[FIX] Python script widget: prevent data loss

[markotoplak]

Issue

Users were losing their scripts:

1. If they added a new enrty to the library (button "+") they lost the current script.
2. If they did not save the script into the library it got lots.

Fixes #3531

Description of changes

1. Adding an entry to the library initializes that script with the current script text.
2. The current script text is saved as a schema_only settings and is restored on load. I also added an option to restore the library version.

Includes

• Code changes
• Tests
• Documentation

[markotoplak]

Currently, this PR is changing a setting on every textChanged. I tried with long texts and it did not seem problematic.

Still, I think saving scriptText belongs to storeSpecificSettings, but it is not called without a context. Should I then rather add a context handler?

[codecov]

Codecov Report

Merging #3529 into master will increase coverage by 0.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #3529      +/-   ##
==========================================
+ Coverage   83.67%   83.68%   +0.01%     
==========================================
  Files         370      370              
  Lines       66174    66213      +39     
==========================================
+ Hits        55369    55412      +43     
+ Misses      10805    10801       -4

[markotoplak]

I changed the widget so that it does not waste time for copying text on every input by subclassing a SettingsHandler. The subclassed SettingsHandler runs a widget's method before packing settings. Ideas for a nicer solution?

[astaric]

ContextHandler calls self.settings_from_widget(widget) in pack_data, which in turn calls widget.storeSpecificSettings().

You could consider "promoting" this behaviour to SettingsHandler thus making it available to all widgets, not just those that use contexts?

All widgets have this method (https://github.com/biolab/orange3/blob/master/Orange/widgets/widget.py#L882) and it does nothing by default so it should not break anything.

[markotoplak]

@astaric, true, but I would do it in some other PR. Also the call to retrieveSpecificSettings should be moved...

[astaric]

Then I would at least use the same widget method (storeSpecificSettings) for the job.

This way, if the functionality is ever moved to SettingsHandler, a search for storeSpecificSettings will find this widget and PrepareSavingSettingsHandler can be removed at that point.

[astaric]

Tested 1. and 2., both work as described.

When multiple scripts in the library are unsaved only the changes of the "active" one are saved in the workflow. The rest are still lost. Asking to save to library or discard when switching active script might be a solution (probably not in this PR)

The "library" allows me to deselect the current item (CMD clicking the currently selected item), and edit the script. The changes are "remembered" in the last selected item, but the changed indicator is not shown. When workflow is saved and restored, the changes are reapplied to the active script and changed indicator is shown.