Bug 80833 [Import/Export] Import exisiting should pre-check for project already in workspace
While it is good that it lets you import projects in the default workspace location, it should not let you select projects that already exist in the workspace (since importing such a project will fail). When searching for .project files in the file system, it could use IWorkspaceRoot.findFilesForLocation followed by checking IFile.exists() to filter out .project files for existing projects.
bundles/org.eclipse.ui.ide/src/org/eclipse/ui/internal/wizards/datatransfer/WizardProjectsImportPage.java
projectsList.refresh(true);
		projectsList.setCheckedElements(getValidProjects());
		setPageComplete(selectedProjects.length > 0);
	}
	/**
	 * Answer a handle to the zip file currently specified as being the source.
	 * Return null if this file does not exist or is not of valid format.
	 */
	protected ZipFile getSpecifiedZipSourceFile() {
		return getSpecifiedZipSourceFile(archivePathField.getText());
	}
	/**
	 * Answer a handle to the zip file currently specified as being the source.
	 * Return null if this file does not exist or is not of valid format.
	 */
	private ZipFile getSpecifiedZipSourceFile(String fileName) {
		if (fileName.length() == 0)
			return null;
		try {
			return new ZipFile(fileName);
		} catch (ZipException e) {
			displayErrorDialog(DataTransferMessages.ZipImport_badFormat);
		} catch (IOException e) {
			displayErrorDialog(DataTransferMessages.ZipImport_couldNotRead);
		}
		archivePathField.setFocus();
		return null;
	}
	/**
	 * Answer a handle to the zip file currently specified as being the source.