Parse non-hierarchical tag input into term IDs before sending to wp_insert_post().

When editing a post, non-hierarchical taxonomy terms are sent as the
comma-separated list entered into the tax_input metabox. Passing these
values directly to `wp_update_post()` meant that they were interpreted as
term slugs rather than term names, causing mismatches when a typed string
matched the slug of one term and the name of a different term. We fix the
problem by preprocessing tax_input data sent from post.php, converting it to
unambiguous term_ids before saving.

Props boonebgorges, ArminBraun.
Fixes #30615.

git-svn-id: https://develop.svn.wordpress.org/trunk@31359 602fd350-edb4-49c9-b593-d223f7449a82

tests/phpunit/tests/admin/includesPost.php

@@ -136,6 +136,45 @@ class Tests_Admin_includesPost extends WP_UnitTestCase {
 		$this->assertEquals( 'draft', get_post( $post->ID )->post_status );
 	}
 
+	/**
+	 * @ticket 30615
+	 */
+	public function test_edit_post_should_parse_tax_input_by_name_rather_than_slug_for_nonhierarchical_taxonomies() {
+		$u = $this->factory->user->create( array( 'role' => 'editor' ) );
+		wp_set_current_user( $u );
+
+		register_taxonomy( 'wptests_tax', array( 'post' ) );
+		$t1 = $this->factory->term->create( array(
+			'taxonomy' => 'wptests_tax',
+			'name' => 'foo',
+			'slug' => 'bar',
+		) );
+		$t2 = $this->factory->term->create( array(
+			'taxonomy' => 'wptests_tax',
+			'name' => 'bar',
+			'slug' => 'foo',
+		) );
+
+		$p = $this->factory->post->create();
+
+		$post_data = array(
+			'post_ID' => $p,
+			'tax_input' => array(
+				'wptests_tax' => 'foo,baz',
+			),
+		);
+
+		edit_post( $post_data );
+
+		$found = wp_get_post_terms( $p, 'wptests_tax' );
+
+		// Should contain the term with the name 'foo', not the slug.
+		$this->assertContains( $t1, wp_list_pluck( $found, 'term_id' ) );
+
+		// The 'baz' tag should have been created.
+		$this->assertContains( 'baz', wp_list_pluck( $found, 'name' ) );
+	}
+
 	/**
 	 * @ticket 27792
 	 */