Ensure the last line is included in projection-based visible regions #3585

danthe1st · 2025-12-15T12:11:27Z

As noticed in #3074 (comment) by @totomomo18, there are situations where the projection-based folding introduced in #3074 hides the last line where it should be shown. In that example, it was due to Windows line endings (\r\n) where the last line was missing and it only moved past the \r but not the \n (it didn't account for the second character).

However, there is another situation where this can happen which is the case if there is additional (non-whitespace) text in the last line after the visible region. In the following example, assume that the visible region starts with { and ends with }:

{
    // ...
} // additional text here

Here, the } would be hidden.

An example where this could happen with JDT is enum constants (because of the , after the constants):

enum ABC {
    SOME_CONSTANT,
    OTHER_CONSTANT
}

The problem with these situations is that projections/folding cannot hide partial lines at the end so it has to show the entire last line. When I implemented #3074, I was assuming that this was an issue with whitespace at the end but I didn't account for further text (it worked perfectly fine with comments and other things in JDT because comments at the end seem to be included in the visible regions set by JDT).

This change ensures that setting the visible region with projections enabled does not hide the last line in case there is additional text at the end of the line or the file is using Windows line endings by fixing the logic for computing the end of the visible region.

github-actions · 2025-12-15T12:55:01Z

Test Results

3 015 files ± 0 3 015 suites ±0 2h 15m 47s ⏱️ + 8m 41s
8 262 tests + 4 8 014 ✅ + 4 248 💤 ±0 0 ❌ ±0
23 610 runs +12 22 819 ✅ +12 791 💤 ±0 0 ❌ ±0

Results for commit c2650ca. ± Comparison against base commit e81ba1c.

♻️ This comment has been updated with latest results.

danthe1st · 2025-12-19T11:46:01Z

@akurtakov Would you like to review that since it seems like this also impacts lsp4e?

Other than that, I think it would be good to get a review on #3456 if possible.

danthe1st · 2026-01-05T12:10:30Z

@iloveeclipse @akurtakov Could this (and also #3456) please be reviewed?

(The recent changes are just rebasing and updating copyright headers)

danthe1st · 2026-01-10T12:34:17Z

@vogella Since others don't really seem to be interested in reviewing these regression fixes, would you like to take a look at this and #3456?

P.S. Sorry if I'm a bit annoying but I would like to get this done before M2 if possible.

vogella · 2026-01-11T16:01:14Z

I try to check this tomorrow.

This change ensures that setting the visible region with projections enabled does not hide the last line in case there is additional text at the end of the line or the file is using Windows line endings.

vogella · 2026-01-12T09:26:13Z

The Pull Request PR #3585 ("Ensure the last line is included in projection-based visible regions") addresses a bug where the last line of a
visible region is incorrectly hidden under specific conditions (e.g., Windows line endings, trailing non-whitespace text).

Analysis

Problem Identification: The PR author clearly explains that the previous logic for calculating computeEndOfVisibleRegion failed to account for:
- Windows line endings (\r\n), where it might only skip the \r but not the \n.
- Non-whitespace content appearing after the designated "end" of the visible region on the same line (e.g., } // comment).
- Since projection folding works on a line-by-line basis, it cannot hide part of a line; it must show the entire line. The original logic was too aggressive in excluding the end of the line.
Implementation:
- ProjectionViewer.java: The updated computeEndOfVisibleRegion logic is much more robust.
  - It now iterates forward from the proposed end index until it hits a line break (\n or \r) or the end of the document. This ensures any trailing content on that line (whitespace or not) is
    included.
  - It explicitly checks for and consumes the newline characters (\n or \r, and specifically \r\n pairs).
  - This effectively snaps the "end" of the visible region to the end of the line containing the requested end offset, which is the correct behavior for line-based folding.
Testing:
- ProjectionViewerTest.java: The PR adds excellent test coverage.
  - testDifferentLineEndings: parameterized to test both \n and \r\n (Windows) line endings.
  - testIncludesLastLineIfAdditionalTextPresent: Specifically tests the } // ... scenario where the suffix was previously causing the line to be hidden.
  - testSetVisibleRegionUntilEOF: Edge case coverage for when the region ends at the very end of the file.
Conventions: The changes adhere to the project's coding style and copyright headers are updated.

Conclusion

Opinion: The PR is valid and the fix is implemented correctly. It addresses a real edge case in the text editor's projection/folding logic that users on Windows or with specific coding styles (trailing
comments) would encounter. The logic change is simple and well-reasoned, and the tests cover the failure cases comprehensively. It is ready to be merged.

vogella · 2026-01-12T11:01:46Z

Thanks @danthe1st

totomomo18 · 2026-01-12T23:53:24Z

Thank you very much @danthe1st and everyone else helping him I really appreciate it. This combination of show only select element and the folding feature make Eclipse even better by having another killer unique feature which the other ides (Vscode and all his forks, Intellij and all other Jetbrains Ides) don't have.
So do I have to wait for the next Eclipse release to use this new killer feature
or can I simply use check for updates to get it today ?

danthe1st · 2026-01-13T06:10:50Z

@totomomo18 You can download the last SDK/I-build at https://download.eclipse.org/eclipse/downloads/. At "Latest Downloads", select the integration build (starting with I2026) and you'll get to https://download.eclipse.org/eclipse/downloads/drops4/I20260112-1800/.
There, select the appropriate Eclipse SDK download (don't download the unit test results).

Please note that this is a daily build that may contain bugs. If you find any, please report them accordingly and include the exact build you used in your report.

danthe1st mentioned this pull request Dec 15, 2025

Prevent IllegalStateException setting visible region with collapsed projection region #3456

Merged

This was referenced Dec 15, 2025

Allow using visible regions with projections #3074

Merged

enable folding with "Only show selected Java element" eclipse-jdt/eclipse.jdt.ui#2302

Merged

FlorianKroiss mentioned this pull request Dec 15, 2025

Renable DocumentLinkReconcilingTest.testClippedDocumentLinkReconciling eclipse-lsp4e/lsp4e#1470

Closed

danthe1st mentioned this pull request Dec 16, 2025

Eclipse new folding feature does not work when use show only selected element feature eclipse-jdt/eclipse.jdt.ui#2264

Closed

danthe1st force-pushed the visible-region-missing-last-line branch from c0dc874 to e3ed532 Compare December 18, 2025 16:12

danthe1st mentioned this pull request Dec 18, 2025

Add N&N for folding with only showing selected elements eclipse-platform/www.eclipse.org-eclipse#460

Merged

RedeemerSK mentioned this pull request Dec 20, 2025

fix: reenable test in DocumentLinkReconcilingTest. Fixes #1470 eclipse-lsp4e/lsp4e#1477

Merged

danthe1st force-pushed the visible-region-missing-last-line branch 2 times, most recently from f719e33 to 2767a44 Compare January 5, 2026 11:17

Ensure the last line is included in projection-based visible regions

c2650ca

This change ensures that setting the visible region with projections enabled does not hide the last line in case there is additional text at the end of the line or the file is using Windows line endings.

vogella force-pushed the visible-region-missing-last-line branch from 2767a44 to c2650ca Compare January 12, 2026 09:20

vogella merged commit 59dbd43 into eclipse-platform:master Jan 12, 2026
18 checks passed

danthe1st deleted the visible-region-missing-last-line branch January 12, 2026 11:44

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Ensure the last line is included in projection-based visible regions #3585

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