modules/python: use typed_kwargs for `install_dir`

This `install_dir` is slightly different than the one in `BuildTarget`
(though I'd like to make them the same in the future). It is only
allowed to be `str | bool | None`, and the implementation has always
assumed this, it would have broken with an array value.

2 files changed, 16 insertions, 4 deletions

diff --git a/docs/markdown/Python-module.md b/docs/markdown/Python-module.md
index 66081762d..8fa99fba7 100644
--- a/docs/markdown/Python-module.md
+++ b/docs/markdown/Python-module.md
@@ -130,6 +130,9 @@ the addition of the following:
 
 Additionally, the following diverge from [[shared_module]]'s default behavior:
 
+- `install_dir` may only be a string, boolean, or unset, but an `array` is not
+  allowed.
+
 - `gnu_symbol_visibility`: if unset, it will default to `'hidden'` on versions
   of Python that support this (the python headers define `PyMODINIT_FUNC` has
   default visibility).
diff --git a/mesonbuild/modules/python.py b/mesonbuild/modules/python.py
index 3d8969f41..78798e5c0 100644
--- a/mesonbuild/modules/python.py
+++ b/mesonbuild/modules/python.py
@@ -22,7 +22,7 @@ from ..interpreterbase import (
     InvalidArguments, typed_pos_args, typed_kwargs, KwargInfo,
     FeatureNew, disablerIfNotFound, InterpreterObject
 )
-from ..mesonlib import MachineChoice, listify
+from ..mesonlib import MachineChoice
 from ..options import OptionKey
 from ..programs import ExternalProgram, NonExistingExternalProgram
 
@@ -51,6 +51,8 @@ if T.TYPE_CHECKING:
 
     class ExtensionModuleKw(SharedModuleKw):
 
+        # Yes, these are different between SharedModule and ExtensionModule
+        install_dir: T.Union[str, bool, None]  # type: ignore[misc]
         subdir: NotRequired[T.Optional[str]]
 
     MaybePythonProg = T.Union[NonExistingExternalProgram, 'PythonExternalProgram']
@@ -140,14 +142,21 @@ class PythonInstallation(_ExternalProgramHolder['PythonExternalProgram']):
 
     @permittedKwargs(mod_kwargs)
     @typed_pos_args('python.extension_module', str, varargs=(str, mesonlib.File, CustomTarget, CustomTargetIndex, GeneratedList, StructuredSources, ExtractedObjects, BuildTarget))
-    @typed_kwargs('python.extension_module', *_MOD_KWARGS, _DEFAULTABLE_SUBDIR_KW, _LIMITED_API_KW, allow_unknown=True)
+    @typed_kwargs(
+        'python.extension_module',
+        *_MOD_KWARGS,
+        _DEFAULTABLE_SUBDIR_KW,
+        _LIMITED_API_KW,
+        KwargInfo('install_dir', (str, bool, NoneType)),
+        allow_unknown=True
+    )
     @InterpreterObject.method('extension_module')
     def extension_module_method(self, args: T.Tuple[str, T.List[BuildTargetSource]], kwargs: ExtensionModuleKw) -> 'SharedModule':
-        if 'install_dir' in kwargs:
+        if kwargs['install_dir'] is not None:
             if kwargs['subdir'] is not None:
                 raise InvalidArguments('"subdir" and "install_dir" are mutually exclusive')
             # the build_target() method now expects this to be correct.
-            kwargs['install_dir'] = listify(kwargs['install_dir'])
+            kwargs['install_dir'] = [kwargs['install_dir']]
         else:
             # We want to remove 'subdir', but it may be None and we want to replace it with ''
             # It must be done this way since we don't allow both `install_dir`