From 277eb2a3def02ce67aa64bc7f172779453d43333 Mon Sep 17 00:00:00 2001
From: Lars Vogel <Lars.Vogel@vogella.com>
Date: Fri, 28 Aug 2026 05:07:58 +0200
Subject: [PATCH] Stop one project's tree file name from protecting another's
 stale file
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removeUnusedTreeFiles shared one exclude list across all projects.
removeFiles drops a name from it once it sees the matching file, but when a
project had no tree file on disk its name stayed in the list. Tree files are
named by a per resource sequence number, so that leftover name can match an
outdated tree file of a later project and keep it from being deleted.

Build the exclude list per resource instead.

Contributes to https://github.com/eclipse-platform/eclipse.platform/issues/2887

Assisted-by: multiple AI agents and layers of automated tooling 🤖
---
 .../core/internal/resources/SaveManager.java  | 33 ++++++++++---------
 1 file changed, 18 insertions(+), 15 deletions(-)

diff --git a/resources/bundles/org.eclipse.core.resources/src/org/eclipse/core/internal/resources/SaveManager.java b/resources/bundles/org.eclipse.core.resources/src/org/eclipse/core/internal/resources/SaveManager.java
index 199e3a1cbbc..7057e89a13c 100644
--- a/resources/bundles/org.eclipse.core.resources/src/org/eclipse/core/internal/resources/SaveManager.java
+++ b/resources/bundles/org.eclipse.core.resources/src/org/eclipse/core/internal/resources/SaveManager.java
@@ -708,30 +708,33 @@ protected void removeUnusedSafeTables() {
 	}
 
 	protected void removeUnusedTreeFiles() {
+		FilenameFilter filter = (dir, name) -> name.endsWith(LocalMetaArea.F_TREE);
 		// root resource
-		List<String> valuables = new ArrayList<>(10);
 		IPath location = workspace.getMetaArea().getTreeLocationFor(workspace.getRoot(), false);
-		valuables.add(location.lastSegment());
-		java.io.File target = location.toFile().getParentFile();
-		FilenameFilter filter = (dir, name) -> name.endsWith(LocalMetaArea.F_TREE);
-		String[] candidates = target.list(filter);
-		if (candidates != null) {
-			removeFiles(target, candidates, valuables);
-		}
+		removeUnusedTreeFiles(location, filter);
 
 		// projects
 		IProject[] projects = workspace.getRoot().getProjects(IContainer.INCLUDE_HIDDEN);
 		for (IProject project : projects) {
-			location = workspace.getMetaArea().getTreeLocationFor(project, false);
-			valuables.add(location.lastSegment());
-			target = location.toFile().getParentFile();
-			candidates = target.list(filter);
-			if (candidates != null) {
-				removeFiles(target, candidates, valuables);
-			}
+			removeUnusedTreeFiles(workspace.getMetaArea().getTreeLocationFor(project, false), filter);
 		}
 	}
 
+	/**
+	 * Deletes every tree file next to the given one, which is the tree file still in
+	 * use for that resource.
+	 */
+	private void removeUnusedTreeFiles(IPath treeLocation, FilenameFilter filter) {
+		java.io.File target = treeLocation.toFile().getParentFile();
+		String[] candidates = target.list(filter);
+		if (candidates == null) {
+			return;
+		}
+		List<String> valuables = new ArrayList<>(1);
+		valuables.add(treeLocation.lastSegment());
+		removeFiles(target, candidates, valuables);
+	}
+
 	protected void reportSnapshotRequestor() {
 		if (snapshotRequestor != null) {
 			Policy.log(snapshotRequestor);