Rewrite `for_*` machine checks in terms of MachineInfo and phase out

It's much better to directly query the machine in question rather than
do some roundabout "is_cross" thing. This is the first step for much
natve- and cross- code path deduplication.

mesonbuild/environment.py

@@ -1161,6 +1161,68 @@ class MachineInfo:
             literal['cpu'],
             literal['endian'])
 
+    def is_windows(self):
+        """
+        Machine is windows?
+        """
+        return self.system == 'windows'
+
+    def is_cygwin(self):
+        """
+        Machine is cygwin?
+        """
+        return self.system == 'cygwin'
+
+    def is_linux(self):
+        """
+        Machine is linux?
+        """
+        return self.system == 'linux'
+
+    def is_darwin(self):
+        """
+        Machine is Darwin (iOS/OS X)?
+        """
+        return self.system in ('darwin', 'ios')
+
+    def is_android(self):
+        """
+        Machine is Android?
+        """
+        return self.system == 'android'
+
+    def is_haiku(self):
+        """
+        Machine is Haiku?
+        """
+        return self.system == 'haiku'
+
+    def is_openbsd(self):
+        """
+        Machine is OpenBSD?
+        """
+        return self.system == 'openbsd'
+
+    # Various prefixes and suffixes for import libraries, shared libraries,
+    # static libraries, and executables.
+    # Versioning is added to these names in the backends as-needed.
+
+    def get_exe_suffix(self):
+        if self.is_windows() or self.is_cygwin():
+            return 'exe'
+        else:
+            return ''
+
+    def get_object_suffix(self):
+        if self.is_windows():
+            return 'obj'
+        else:
+            return 'o'
+
+    def libdir_layout_is_win(self):
+        return self.is_windows() \
+            or self.is_cygwin()
+
 class MachineInfos(PerMachine):
     def __init__(self):
         super().__init__(None, None, None)

mesonbuild/mesonlib.py

@@ -358,77 +358,93 @@ def is_dragonflybsd():
 def is_freebsd():
     return platform.system().lower() == 'freebsd'
 
+def _get_machine_is_cross(env, is_cross):
+    """
+    This is not morally correct, but works for now. For cross builds the build
+    and host machines differ. `is_cross == true` means the host machine, while
+    `is_cross == false` means the build machine. Both are used in practice,
+    even though the documentation refers to the host machine implying we should
+    hard-code it. For non-cross builds `is_cross == false` is passed but the
+    host and build machines are identical so it doesn't matter.
+
+    Users for `for_*` should instead specify up front which machine they want
+    and query that like:
+
+        env.machines[MachineChoice.HOST].is_haiku()
+
+    """
+    for_machine = MachineChoice.HOST if is_cross else MachineChoice.BUILD
+    return env.machines[for_machine]
+
 def for_windows(is_cross, env):
     """
     Host machine is windows?
 
+    Deprecated: Please use `env.machines[for_machine].is_windows()`.
+
     Note: 'host' is the machine on which compiled binaries will run
     """
-    if not is_cross:
-        return is_windows()
-    return env.cross_info.get_host_system() == 'windows'
+    return _get_machine_is_cross(env, is_cross).is_windows()
 
 def for_cygwin(is_cross, env):
     """
     Host machine is cygwin?
 
+    Deprecated: Please use `env.machines[for_machine].is_cygwin()`.
+
     Note: 'host' is the machine on which compiled binaries will run
     """
-    if not is_cross:
-        return is_cygwin()
-    return env.cross_info.get_host_system() == 'cygwin'
+    return _get_machine_is_cross(env, is_cross).is_cygwin()
 
 def for_linux(is_cross, env):
     """
     Host machine is linux?
 
+    Deprecated: Please use `env.machines[for_machine].is_linux()`.
+
     Note: 'host' is the machine on which compiled binaries will run
     """
-    if not is_cross:
-        return is_linux()
-    return env.cross_info.get_host_system() == 'linux'
+    return _get_machine_is_cross(env, is_cross).is_linux()
 
 def for_darwin(is_cross, env):
     """
     Host machine is Darwin (iOS/OS X)?
 
+    Deprecated: Please use `env.machines[for_machine].is_darwin()`.
+
     Note: 'host' is the machine on which compiled binaries will run
     """
-    if not is_cross:
-        return is_osx()
-    return env.cross_info.get_host_system() in ('darwin', 'ios')
+    return _get_machine_is_cross(env, is_cross).is_darwin()
 
 def for_android(is_cross, env):
     """
     Host machine is Android?
 
+    Deprecated: Please use `env.machines[for_machine].is_android()`.
+
     Note: 'host' is the machine on which compiled binaries will run
     """
-    if not is_cross:
-        return is_android()
-    return env.cross_info.get_host_system() == 'android'
+    return _get_machine_is_cross(env, is_cross).is_android()
 
 def for_haiku(is_cross, env):
     """
     Host machine is Haiku?
 
+    Deprecated: Please use `env.machines[for_machine].is_haiku()`.
+
     Note: 'host' is the machine on which compiled binaries will run
     """
-    if not is_cross:
-        return is_haiku()
-    return env.cross_info.get_host_system() == 'haiku'
+    return _get_machine_is_cross(env, is_cross).is_haiku()
 
 def for_openbsd(is_cross, env):
     """
     Host machine is OpenBSD?
 
+    Deprecated: Please use `env.machines[for_machine].is_openbsd()`.
+
     Note: 'host' is the machine on which compiled binaries will run
     """
-    if not is_cross:
-        return is_openbsd()
-    elif env.cross_info.has_host():
-        return env.cross_info.config['host_machine']['system'] == 'openbsd'
-    return False
+    return _get_machine_is_cross(env, is_cross).is_openbsd()
 
 def exe_exists(arglist):
     try: