Use a global copy buffer

[amolenaar]

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Documentation content changes

What is the current behavior?

When you copy some items in a diagram, you can only paste them in the same model.

Issue Number: #463

What is the new behavior?

You can copy, and then paste the items in a different diagram. The diagram items are backed by their model elements.

Does this PR introduce a breaking change?

• Yes
• No

Other information

The current implementation (a global variable) is not really nice. But it proves the application can handle this copy/paste behavior. The actual behavior should work via an gaphor.appservice. However, there's no way to inject an app service in a session. And I'm not sure if we want to.

[sourcery-ai]

Sourcery Code Quality Report

✅  Merging this PR will increase code quality in the affected files by 1.18%.

Quality metrics	Before	After	Change
Complexity	1.33 ⭐	1.23 ⭐	-0.10 👍
Method Length	44.27 ⭐	43.38 ⭐	-0.89 👍
Working memory	4.13 ⭐	3.77 ⭐	-0.36 👍
Quality	89.04% ⭐	90.22% ⭐	1.18% 👍

Other metrics	Before	After	Change
Lines	172	153	-19

Changed files	Quality Before	Quality After	Quality Change
gaphor/services/copyservice.py	89.93% ⭐	91.83% ⭐	1.90% 👍
gaphor/services/tests/test_copyservice.py	86.60% ⭐	86.60% ⭐	0.00%

Here are some functions in these files that still need a tune-up:

File	Function	Complexity	Length	Working Memory	Quality	Recommendation
gaphor/services/tests/test_copyservice.py	CopyServiceTestCase._skip_test_copy_paste_undo	0	155 😞	5 ⭐	74.05% 🙂	Try splitting into smaller methods

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• ⛔ very poor

The 👍 and 👎 indicate whether the quality has improved or gotten worse with this pull request.

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Let us know what you think of it by mentioning @sourcery-ai in a comment.

[amolenaar]

I want to leave it as it is, with the global copy variable. Alternative would be to use a application service instead. But we'd better improve this bit when (if) we migrate to GTK4.

[danyeaw]

Cool, I agree that this will work until we migrate to GTK4 eventually 👍