmSourceFile const*>::const_iterator it =
          objectSources.begin();
        it != objectSources.end(); ++it) {
@@ -836,6 +837,12 @@ void cmGlobalVisualStudioGenerator::AddSymbolExportCommand(
     // It must exist because we populated the mapping just above.
     assert(!map_it->second.empty());
     std::string objFile = obj_dir + map_it->second;
+    objs.push_back(objFile);
+  }
+  gt->UseObjectLibraries(objs, configName);
+  for (std::vector<std::string>::iterator it = objs.begin(); it != objs.end();
+       ++it) {
+    std::string objFile = *it;
     // replace $(ConfigurationName) in the object names
     cmSystemTools::ReplaceString(objFile, this->GetCMakeCFGIntDir(),
                                  configName.c_str());

Tests/RunCMake/AutoExportDll/AutoExport.cmake

@@ -2,7 +2,9 @@ project(autoexport)
 set(CMAKE_WINDOWS_EXPORT_ALL_SYMBOLS TRUE)
 set(CMAKE_RUNTIME_OUTPUT_DIRECTORY ${autoexport_BINARY_DIR}/bin)
 add_subdirectory(sub)
-add_library(autoexport SHARED hello.cxx world.cxx foo.c)
+add_library(objlib OBJECT objlib.c)
+set_property(TARGET objlib PROPERTY POSITION_INDEPENDENT_CODE 1)
+add_library(autoexport SHARED hello.cxx world.cxx foo.c $<TARGET_OBJECTS:objlib>)
 
 add_executable(say say.cxx)
 if(MSVC)

Tests/RunCMake/AutoExportDll/objlib.c

@@ -0,0 +1,4 @@
+int objlib()
+{
+  return 7;
+}

Tests/RunCMake/AutoExportDll/say.cxx

@@ -11,6 +11,7 @@ extern "C" {
 int WINAPI foo();
 // test regular C
 int bar();
+int objlib();
 }
 
 // test c++ functions
@@ -39,6 +40,7 @@ int main()
   foo();
   printf("\n");
   bar();
+  objlib();
   printf("\n");
   return 0;
 }