Fold unchanged regions in the unified diff

team/bundles/org.eclipse.compare/compare/org/eclipse/compare/internal/CompareMessages.java

@@ -148,6 +148,8 @@ private CompareMessages() {
 	public static String UnifiedDiff_openTwoWayCompare_tooltip;
 	public static String UnifiedDiff_cannotEditFile_title;
 	public static String UnifiedDiff_cannotEditFile_message;
+	public static String UnifiedDiff_expandUnchangedLine;
+	public static String UnifiedDiff_expandUnchangedLines;
 
 	static {
 		NLS.initializeMessages(BUNDLE_NAME, CompareMessages.class);

team/bundles/org.eclipse.compare/compare/org/eclipse/compare/internal/CompareMessages.properties

@@ -163,3 +163,5 @@ UnifiedDiff_revert=Revert
 UnifiedDiff_openTwoWayCompare_tooltip=Open in 2-way Compare Editor
 UnifiedDiff_cannotEditFile_title=Cannot edit file
 UnifiedDiff_cannotEditFile_message=Cannot edit file {0}: {1}
+UnifiedDiff_expandUnchangedLine=Expand 1 unchanged line
+UnifiedDiff_expandUnchangedLines=Expand {0} unchanged lines

team/bundles/org.eclipse.compare/compare/org/eclipse/compare/internal/CompareUIPlugin.java

@@ -263,6 +263,10 @@ Collection<T> getAll() {
 
 	public static final int NO_DIFFERENCE = 10000;
 
+	// Number of unchanged context lines kept around each change when the unified
+	// diff collapses unchanged regions.
+	private static final int UNIFIED_DIFF_CONTEXT_LINES = 3;
+
 	/**
 	 * The plugin singleton.
 	 */
@@ -627,6 +631,7 @@ private boolean openUnifiedDiffInEditor(final CompareEditorInput input, final IW
 										: null)
 								.ignoreWhiteSpace(Utilities.getBoolean(input.getCompareConfiguration(),
 										CompareConfiguration.IGNORE_WHITESPACE, false))
+								.foldUnchanged(UNIFIED_DIFF_CONTEXT_LINES)
 								.open();
 						return status.isOK();
 					}
@@ -654,6 +659,7 @@ private boolean openUnifiedDiffInEditor(final CompareEditorInput input, final IW
 										: null)
 								.ignoreWhiteSpace(Utilities.getBoolean(input.getCompareConfiguration(),
 										CompareConfiguration.IGNORE_WHITESPACE, false))
+								.foldUnchanged(UNIFIED_DIFF_CONTEXT_LINES)
 								.open();
 						return status.isOK();
 					}

team/bundles/org.eclipse.compare/compare/org/eclipse/compare/unifieddiff/UnifiedDiff.java

@@ -62,6 +62,7 @@ public static final class Builder {
 		private List<Action> additionalActions;
 		private TokenComparatorFactory tokenComparatorFactory;
 		private IgnoreWhitespaceContributorFactory ignoreWhitespaceContributorFactory;
+		private int foldContextLines = -1;
 
 		private Builder(ITextEditor editor, String source, UnifiedDiffMode mode) {
 			this.editor = Objects.requireNonNull(editor, "Editor cannot be null"); //$NON-NLS-1$
@@ -89,9 +90,19 @@ public Builder ignoreWhiteSpace(boolean value) {
 			return this;
 		}
 
+		/**
+		 * Collapses unchanged regions between diffs, keeping the given number of
+		 * context lines (at least one) around each change. A negative value disables
+		 * folding.
+		 */
+		public Builder foldUnchanged(int contextLines) {
+			this.foldContextLines = contextLines;
+			return this;
+		}
+
 		public IStatus open() {
 			return UnifiedDiffManager.open(editor, source, mode, additionalActions, tokenComparatorFactory,
-					ignoreWhitespaceContributorFactory, ignoreWhiteSpace);
+					ignoreWhitespaceContributorFactory, ignoreWhiteSpace, foldContextLines);
 		}
 	}
 }

team/bundles/org.eclipse.compare/compare/org/eclipse/compare/unifieddiff/internal/UnifiedDiffCodeMiningProvider.java

@@ -25,6 +25,7 @@
 import java.util.concurrent.CompletableFuture;
 import java.util.function.Consumer;
 
+import org.eclipse.compare.internal.CompareMessages;
 import org.eclipse.compare.unifieddiff.UnifiedDiffMode;
 import org.eclipse.compare.unifieddiff.internal.UnifiedDiffManager.UnifiedDiff;
 import org.eclipse.core.runtime.IProgressMonitor;
@@ -49,6 +50,7 @@
 import org.eclipse.jface.text.source.SourceViewer;
 import org.eclipse.jface.text.source.inlined.LineFooterAnnotation;
 import org.eclipse.jface.text.source.inlined.LineHeaderAnnotation;
+import org.eclipse.osgi.util.NLS;
 import org.eclipse.swt.SWT;
 import org.eclipse.swt.custom.StyleRange;
 import org.eclipse.swt.custom.StyledText;
@@ -156,6 +158,9 @@ public CompletableFuture<List<? extends ICodeMining>> provideCodeMinings(ITextVi
 				}
 			}
 			if (existingMinings.size() > 0) {
+				// the expander minings are recreated instead of reused so that they
+				// reflect the current expansion state of the folds
+				createFoldRegionCodeMinings(viewer, existingMinings);
 				return CompletableFuture.completedFuture(existingMinings);
 			}
 		}
@@ -164,9 +169,13 @@ public CompletableFuture<List<? extends ICodeMining>> provideCodeMinings(ITextVi
 		// take an immutable snapshot so the async iteration cannot observe
 		// concurrent modifications when accept/hide actions mutate the live list
 		List<UnifiedDiff> diffsSnapshot = List.copyOf(diffs);
+		// created on the calling thread because it reads the projection annotation model
+		List<ICodeMining> foldMinings = new ArrayList<>();
+		createFoldRegionCodeMinings(viewer, foldMinings);
 		return CompletableFuture.supplyAsync(() -> {
 			List<ICodeMining> minings = new ArrayList<>();
 			createLineHeaderCodeMinings(diffsSnapshot, minings, viewer, tabWidth);
+			minings.addAll(foldMinings);
 			return minings;
 		});
 	}
@@ -274,6 +283,53 @@ private void createLineHeaderCodeMinings(List<UnifiedDiff> diffs, List<ICodeMini
 		}
 	}
 
+	/**
+	 * Creates one clickable expander mining per collapsed unchanged-region fold,
+	 * shown as e.g. "Expand 42 unchanged lines" above the fold's caption line.
+	 */
+	private void createFoldRegionCodeMinings(ITextViewer viewer, List<ICodeMining> minings) {
+		IDocument doc = viewer.getDocument();
+		if (doc == null) {
+			return;
+		}
+		Map<Annotation, Position> folds = UnifiedDiffManager.getCollapsedFoldRegions(viewer);
+		for (Map.Entry<Annotation, Position> fold : folds.entrySet()) {
+			Position position = fold.getValue();
+			try {
+				int firstLine = doc.getLineOfOffset(position.getOffset());
+				int lastLine = position.getLength() > 0
+						? doc.getLineOfOffset(position.getOffset() + position.getLength() - 1)
+						: firstLine;
+				// the first line of the region stays visible as the fold's caption
+				int hiddenLines = lastLine - firstLine;
+				if (hiddenLines <= 0) {
+					continue;
+				}
+				minings.add(new FoldedRegionCodeMining(new Position(position.getOffset(), 1), this, viewer,
+						fold.getKey(), hiddenLines));
+			} catch (BadLocationException e) {
+				error(e);
+			}
+		}
+	}
+
+	static class FoldedRegionCodeMining extends LineHeaderCodeMining {
+
+		private final String expandLabel;
+
+		public FoldedRegionCodeMining(Position position, ICodeMiningProvider provider, ITextViewer viewer,
+				Annotation foldAnnotation, int hiddenLines) throws BadLocationException {
+			super(position, provider, e -> UnifiedDiffManager.expandFoldRegion(viewer, foldAnnotation));
+			this.expandLabel = hiddenLines == 1 ? CompareMessages.UnifiedDiff_expandUnchangedLine
+					: NLS.bind(CompareMessages.UnifiedDiff_expandUnchangedLines, Integer.valueOf(hiddenLines));
+		}
+
+		@Override
+		public String getLabel() {
+			return this.expandLabel;
+		}
+	}
+
 	static class UnifiedDiffFooterCodeMining extends DocumentFooterCodeMining {
 		private final String unifiedDiffLabel;
 		private final Color deletionBackgroundColor;