Bug 29755 Attach source does not allow one to select a folder... [build path]
When opening some .class that does not yet have a source attachment eclipse shows a text version of the interface defintion and a button for Attaching source. When pressing this button a window appaer where one can enter the name/location of a folder, zip or jar for the source. There are also a button for choosing it via a file selection dialog and this works fine for zip and jar files - but not for selecting a directory :( Workaround is just to enter the directory manually.
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/wizards/buildpaths/SourceAttachmentBlock.java
return null;
	}	
	
	private IStatus updateFileNameStatus() {
		StatusInfo status= new StatusInfo();
		fResolvedFile= null;
		fFileVariablePath= null;
		
		String fileName= fFileNameField.getText();
		if (fileName.length() == 0) {
			
			return status;
		} else {
			if (!Path.EMPTY.isValidPath(fileName)) {
				status.setError(NewWizardMessages.getString("SourceAttachmentBlock.filename.error.notvalid")); 
				return status;
			}
			IPath filePath= new Path(fileName);
			IPath resolvedPath;
			if (isVariableEntry()) {
				if (filePath.getDevice() != null) {
					status.setError(NewWizardMessages.getString("SourceAttachmentBlock.filename.error.deviceinpath")); 
					return status;
				}
				String varName= filePath.segment(0);
				if (varName == null) {
					status.setError(NewWizardMessages.getString("SourceAttachmentBlock.filename.error.notvalid")); 
					return status;
				}
				fFileVariablePath= JavaCore.getClasspathVariable(varName);