Add tests for triple/double click mouse selection behaviors; fix extension_in_progress not being cleared on selection reset

Agent-Logs-Url: https://github.com/kovidgoyal/kitty/sessions/3ee2e09c-5400-46f6-a556-0bba0e9dcff8

Co-authored-by: kovidgoyal <1308621+kovidgoyal@users.noreply.github.com>

kitty/screen.c

@@ -46,6 +46,7 @@ static const ScreenModes empty_modes = {0, .mDECAWM=true, .mDECTCEM=true, .mDECA
 static void
 clear_selection(Selections *selections) {
     selections->in_progress = false;
+    selections->extension_in_progress = false;
     selections->extend_mode = EXTEND_CELL;
     selections->count = 0;
 }

kitty_tests/mouse.py

@@ -8,6 +8,7 @@ from kitty.fast_data_types import (
     GLFW_MOD_CONTROL,
     GLFW_MOUSE_BUTTON_LEFT,
     GLFW_MOUSE_BUTTON_RIGHT,
+    MOUSE_SELECTION_WORD_AND_LINE_FROM_POINT,
     create_mock_window,
     mock_mouse_selection,
     send_mock_mouse_event_to_window,
@@ -83,11 +84,11 @@ class TestMouse(BaseTest):
                 from kitty.window import as_text
                 self.ae(sl, q, f'{sl!r} != {q!r} after movement to x={x} y={y}. Screen contents: {as_text(s)!r}')
 
-        def multi_click(x=0, y=0, count=2):
+        def multi_click(x=0, y=0, count=2, modifiers=0):
             clear_click_queue = True
             while count > 0:
                 count -= 1
-                ev(GLFW_MOUSE_BUTTON_LEFT, x=x, y=y, clear_click_queue=clear_click_queue)
+                ev(GLFW_MOUSE_BUTTON_LEFT, x=x, y=y, modifiers=modifiers, clear_click_queue=clear_click_queue)
                 clear_click_queue = False
 
         def scroll(x=0, y=0, up=True):
@@ -313,3 +314,68 @@ class TestMouse(BaseTest):
         s.draw('12345')
         press(x=0, y=0)
         move(x=2, y=2, q='abcde\n\n12')
+
+        # Line from begin select (alt+triple click): selects from column 0
+        # (including any leading whitespace), unlike normal triple click which strips it
+        s.reset()
+        s.draw(' 123')
+        s.linefeed(), s.carriage_return()
+        s.draw(' 456')
+        s.linefeed(), s.carriage_return()
+        multi_click(x=1, count=3, modifiers=GLFW_MOD_ALT)
+        self.ae(sel(), ' 123')
+        multi_click(x=1, count=3)
+        self.ae(sel(), '123')
+        multi_click(x=1, count=3, modifiers=GLFW_MOD_ALT)
+        move(y=1)
+        self.ae(sel(), ' 123\n 456')
+        release()
+
+        # Line from point select (ctrl+alt+triple click): selects from click
+        # position to end of line; cannot start before the first non-blank char
+        s.reset()
+        s.draw(' 123')
+        s.linefeed(), s.carriage_return()
+        s.draw(' 456')
+        s.linefeed(), s.carriage_return()
+        multi_click(x=2, count=3, modifiers=GLFW_MOD_ALT | GLFW_MOD_CONTROL)
+        self.ae(sel(), '23')
+        # click before first non-blank: selection starts at first non-blank
+        multi_click(x=0, count=3, modifiers=GLFW_MOD_ALT | GLFW_MOD_CONTROL)
+        self.ae(sel(), '123')
+        # click past last non-blank char: no selection created
+        multi_click(x=4, count=3, modifiers=GLFW_MOD_ALT | GLFW_MOD_CONTROL)
+        self.ae(sel(), '')
+        # drag to next line
+        multi_click(x=2, count=3, modifiers=GLFW_MOD_ALT | GLFW_MOD_CONTROL)
+        move(y=1)
+        self.ae(sel(), '23\n 456')
+        release()
+
+        # Word and line from point: selects the word at the click point and
+        # extends the selection to the end of the line
+        sel_word_and_line = MOUSE_SELECTION_WORD_AND_LINE_FROM_POINT
+        s.reset()
+        s.draw('ab cd')
+        press(x=0)
+        mock_mouse_selection(w, GLFW_MOUSE_BUTTON_LEFT, sel_word_and_line)
+        self.ae(sel(), 'ab cd')
+        press(x=3)
+        mock_mouse_selection(w, GLFW_MOUSE_BUTTON_LEFT, sel_word_and_line)
+        self.ae(sel(), 'cd')
+        # click on space: no word, selects from space to end of line
+        press(x=2)
+        mock_mouse_selection(w, GLFW_MOUSE_BUTTON_LEFT, sel_word_and_line)
+        self.ae(sel(), ' cd')
+        # click past last non-blank char: no selection created
+        press(x=4)
+        mock_mouse_selection(w, GLFW_MOUSE_BUTTON_LEFT, sel_word_and_line)
+        self.ae(sel(), '')
+
+        # Double-click on whitespace: no word found, no selection created
+        s.reset()
+        s.draw('ab cd')
+        multi_click(x=2)
+        self.ae(sel(), '')
+        multi_click(x=2.4)
+        self.ae(sel(), '')