{Core} improve tab completion performance

.vscode/launch.json

@@ -38,6 +38,26 @@
                 "--help"
             ],
             "console": "integratedTerminal",
+        },
+        {
+            "name": "Azure CLI Debug Tab Completion (External Console)",
+            "type": "debugpy",
+            "request": "launch",
+            "program": "${workspaceFolder}/src/azure-cli/azure/cli/__main__.py",
+            "args": [],
+            "console": "externalTerminal",
+            "cwd": "${workspaceFolder}",
+            "env": {
+                "_ARGCOMPLETE": "1",
+                "COMP_LINE": "az vm create --",
+                "COMP_POINT": "18",
+                "_ARGCOMPLETE_SUPPRESS_SPACE": "0",
+                "_ARGCOMPLETE_IFS": "\n",
+                "_ARGCOMPLETE_SHELL": "powershell",
+                "ARGCOMPLETE_USE_TEMPFILES": "1",
+                "_ARGCOMPLETE_STDOUT_FILENAME": "C:\\temp\\az_debug_completion.txt"
+            },
+            "justMyCode": false
         }
     ]
 }

src/azure-cli-core/azure/cli/core/__init__.py

@@ -432,9 +432,23 @@ def _get_extension_suppressions(mod_loaders):
             index_result = command_index.get(args)
             if index_result:
                 index_modules, index_extensions = index_result
+                # Special case for top-level completion - create minimal command groups
+                if index_modules == '__top_level_completion__':
+                    from azure.cli.core.commands import AzCliCommand
+                    # index_extensions contains the command names, not extensions
+                    for cmd_name in index_extensions:
+                        # Create a minimal command entry for tab completion
+                        # This allows argparse to see the command without loading the module
+                        if cmd_name not in self.command_table:
+                            self.command_table[cmd_name] = AzCliCommand(
+                                self, cmd_name, lambda: None
+                            )
+                    return self.command_table
+
                 # Always load modules and extensions, because some of them (like those in
                 # ALWAYS_LOADED_EXTENSIONS) don't expose a command, but hooks into handlers in CLI core
                 _update_command_table_from_modules(args, index_modules)
+
                 # The index won't contain suppressed extensions
                 _update_command_table_from_extensions([], index_extensions)
 
@@ -597,6 +611,13 @@ def get(self, args):
         # Make sure the top-level command is provided, like `az version`.
         # Skip command index for `az` or `az --help`.
         if not args or args[0].startswith('-'):
+            # For top-level completion (az [tab])
+            if not args and self.cli_ctx.data.get('completer_active'):
+                # Return a special marker so we know to skip module loading for top-level completion
+                index = self.INDEX[self._COMMAND_INDEX]
+                all_commands = list(index.keys())
+                logger.debug("Top-level completion: %d commands available", len(all_commands))
+                return '__top_level_completion__', all_commands  # special marker, command list
             return None
 
         # Get the top-level command, like `network` in `network vnet create -h`

src/azure-cli-core/azure/cli/core/tests/test_argcomplete.py

@@ -64,3 +64,21 @@ def dummy_completor(*args, **kwargs):
         with open('argcomplete.out') as f:
             self.assertEqual(f.read(), 'dummystorage ')
         os.remove('argcomplete.out')
+
+    def test_top_level_completion(self):
+        """Test that top-level completion (az [tab]) returns command names from index"""
+        import os
+        import sys
+
+        if sys.platform == 'win32':
+            self.skipTest('Skip argcomplete test on Windows')
+
+        run_cmd(['az'], env=self.argcomplete_env('az ', '3'))
+        with open('argcomplete.out') as f:
+            completions = f.read().split()
+            # Verify common top-level commands are present
+            self.assertIn('account', completions)
+            self.assertIn('vm', completions)
+            self.assertIn('network', completions)
+            self.assertIn('storage', completions)
+        os.remove('argcomplete.out')