Allow using visible regions with projections

[danthe1st]

This is my attempt to fix #3073 in order to implement eclipse-jdt/eclipse.jdt.ui#2264

Description

ProjectionViewer currently cannot use visible regions and projections together (except by calling enableProjections() after setVisibleRegions in which case it will show a wrong region). This PR changes the implementation of visible regions to collapse everything outside the visible region.

Note

This PR does not allow collapsing or expanding any projection/folding regions outside of the declared visible region (e.g. by other code modifying the document in some way or if a projection region is partially in the visible region).

Aside from that, this implementation has the following effect: If setVisibleRegion is called with a region that is fully collapsed, the editor is basically empty. If another behavior is desired, it would be good to know what the better behavior is.

testing with JDT

To test this with JDT as requested in eclipse-jdt/eclipse.jdt.ui#2264, do the following:

• Create a workspace with eclipse.platform.ui and JDT-UI set up (I did so by creating a Target Platform and added whatever I thought was necessary until I no longer got any errors but I have no idea how to properly do that)
• Use the changes in eclipse.platform.ui
• Apply enable folding with "Only show selected Java element" eclipse-jdt/eclipse.jdt.ui#2302 with JDT-UI:
• Create an "Eclipse Application" run configuration with this version of Eclipse Platform and the patched version of JDT-UI and start it
• Enable Window > Preferences > Java > Editor > "Only show the selected Java Element"
• Make sure folding is enabled at Window > Preferences > Java > Editor > Folding
• Open a Java class
• Select elements in the outline and observe that only the "selected element" is shown in the editor and folding still works (whether it's normal folding, custom folding regions, "Extended Folding", etc shouldn't make a difference)
  
• If "Enhanced Folding" is active, make sure that preserve contextual information with enhanced folding eclipse-jdt/eclipse.jdt.ui#2410 is available as well

[github-actions]

Test Results

 2 778 files  ± 0   2 778 suites  ±0   1h 36m 42s ⏱️ - 7m 29s
 7 943 tests +11   7 714 ✅ +11  228 💤 ±0  1 ❌ ±0 
23 384 runs  +33  22 637 ✅ +33  746 💤 ±0  1 ❌ ±0 

For more details on these failures, see this check.

Results for commit da38e3d. ± Comparison against base commit 477d106.

♻️ This comment has been updated with latest results.

[iloveeclipse]

@danthe1st : thanks for PR, few things:

1. Please rebase on master
2. Please squash two commits into one
3. Please update commit message to follow commit message guidelines: https://github.com/eclipse-platform/.github/blob/main/CONTRIBUTING.md#commit-message-recommendations

[danthe1st]

@danthe1st : thanks for PR, few things:

1. Please rebase on master

2. Please squash two commits into one

3. Please update commit message to follow commit message guidelines: https://github.com/eclipse-platform/.github/blob/main/CONTRIBUTING.md#commit-message-recommendations

I'll make sure to do that once I located and fixed a remaining issue in combination with JDT (if I select a method that's within a custom folding region and enter text, it seems to show "too much" text for some reason). While I think that's an issue with JDT-UI (it only seems to happen with custom folding regions and extended folding), I want to be sure about it first (and I opened this PR before everything is finished to make it visible in advance/allow for discussion if applicable).

[danthe1st]

I have made the requested changes. However, I want to note the following:

• This has an impact on behavior(al compatibility). If some project/plugin/whatever calls enableProjections() and setVisibleRegion on some ProjectionViewer, this PR affects what is shown to the user.
• I didn't do performance testing.
• I think it would be a good idea for someone from JDT (or other projects if make use of this?) to test it before this is merged.

[danthe1st]

I am not sure why the Jenkins build seems to have issues getting tycho set up (maybe issues with https://repo.eclipse.org/?)

[merks]

Yes there are infrastructure problems again:

• https://gitlab.eclipse.org/eclipsefdn/helpdesk/-/issues/6377
• https://gitlab.eclipse.org/eclipsefdn/helpdesk/-/issues/6378

I restarted the build.

[merks]

It looks like there was a test failure:

https://ci.eclipse.org/platform/job/eclipse.platform.ui/job/PR-3074/lastCompletedBuild/testReport/

[danthe1st]

I now switched to an approach that should have fewer side effects. Instead of adding additional projection regions, I am now using the expand() and collapse() methods directly.

[danthe1st]

@iloveeclipse Would you like to re-review this (and eclipse-jdt/eclipse.jdt.ui#2302) at some point when you have time? I think I forgot to mention that I have made the requested changes.

[danthe1st]

As I didn't get any feedback until now, I made the following choice (can still be changed if there are good reasons for it):

Since it is possible for changes outside of the visible region to happen (e.g. using custom actions, other code adding projection regions or anything else that might modify the document) and users wouldn't be interested to see stuff outside of the visible region, I decided to change the logic to ignore collapsing and expanding outside of the visible region.

I also adjusted the description accordingly.

This PR does not allow collapsing or expanding any projection/folding regions outside of the declared visible region (e.g. by other code modifying the document in some way or if a projection region is partially in the visible region).

[laeubi]

@mickaelistria can you help reviewing this?

[danthe1st]

It seems like this PR missed M1 now. Would it be possible to get this reviewed before M2 (with sufficient time left for eclipse-jdt/eclipse.jdt.ui#2302)?
@mickaelistria

Or would it be better to wait for another release cycle (2026-03)? But even in that case, it would be better to get this reviewed at some point.

[mickaelistria]

I won't review in details but this patch adds many good tests, is actually a fix, has no new API and all payload changes are internal and isolated; and code is understandable enough. So let's merge and worth case, we can revert it.

[iloveeclipse]

This PR caused regression: #3380
@mickaelistria, @danthe1st : could you please check?

[iloveeclipse]

This PR caused another regression: eclipse-jdt/eclipse.jdt.ui#2532

@mickaelistria, @danthe1st : please follow up. The way the listener is added & removed is not OK, as it will be not always removed. A simple solution is doable, I've posted it on the bug, but I'm not sure if that is enough.

[mickaelistria]

@danthe1st @iloveeclipse I think we should give about a week for a fix to be pushed, and if nothing has happened before that, we can revert.

[cdietrich]

causes breaking change in Xtext comment editing strategy eclipse-xtext/xtext#3531