bpo-37706: IDLE - fix sidebar code bug and drag tests (GH-15103)

Convert mouse y to line number in the sidebar rather than the text.
(cherry picked from commit 86f1a18abfee5939452f468d80de998918e2afd2)

Co-authored-by: Tal Einat <taleinat+github@gmail.com>

2 files changed, 37 insertions, 28 deletions

diff --git a/Lib/idlelib/idle_test/htest.py b/Lib/idlelib/idle_test/htest.py
index 6990af5..1373b76 100644
--- a/Lib/idlelib/idle_test/htest.py
+++ b/Lib/idlelib/idle_test/htest.py
@@ -210,13 +210,20 @@ _linenumbers_drag_scrolling_spec = {
     'file': 'sidebar',
     'kwds': {},
     'msg': textwrap.dedent("""\
-        Click on the line numbers and drag down below the edge of the
+        1. Click on the line numbers and drag down below the edge of the
         window, moving the mouse a bit and then leaving it there for a while.
         The text and line numbers should gradually scroll down, with the
         selection updated continuously.
-        Do the same as above, dragging to above the window. The text and line
+
+        2. With the lines still selected, click on a line number above the
+        selected lines. Only the line whose number was clicked should be
+        selected.
+
+        3. Repeat step #1, dragging to above the window. The text and line
         numbers should gradually scroll up, with the selection updated
-        continuously."""),
+        continuously.
+
+        4. Repeat step #2, clicking a line number below the selection."""),
     }
 
 _multi_call_spec = {
diff --git a/Lib/idlelib/idle_test/test_sidebar.py b/Lib/idlelib/idle_test/test_sidebar.py
index 07e8f2e..0f5b4c7 100644
--- a/Lib/idlelib/idle_test/test_sidebar.py
+++ b/Lib/idlelib/idle_test/test_sidebar.py
@@ -240,7 +240,6 @@ class LineNumbersTest(unittest.TestCase):
         self.assert_sidebar_n_lines(1)
         self.assertEqual(get_width(), 1)
 
-    @unittest.skipIf(platform == 'darwin', 'test tk version dependent')
     def test_click_selection(self):
         self.linenumber.show_sidebar()
         self.text.insert('1.0', 'one\ntwo\nthree\nfour\n')
@@ -254,44 +253,47 @@ class LineNumbersTest(unittest.TestCase):
 
         self.assertEqual(self.get_selection(), ('2.0', '3.0'))
 
-    @unittest.skipIf(platform == 'darwin', 'test tk version dependent')
-    def test_drag_selection_down(self):
-        self.linenumber.show_sidebar()
-        self.text.insert('1.0', 'one\ntwo\nthree\nfour\nfive\n')
-        self.root.update()
+    def simulate_drag(self, start_line, end_line):
+        start_x, start_y = self.get_line_screen_position(start_line)
+        end_x, end_y = self.get_line_screen_position(end_line)
 
-        # Drag from the second line to the fourth line.
-        start_x, start_y = self.get_line_screen_position(2)
-        end_x, end_y = self.get_line_screen_position(4)
         self.linenumber.sidebar_text.event_generate('<Button-1>',
                                                     x=start_x, y=start_y)
-        self.linenumber.sidebar_text.event_generate('<B1-Motion>',
-                                                    x=start_x, y=start_y)
-        self.linenumber.sidebar_text.event_generate('<B1-Motion>',
-                                                    x=end_x, y=end_y)
+        self.root.update()
+
+        def lerp(a, b, steps):
+            """linearly interpolate from a to b (inclusive) in equal steps"""
+            last_step = steps - 1
+            for i in range(steps):
+                yield ((last_step - i) / last_step) * a + (i / last_step) * b
+
+        for x, y in zip(
+                map(int, lerp(start_x, end_x, steps=11)),
+                map(int, lerp(start_y, end_y, steps=11)),
+        ):
+            self.linenumber.sidebar_text.event_generate('<B1-Motion>', x=x, y=y)
+            self.root.update()
+
         self.linenumber.sidebar_text.event_generate('<ButtonRelease-1>',
                                                     x=end_x, y=end_y)
         self.root.update()
+
+    def test_drag_selection_down(self):
+        self.linenumber.show_sidebar()
+        self.text.insert('1.0', 'one\ntwo\nthree\nfour\nfive\n')
+        self.root.update()
+
+        # Drag from the second line to the fourth line.
+        self.simulate_drag(2, 4)
         self.assertEqual(self.get_selection(), ('2.0', '5.0'))
 
-    @unittest.skipIf(platform == 'darwin', 'test tk version dependent')
     def test_drag_selection_up(self):
         self.linenumber.show_sidebar()
         self.text.insert('1.0', 'one\ntwo\nthree\nfour\nfive\n')
         self.root.update()
 
         # Drag from the fourth line to the second line.
-        start_x, start_y = self.get_line_screen_position(4)
-        end_x, end_y = self.get_line_screen_position(2)
-        self.linenumber.sidebar_text.event_generate('<Button-1>',
-                                                    x=start_x, y=start_y)
-        self.linenumber.sidebar_text.event_generate('<B1-Motion>',
-                                                    x=start_x, y=start_y)
-        self.linenumber.sidebar_text.event_generate('<B1-Motion>',
-                                                    x=end_x, y=end_y)
-        self.linenumber.sidebar_text.event_generate('<ButtonRelease-1>',
-                                                    x=end_x, y=end_y)
-        self.root.update()
+        self.simulate_drag(4, 2)
         self.assertEqual(self.get_selection(), ('2.0', '5.0'))
 
     def test_scroll(self):