Accept auto-suggestions with 'l' in Vi navigation mode

src/prompt_toolkit/key_binding/bindings/auto_suggest.py

@@ -7,7 +7,7 @@
 import re
 
 from prompt_toolkit.application.current import get_app
-from prompt_toolkit.filters import Condition, emacs_mode
+from prompt_toolkit.filters import Condition, emacs_mode, vi_navigation_mode
 from prompt_toolkit.key_binding.key_bindings import KeyBindings
 from prompt_toolkit.key_binding.key_processor import KeyPressEvent
 
@@ -38,9 +38,25 @@ def suggestion_available() -> bool:
             and app.current_buffer.document.is_cursor_at_the_end
         )
 
+    @Condition
+    def suggestion_available_vi_navigation() -> bool:
+        # In Vi navigation mode, the cursor can never move past the last
+        # character (unlike insert mode), so `is_cursor_at_the_end` can
+        # never be true for a non-empty buffer. Being on the last character
+        # is the navigation-mode equivalent of "at the end" here.
+        app = get_app()
+        buffer = app.current_buffer
+        document = buffer.document
+        return (
+            buffer.suggestion is not None
+            and len(buffer.suggestion.text) > 0
+            and document.cursor_position >= len(document.text) - 1
+        )
+
     @handle("c-f", filter=suggestion_available)
     @handle("c-e", filter=suggestion_available)
     @handle("right", filter=suggestion_available)
+    @handle("l", filter=suggestion_available_vi_navigation & vi_navigation_mode)
     def _accept(event: E) -> None:
         """
         Accept suggestion.
@@ -49,6 +65,11 @@ def _accept(event: E) -> None:
         suggestion = b.suggestion
 
         if suggestion:
+            # In Vi navigation mode the cursor sits *on* the last character
+            # rather than past it, so move to the true end before inserting,
+            # otherwise the suggestion would be spliced in before that
+            # character instead of appended.
+            b.cursor_position = len(b.text)
             b.insert_text(suggestion.text)
 
     @handle("escape", "f", filter=suggestion_available & emacs_mode)

tests/test_cli.py

@@ -5,10 +5,12 @@
 
 from __future__ import annotations
 
+import asyncio
 from functools import partial
 
 import pytest
 
+from prompt_toolkit.auto_suggest import AutoSuggestFromHistory
 from prompt_toolkit.clipboard import ClipboardData, InMemoryClipboard
 from prompt_toolkit.enums import EditingMode
 from prompt_toolkit.filters import ViInsertMode
@@ -37,6 +39,7 @@ def _feed_cli_with_input(
     multiline=False,
     check_line_ending=True,
     key_bindings=None,
+    auto_suggest=None,
 ):
     """
     Create a Prompt, feed it with the given user input and return the CLI
@@ -58,6 +61,7 @@ def _feed_cli_with_input(
             multiline=multiline,
             clipboard=clipboard,
             key_bindings=key_bindings,
+            auto_suggest=auto_suggest,
         )
 
         _ = session.prompt()
@@ -607,6 +611,47 @@ def test_vi_cursor_movements():
     assert result.text == "heXlo"
 
 
+def test_vi_accept_suggestion_with_l():
+    """
+    In Vi navigation mode, 'l' should accept an available auto-suggestion,
+    the same way the right arrow key already does (fish-shell style).
+
+    This can't use `_feed_cli_with_input`: auto-suggestions are computed by
+    a background asyncio task scheduled on text changes, so the key(s) that
+    accept the suggestion have to be sent as a separate write, after
+    yielding to the event loop, or the suggestion never gets computed in
+    time.
+    """
+
+    async def run(after_escape):
+        history = InMemoryHistory()
+        history.append_string("hello world")
+
+        with create_pipe_input() as inp:
+            session = PromptSession(
+                input=inp,
+                output=DummyOutput(),
+                editing_mode=EditingMode.VI,
+                history=history,
+                auto_suggest=AutoSuggestFromHistory(),
+            )
+            task = asyncio.ensure_future(session.app.run_async())
+            inp.send_text("hello")
+            await asyncio.sleep(0.05)  # Let the suggestion get computed.
+            inp.send_text("\x1b" + after_escape + "\r")
+            return await asyncio.wait_for(task, timeout=2)
+
+    # In navigation mode, the cursor sits *on* the last character (unlike
+    # insert mode), so a single "l" both counts as "at the end" and accepts
+    # the suggestion.
+    assert asyncio.run(run("l")) == "hello world"
+
+    # Away from the last character (here, moved to the start with "0"),
+    # "l" keeps its normal meaning of moving the cursor one position right,
+    # even though a suggestion is available.
+    assert asyncio.run(run("0l")) == "hello"
+
+
 def test_vi_operators():
     feed = partial(_feed_cli_with_input, editing_mode=EditingMode.VI)