Fix PromptSession validator=None reset

src/prompt_toolkit/shortcuts/prompt.py

@@ -225,6 +225,13 @@ class CompleteStyle(str, Enum):
 _T = TypeVar("_T")
 
 
+class _Unset:
+    pass
+
+
+_UNSET = _Unset()
+
+
 class PromptSession(Generic[_T]):
     """
     PromptSession for a prompt application, which can be used as a GNU Readline
@@ -910,7 +917,7 @@ def prompt(
         validate_while_typing: FilterOrBool | None = None,
         complete_style: CompleteStyle | None = None,
         auto_suggest: AutoSuggest | None = None,
-        validator: Validator | None = None,
+        validator: Validator | None | _Unset = _UNSET,
         clipboard: Clipboard | None = None,
         mouse_support: FilterOrBool | None = None,
         input_processors: list[Processor] | None = None,
@@ -940,10 +947,10 @@ class itself. For these, passing in ``None`` will keep the current
         attribute for the session, which means that it applies to the current,
         but also to the next prompts.
 
-        Note that in order to erase a ``Completer``, ``Validator`` or
-        ``AutoSuggest``, you can't use ``None``. Instead pass in a
-        ``DummyCompleter``, ``DummyValidator`` or ``DummyAutoSuggest`` instance
-        respectively. For a ``Lexer`` you can pass in an empty ``SimpleLexer``.
+        Note that in order to erase a ``Completer`` or ``AutoSuggest``, you
+        can't use ``None``. Instead pass in a ``DummyCompleter`` or
+        ``DummyAutoSuggest`` instance respectively. For a ``Lexer`` you can
+        pass in an empty ``SimpleLexer``.
 
         Additional arguments, specific for this prompt:
 
@@ -1024,8 +1031,8 @@ class itself. For these, passing in ``None`` will keep the current
             self.complete_style = complete_style
         if auto_suggest is not None:
             self.auto_suggest = auto_suggest
-        if validator is not None:
-            self.validator = validator
+        if validator is not _UNSET:
+            self.validator = cast(Validator | None, validator)
         if clipboard is not None:
             self.clipboard = clipboard
         if mouse_support is not None:
@@ -1150,7 +1157,7 @@ async def prompt_async(
         validate_while_typing: FilterOrBool | None = None,
         complete_style: CompleteStyle | None = None,
         auto_suggest: AutoSuggest | None = None,
-        validator: Validator | None = None,
+        validator: Validator | None | _Unset = _UNSET,
         clipboard: Clipboard | None = None,
         mouse_support: FilterOrBool | None = None,
         input_processors: list[Processor] | None = None,
@@ -1221,8 +1228,8 @@ async def prompt_async(
             self.complete_style = complete_style
         if auto_suggest is not None:
             self.auto_suggest = auto_suggest
-        if validator is not None:
-            self.validator = validator
+        if validator is not _UNSET:
+            self.validator = cast(Validator | None, validator)
         if clipboard is not None:
             self.clipboard = clipboard
         if mouse_support is not None:

tests/test_cli.py

@@ -5,6 +5,7 @@
 
 from __future__ import annotations
 
+import asyncio
 from functools import partial
 
 import pytest
@@ -19,6 +20,7 @@
 from prompt_toolkit.key_binding.key_bindings import KeyBindings
 from prompt_toolkit.output import DummyOutput
 from prompt_toolkit.shortcuts import PromptSession
+from prompt_toolkit.validation import Validator
 
 
 def _history():
@@ -71,6 +73,58 @@ def test_simple_text_input():
     assert cli.current_buffer.text == "hello"
 
 
+def test_prompt_validator_none_clears_session_validator():
+    validator = Validator.from_callable(lambda text: True)
+
+    with create_pipe_input() as inp:
+        inp.send_text("hello\r")
+        session = PromptSession(
+            input=inp,
+            output=DummyOutput(),
+            validator=validator,
+        )
+
+        session.prompt(validator=None)
+
+    assert session.validator is None
+
+
+def test_prompt_without_validator_keeps_session_validator():
+    validator = Validator.from_callable(lambda text: True)
+
+    with create_pipe_input() as inp:
+        inp.send_text("hello\r")
+        session = PromptSession(
+            input=inp,
+            output=DummyOutput(),
+            validator=validator,
+        )
+
+        session.prompt()
+
+    assert session.validator is validator
+
+
+def test_prompt_async_validator_none_clears_session_validator():
+    validator = Validator.from_callable(lambda text: True)
+
+    async def run_prompt() -> PromptSession[str]:
+        with create_pipe_input() as inp:
+            inp.send_text("hello\r")
+            session = PromptSession(
+                input=inp,
+                output=DummyOutput(),
+                validator=validator,
+            )
+
+            await session.prompt_async(validator=None)
+
+        return session
+
+    session = asyncio.run(run_prompt())
+    assert session.validator is None
+
+
 def test_emacs_cursor_movements():
     """
     Test cursor movements with Emacs key bindings.