CMake < 3.14: set IOS variable to 1?

[SpaceIm]

In CMakeLists, there is a lot of logic based on IOS variable, but this variable is never set to 1 when CMAKE_SYSTEM_NAME is iOS.
CMake does that automatically, but only since 3.14: https://cmake.org/cmake/help/latest/variable/IOS.html

In the meantime, CMake min version in sdl CMakeLists is 3.0.0, so I think that it should still be handled manually in CMakeLists.

[SpaceIm]

Maybe something like this, even if it's a little bit cumbersome:

...
elseif(APPLE)
  if(CMAKE_SYSTEM_NAME MATCHES ".*Darwin.*")
    set(DARWIN TRUE)
  elseif(CMAKE_SYSTEM_NAME MATCHES ".*MacOS.*")
    set(MACOSX TRUE)
  elseif(CMAKE_SYSTEM_NAME MATCHES ".*tvOS.*")
    set(TVOS TRUE)
  elseif(CMAKE_SYSTEM_NAME MATCHES ".*iOS.*")
    # could be set unconditionally, it's just a reminder to remove this logic if CMake min version is bumped to 3.14
    if(CMAKE_VERSION VERSION_LESS 3.14)
      set(IOS TRUE)
    endif()
  endif()
  # what about watchOS?
...

[icculus]

if(CMAKE_SYSTEM_NAME MATCHES ".*Darwin.*")
   set(DARWIN TRUE)
 elseif(CMAKE_SYSTEM_NAME MATCHES ".*MacOS.*")
   set(MACOSX TRUE)
 elseif(CMAKE_SYSTEM_NAME MATCHES ".*tvOS.*")
   set(TVOS TRUE)

...are all of these necessary? If this isn't causing a problem beyond the missing IOS variable, I'd rather not bulk this up as a defensive measure.

(if we need them explicitly set, though, then yeah, let's do it.)

[okuoku]

Generally speaking, we should not dispatch platforms inside CMake project since Apple's recommendation is feature detection macros (Macro itself still have versioning issue though: #4475 ). It seems current SDL2 codebase largely follows this.

...are all of these necessary?

DARWIN, MACOSX and TVOS exist current SDL2 codebase. History:

• DARWIN and MACOSX : These are from day1. spurious/SDL-mirror@7b16b85 these could be APPLE but SDL2 calls these platforms darwin so I guess the original author defined DARWIN instead. (In 2012, OpenDarwin derived was still there.) CMake calls darwin as APPLE entirely.
• TVOS : was added in ec65a34 TVOS name is compatible with unofficial CMake iOS support ( https://github.com/leetal/ios-cmake ).

IMHO we should follow CMake upstream thus we can depend on APPLE and IOS. DARWIN and most of MACOSX can be safely translated into APPLE and some of them might be if(APPLE AND NOT IOS). Every TVOS occurrences can be translated into IOS. Since CMAKE_SYSTEM_NAME is not utilized in unofficial(ios-cmake) CMake support, I don't think it worked CMake prior to 3.14 anyway for iOS/tvOS.