install,export: Maybe transform OBJECT libraries to INTERFACE libraries

Teach the `install` and `export` commands to support installing and
exporting `OBJECT` libraries without their object files.  Transform
them to `INTERFACE` libraries in such cases.

For `install(TARGETS)`, activate this when no destination for the object
files is specified.  For `export`, activate this only under Xcode with
multiple architectures when we have no well-defined object file
locations to give to clients.

3 files changed, 31 insertions, 5 deletions

diff --git a/Tests/ExportImport/Export/CMakeLists.txt b/Tests/ExportImport/Export/CMakeLists.txt
index eeae3f0..4f663f6 100644
--- a/Tests/ExportImport/Export/CMakeLists.txt
+++ b/Tests/ExportImport/Export/CMakeLists.txt
@@ -83,11 +83,13 @@ set_property(TARGET testLib7 PROPERTY OUTPUT_NAME testLib7-$<CONFIG>)
 add_library(testLib8 OBJECT testLib8A.c testLib8B.c sub/testLib8C.c)
 
 if(NOT CMAKE_GENERATOR STREQUAL "Xcode" OR NOT CMAKE_OSX_ARCHITECTURES MATCHES "[;$]")
-  set(maybe_testLib8 testLib8)
+  set(maybe_OBJECTS_DESTINATION OBJECTS DESTINATION $<1:lib>)
 else()
-  set(maybe_testLib8 "")
+  set(maybe_OBJECTS_DESTINATION "")
 endif()
 
+add_library(testLib9Obj OBJECT testLib9Obj.c)
+
 # Test using the target_link_libraries command to set the
 # LINK_INTERFACE_LIBRARIES* properties.  We construct two libraries
 # providing the same two symbols.  In each library one of the symbols
@@ -483,7 +485,7 @@ install(
   TARGETS
   testExe1 testLib1 testLib2 testExe2 testLib3 testLib4 testExe3 testExe4
   testExe2lib testLib4lib testLib4libdbg testLib4libopt
-  testLib6 testLib7 ${maybe_testLib8}
+  testLib6 testLib7 testLib8
   testLibCycleA testLibCycleB
   testLibNoSONAME
   cmp0022NEW cmp0022OLD
@@ -492,10 +494,15 @@ install(
   RUNTIME DESTINATION $<1:bin>
   LIBRARY DESTINATION $<1:lib> NAMELINK_SKIP
   ARCHIVE DESTINATION $<1:lib>
-  OBJECTS DESTINATION $<1:lib>
+  ${maybe_OBJECTS_DESTINATION}
   FRAMEWORK DESTINATION Frameworks
   BUNDLE DESTINATION Applications
   )
+install(
+  TARGETS
+  testLib9Obj
+  EXPORT exp
+  )
 if (APPLE)
   file(COPY testLib4.h DESTINATION ${CMAKE_CURRENT_BINARY_DIR}/testLib4.framework/Headers)
   file(COPY testLib4.h DESTINATION ${CMAKE_CURRENT_BINARY_DIR}/Debug/testLib4.framework/Headers)
@@ -545,7 +552,8 @@ export(TARGETS testExe1 testLib1 testLib2 testLib3
   FILE ExportBuildTree.cmake
   )
 export(TARGETS testExe2 testLib4 testLib5 testLib6 testLib7 testExe3 testExe4 testExe2lib
-  ${maybe_testLib8}
+  testLib8
+  testLib9Obj
   testLib4lib testLib4libdbg testLib4libopt
   testLibCycleA testLibCycleB
   testLibNoSONAME
diff --git a/Tests/ExportImport/Export/testLib9Obj.c b/Tests/ExportImport/Export/testLib9Obj.c
new file mode 100644
index 0000000..6a13e48
--- /dev/null
+++ b/Tests/ExportImport/Export/testLib9Obj.c
@@ -0,0 +1,4 @@
+int testLib9Obj(void)
+{
+  return 0;
+}
diff --git a/Tests/ExportImport/Import/A/CMakeLists.txt b/Tests/ExportImport/Import/A/CMakeLists.txt
index 01960ea..6d16cb7 100644
--- a/Tests/ExportImport/Import/A/CMakeLists.txt
+++ b/Tests/ExportImport/Import/A/CMakeLists.txt
@@ -229,6 +229,8 @@ add_library(imp_lib1b STATIC imp_lib1.c)
 target_link_libraries(imp_lib1b bld_testLib2)
 
 if(NOT CMAKE_GENERATOR STREQUAL "Xcode" OR NOT CMAKE_OSX_ARCHITECTURES MATCHES "[;$]")
+  set(bld_objlib_type OBJECT_LIBRARY)
+
   # Create a executable that is using objects imported from the install tree
   add_executable(imp_testLib8 imp_testLib8.c $<TARGET_OBJECTS:exp_testLib8>)
 
@@ -236,6 +238,18 @@ if(NOT CMAKE_GENERATOR STREQUAL "Xcode" OR NOT CMAKE_OSX_ARCHITECTURES MATCHES "
     # Create a executable that is using objects imported from the build tree
     add_executable(imp_testLib8b imp_testLib8.c $<TARGET_OBJECTS:bld_testLib8>)
   endif()
+else()
+  set(bld_objlib_type INTERFACE_LIBRARY)
+endif()
+
+# Check that object libraries were transformed on export as expected.
+get_property(type TARGET exp_testLib9Obj PROPERTY TYPE)
+if(NOT type STREQUAL INTERFACE_LIBRARY)
+  message(FATAL_ERROR "exp_testLib9Obj type is '${type}', not 'INTERFACE_LIBRARY'")
+endif()
+get_property(type TARGET bld_testLib9Obj PROPERTY TYPE)
+if(NOT type STREQUAL "${bld_objlib_type}")
+  message(FATAL_ERROR "bld_testLib9Obj type is '${type}', not '${bld_objlib_type}'")
 endif()
 
 #-----------------------------------------------------------------------------