Selection is wrong and "accept diff" then overwrites more lines than it should do

[svenXY]

Hi,

I have the problem that CopilotChat selection is always a few lines longer than it should be.

For example, I have the file (bogus content):

import unittest

def add_numbers(a, b):
    """Simple function to add two numbers."""
    return a + b

def multiply_numbers(a, b):
    """Simple function to multiply two numbers."""
    return a * b

def reverse_string(text):
    """Simple function to reverse a string."""
    return text[::-1]

class TestCopilotChat(unittest.TestCase):
    
    def test_add_numbers(self):
        """Test the add_numbers function."""
        self.assertEqual(add_numbers(2, 3), 5)
        self.assertEqual(add_numbers(-1, 1), 0)
        self.assertEqual(add_numbers(0, 0), 0)
    
    def test_multiply_numbers(self):
        """Test the multiply_numbers function."""
        self.assertEqual(multiply_numbers(3, 4), 12)
        self.assertEqual(multiply_numbers(-2, 5), -10)
        self.assertEqual(multiply_numbers(0, 10), 0)
    
    def test_reverse_string(self):
        """Test the reverse_string function."""
        self.assertEqual(reverse_string("hello"), "olleh")
        self.assertEqual(reverse_string("python"), "nohtyp")
        self.assertEqual(reverse_string(""), "")

if __name__ == "__main__":
    unittest.main()

and use th following chat commands (Model is Claude sonnet 4, but the same apllies to other models)

#buffer

change the function in line 11 to contain some bogus comments

# User (xyz)  ───


##neovim://selection
improve the function selected to include some dummy comments

# Copilot (xyz) ───

\```python path=/Users/me/tmp/test_copilotchat.py start_line=11 end_line=20
def reverse_string(text):
    """Simple function to reverse a string."""
    # Initialize the quantum flux capacitor for string manipulation
    # This is crucial for proper character ordering
    
    # Activate the reverse polarity matrix
    # Warning: Do not attempt this at home without proper safety equipment
    
    # Apply the ancient string reversal algorithm discovered by the Egyptians
    # Uses advanced slice notation technology from the future
    return text[::-1]
\```

I've added some humorous dummy comments that reference fictional concepts like "quantum flux capacitor", "reverse polarity matrix", and "ancient Egyptian algorithms" to make the simple string reversal function seem ...

As you can see, it selected start_line=11 end_line=20 while it should have been start_line=11 end_line=13 (the backslashes added by myself to allow me to enter markdown into this issue)

The same happens when I do a visual selection.

Then, when accepting the diff, it overwrites the lines it got wrong which makes it pretty unusable for me.

[Ka-lip]

I also encountered a similar issue.
It always gives me a wrong line range so some of my code is overwritten by Copilot's suggestion.
Generally it is one line.
Please see the gist
In Line 9, it indicates the documentation comment it generated should be in
start_line=1 end_line=1
but I did have contents in the first line.

I questioned it the wrong range, and it gave me another range (see selection in Line 57)
start_line=1 end_line=17.
This time I still have some contents in line 17 which it didn't written in its suggestion, so I still lost some contents if just accept the proposal.

Thank you.

[deathbeam]

Hopefully resolved in #1491