Add kernel and subsystem properties to machine objects.

cross/iphone.txt

@@ -25,6 +25,8 @@ has_function_hfkerhisadf = false
 
 [host_machine]
 system = 'darwin'
+subsystem = 'ios'
+kernel = 'xnu'
 cpu_family = 'aarch64'
 cpu = 'aarch64'
 endian = 'little'

cross/tvos.txt

@@ -22,6 +22,8 @@ has_function_hfkerhisadf = false
 
 [host_machine]
 system = 'darwin'
+subsystem = 'tvos'
+kernel = 'xnu'
 cpu_family = 'arm'
 cpu = 'arm64'
 endian = 'little'

docs/markdown/Cross-compilation.md

@@ -212,6 +212,8 @@ target machines look the same. Here is a sample for host machine.
 ```ini
 [host_machine]
 system = 'windows'
+subsystem = 'windows'
+kernel = 'nt'
 cpu_family = 'x86'
 cpu = 'i686'
 endian = 'little'
@@ -221,9 +223,13 @@ These values define the machines sufficiently for cross compilation
 purposes. The corresponding target definition would look the same but
 have `target_machine` in the header. These values are available in
 your Meson scripts. There are three predefined variables called,
-surprisingly, [[@build_machine]], [[@host_machine]] and [[@target_machine]].
-Determining the operating system of your host machine is simply a
-matter of calling `host_machine.system()`.
+surprisingly, [[@build_machine]], [[@host_machine]] and
+[[@target_machine]]. Determining the operating system of your host
+machine is simply a matter of calling `host_machine.system()`.
+Starting from version 1.2.0 you can get more fine grained information
+using the `.subsystem()` and `.kernel()` methods. The return values of
+these functions are documented in [the reference table
+page](Reference-tables.md).
 
 There are two different values for the CPU. The first one is
 `cpu_family`. It is a general type of the CPU. This should have a

docs/markdown/Reference-tables.md

@@ -163,9 +163,44 @@ These are provided by the `.system()` method call.
 Any string not listed above is not guaranteed to remain stable in
 future releases.
 
+## Kernel names (since 1.2.0)
+
+Native names as returned by the `.kernel()` method.
+
+| Value               | Comment                         |
+| -----               | -------                         |
+| linux   | |
+| freebsd | |
+| openbsd | |
+| netbsd  | |
+| nt      | |
+| xnu                 | Kernel of various Apple OSes    |
+| sunos | |
+| dragonfly | |
+| haiku| |
+| none                 | For e.g. bare metal embedded    |
+
+
+## Subsystem names (since 1.2.0)
+
+A more specific description of the system in question. Most values are
+meant to be used in cross files only, as those platforms can not run
+Meson natively.
+
+| Value               | Comment                         |
+| -----               | -------                         |
+| macos               | Apple macOS (formerly OSX)      |
+| ios                 | Apple iOS                       |
+| ios-simulator       |                                 |
+| tvos                | Apple tvOS                      |
+| tvos-simulator      |                                 |
+| watchos             | Apple watchOS                   |
+| watchos-simulator   |                                 |
+
 ## Language arguments parameter names
 
-These are the parameter names for passing language specific arguments to your build target.
+These are the parameter names for passing language specific arguments
+to your build target.
 
 | Language      | compiler name | linker name       |
 | ------------- | ------------- | ----------------- |

docs/markdown/snippets/moremachinedata.md

@@ -0,0 +1,12 @@
+## Machine objects get `kernel` and `subsystem` properties
+
+Meson has traditionally provided a `system` property to detect the
+system being run on. However this is not enough to reliably
+differentiate between e.g. an iOS platform from a watchOS one. Two new
+properties, namely `kernel` and `subsystem` have been added so these
+setups can be reliably detected.
+
+These new properties are not necessary in cross files for now, but if
+they are not defined and a build file tries to access them, Meson will
+exit with a hard error. It is expected that at some point in the
+future defining the new properties will become mandatory.

mesonbuild/envconfig.py

@@ -260,6 +260,8 @@ class MachineInfo(HoldableObject):
     cpu_family: str
     cpu: str
     endian: str
+    kernel: T.Optional[str]
+    subsystem: T.Optional[str]
 
     def __post_init__(self) -> None:
         self.is_64_bit: bool = self.cpu_family in CPU_FAMILIES_64_BIT
@@ -283,7 +285,11 @@ class MachineInfo(HoldableObject):
         if endian not in ('little', 'big'):
             mlog.warning(f'Unknown endian {endian}')
 
-        return cls(literal['system'], cpu_family, literal['cpu'], endian)
+        system = literal['system']
+        kernel = literal.get('kernel', None)
+        subsystem = literal.get('subsystem', None)
+
+        return cls(system, cpu_family, literal['cpu'], endian, kernel, subsystem)
 
     def is_windows(self) -> bool:
         """

mesonbuild/environment.py

@@ -395,6 +395,27 @@ def detect_cpu(compilers: CompilersDict) -> str:
     # detect_cpu_family() above.
     return trial
 
+KERNEL_MAPPINGS: T.Mapping[str, str] = {'freebsd': 'freebsd',
+                                        'openbsd': 'openbsd',
+                                        'netbsd': 'netbsd',
+                                        'windows': 'nt',
+                                        'android': 'linux',
+                                        'linux': 'linux',
+                                        'cygwin': 'nt',
+                                        'darwin': 'xnu',
+                                        'sunos': 'sunos',
+                                        'dragonfly': 'dragonfly',
+                                        'haiku': 'haiku',
+                                        }
+
+def detect_kernel(system: str) -> T.Optional[str]:
+    return KERNEL_MAPPINGS.get(system, None)
+
+def detect_subsystem(system: str) -> T.Optional[str]:
+    if system == 'darwin':
+        return 'macos'
+    return system
+
 def detect_system() -> str:
     if sys.platform == 'cygwin':
         return 'cygwin'
@@ -411,11 +432,14 @@ def detect_machine_info(compilers: T.Optional[CompilersDict] = None) -> MachineI
     underlying ''detect_*'' method can be called to explicitly use the
     partial information.
     """
+    system = detect_system()
     return MachineInfo(
-        detect_system(),
+        system,
         detect_cpu_family(compilers) if compilers is not None else None,
         detect_cpu(compilers) if compilers is not None else None,
-        sys.byteorder)
+        sys.byteorder,
+        detect_kernel(system),
+        detect_subsystem(system))
 
 # TODO make this compare two `MachineInfo`s purely. How important is the
 # `detect_cpu_family({})` distinction? It is the one impediment to that.

mesonbuild/interpreter/interpreterobjects.py

@@ -639,6 +639,8 @@ class MachineHolder(ObjectHolder['MachineInfo']):
                              'cpu': self.cpu_method,
                              'cpu_family': self.cpu_family_method,
                              'endian': self.endian_method,
+                             'kernel': self.kernel_method,
+                             'subsystem': self.subsystem_method,
                              })
 
     @noPosargs
@@ -661,6 +663,21 @@ class MachineHolder(ObjectHolder['MachineInfo']):
     def endian_method(self, args: T.List[TYPE_var], kwargs: TYPE_kwargs) -> str:
         return self.held_object.endian
 
+    @noPosargs
+    @noKwargs
+    def kernel_method(self, args: T.List[TYPE_var], kwargs: TYPE_kwargs) -> str:
+        if self.held_object.kernel is not None:
+            return self.held_object.kernel
+        raise InterpreterException('Kernel not defined or could not be autodetected.')
+
+    @noPosargs
+    @noKwargs
+    def subsystem_method(self, args: T.List[TYPE_var], kwargs: TYPE_kwargs) -> str:
+        if self.held_object.subsystem is not None:
+            return self.held_object.subsystem
+        raise InterpreterException('Subsystem not defined or could not be autodetected.')
+
+
 class IncludeDirsHolder(ObjectHolder[build.IncludeDirs]):
     pass
 

mesonbuild/scripts/env2mfile.py

@@ -44,6 +44,10 @@ def add_arguments(parser: 'argparse.ArgumentParser') -> None:
                         help='Generate a native compilation file.')
     parser.add_argument('--system', default=None,
                         help='Define system for cross compilation.')
+    parser.add_argument('--subsystem', default=None,
+                        help='Define subsystem for cross compilation.')
+    parser.add_argument('--kernel', default=None,
+                        help='Define kernel for cross compilation.')
     parser.add_argument('--cpu', default=None,
                         help='Define cpu for cross compilation.')
     parser.add_argument('--cpu-family', default=None,
@@ -61,6 +65,8 @@ class MachineInfo:
         self.cmake: T.Dict[str, T.Union[str, T.List[str]]] = {}
 
         self.system: T.Optional[str] = None
+        self.subsystem: T.Optional[str] = None
+        self.kernel: T.Optional[str] = None
         self.cpu: T.Optional[str] = None
         self.cpu_family: T.Optional[str] = None
         self.endian: T.Optional[str] = None
@@ -181,6 +187,8 @@ def detect_cross_debianlike(options: T.Any) -> MachineInfo:
         data[k] = v
     host_arch = data['DEB_HOST_GNU_TYPE']
     host_os = data['DEB_HOST_ARCH_OS']
+    host_subsystem = host_os
+    host_kernel = 'linux'
     host_cpu_family = deb_cpu_family_map.get(data['DEB_HOST_GNU_CPU'],
                                              data['DEB_HOST_GNU_CPU'])
     host_cpu = deb_cpu_map.get(data['DEB_HOST_ARCH'],
@@ -213,6 +221,8 @@ def detect_cross_debianlike(options: T.Any) -> MachineInfo:
     except ValueError:
         pass
     infos.system = host_os
+    infos.subsystem = host_subsystem
+    infos.kernel = host_kernel
     infos.cpu_family = host_cpu_family
     infos.cpu = host_cpu
     infos.endian = host_endian
@@ -260,6 +270,11 @@ def write_machine_file(infos: MachineInfo, ofilename: str, write_system_info: bo
             ofile.write(f"cpu_family = '{infos.cpu_family}'\n")
             ofile.write(f"endian = '{infos.endian}'\n")
             ofile.write(f"system = '{infos.system}'\n")
+            if infos.subsystem:
+                ofile.write(f"subsystem = '{infos.subsystem}'\n")
+            if infos.kernel:
+                ofile.write(f"kernel = '{infos.kernel}'\n")
+
     os.replace(tmpfilename, ofilename)
 
 def detect_language_args_from_envvars(langname: str, envvar_suffix: str = '') -> T.Tuple[T.List[str], T.List[str]]:
@@ -306,7 +321,7 @@ def detect_properties_from_envvars(infos: MachineInfo, envvar_suffix: str = '')
         infos.properties['sys_root'] = var
 
 def detect_cross_system(infos: MachineInfo, options: T.Any) -> None:
-    for optname in ('system', 'cpu', 'cpu_family', 'endian'):
+    for optname in ('system', 'subsystem', 'kernel', 'cpu', 'cpu_family', 'endian'):
         v = getattr(options, optname)
         if not v:
             mlog.error(f'Cross property "{optname}" missing, set it with --{optname.replace("_", "-")}.')