gh-118878: Pyrepl: show completions menu below the current line

Lib/_pyrepl/commands.py

@@ -282,7 +282,7 @@ def do(self) -> None:
             x, y = r.pos2xy()
             new_y = y + 1
 
-            if new_y > r.max_row():
+            if r.eol() == len(b):
                 if r.historyi < len(r.history):
                     r.select_item(r.historyi + 1)
                     r.pos = r.eol(0)
@@ -309,7 +309,7 @@ def do(self) -> None:
 class left(MotionCommand):
     def do(self) -> None:
         r = self.reader
-        for i in range(r.get_arg()):
+        for _ in range(r.get_arg()):
             p = r.pos - 1
             if p >= 0:
                 r.pos = p
@@ -321,7 +321,7 @@ class right(MotionCommand):
     def do(self) -> None:
         r = self.reader
         b = r.buffer
-        for i in range(r.get_arg()):
+        for _ in range(r.get_arg()):
             p = r.pos + 1
             if p <= len(b):
                 r.pos = p

Lib/_pyrepl/completing_reader.py

@@ -260,10 +260,15 @@ def after_command(self, cmd: Command) -> None:
     def calc_screen(self) -> list[str]:
         screen = super().calc_screen()
         if self.cmpltn_menu_visible:
-            ly = self.lxy[1]
+            # We display the completions menu below the current prompt
+            ly = self.lxy[1] + 1
             screen[ly:ly] = self.cmpltn_menu
-            self.screeninfo[ly:ly] = [(0, [])]*len(self.cmpltn_menu)
-            self.cxy = self.cxy[0], self.cxy[1] + len(self.cmpltn_menu)
+            # If we're not in the middle of multiline edit, don't append to screeninfo
+            # since that screws up the position calculation in pos2xy function.
+            # This is a hack to prevent the cursor jumping
+            # into the completions menu when pressing left or down arrow.
+            if self.pos != len(self.buffer):
+                self.screeninfo[ly:ly] = [(0, [])]*len(self.cmpltn_menu)
         return screen
 
     def finish(self) -> None:

Lib/test/test_pyrepl/test_pyrepl.py

@@ -850,7 +850,7 @@ def test_global_namespace_completion(self):
         output = multiline_input(reader, namespace)
         self.assertEqual(output, "python")
 
-    def test_updown_arrow_with_completion_menu(self):
+    def test_up_down_arrow_with_completion_menu(self):
         """Up arrow in the middle of unfinished tab completion when the menu is displayed
         should work and trigger going back in history. Down arrow should subsequently
         get us back to the incomplete command."""
@@ -860,6 +860,7 @@ def test_updown_arrow_with_completion_menu(self):
         events = itertools.chain(
             code_to_events(code),
             [
+                Event(evt="key", data="down", raw=bytearray(b"\x1bOB")),
                 Event(evt="key", data="up", raw=bytearray(b"\x1bOA")),
                 Event(evt="key", data="down", raw=bytearray(b"\x1bOB")),
             ],

Lib/test/test_pyrepl/test_reader.py

@@ -295,8 +295,8 @@ def test_completions_updated_on_key_press(self):
 
         actual = reader.screen
         self.assertEqual(len(actual), 2)
-        self.assertEqual(actual[0].rstrip(), "itertools.accumulate(")
-        self.assertEqual(actual[1], f"{code}a")
+        self.assertEqual(actual[0], f"{code}a")
+        self.assertEqual(actual[1].rstrip(), "itertools.accumulate(")
 
     def test_key_press_on_tab_press_once(self):
         namespace = {"itertools": itertools}

Misc/NEWS.d/next/Library/2024-07-14-23-19-20.gh-issue-119257.9OEzcN.rst

@@ -0,0 +1,2 @@
+Show tab completions menu below the current line, which results in less
+janky behaviour, and fixes a cursor movement bug. Patch by Daniel Hollas