export(): Document undefined behavior of location properties

Since the export() command needs to know the final location of a target
in the build tree we cannot allow properties affecting the location or
name of a target file to be set after the target is passed to export().

Fix a violation of this rule in the SimpleInstall test.

1 files changed, 2 insertions, 0 deletions

diff --git a/Source/cmExportCommand.h b/Source/cmExportCommand.h
index f33e9e2..eb19d2e 100644
--- a/Source/cmExportCommand.h
+++ b/Source/cmExportCommand.h
@@ -13,6 +13,7 @@
 #define cmExportCommand_h
 
 #include "cmCommand.h"
+#include "cmDocumentLocationUndefined.h"
 
 class cmExportBuildFileGenerator;
 
@@ -80,6 +81,7 @@ public:
       "should never be installed.  "
       "See the install(EXPORT) command to export targets from an "
       "installation tree."
+      CM_LOCATION_UNDEFINED_BEHAVIOR("passing it to this command")
       "\n"
       "  export(PACKAGE <name>)\n"
       "Store the current build directory in the CMake user package registry "