python: Add platlibdir and purelibdir options

docs/markdown/Builtin-options.md

@@ -260,3 +260,23 @@ The value is overridden in this order:
 - Value from command line if set
 
 Since 0.56.0 `warning_level` can also be defined per subproject.
+
+## Module options
+
+Some Meson modules have built-in options. They can be set by prefixing the option
+name with the module name: `-D<module>.<option>=<value>` (e.g. `-Dpython.platlibdir=/foo`).
+
+### Python module
+
+| Option           | Default value | Possible values | Description |
+| ------           | ------------- | --------------- | ----------- |
+| platlibdir       |               | Directory path  | Directory for site-specific, platform-specific files (Since 0.60.0) |
+| purelibdir       |               | Directory path  | Directory for site-specific, non-platform-specific files  (Since 0.60.0) |
+
+*Since 0.60.0* `python.platlibdir` and `python.purelibdir` options are used by
+python module methods `python.install_sources()` and `python.get_install_dir()`.
+By default Meson tries to detect the correct installation path, but make them
+relative to the installation `prefix`, which will often result in installed python
+modules to not be found by the interpreter unless `prefix` is `/usr` on Linux,
+or for example `C:\Python39` on Windows. These options can be absolute paths
+outside of `prefix`.

docs/markdown/Python-module.md

@@ -128,6 +128,9 @@ Install actual python sources (`.py`).
 All positional and keyword arguments are the same as for
 [[install_data]], with the addition of the following:
 
+*Since 0.60.0* `python.platlibdir` and `python.purelibdir` options can be used
+to control the default installation path. See [Python module options](Builtin-options.md#python-module).
+
 - `pure`: On some platforms, architecture independent files are
   expected to be placed in a separate directory. However, if the
   python sources should be installed alongside an extension module
@@ -154,6 +157,9 @@ directly, for example when using [[configure_file]].
 This function accepts no arguments, its keyword arguments are the same
 as [][`install_sources()`].
 
+*Since 0.60.0* `python.platlibdir` and `python.purelibdir` options can be used
+to control the default installation path. See [Python module options](Builtin-options.md#python-module).
+
 **Returns**: A string
 
 #### `language_version()`

docs/markdown/snippets/python_install_path.md

@@ -0,0 +1,12 @@
+## Override python installation paths
+
+The `python` module now has options to control where modules are installed:
+- python.platlibdir: Directory for site-specific, platform-specific files.
+- python.purelibdir: Directory for site-specific, non-platform-specific files.
+
+Those options are used by python module methods `python.install_sources()` and
+`python.get_install_dir()`. By default Meson tries to detect the correct installation
+path, but make them relative to the installation `prefix`, which will often result
+in installed python modules to not be found by the interpreter unless `prefix`
+is `/usr` on Linux, or for example `C:\Python39` on Windows. These new options
+can be absolute paths outside of `prefix`.

mesonbuild/coredata.py

@@ -1188,6 +1188,12 @@ BUILTIN_CORE_OPTIONS: 'KeyedOptionDictType' = OrderedDict([
     (OptionKey('werror'),          BuiltinOption(UserBooleanOption, 'Treat warnings as errors', False, yielding=False)),
     (OptionKey('wrap_mode'),       BuiltinOption(UserComboOption, 'Wrap mode', 'default', choices=['default', 'nofallback', 'nodownload', 'forcefallback', 'nopromote'])),
     (OptionKey('force_fallback_for'), BuiltinOption(UserArrayOption, 'Force fallback for those subprojects', [])),
+
+    # Python module
+    (OptionKey('platlibdir', module='python'),
+     BuiltinOption(UserStringOption, 'Directory for site-specific, platform-specific files.', '')),
+    (OptionKey('purelibdir', module='python'),
+     BuiltinOption(UserStringOption, 'Directory for site-specific, non-platform-specific files.', '')),
 ])
 
 BUILTIN_OPTIONS = OrderedDict(chain(BUILTIN_DIR_OPTIONS.items(), BUILTIN_CORE_OPTIONS.items()))
@@ -1203,6 +1209,8 @@ BULITIN_DIR_NOPREFIX_OPTIONS: T.Dict[OptionKey, T.Dict[str, str]] = {
     OptionKey('sysconfdir'):     {'/usr': '/etc'},
     OptionKey('localstatedir'):  {'/usr': '/var',     '/usr/local': '/var/local'},
     OptionKey('sharedstatedir'): {'/usr': '/var/lib', '/usr/local': '/var/local/lib'},
+    OptionKey('platlibdir', module='python'): {},
+    OptionKey('purelibdir', module='python'): {},
 }
 
 FORBIDDEN_TARGET_NAMES = {'clean': None,

mesonbuild/mesonlib/universal.py

@@ -2100,7 +2100,7 @@ class OptionKey:
     def __hash__(self) -> int:
         return self._hash
 
-    def _to_tuple(self):
+    def _to_tuple(self) -> T.Tuple[str, OptionType, str, str, MachineChoice, str]:
         return (self.subproject, self.type, self.lang or '', self.module or '', self.machine, self.name)
 
     def __eq__(self, other: object) -> bool:

mesonbuild/modules/python.py

@@ -374,7 +374,7 @@ class PythonExternalProgram(ExternalProgram):
             return mesonlib.version_compare(version, '>= 3.0')
         return True
 
-    def sanity(self) -> bool:
+    def sanity(self, state: T.Optional['ModuleState'] = None) -> bool:
         # Sanity check, we expect to have something that at least quacks in tune
         cmd = self.get_command() + ['-c', INTROSPECT_COMMAND]
         p, stdout, stderr = mesonlib.Popen_safe(cmd)
@@ -392,19 +392,24 @@ class PythonExternalProgram(ExternalProgram):
             variables = info['variables']
             info['suffix'] = variables.get('EXT_SUFFIX') or variables.get('SO') or variables.get('.so')
             self.info = T.cast('PythonIntrospectionDict', info)
-            self.platlib = self._get_path('platlib')
+            self.platlib = self._get_path(state, 'platlib')
-            self.purelib = self._get_path('purelib')
+            self.purelib = self._get_path(state, 'purelib')
             return True
         else:
             return False
 
-    def _get_path(self, key: str) -> None:
+    def _get_path(self, state: T.Optional['ModuleState'], key: str) -> None:
+        if state:
+            value = state.get_option(f'{key}dir', module='python')
+            if value:
+                return value
         user_dir = str(Path.home())
         sys_paths = self.info['sys_paths']
         rel_path = self.info['install_paths'][key][1:]
         if not any(p.endswith(rel_path) for p in sys_paths if not p.startswith(user_dir)):
             mlog.warning('Broken python installation detected. Python files',
-                         'installed by Meson might not be found by python interpreter.',
+                         'installed by Meson might not be found by python interpreter.\n',
+                         f'This warning can be avoided by setting "python.{key}dir" option.',
                          once=True)
         return rel_path
 
@@ -697,7 +702,7 @@ class PythonModule(ExtensionModule):
                 raise mesonlib.MesonException('{} is missing modules: {}'.format(name_or_path or 'python', ', '.join(missing_modules)))
             return NonExistingExternalProgram()
         else:
-            sane = python.sanity()
+            sane = python.sanity(state)
 
             if sane:
                 return python

test cases/python/7 install path/meson.build

@@ -0,0 +1,10 @@
+project('install path',
+  default_options: [
+    'python.purelibdir=/pure',
+    'python.platlibdir=/plat'
+  ]
+)
+
+py = import('python').find_installation()
+py.install_sources('test.py')
+py.install_sources('test.py', pure: false)

test cases/python/7 install path/test.json

@@ -0,0 +1,6 @@
+{
+  "installed": [
+    {"type": "file", "file": "plat/test.py"},
+    {"type": "file", "file": "pure/test.py"}
+  ]
+}

unittests/datatests.py

@@ -126,7 +126,8 @@ class DataTests(unittest.TestCase):
         subsections = tee(re.finditer(r"^### (.+)$", content, re.MULTILINE))
         subcontent1 = self._get_section_content("Directories", subsections[0], content)
         subcontent2 = self._get_section_content("Core options", subsections[1], content)
-        for subcontent in (subcontent1, subcontent2):
+        subcontent3 = self._get_section_content("Module options", sections, md)
+        for subcontent in (subcontent1, subcontent2, subcontent3):
             # Find the option names
             options = set()
             # Match either a table row or a table heading separator: | ------ |
@@ -145,8 +146,8 @@ class DataTests(unittest.TestCase):
             found_entries |= options
 
         self.assertEqual(found_entries, {
-            *(str(k) for k in mesonbuild.coredata.BUILTIN_OPTIONS),
+            *(str(k.evolve(module=None)) for k in mesonbuild.coredata.BUILTIN_OPTIONS),
-            *(str(k) for k in mesonbuild.coredata.BUILTIN_OPTIONS_PER_MACHINE),
+            *(str(k.evolve(module=None)) for k in mesonbuild.coredata.BUILTIN_OPTIONS_PER_MACHINE),
         })
 
         # Check that `buildtype` table inside `Core options` matches how