Add config options related to Vi input mode

Setting `vi_start_in_nav_mode` to `True` enables `NAVIGATION` mode on startup.
The issue is that due to the current behaviour of `ViState.reset()` input mode
gets resetted back to `INSERT` on the every iteration of the main loop. In order
to at one hand to provide the user with desired behaviour and on the other hand
doesn't introduce breaking changes the other option `vi_keep_last_used_mode` was
introduced which sets `input_mode` to the state observed before reset.

`vi_keep_last_used_mode` can be useful even with `vi_start_in_nav_mode` set to
`False` in the case the user prefer to start in `INSERT` mode but still wants to
maintain the last mode he was in.

In the case of `vi_keep_last_used_mode` set to `False` and
`vi_start_in_nav_mode` to `True` `NAVIGATION` mode is set on every iteration the
same way `INSERT` was set before this commit.

Fixes #258.

examples/ptpython_config/config.py

@@ -119,6 +119,12 @@ def configure(repl):
     # Syntax.
     repl.enable_syntax_highlighting = True
 
+    # Get into Vi navigation mode at startup
+    repl.vi_start_in_nav_mode = False
+
+    # Preserve last used Vi input mode between main loop iterations
+    repl.vi_keep_last_used_mode = False
+
     # Install custom colorscheme named 'my-colorscheme' and use it.
     """
     repl.install_ui_colorscheme('my-colorscheme', _custom_ui_colorscheme)

ptpython/python_input.py

@@ -298,6 +298,12 @@ def __init__(
         # (Never run more than one at the same time.)
         self._get_signatures_thread_running: bool = False
 
+        # Get into Vi navigation mode at startup
+        self.vi_start_in_nav_mode: bool = False
+
+        # Preserve last used Vi input mode between main loop iterations
+        self.vi_keep_last_used_mode: bool = False
+
         self.style_transformation = merge_style_transformations(
             [
                 ConditionalStyleTransformation(
@@ -327,6 +333,9 @@ def __init__(
         if vi_mode:
             self.app.editing_mode = EditingMode.VI
 
+        if vi_mode and self.vi_start_in_nav_mode:
+            self.app.vi_state.input_mode = InputMode.NAVIGATION
+
     def _accept_handler(self, buff: Buffer) -> bool:
         app = get_app()
         app.exit(result=buff.text)

ptpython/repl.py

@@ -22,6 +22,7 @@
     merge_formatted_text,
 )
 from prompt_toolkit.formatted_text.utils import fragment_list_width
+from prompt_toolkit.key_binding.vi_state import InputMode
 from prompt_toolkit.patch_stdout import patch_stdout as patch_stdout_context
 from prompt_toolkit.shortcuts import clear_title, print_formatted_text, set_title
 from prompt_toolkit.utils import DummyContext
@@ -70,9 +71,19 @@ def prompt() -> str:
                 # This happens when the user used `asyncio.run()`.
                 old_loop = None
 
+            # Capture the current input_mode in order to restore it after reset,
+            # for ViState.reset() sets it to InputMode.INSERT unconditionally and
+            # doesn't accept any arguments despite the docstring says otherwise.
+            def pre_run(last_input_mode=self.app.vi_state.input_mode):
+                if self.vi_keep_last_used_mode:
+                    self.app.vi_state.input_mode = last_input_mode
+
+                if not self.vi_keep_last_used_mode and self.vi_start_in_nav_mode:
+                    self.app.vi_state.input_mode = InputMode.NAVIGATION
+
             asyncio.set_event_loop(self.pt_loop)
             try:
-                return self.app.run()  # inputhook=inputhook)
+                return self.app.run(pre_run)  # inputhook=inputhook)
             finally:
                 # Restore the original event loop.
                 asyncio.set_event_loop(old_loop)