python module: make external program wrapper have access to useful metadata

Basically just reorganize code. Try to make it a little neater, while
we're at it.

(cherry picked from commit d9a9c3b5da)

mesonbuild/modules/python.py

@@ -309,12 +309,43 @@ class PythonExternalProgram(ExternalProgram):
             'version': '0.0',
         }
 
+    def _check_version(self, version: str) -> bool:
+        if self.name == 'python2':
+            return mesonlib.version_compare(version, '< 3.0')
+        elif self.name == 'python3':
+            return mesonlib.version_compare(version, '>= 3.0')
+        return True
+
+    def sanity(self) -> 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)
+        try:
+            info = json.loads(stdout)
+        except json.JSONDecodeError:
+            info = None
+            mlog.debug('Could not introspect Python (%s): exit code %d' % (str(p.args), p.returncode))
+            mlog.debug('Program stdout:\n')
+            mlog.debug(stdout)
+            mlog.debug('Program stderr:\n')
+            mlog.debug(stderr)
+
+        if info is not None and self._check_version(info['version']):
+            variables = info['variables']
+            info['suffix'] = variables.get('EXT_SUFFIX') or variables.get('SO') or variables.get('.so')
+            self.info = T.cast('PythonIntrospectionDict', info)
+            return True
+        else:
+            return False
+
+
 class PythonInstallation(ExternalProgramHolder):
     def __init__(self, python, interpreter):
         ExternalProgramHolder.__init__(self, python, interpreter)
         info = python.info
         prefix = self.interpreter.environment.coredata.get_option(mesonlib.OptionKey('prefix'))
         self.variables = info['variables']
+        self.suffix = info['suffix']
         self.paths = info['paths']
         install_paths = info['install_paths']
         self.platlib_install_path = os.path.join(prefix, install_paths['platlib'][1:])
@@ -360,11 +391,9 @@ class PythonInstallation(ExternalProgramHolder):
                 new_deps.append(dep)
             kwargs['dependencies'] = new_deps
 
-        suffix = self.variables.get('EXT_SUFFIX') or self.variables.get('SO') or self.variables.get('.so')
-
         # msys2's python3 has "-cpython-36m.dll", we have to be clever
         # FIXME: explain what the specific cleverness is here
-        split, suffix = suffix.rsplit('.', 1)
+        split, suffix = self.suffix.rsplit('.', 1)
         args[0] += split
 
         kwargs['name_prefix'] = ''
@@ -518,12 +547,6 @@ class PythonModule(ExtensionModule):
         else:
             return None
 
-    def _check_version(self, name_or_path, version):
-        if name_or_path == 'python2':
-            return mesonlib.version_compare(version, '< 3.0')
-        elif name_or_path == 'python3':
-            return mesonlib.version_compare(version, '>= 3.0')
-        return True
 
     @FeatureNewKwargs('python.find_installation', '0.49.0', ['disabler'])
     @FeatureNewKwargs('python.find_installation', '0.51.0', ['modules'])
@@ -603,21 +626,9 @@ class PythonModule(ExtensionModule):
                 raise mesonlib.MesonException('{} is missing modules: {}'.format(name_or_path or 'python', ', '.join(missing_modules)))
             return NonExistingExternalProgram()
         else:
-            # Sanity check, we expect to have something that at least quacks in tune
-            try:
-                cmd = python.get_command() + ['-c', INTROSPECT_COMMAND]
-                p, stdout, stderr = mesonlib.Popen_safe(cmd)
-                info = json.loads(stdout)
-            except json.JSONDecodeError:
-                info = None
-                mlog.debug('Could not introspect Python (%s): exit code %d' % (str(p.args), p.returncode))
-                mlog.debug('Program stdout:\n')
-                mlog.debug(stdout)
-                mlog.debug('Program stderr:\n')
-                mlog.debug(stderr)
-
-            if isinstance(info, dict) and 'version' in info and self._check_version(name_or_path, info['version']):
-                python.info = info
+            sane = python.sanity()
+
+            if sane:
                 return python
             else:
                 if required: