[cmake-developers] Generator expressisons in target properties

[Stephen Kelly]

Stephen Kelly wrote:
> 1) Policy
> 
> The include directories and compile definitions are set by the
> target_link_libraries command. It might make sense to add a policy for
> that feature, as otherwise the order of include directories would change,
> eg:
> 
>  add_executable(foo ...)
>  target_link_libraries(foo bar bat)
>  include_directories(${bat_INCLUDE_DIRS} ${bar_INCLUDE_DIRS})
> 

I'd like to return to this issue.

 add_executable(foo ...)
 target_link_libraries(foo bar bat)
 include_directories(${bat_INCLUDE_DIRS} ${bar_INCLUDE_DIRS})

will generate 

 -Ibat -Ibar 

before my topic, and 

 -Ibar -Ibat

afterward.

I think I can add a policy for this by keeping track of whether each include 
came from a tll() call or another method. If another method tries to add an 
include which is already there, check if it is there because of a tll() 
call, and if it is, remove it from there and append it in the new call.

This will require that the INCLUDE_DIRECTORIES properties not be handled in 
the regular way, but as a std::vector<IncludeDirectoryEntry> where:

struct IncludeDirectoryEntry 
{
  cmCompiledGeneratorExpression ge;
  bool IsCMP0020Entry; 
};

On the plus-side this means that we'll get proper backtraces from errors in 
generator expressions for includes.

Any thoughts on that?

Thanks,

Steve.