fix ClasspathComputer: ignore if oldEntry not found #820

fixes random failing ClasspathUpdaterTest

When IJavaProject.setRawClasspath() is explicitly called with
ClasspathEntries distinct from PDE (like in the Test), and then later
PDEs UpdateClasspathJob is executed it can't compute the "oldEntry" and
fails with "... is not on its projects build path". The Message is
correct - it was manually removed from the projects build path. That
state should just be ignored so that PDE continues to set the
IClasspathEntries computed by PDE.

#820

Author: Jörg Kubitz

ui/org.eclipse.pde.core/src/org/eclipse/pde/internal/core/ClasspathComputer.java

@@ -267,17 +267,23 @@ private static void addLibraryEntry(IPluginLibrary library, Map<String, IPath> s
 
 		IPackageFragmentRoot root = context.javaProject.getPackageFragmentRoot(jarFile);
 		if (root.exists() && root.getKind() == IPackageFragmentRoot.K_BINARY) {
-			IClasspathEntry oldEntry = root.getRawClasspathEntry();
-			// If we have the same binary root but new or different source, we
-			// should recreate the entry. That is when the source attachment:
-			// - is not defined: the default could be available now, or
-			// - is overridden with a different value.
-			if ((sourceAttachment == null && oldEntry.getSourceAttachmentPath() != null)
-					|| (sourceAttachment != null && sourceAttachment.equals(oldEntry.getSourceAttachmentPath()))) {
-				context.reloaded.add(oldEntry);
-				return;
+			try {
+				IClasspathEntry oldEntry = root.getRawClasspathEntry();
+				// If we have the same binary root but new or different source, we
+				// should recreate the entry. That is when the source attachment:
+				// - is not defined: the default could be available now, or
+				// - is overridden with a different value.
+				if ((sourceAttachment == null && oldEntry.getSourceAttachmentPath() != null)
+						|| (sourceAttachment != null && sourceAttachment.equals(oldEntry.getSourceAttachmentPath()))) {
+					context.reloaded.add(oldEntry);
+					return;
+				}
+				isExported = oldEntry.isExported();
+			} catch (JavaModelException ignored) {
+				// For example ELEMENT_NOT_ON_CLASSPATH is expected when
+				// rawclasspath was changed manually.
+				// In any case PDE can not solve any issue beside ignoring it.
 			}
-			isExported = oldEntry.isExported();
 		}
 		reloadClasspathEntry(jarFile, name, sourceAttachment, isExported, context);
 	}