Don't add the wp:attachment_url for non-attachment post types.

packages/wxr/src/1.2/index.js

@@ -77,6 +77,11 @@ class WXRDriver {
 				return;
 			}
 
+			// Skip any fields that have a filter which fails for this data blob.
+			if ( field.filter && ! field.filter( data ) ) {
+				return;
+			}
+
 			// If the field is read-only, get the default value.
 			if ( field.hasOwnProperty( 'writeable' ) && ! field.writeable ) {
 				validatedData[ field.name ] = field.default(

packages/wxr/src/1.2/schema.js

@@ -324,6 +324,7 @@ module.exports = {
 				name: 'attachment_url',
 				type: 'string',
 				element: 'wp:attachment_url',
+				filter: ( data ) => data.type === 'attachment',
 			},
 			{
 				name: 'terms',

packages/wxr/src/1.2/test/__snapshots__/posts.js.snap

@@ -64,7 +64,6 @@ exports[`Posts All fields are written as expected 1`] = `
 		<wp:post_type><![CDATA[post]]></wp:post_type>
 		<wp:post_password><![CDATA[a-strong-password]]></wp:post_password>
 		<wp:is_sticky>NaN</wp:is_sticky>
-		<wp:attachment_url><![CDATA[https://make.wordpress.org]]></wp:attachment_url>
 		<category domain=\\"category\\" nicename=\\"some-cat\\">Some Category</category>
 		<category domain=\\"tag\\" nicename=\\"some-tag\\">Some Tag</category>
 		<category domain=\\"my-tax\\" nicename=\\"some-term\\">Some Term</category>
@@ -76,3 +75,50 @@ exports[`Posts All fields are written as expected 1`] = `
 </channel>
 </rss>"
 `;
+
+exports[`Posts attachment_url is only included for the attachment post type 1`] = `
+"<?xml version=\\"1.0\\" encoding=\\"UTF-8\\" ?>
+
+<!-- This is a WordPress eXtended RSS file generated by the \\"Free (as in Speech)\\" browser extension, as an export of your site. -->
+<!-- It contains information about your site's posts, pages, comments, categories, and other content. -->
+<!-- You may use this file to transfer that content from one site to another. -->
+<!-- This file is not intended to serve as a complete backup of your site. -->
+
+<!-- To import this information into a WordPress site follow these steps: -->
+<!-- 1. Log in to that site as an administrator. -->
+<!-- 2. Go to Tools: Import in the WordPress admin panel. -->
+<!-- 3. Install the \\"WordPress\\" importer from the list. -->
+<!-- 4. Activate & Run Importer. -->
+<!-- 5. Upload this file using the form provided on that page. -->
+<!-- 6. You will first be asked to map the authors in this export file to users -->
+<!--    on the site. For each author, you may choose to map to an -->
+<!--    existing user on the site or to create a new user. -->
+<!-- 7. WordPress will then import each of the posts, pages, comments, categories, etc. -->
+<!--    contained in this file into your site. -->
+
+<rss version=\\"2.0\\"
+	xmlns:excerpt=\\"http://wordpress.org/export/1.2/excerpt/\\"
+	xmlns:content=\\"http://purl.org/rss/1.0/modules/content/\\"
+	xmlns:wfw=\\"http://wellformedweb.org/CommentAPI/\\"
+	xmlns:dc=\\"http://purl.org/dc/elements/1.1/\\"
+	xmlns:wp=\\"http://wordpress.org/export/1.2/\\"
+>
+<channel>
+	<item>
+		<title><![CDATA[A Page Title]]></title>
+		<description></description>
+		<wp:comment_status><![CDATA[open]]></wp:comment_status>
+		<wp:post_type><![CDATA[page]]></wp:post_type>
+		<wp:is_sticky>0</wp:is_sticky>
+	</item>
+	<item>
+		<title><![CDATA[An Attachment Title]]></title>
+		<description></description>
+		<wp:comment_status><![CDATA[open]]></wp:comment_status>
+		<wp:post_type><![CDATA[attachment]]></wp:post_type>
+		<wp:is_sticky>0</wp:is_sticky>
+		<wp:attachment_url><![CDATA[https://make.wordpress.org]]></wp:attachment_url>
+	</item>
+</channel>
+</rss>"
+`;

packages/wxr/src/1.2/test/posts.js

@@ -79,4 +79,25 @@ describe( 'Posts', () => {
 
 		expect( xml ).toMatchSnapshot();
 	} );
+
+	test( 'attachment_url is only included for the attachment post type', async () => {
+		const wxr = new WXRDriver();
+		await wxr.connect();
+
+		wxr.addPost( {
+			title: 'A Page Title',
+			type: 'page',
+			attachment_url: 'https://make.wordpress.org', // Won't be written for this post type.
+		} );
+
+		wxr.addPost( {
+			title: 'An Attachment Title',
+			type: 'attachment',
+			attachment_url: 'https://make.wordpress.org',
+		} );
+
+		const xml = await wxr.export();
+
+		expect( xml ).toMatchSnapshot();
+	} );
 } );