Compare editor not setting the dirty flag when comparing file with git HEAD

[fpierrat]

Hi,
Initially posted here: eclipse-egit/egit#175
But it seems it's no Egit issue, but a PDT issue (see comments there).

Version

7.6.0.202603022253-r
Operating System

Windows
Eclipse version

4.39.0.v20260226-0420
Bug description

I'd like to partially stage changes to a file.
The modified file is saved and appears in the "Unstaged Changes" panel of the staging view.
Right-click + Compare with index => I can see my changes in the compare view, "Local:" on the left side, "Index (editable)" on the right side

Now I'm trying to edit the "editable" right side. Be it direct keybord edits, be it "Copy current change from left to right" click, Eclipse doesn't see the right panel's content as modified:

no "*" prefix on the "Cmpare myscript.php Current and Index" tab
"save" and "save as" icons disabled
menu file/save, save as, save all disabled
ctrl-S = no effect

I did following tests to troubleshoot or at least analyse possible causes:

try this on a brand new project, new git, it worked once, then no more (not even on another brand new project+git later)
created even a new workspace with new project and new git => no success
at some point, I finally had the compared Index seen as modified and saveable, but no idea why, and then no more, again. I couldn't find out yet, what unblocked the situation.

Please note: when comparing 2 files using "compare with each other", there's no problem, each edit right or left is detected and can be saved.

Please tell me what complementary information I can bring...
It seems to work perfectly for others (eclipse-egit/egit#28 (comment)), so there probably is something in my Eclipse/workspace/project configuration, where should I be looking?
Actual behavior

Any modification in the right "editable" Index part is ignored and can't be saved.
Image

Initial compare view:
Image

After a few edits and copy-left-to-right-clicks: no "modified" asterisk in tab, no active save buttons
Image
Expected behavior

I expect to be able to save the edits in the "editable" right part, so I can proceed to partial commits

[tomaswolf]

To clarify: this has nothing to do with EGit. Here's a reproducer with only PDT:

1. Create a PHP project.
2. Create a PHP file.
3. Create another file "something.x" with some text in it.
4. Select both files in the project explorer.
5. Choose "Compare with→Each other" from the context menu in the project explorer.
6. The compare editor opens with "PHP Source Compare".
7. Edit the side showing "something.x".

Actual result: compare editor is not marked dirty, and "Save" is disabled.

Expected result: compare editor is marked dirty, and "Save" is enabled.

Eclipse Version: 2026-03 (4.39.0) Build id: 20260305-0817
PDT: 8.4.0.202512011310

Likely cause:

At

pdt/plugins/org.eclipse.php.ui/src/org/eclipse/php/internal/ui/compare/PHPTextMergeViewer.java

Line 89 in 80d2e08

super.setDocument(createStructuredDocument(document), annotationModel, modelRangeOffset,

and

pdt/plugins/org.eclipse.php.ui/src/org/eclipse/php/internal/ui/compare/PHPTextMergeViewer.java

Line 106 in 80d2e08

newDoc = StructuredDocumentFactory.getNewStructuredDocumentInstance(new PHPSourceParser());

PDT sets a completely different document on the text viewer for the "something.x" file.

This "structured document" is completely disconnected from the document provider, document, and ISharedDocumentAdapter that comes from the compare editor's input.

As a result the compare editor is blissfully unaware of any edits in that text editor.

Additional information:

This is a very old bug, see https://bugs.eclipse.org/bugs/show_bug.cgi?id=514927 .

[tomaswolf]

@zulus, it would be good if this nine years old bug could be fixed in PDT. It breaks partial staging of PHP files in EGit.