Handle readline completion in one-row terminals

src/prompt_toolkit/key_binding/bindings/completion.py

@@ -105,7 +105,8 @@ def _display_completions_like_readline(
         term_width, max(get_cwidth(c.display_text) for c in completions) + 1
     )
     column_count = max(1, term_width // max_compl_width)
-    completions_per_page = column_count * (term_height - 1)
+    # Keep at least one row when the terminal has no room for the pager.
+    completions_per_page = column_count * max(1, term_height - 1)
     page_count = int(math.ceil(len(completions) / float(completions_per_page)))
     # Note: math.ceil can return float on Python2.
 

tests/test_completion_bindings.py

@@ -0,0 +1,60 @@
+from __future__ import annotations
+
+import asyncio
+from contextlib import asynccontextmanager
+from importlib import import_module
+from unittest.mock import AsyncMock, Mock
+
+import pytest
+
+from prompt_toolkit.application import Application
+from prompt_toolkit.completion import Completion
+from prompt_toolkit.data_structures import Size
+from prompt_toolkit.formatted_text import fragment_list_to_text
+from prompt_toolkit.input import DummyInput
+from prompt_toolkit.key_binding.bindings import completion
+from prompt_toolkit.output import DummyOutput
+
+
+@pytest.mark.parametrize("rows, page_count", [(1, 3), (2, 3), (24, 1)])
+def test_readline_completion_pagination_in_short_terminal(
+    monkeypatch, rows, page_count
+):
+    class Output(DummyOutput):
+        def get_size(self):
+            return Size(rows=rows, columns=12)
+
+    @asynccontextmanager
+    async def in_terminal(**kwargs):
+        yield
+
+    confirm = AsyncMock(return_value=True)
+    more = AsyncMock(return_value=True)
+    monkeypatch.setattr(completion, "in_terminal", in_terminal)
+    monkeypatch.setattr(
+        import_module("prompt_toolkit.shortcuts.prompt"),
+        "create_confirm_session",
+        Mock(return_value=Mock(prompt_async=confirm)),
+    )
+    monkeypatch.setattr(
+        completion, "_create_more_session", Mock(return_value=Mock(prompt_async=more))
+    )
+    app = Application(input=DummyInput(), output=Output())
+    printed = Mock()
+    monkeypatch.setattr(app, "print_text", printed)
+    words = ["alpha", "bravo", "delta", "gamma", "omega", "sigma"]
+
+    async def run():
+        await completion._display_completions_like_readline(
+            app, [Completion(word) for word in words]
+        )
+
+    asyncio.run(run())
+
+    assert printed.call_count == page_count
+    assert confirm.await_count == (1 if page_count > 1 else 0)
+    assert more.await_count == page_count - 1
+    output = "".join(
+        fragment_list_to_text(call.args[0]) for call in printed.call_args_list
+    )
+    assert sorted(output.split()) == sorted(words)