Add OpenHarmony (OHOS) support as an Android subsystem

OHOS behaves like Android: applications are shared libraries and
shared libraries are not versioned. But it uses musl instead of
Bionic. Model it as an Android subsystem rather than a separate
system: machine files set system = 'android' and subsystem = 'ohos',
so is_android() applies and all Android handling (unversioned
libfoo.so, the zlib include exception, PIE, android_exe_type) is
inherited automatically.

Add a MachineInfo.is_ohos() predicate (is_android() and subsystem ==
'ohos') and use it to set CMAKE_SYSTEM_NAME = OHOS for CMake subprojects,
since CMake has a dedicated OHOS system name.

docs/markdown/Reference-tables.md

@@ -162,7 +162,7 @@ These are provided by the `.system()` method call.
 
 | Value               | Comment                         |
 | -----               | -------                         |
-| android             | |
+| android             | Android or OpenHarmony / HarmonyOS (OHOS) |
 | cygwin              | Cygwin or MSYS2 environment on Windows |
 | darwin              | Either OSX or iOS |
 | dragonfly           | DragonFly BSD |
@@ -208,6 +208,10 @@ 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.
 
+### `darwin` subsystems
+
+Set when `system` is `darwin`.
+
 | Value               | Comment                         |
 | -----               | -------                         |
 | macos               | Apple macOS (formerly OSX)      |
@@ -220,6 +224,15 @@ Meson natively.
 | watchos             | Apple watchOS                   |
 | watchos-simulator   |                                 |
 
+### `android` subsystems (since 1.12.0)
+
+Set when `system` is `android`.
+
+| Value               | Comment                         |
+| -----               | -------                         |
+| android             | Android (Bionic libc)           |
+| ohos                | OpenHarmony / HarmonyOS (OHOS)  |
+
 ## Language arguments parameter names
 
 These are the parameter names for passing language specific arguments

docs/markdown/snippets/ohos-support.md

@@ -0,0 +1,20 @@
+## OpenHarmony (OHOS) is now recognized as an Android subsystem
+
+Meson now recognizes OpenHarmony / HarmonyOS (OHOS). OHOS behaves like
+Android -- applications are shared libraries, shared libraries are not
+versioned, and so on -- but uses musl instead of Bionic. It is therefore
+modelled as an Android subsystem rather than a separate system.
+
+Machine files select it in the `[host_machine]` section with:
+
+```ini
+[host_machine]
+system = 'android'
+subsystem = 'ohos'
+```
+
+With this, `host_machine.system()` is `'android'` (so all Android handling
+applies, including unversioned `libfoo.so` output) while
+`host_machine.subsystem()` is `'ohos'`. When cross-compiling a CMake
+subproject, the toolchain file generated by the CMake module sets
+`CMAKE_SYSTEM_NAME = OHOS`.

mesonbuild/cmake/toolchain.py

@@ -155,7 +155,13 @@ class CMakeToolchain:
         # Only set these in a cross build. Otherwise CMake will trip up in native
         # builds and thing they are cross (which causes TRY_RUN() to break)
         if self.env.is_cross_build(when_building_for=self.for_machine):
-            defaults['CMAKE_SYSTEM_NAME'] = [SYSTEM_MAP.get(self.minfo.system, self.minfo.system)]
+            # OHOS is modelled as an Android subsystem in meson, but CMake has a
+            # dedicated OHOS system name, so map it explicitly.
+            if self.minfo.is_ohos():
+                system_name = 'OHOS'
+            else:
+                system_name = SYSTEM_MAP.get(self.minfo.system, self.minfo.system)
+            defaults['CMAKE_SYSTEM_NAME'] = [system_name]
             defaults['CMAKE_SYSTEM_PROCESSOR'] = [self.minfo.cpu_family]
 
         defaults['CMAKE_SIZEOF_VOID_P'] = ['8' if self.minfo.is_64_bit else '4']

mesonbuild/envconfig.py

@@ -344,6 +344,17 @@ class MachineInfo(HoldableObject):
         """
         return self.system == 'android'
 
+    def is_ohos(self) -> bool:
+        """
+        Machine is OpenHarmony (OHOS)?
+
+        OHOS is modelled as an Android subsystem: it behaves like Android
+        (apps are shared libraries, no versioned sonames, ...) but uses musl
+        instead of Bionic. Machine files select it with system = 'android'
+        and subsystem = 'ohos'.
+        """
+        return self.is_android() and self.subsystem == 'ohos'
+
     def is_haiku(self) -> bool:
         """
         Machine is Haiku?

unittests/internaltests.py

@@ -54,6 +54,22 @@ from .helpers import *
 
 class InternalTests(unittest.TestCase):
 
+    def test_machine_info_is_ohos(self):
+        def machine(system: str, subsystem: str) -> mesonbuild.envconfig.MachineInfo:
+            return mesonbuild.envconfig.MachineInfo(
+                system=system, cpu_family='aarch64', cpu='aarch64',
+                endian='little', kernel='linux', subsystem=subsystem)
+
+        # OHOS is modelled as an Android subsystem.
+        ohos = machine('android', 'ohos')
+        self.assertTrue(ohos.is_ohos())
+        self.assertTrue(ohos.is_android())
+
+        # Plain Android is not OHOS.
+        self.assertFalse(machine('android', 'android').is_ohos())
+        # A non-Android system with an 'ohos' subsystem is not OHOS either.
+        self.assertFalse(machine('linux', 'ohos').is_ohos())
+
     def test_version_number(self):
         self.assertEqual(search_version('foobar 1.2.3'), '1.2.3')
         self.assertEqual(search_version('1.2.3'), '1.2.3')