Fix KeyError in Python module

0e7fb07 introduced a subtile bug in the Python module.
If a python version is found, but is missing a required module,
it is added to the list of python installations, but the
`run_bytecompile` attribute for that version was not initialized.
Therefore, if any other python version added something to install, it
was raising a KeyError when trying to read the `run_bytecompile`
attribute for the python version with missing module.

mesonbuild/modules/python.py

@@ -74,6 +74,7 @@ class PythonExternalProgram(BasicPythonExternalProgram):
         if ret:
             self.platlib = self._get_path(state, 'platlib')
             self.purelib = self._get_path(state, 'purelib')
+            self.run_bytecompile.setdefault(self.info['version'], False)
         return ret
 
     def _get_path(self, state: T.Optional['ModuleState'], key: str) -> str:
@@ -544,7 +545,6 @@ class PythonModule(ExtensionModule):
             assert isinstance(python, PythonExternalProgram), 'for mypy'
             python = copy.copy(python)
             python.pure = kwargs['pure']
-            python.run_bytecompile.setdefault(python.info['version'], False)
             return python
 
         raise mesonlib.MesonBugException('Unreachable code was reached (PythonModule.find_installation).')

test cases/python/5 modules kwarg/meson.build

@@ -1,7 +1,19 @@
-project('python kwarg')
+project('python kwarg',
+    default_options: [
+        'python.bytecompile=-1',
+        'python.purelibdir=/pure',
+    ]
+)
 
 py = import('python')
-prog_python = py.find_installation('python3', modules : ['os', 'sys', 're'])
+prog_python = py.find_installation('python3', modules : ['os', 'sys', 're'], pure: true)
 assert(prog_python.found() == true, 'python not found when should be')
+
+# In meson 1.2 - 1.3.2, there was a bug when a python installation
+# with a different version did not have a module, and we try to install
+# something with another python version...
+py.find_installation('python3.7', modules: ['notamodule'], required: false)
+prog_python.install_sources('a.py')
+
 prog_python = py.find_installation('python3', modules : ['thisbetternotexistmod'], required : false)
 assert(prog_python.found() == false, 'python not found but reported as found')

test cases/python/5 modules kwarg/test.json

@@ -0,0 +1,5 @@
+{
+    "installed": [
+        { "type": "python_file", "file": "pure/a.py"}
+    ]
+}