Use "natural" diff order by default in compare editor

[iloveeclipse]

Left is base/original, right is local/modified

See eclipse-platform/eclipse.platform.ui#3776

[iloveeclipse]

Test failures are to expect, let see how many.

[github-actions]

Test Results

    54 files  ±0      54 suites  ±0   35m 12s ⏱️ - 1m 53s
 4 546 tests ±0   4 523 ✅ +1   23 💤 ±0  0 ❌  - 1 
12 234 runs  ±0  12 075 ✅ +1  159 💤 ±0  0 ❌  - 1 

Results for commit 1e9f9e6. ± Comparison against base commit 2776d6f.

♻️ This comment has been updated with latest results.

[Copilot]

Pull request overview

Adjusts Eclipse Compare so the default presentation uses “natural” diff ordering (base/original on the left, local/modified on the right), aligning with the linked issue and reducing user confusion.

Changes:

• Set the default compare preference to open in mirrored (swapped) mode.
• Fix MirroredMergeViewerContentProvider to correctly mirror left/right error reporting.
• Update TextMergeViewerTest inputs for the new default ordering and add a test-only workaround to avoid a modal dialog during a copy+modify scenario.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 4 comments.

File	Description
team/tests/org.eclipse.compare.tests/src/org/eclipse/compare/tests/TextMergeViewerTest.java	Updates test setup for swapped-by-default ordering and adds test flags to suppress a modal dialog.
team/bundles/org.eclipse.compare/compare/org/eclipse/compare/internal/MirroredMergeViewerContentProvider.java	Ensures left/right error setters mirror correctly when the provider swaps sides for display.
team/bundles/org.eclipse.compare/compare/org/eclipse/compare/internal/ComparePreferencePage.java	Changes the default preference so compare opens mirrored/swapped by default.

Comments suppressed due to low confidence (1)

team/tests/org.eclipse.compare.tests/src/org/eclipse/compare/tests/TextMergeViewerTest.java:414

• This test now initializes the DiffNode with content on the model right side and then calls viewer.copy(true /* leftToRight */) followed by getDocument(false /* right */) edits. With mirroring enabled by default, the displayed right document corresponds to the model left contributor, so the post-conditions should assert testNode.getLeft() was updated (not getRight()).

			viewer.copy(true /* leftToRight */);
			IDocument doc = getDocument(false /* right */);
			doc.set(newText);
			saveViewerContents();

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[Copilot]

Pull request overview

Adjusts Eclipse Compare UI to use the “natural” left/right ordering by default (base/original on the left, local/modified on the right), aligning the compare editor’s default presentation with the expectation in eclipse-platform/eclipse.platform.ui#3776.

Changes:

• Flip the default for the ComparePreferencePage.SWAPPED preference to enable mirroring by default.
• Fix MirroredMergeViewerContentProvider to correctly swap left/right error routing.
• Update TextMergeViewerTest to account for mirrored orientation when invoking copy/edit operations.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
team/tests/org.eclipse.compare.tests/src/org/eclipse/compare/tests/TextMergeViewerTest.java	Adjusts merge/copy/edit tests to behave correctly when the compare viewer is mirrored by default.
team/bundles/org.eclipse.compare/compare/org/eclipse/compare/internal/MirroredMergeViewerContentProvider.java	Swaps left/right error delegation to match the mirrored (display-swapped) semantics.
team/bundles/org.eclipse.compare/compare/org/eclipse/compare/internal/ComparePreferencePage.java	Changes the default value of the “Swap left and right” preference to true (mirrored by default).

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