JavaBuilder.getRequiredProjects() path matching fix

Before this change, full build could be triggered instead of incremental
one for projects with external libraries on classpath, if the first
segment of the external library path matches some workspace project
name. In such case, instead of the expected external folders project
that hosts the library, some fully unrelated project is returned as
required by the builder. With that, no delta is found for the actually
required external folders project during incremental build. No delta for
some project on classpath means full rebuild for the project.

The patch tries to improve the way the corresponding projects found for
the binary classpath entries, checking first to match existing external
folders and only after that the (possibly wrong) workspace match on
first path segment.

Additionally binaryLocationsPerProject map, which used in the delta
handling, changed to linked one (code iterates over this map few times),
to have more reproducible builder behavior in general.

See eclipse-pde/eclipse.pde#2244 (comment)

Fix eclipse-jdt#4921

Author: iloveeclipse

org.eclipse.jdt.core/model/org/eclipse/jdt/internal/core/builder/JavaBuilder.java

@@ -23,6 +23,7 @@
 import java.util.Date;
 import java.util.HashMap;
 import java.util.HashSet;
+import java.util.LinkedHashMap;
 import java.util.LinkedHashSet;
 import java.util.Map;
 import java.util.Map.Entry;
@@ -74,8 +75,8 @@ public class JavaBuilder extends IncrementalProjectBuilder {
 String[] extraResourceFolderFilters;
 public static final String SOURCE_ID = "JDT"; //$NON-NLS-1$
 
-public static boolean DEBUG = false;
-public static boolean SHOW_STATS = false;
+public static boolean DEBUG;
+public static boolean SHOW_STATS;
 
 /**
  * Bug 549457: In case auto-building on a JDT core settings change (e.g. compiler compliance) is not desired,
@@ -487,7 +488,7 @@ private Map<IProject, IResourceDelta> findDeltas() {
 				}
 			} else {
 				if (DEBUG) {
-					trace("JavaBuilder: Missing delta for: " + p.getName());	 //$NON-NLS-1$
+					trace("JavaBuilder: Missing delta for: " + p.getName()); //$NON-NLS-1$
 				}
 				this.notifier.subTask(""); //$NON-NLS-1$
 				return null;
@@ -527,13 +528,34 @@ private IProject[] getRequiredProjects(boolean includeBinaryPrerequisites) {
 				case IClasspathEntry.CPE_LIBRARY :
 					if (includeBinaryPrerequisites && path.segmentCount() > 0) {
 						// some binary resources on the class path can come from projects that are not included in the project references
-						IResource resource = this.workspaceRoot.findMember(path.segment(0));
-						if (resource instanceof IProject) {
-							p = (IProject) resource;
+						IResource resource = null;
+
+						// Try to check first if the full binary entry path exactly matches an external folder,
+						// before assuming its first segment matches some project name in the workspace
+						resource = externalFoldersManager.getFolder(path);
+						if (DEBUG && resource != null && !path.lastSegment().contains("jrt-fs.jar")) { //$NON-NLS-1$
+							trace("JavaBuilder: found resource containing binary classpath entry: \nExternal: " + this.currentProject.getName() + " -> " + path); //$NON-NLS-1$ //$NON-NLS-2$
+						}
+
+						// Second try: it could be a full workspace path, where first segment is the project name.
+						// Note, the path may not exist physically yet, it is allowed to reference not (yet) existing resources.
+						// Unfortunately this can also match fully unrelated projects in the workspace on Linux/Mac,
+						// current .classpath format does not provide possibilities to ensure that
+						// "<classpathentry kind="lib" path="/some/folder/name"/>"
+						// specifies an absolute OS path or full workspace path, both may not exist yet.
+						if (resource == null && path.isAbsolute() && path.getDevice() == null) {
+							resource = this.workspaceRoot.findMember(path.segment(0));
+						}
+
+						if (resource != null) {
+							p = resource.getProject();
+							if (DEBUG && !path.lastSegment().contains("jrt-fs.jar")) { //$NON-NLS-1$
+								trace("JavaBuilder: found workspace project containing binary classpath entry: \nExternal: " + this.currentProject.getName() + " -> " + path); //$NON-NLS-1$ //$NON-NLS-2$
+							}
 						} else {
-							resource = externalFoldersManager.getFolder(path);
-							if (resource != null)
-								p = resource.getProject();
+							if (DEBUG && !path.lastSegment().contains("jrt-fs.jar")) { //$NON-NLS-1$
+								trace("JavaBuilder: Could not find resource containing binary classpath entry: \n" + this.currentProject.getName() + " -> " + path); //$NON-NLS-1$ //$NON-NLS-2$
+							}
 						}
 					}
 			}
@@ -695,7 +717,7 @@ private int initializeBuilder(int kind, boolean forBuild) throws CoreException {
 		}
 	}
 
-	this.binaryLocationsPerProject = new HashMap<>(3);
+	this.binaryLocationsPerProject = new LinkedHashMap<>(3);
 	this.nameEnvironment = new NameEnvironment(this.workspaceRoot, this.javaProject, this.binaryLocationsPerProject, this.notifier, CompilationGroup.MAIN, JavaProject.NO_RELEASE);
 	this.testNameEnvironment = new NameEnvironment(this.workspaceRoot, this.javaProject, this.binaryLocationsPerProject, this.notifier, CompilationGroup.TEST, JavaProject.NO_RELEASE);