gh-95511: IDLE - fix Shell context menu copy-with-prompts bug (GH-95512)

If one selects whole lines, as the sidebar makes easy, do not
add an extra line.  Only move the end of a selection to the
beginning of the next line when not already at the beginning
of a line.  (Also improve the surrounding code.)
(cherry picked from commit fc31a13dc1799b8d972c1f4ea49f27090aed7f48)

Co-authored-by: Terry Jan Reedy <tjreedy@udel.edu>

1 files changed, 10 insertions, 12 deletions

diff --git a/Lib/idlelib/pyshell.py b/Lib/idlelib/pyshell.py
index 2e54a81..3806122 100755
--- a/Lib/idlelib/pyshell.py
+++ b/Lib/idlelib/pyshell.py
@@ -996,19 +996,17 @@ class PyShell(OutputWindow):
         and/or last lines is selected.
         """
         text = self.text
-
-        selection_indexes = (
-            self.text.index("sel.first linestart"),
-            self.text.index("sel.last +1line linestart"),
-        )
-        if selection_indexes[0] is None:
-            # There is no selection, so do nothing.
-            return
-
-        selected_text = self.text.get(*selection_indexes)
+        selfirst = text.index('sel.first linestart')
+        if selfirst is None:  # Should not be possible.
+            return  # No selection, do nothing.
+        sellast = text.index('sel.last')
+        if sellast[-1] != '0':
+            sellast = text.index("sel.last+1line linestart")
+
+        selected_text = self.text.get(selfirst, sellast)
         selection_lineno_range = range(
-            int(float(selection_indexes[0])),
-            int(float(selection_indexes[1]))
+            int(float(selfirst)),
+            int(float(sellast))
         )
         prompts = [
             self.shell_sidebar.line_prompts.get(lineno)