Add support for creating workspace private project descriptions

Currently importing a project into eclipse requires the creation of a
physical file name .project in the root of the project. this has several
drawbacks for tools that automatically discover projects and import them
for the user as it creates new files and possibly dirty their working
tree. Other tools use a single folder for this purpose or don't require
any permanent files in the working-tree itself. Even Eclipse has already
such concept that is used when a project is located outside the
workspace.

This now adds a new feature called "workspace private project" that only
holds the basic information in the location file in the workspace
directory, any additional information might be needed to restore by a
tool that uses workspace private projects.

Author: laeubi

resources/bundles/org.eclipse.core.resources/META-INF/MANIFEST.MF

@@ -2,7 +2,7 @@ Manifest-Version: 1.0
 Bundle-ManifestVersion: 2
 Bundle-Name: %pluginName
 Bundle-SymbolicName: org.eclipse.core.resources; singleton:=true
-Bundle-Version: 3.22.200.qualifier
+Bundle-Version: 3.23.0.qualifier
 Bundle-Activator: org.eclipse.core.resources.ResourcesPlugin
 Bundle-Vendor: %providerName
 Bundle-Localization: plugin

resources/bundles/org.eclipse.core.resources/src/org/eclipse/core/internal/localstore/FileSystemResourceManager.java

@@ -683,7 +683,7 @@ public boolean internalWrite(IProject target, IProjectDescription description, i
 		if (hasPrivateChanges)
 			getWorkspace().getMetaArea().writePrivateDescription(target);
 		//can't do anything if there's no description
-		if (!hasPublicChanges || (description == null))
+		if (!hasPublicChanges || (description == null) || description.isWorkspacePrivate())
 			return false;
 
 		//write the model to a byte array
@@ -938,9 +938,15 @@ public ProjectDescription read(IProject target, boolean creation) throws CoreExc
 		if (creation) {
 			privateDescription = new ProjectDescription();
 			getWorkspace().getMetaArea().readPrivateDescription(target, privateDescription);
+			if (privateDescription.isWorkspacePrivate()) {
+				return privateDescription;
+			}
 			projectLocation = privateDescription.getLocationURI();
 		} else {
 			IProjectDescription description = ((Project) target).internalGetDescription();
+			if (description instanceof ProjectDescription impl && impl.isWorkspacePrivate()) {
+				return impl;
+			}
 			if (description != null && description.getLocationURI() != null) {
 				projectLocation = description.getLocationURI();
 			}

resources/bundles/org.eclipse.core.resources/src/org/eclipse/core/internal/resources/LocalMetaArea.java

@@ -347,9 +347,16 @@ public ProjectDescription readOldDescription(IProject project) throws CoreExcept
 	 *        UTF - configName if hasConfigName
 	 *        ... repeat for number of referenced configurations
 	 *      ... repeat for number of build configurations with references
+	 * since 3.23:
+	 *    bool - private flag if project should only be read from its private project configuration
+	 *    int - number of natures
+	 *      UTF - nature id
+	 *      ... repeated for N natures
 	 */
 	public void readPrivateDescription(IProject target, ProjectDescription description) {
 		IPath locationFile = locationFor(target).append(F_PROJECT_LOCATION);
+		String name = target.getName();
+		description.setName(name);
 		java.io.File file = locationFile.toFile();
 		if (!file.exists()) {
 			locationFile = getBackupLocationFor(locationFile);
@@ -370,7 +377,7 @@ public void readPrivateDescription(IProject target, ProjectDescription descripti
 				}
 			} catch (Exception e) {
 				//don't allow failure to read the location to propagate
-				String msg = NLS.bind(Messages.resources_exReadProjectLocation, target.getName());
+				String msg = NLS.bind(Messages.resources_exReadProjectLocation, name);
 				Policy.log(new ResourceStatus(IStatus.ERROR, IResourceStatus.FAILED_READ_METADATA, target.getFullPath(), msg, e));
 			}
 			//try to read the dynamic references - will fail for old location files
@@ -408,6 +415,14 @@ public void readPrivateDescription(IProject target, ProjectDescription descripti
 				m.put(configName, refs);
 			}
 			description.setBuildConfigReferences(m);
+			// read parts since 3.23
+			description.setWorkspacePrivate(dataIn.readBoolean());
+			int natures = dataIn.readInt();
+			String[] natureIds = new String[natures];
+			for (int i = 0; i < natureIds.length; i++) {
+				natureIds[i] = dataIn.readUTF();
+			}
+			description.setNatureIds(natureIds);
 		} catch (IOException e) {
 			//ignore - this is an old location file or an exception occurred
 			// closing the stream
@@ -470,6 +485,14 @@ public void writePrivateDescription(IProject target) throws CoreException {
 					}
 				}
 			}
+			// write parts since 3.23
+			dataOut.writeBoolean(desc.isWorkspacePrivate());
+			String[] natureIds = desc.getNatureIds();
+			dataOut.writeInt(natureIds.length);
+			for (String id : natureIds) {
+				dataOut.writeUTF(id);
+			}
+			dataOut.flush();
 			output.succeed();
 		} catch (IOException e) {
 			String message = NLS.bind(Messages.resources_exSaveProjectLocation, target.getName());

resources/bundles/org.eclipse.core.resources/src/org/eclipse/core/internal/resources/Project.java

@@ -326,7 +326,7 @@ public void create(IProjectDescription description, int updateFlags, IProgressMo
 					updateDescription();
 					// make sure the .location file is written
 					workspace.getMetaArea().writePrivateDescription(this);
-				} else {
+				} else if (!desc.isWorkspacePrivate()) {
 					// write out the project
 					writeDescription(IResource.FORCE);
 				}

resources/bundles/org.eclipse.core.resources/src/org/eclipse/core/internal/resources/ProjectDescription.java

@@ -124,6 +124,7 @@ public class ProjectDescription extends ModelObject implements IProjectDescripti
 	protected URI location = null;
 	protected volatile String[] natures = EMPTY_STRING_ARRAY;
 	protected URI snapshotLocation = null;
+	private boolean privateFlag;
 
 	public ProjectDescription() {
 		super();
@@ -546,6 +547,10 @@ public boolean hasPrivateChanges(ProjectDescription description) {
 		// Configuration level references
 		if (configRefsHaveChanges(dynamicConfigRefs, description.dynamicConfigRefs))
 			return true;
+		// has natures changed?
+		if (!Set.of(natures).equals(Set.of(description.natures))) {
+			return true;
+		}
 
 		return false;
 	}
@@ -978,4 +983,14 @@ private static IProject[] computeDynamicReferencesForProject(IBuildConfiguration
 		}
 		return result.toArray(new IProject[0]);
 	}
+
+	@Override
+	public boolean isWorkspacePrivate() {
+		return privateFlag;
+	}
+
+	@Override
+	public void setWorkspacePrivate(boolean privateFlag) {
+		this.privateFlag = privateFlag;
+	}
 }

resources/bundles/org.eclipse.core.resources/src/org/eclipse/core/internal/resources/SaveManager.java

@@ -1371,6 +1371,9 @@ protected void saveMetaInfo(MultiStatus problems, IProgressMonitor monitor) thro
 	 * @return Status object containing non-critical warnings, or an OK status.
 	 */
 	protected IStatus saveMetaInfo(Project project, IProgressMonitor monitor) throws CoreException {
+		if (project.internalGetDescription().isWorkspacePrivate()) {
+			return Status.OK_STATUS;
+		}
 		long start = System.currentTimeMillis();
 		//if there is nothing on disk, write the description
 		if (!workspace.getFileSystemManager().hasSavedDescription(project)) {

resources/bundles/org.eclipse.core.resources/src/org/eclipse/core/resources/IProjectDescription.java

@@ -175,6 +175,13 @@ public interface IProjectDescription {
 	 */
 	ICommand newCommand();
 
+	/**
+	 * @return <code>true</code> if this project is only persisted in the private
+	 *         workspace area
+	 * @since 3.23
+	 */
+	boolean isWorkspacePrivate();
+
 	/**
 	 * Sets the active configuration for the described project.
 	 * <p>
@@ -385,4 +392,12 @@ public interface IProjectDescription {
 	 * @see #getReferencedProjects()
 	 */
 	void setReferencedProjects(IProject[] projects);
+
+	/**
+	 * Sets the project to be only persisted into the private workspace area and not
+	 * into a physical <code>.project</code> file in the root of the project folder.
+	 *
+	 * @since 3.23
+	 */
+	void setWorkspacePrivate(boolean privateFlag);
 }