Add OBJECT_LIBRARY target type

This library type can compile sources to object files but does not link
or archive them.  It will be useful to reference from executable and
normal library targets for direct inclusion of object files in them.

Diagnose and reject the following as errors:

* An OBJECT library may not be referenced in target_link_libraries.

* An OBJECT library may contain only compiling sources and supporting
  headers and custom commands.  Other source types that are not normally
  ignored are not allowed.

* An OBJECT library may not have PRE_BUILD, PRE_LINK, or POST_BUILD
  commands.

* An OBJECT library may not be installed, exported, or imported.

Some of these cases may be supported in the future but are not for now.

Teach the VS generator that OBJECT_LIBRARY targets are "linkable" just
like STATIC_LIBRARY targets for the LinkLibraryDependencies behavior.

1 files changed, 13 insertions, 0 deletions

diff --git a/Source/cmComputeLinkDepends.cxx b/Source/cmComputeLinkDepends.cxx
index ddff2d9215..055aab0321 100644
--- a/Source/cmComputeLinkDepends.cxx
+++ b/Source/cmComputeLinkDepends.cxx
@@ -633,6 +633,19 @@ cmTarget* cmComputeLinkDepends::FindTargetToLink(int depender_index,
     tgt = 0;
     }
 
+  if(tgt && tgt->GetType() == cmTarget::OBJECT_LIBRARY)
+    {
+    cmOStringStream e;
+    e << "Target \"" << this->Target->GetName() << "\" links to "
+      "OBJECT library \"" << tgt->GetName() << "\" but this is not "
+      "allowed.  "
+      "One may link only to STATIC or SHARED libraries, or to executables "
+      "with the ENABLE_EXPORTS property set.";
+    this->CMakeInstance->IssueMessage(cmake::FATAL_ERROR, e.str(),
+                                      this->Target->GetBacktrace());
+    tgt = 0;
+    }
+
   // Return the target found, if any.
   return tgt;
 }