Honor multiline filters in TextArea layout

src/prompt_toolkit/widgets/base.py

@@ -127,7 +127,8 @@ class TextArea:
     Buffer attributes:
 
     :param text: The initial text.
-    :param multiline: If True, allow multiline input.
+    :param multiline: A bool or :class:`~prompt_toolkit.filters.Filter`
+        controlling whether multiline input is allowed.
     :param completer: :class:`~prompt_toolkit.completion.Completer` instance
         for auto completion.
     :param complete_while_typing: Boolean.
@@ -252,19 +253,16 @@ def __init__(
             focus_on_click=focus_on_click,
         )
 
-        if multiline:
-            if scrollbar:
-                right_margins = [ScrollbarMargin(display_arrows=True)]
-            else:
-                right_margins = []
-            if line_numbers:
-                left_margins = [NumberedMargin()]
-            else:
-                left_margins = []
+        if scrollbar:
+            right_margins = [
+                ConditionalMargin(ScrollbarMargin(display_arrows=True), multiline)
+            ]
         else:
-            height = D.exact(1)
-            left_margins = []
             right_margins = []
+        if line_numbers:
+            left_margins = [ConditionalMargin(NumberedMargin(), multiline)]
+        else:
+            left_margins = []
 
         style = "class:text-area " + style
 
@@ -273,7 +271,7 @@ def __init__(
             height = D(min=1)
 
         self.window = Window(
-            height=height,
+            height=lambda: height if is_true(multiline) else D.exact(1),
             width=width,
             dont_extend_height=dont_extend_height,
             dont_extend_width=dont_extend_width,

tests/test_widgets.py

@@ -1,8 +1,18 @@
 from __future__ import annotations
 
+from asyncio import run, wait_for
+
+import pytest
+
+from prompt_toolkit.application import Application, get_app
+from prompt_toolkit.filters import Always, Condition, Never
 from prompt_toolkit.formatted_text import fragment_list_to_text
-from prompt_toolkit.layout import to_window
-from prompt_toolkit.widgets import Button
+from prompt_toolkit.input import create_pipe_input
+from prompt_toolkit.key_binding import KeyBindings
+from prompt_toolkit.layout import Layout, UIContent, to_window
+from prompt_toolkit.layout.dimension import to_dimension
+from prompt_toolkit.output import DummyOutput
+from prompt_toolkit.widgets import Button, TextArea
 
 
 def _to_text(button: Button) -> str:
@@ -18,3 +28,78 @@ def test_default_button():
 def test_custom_button():
     button = Button("Exit", left_symbol="[", right_symbol="]")
     assert _to_text(button) == "[   Exit   ]"
+
+
+@pytest.mark.parametrize(
+    "multiline, enabled",
+    [
+        (True, True),
+        (False, False),
+        (Always(), True),
+        (Never(), False),
+        (Condition(lambda: True), True),
+        (Condition(lambda: False), False),
+    ],
+)
+def test_text_area_multiline_filter(multiline, enabled):
+    area = TextArea(multiline=multiline, height=5, line_numbers=True, scrollbar=True)
+    assert area.buffer.multiline() is enabled
+    dimension = to_dimension(area.window.height)
+    assert dimension.min == dimension.max == (5 if enabled else 1)
+    get_content = lambda: UIContent(line_count=2)
+    assert sum(m.get_width(get_content) for m in area.window.left_margins) == (
+        3 if enabled else 0
+    )
+    assert sum(m.get_width(get_content) for m in area.window.right_margins) == (
+        1 if enabled else 0
+    )
+
+
+def test_text_area_multiline_filter_updates_layout():
+    enabled = False
+    height = 5
+    area = TextArea(
+        multiline=Condition(lambda: enabled),
+        height=lambda: height,
+        line_numbers=True,
+        scrollbar=True,
+    )
+    get_content = lambda: UIContent(line_count=2)
+
+    for enabled, height in [(False, 5), (True, 5), (True, 7), (False, 7), (True, 7)]:
+        assert area.buffer.multiline() is enabled
+        dimension = to_dimension(area.window.height)
+        assert dimension.min == dimension.max == (height if enabled else 1)
+        assert sum(m.get_width(get_content) for m in area.window.left_margins) == (
+            3 if enabled else 0
+        )
+        assert sum(m.get_width(get_content) for m in area.window.right_margins) == (
+            1 if enabled else 0
+        )
+
+
+def test_text_area_multiline_filter_changes_enter_behavior():
+    async def check():
+        enabled = True
+        bindings = KeyBindings()
+
+        @bindings.add("c-t")
+        def toggle(event):
+            nonlocal enabled
+            enabled = not enabled
+
+        area = TextArea(
+            multiline=Condition(lambda: enabled),
+            accept_handler=lambda buffer: get_app().exit(result=buffer.text),
+        )
+        with create_pipe_input() as pipe_input:
+            app = Application(
+                layout=Layout(area),
+                key_bindings=bindings,
+                input=pipe_input,
+                output=DummyOutput(),
+            )
+            pipe_input.send_text("first\r\x14second\r")
+            assert await wait_for(app.run_async(), timeout=3) == "first\nsecond"
+
+    run(check())