[cmake-developers] source_group and generator expressions

[Sebastian Holtermann]

Am 16.05.2017 um 15:11 schrieb Brad King:
> On 05/16/2017 05:52 AM, Sebastian Holtermann wrote:
>> There are two ways to achieve this
>> 1) Put TARGETNAME_autogen/$<CONFIG>/moc_compilation.cpp
>>    into AUTOGEN_SOURCE_GROUP
>>    - Requires gen. exp. support in source_group
>>
>> 2) Manually replace $<CONFIG> for all configurations and put all
>>    variants into the AUTOGEN_SOURCE_GROUP
>>    - Does not require gen. exp. support in source_group
>>    - May flood the source_group with files from an other configurations?
>>      Are source groups even configuration aware?
>>
>> I'd prefer 1) but does source_group support generator expressions?
> 
> I don't think so, but it could be taught to do so.  The main challenge
> is supporting per-configuration sources, and that would have to be
> solved for either approach.

I thought per configuration source were supported already :/.

> Source groups are used in IDE generators to organize source files.
> The IDE project file formats tend to not have the Configuration
> as a parameter to their source groups.  Instead all sources for
> all configurations get listed and then individual sources can be
> marked with conditions on a per-configuration basis.
> 
> Recently I refactored the VS generators to support per-config
> source generation (via per-config exclusion rules).  Currently
> it is limited somewhat artificially but the main generation
> infrastructure is there.
> 
> OTOH the Xcode generator does not have a good way to do per-config
> source files.  It has very limited support for excluding source
> files on a per-config basis but only by the *file name* ignoring
> the directory.

Okay, that would disallow
TARGETNAME_autogen/$<CONFIG>/moc_compilation.cpp because of the
non-unique file name.

Would TARGETNAME_autogen/moc_compilation_$<CONFIG>.cpp work with the
current state of VS and XCode? The file name is pretty much unique.

Or maybe using $<CONFIG> is not the best idea at all.
Much more useful in this AUTOGEN case (and maybe easier to implement?)
would be a cmGeneratorTarget::AddSource method that takes a second
configuration parameter. In fact that would be ideal because on the
AUTOGEN generated files the properties "GENERATED" and "SKIP_AUTOGEN"
must be set. This requires access to the cmSourceFile which is not
available when using the $<CONFIG> generator expression in the current
cmGeneratorTarget::AddSource.
Also cmGeneratorTarget::AddIncludeDirectory with configuration parameter
would be required to pass per configuration include directories.

Having the two methods available is the best solution I can see at the
moment. I can't do that though, my understanding of the CMake generators
is too limited for that.

- Sebastian