Michael Scott wrote:
> Hi,
>
> I'm planning on having a look at the CMake issue "Allow ALIAS of
> IMPORTED targets", 0015569. After reading the thread between yourself
> and Marc, I wanted to ask a couple of things before I start going
> further with it.
Thanks for working on this.
> The proposed change would be for the add_library and add_executable
> commands only right?
Yes, I guess so.
> Having a quick look at the code for those two commands, they
> specifically check for a combination of ALIAS and IMPORTED and don't
> allow it. I'm guessing that the required changes to allow both
> simultaneously wouldn't be to just remove this check, there would be
> other areas to modify as well right?
Perhaps. Finding that out is the real task :). I don't have all the answers
to it. The specific disallowing of ALIAS and IMPORTED together by issuing an
error was a way to defer finding those answers while not being required to
maintain compatibility with a particular behavior. I didn't want finding
those answers to delay getting the ALIAS feature in, because it was useful
already as it was.
Now, we have time to consider all of the implications of allowing this as
part of the design.
For example, if an ALIAS can be IMPORTED, does it makes sense that it can be
exported with export() and install(EXPORT)?
If we have
add_library(CoreStatic ${Core_SRCS})
add_library(MyNS::Core ALIAS CoreStatic)
and I export both of them with the NAMESPACE 'MyNS::', do I end up with
MyNS::MyNS::Core
?
Or would the exporting code strip of everything before a '::' in the alias
name?
Or should exporting ALIAS targets still be disallowed?
The two use cases described in
http://thread.gmane.org/gmane.comp.programming.tools.cmake.user/52452
seem like they would not benefit from exporting ALIAS targets.
A reasonable way forward might be:
* Keep the restriction that ALIAS targets may not be exported.
* Remove the code disallowing ALIAS IMPORTED targets.
* Remove the unit test proving it is not allowed
* Add new unit tests that it basically works
* Add a unit test for using an ALIAS with try_compile(LINK_LIBRARIES)
* (Anything else that comes up along the way)
Thanks,
Steve.
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