add post_type arg to term links (narrow down the query)

termlink-filters.php

<?php

// output function extracted from a custom term list widget

function scl_list_terms( $taxonomy ) {
  
    $labels = get_taxonomy_labels( $taxonomy );
    $tax_args = array(
			'taxonomy'	=> $taxonomy,
			'title_li'	=> '',
			'show_option_none' => $labels->not_found,
		);

		$tax_args = apply_filters( 'widget_tax_menu_args', $tax_args );
		add_filter( 'term_link', 'scl_taxonomy_link_for_post_type', 10, 3 );
		printf( '<ul class="tax-term-list">%s</ul>', wp_list_categories( $tax_args ) );
		remove_filter( 'term_link', 'scl_taxonomy_link_for_post_type', 10 );
}

function scl_taxonomy_link_for_post_type( $termlink, $term, $taxonomy ) {
	
	$tax_obj = get_taxonomy( $taxonomy );
	
	// if this is not a shared taxonomy, bail
	if ( count( $tax_obj->object_type ) == 1 )
		return $termlink;
	
	// cf. https://gist.github.com/sillybean/c725ea4620e9d434e71927ab41879f38
	$post_type = scl_find_post_type();
	
	if ( !isset( $post_type ) || 'any' == $post_type )
		return $termlink;
	
	$termlink = add_query_arg( 'post_type', $post_type, $termlink );
	return $termlink;
}