IDLE right click outside of any selection should clear it

[terryjreedy]

BPO	39885
Nosy	@terryjreedy, @miss-islington
PRs	bpo-39885: IDLE context menu clears selection  #18859 [3.8] bpo-39885: IDLE context menu clears selection (GH-18859) #18860 [3.7] bpo-39885: IDLE context menu clears selection (GH-18859) #18861 bpo-39885: IDLE: Leave selection when right click within #18951 [3.9] bpo-39885: Make IDLE context menu cut and copy work again (GH-18951) #20522 [3.8] bpo-39885: Make IDLE context menu cut and copy work again (GH-18951) #20523 [3.7] bpo-39885: Make IDLE context menu cut and copy work again (GH-18951) #20524

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = 'https://github.com/terryjreedy'
closed_at = <Date 2020-05-29.23:31:23.218>
created_at = <Date 2020-03-07.05:08:09.444>
labels = ['type-bug', '3.8', '3.9', '3.10', 'expert-IDLE', '3.7']
title = 'IDLE right click outside of any selection should clear it'
updated_at = <Date 2020-05-29.23:31:23.216>
user = 'https://github.com/terryjreedy'

bugs.python.org fields:

activity = <Date 2020-05-29.23:31:23.216>
actor = 'terry.reedy'
assignee = 'terry.reedy'
closed = True
closed_date = <Date 2020-05-29.23:31:23.218>
closer = 'terry.reedy'
components = ['IDLE']
creation = <Date 2020-03-07.05:08:09.444>
creator = 'terry.reedy'
dependencies = []
files = []
hgrepos = []
issue_num = 39885
keywords = ['patch']
message_count = 12.0
messages = ['363577', '363578', '363580', '363581', '363675', '363676', '363677', '363991', '370337', '370339', '370340', '370341']
nosy_count = 2.0
nosy_names = ['terry.reedy', 'miss-islington']
pr_nums = ['18859', '18860', '18861', '18951', '20522', '20523', '20524']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue39885'
versions = ['Python 3.7', 'Python 3.8', 'Python 3.9', 'Python 3.10']

[terryjreedy]

In text editors, right click commonly brings up a context menu, often including Cut, Copy, Paste, and Delete, with inapplicable entries grayed out. There are at least 2 'standard' behaviors (at least on Windows) with respect to the cursor and selections.

0 (Examples: Windows Notepad and Firefox entry box). The cursor stays where it is and a selection stays selected, even if one has scrolled the cursor and possible selection off the screen with mousewheel or scrollbar. Paste inserts at the possibly hidden cursor, deleting any possibly hidden selection. The view jumps back to the cursor after Paste but not after Copy and Close (Esc).

1 (Examples: Windows Notepad++ and Libre Office). The cursor jumps to the spot of the click, the same as with a left click. Any selection, possibly not visible, is unselected, the same as with a left click. Exception: a right click within an exception leaves the selection and cursor (at one of the ends) alone.

IDLE follows a bit of each pattern and neither. Right click always moves the cursor, even within a selection, but never clears a selection. I believe that this is an accident of history. Originally, context menus only had 'Go to file/line' in Shell and grep output and 'Set/Clear Breakpoint' in editors. There was no reason to touch a selection even if the cursor was moved. Cut/Copy/Paste were added in 2012 because they are standard.

To really be standard, right click should consistently act like left click and unselect. This prevents accidental deletion. This would also be consistent with making 'Go to line' act the same.

Also, right click within a selection should not move the cursor.

[terryjreedy]

Spinoff from bpo-39852. At least the selection clear code added there should be pulled into a module level function and tested.

[terryjreedy]

(Mozilla) Thunderbird, unlike (Mozilla) Firefox, has move/clear right clicks.