[cmake-developers] iOS: direction to official support and questions

[Raffi Enficiaud]

Hi CMake ML,

I am quite new to the topic of making toolchain files. However I need to 
build a not so trivial application for iOS and I want to do it with 
CMake, and if possible walk toward an official support of iOS in CMake.

I have looked a bit to the Android toolchains, and I have to say I found 
those quite complicated as a first reading :)

The target application I am building uses Qt and Boost.

So far, I have managed to have an IOS toolchain file that is generating 
a looking good XCode project, that I can compile properly (up until 
signing).

I can share the toolchain file: it is a collection of things I have 
found on the internet, but trimmed from what I think was not necessary. 
It is still in a not so nice state, but I am currently cleaning it.

There are things that I think are weird though:

* I need to have:
```
set(CMAKE_FIND_ROOT_PATH
     ${CMAKE_IOS_DEVELOPER_ROOT}
     ${CMAKE_IOS_SDK_ROOT}
     ${CMAKE_PREFIX_PATH}
     /path/to/boost_1_64_0_build/install
     CACHE string  "iOS find search path root")
```

where this path is hard coded, and points to the fat static libraries 
prefix path of boost. If I remove this path, FindBoost does not find the 
boost libraries anymore (of course I am passing BOOST_ROOT). In 
addition, I have this:

```
set (CMAKE_SYSTEM_FRAMEWORK_PATH
	${CMAKE_IOS_SDK_ROOT}/System/Library/Frameworks
	${CMAKE_IOS_SDK_ROOT}/System/Library/PrivateFrameworks
	${CMAKE_IOS_SDK_ROOT}/Developer/Library/Frameworks
)

set(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM ONLY)
set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)
set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)
```

this looks ok to me, as we are cross compiling.
Is this a problem of FindBoost, or the combinations of the options that 
are not ok?

* I need to add:
```
set(CMAKE_MACOSX_BUNDLE YES)
set(CMAKE_XCODE_ATTRIBUTE_CODE_SIGNING_REQUIRED "NO")
```

and this comes from https://public.kitware.com/Bug/view.php?id=15329 . 
As I understand it, this is a problem of try_compile: as signing of 
application is required for generating a binary for iOS, this one fails 
very early when CMake discovers the capabilities of the compiler. Some 
people made a workaround by short-cutting the compiler checks, which is 
to me a wrong direction to take. As mentioned in this ticket, the right 
solution would be that the try_compile commands not to require signing 
of the binaries (or sthg similar).
This is explained here: http://public.kitware.com/Bug/view.php?id=12288

* is this one https://cmake.org/Bug/view.php?id=12640 addressed?

* I am seeing exchanges concerning the IOS_INSTALL_COMBINED. Does this 
has something to do with toolchain? What is meant by "installation" in 
this case? Sorry for my naive question, but I do not understand the 
workflow very well.

* how can I have unit tests of the toolchain in a CI fashion. Ideally, I 
would like to have a target cross-compiled with this toolchain, and then 
running the iPhoneSimulator, and check the result (return code, process, 
command whatever).
Does anyone have experience with this?

Thanks,
Raffi