[cmd] Do not allow ctu-ast-mode in non-CTU mode

Option ctu-ast-mode is only meaningful if ctu mode is active.
Exit early if ctu-ast-mode is specified but ctu mode is not enabled.

analyzer/codechecker_analyzer/cmd/analyze.py

@@ -510,7 +510,7 @@ def add_arguments_to_parser(parser):
                                   action='store',
                                   dest='ctu_ast_mode',
                                   choices=['load-from-pch', 'parse-on-demand'],
-                                  default='parse-on-demand',
+                                  default=argparse.SUPPRESS,
                                   help="Choose the way ASTs are loaded during "
                                        "CTU analysis. Mode 'load-from-pch' "
                                        "generates PCH format serialized ASTs "
@@ -852,6 +852,11 @@ def main(args):
     # Process the skip list if present.
     skip_handler = __get_skip_handler(args)
 
+    # CTU loading mode is only meaningful if CTU itself is enabled.
+    if 'ctu_ast_mode' in args and 'ctu_phases' not in args:
+        LOG.error("Analyzer option 'ctu-ast-mode' requires CTU mode enabled")
+        sys.exit(1)
+
     # Enable alpha uniqueing by default if ctu analysis is used.
     if 'none' in args.compile_uniqueing and 'ctu_phases' in args:
         args.compile_uniqueing = "alpha"

analyzer/tests/functional/ctu/test_ctu.py

@@ -14,6 +14,7 @@
 import shutil
 import unittest
 
+from subprocess import run
 from typing import IO
 
 from libtest import env
@@ -78,6 +79,16 @@ def tearDown(self):
         shutil.rmtree(self.report_dir, ignore_errors=True)
         os.chdir(self.__old_pwd)
 
+    @skipUnlessCTUCapable
+    def test_ctu_loading_mode_requires_ctu_mode(self):
+        """ Test ctu-ast-mode option requires ctu mode enabled. """
+        cmd = [self._codechecker_cmd, 'analyze', '-o', self.report_dir,
+               '--analyzers', 'clangsa', '--ctu-ast-mode=load-from-pch',
+               self.buildlog]
+
+        self.assertEqual(1,
+                         run(cmd, cwd=self.test_dir, env=self.env).returncode)
+
     @skipUnlessCTUCapable
     def test_ctu_all_ast_dump_based(self):
         """ Test full CTU AST-dump based analysis. """