[@astrojs/rss] Quality-of-Life Improvement to items property-relate…

…d error (#9299)

* This commit addresses a quality-of-life concern when setting up a RSS feed
when using collections. Specifically, it provides more context to the error
message thrown when the object passed to the `items` property is missing any
of the three required keys or if one of those keys is mistyped.

* Add changeset

* Update .changeset with properly formatted update structure

@sarah11918 suggested a change to the verbiage that properly formatted the update detail in question. Accepting the suggestion.

Co-authored-by: Sarah Rainsberger <sarah@rainsberger.ca>

---------

Co-authored-by: Sarah Rainsberger <sarah@rainsberger.ca>

.changeset/thirty-hairs-pump.md

@@ -0,0 +1,5 @@
+---
+'@astrojs/rss': patch
+---
+
+Improves the `@astrojs/rss` error message thrown when the object passed to the `items` property is missing any of the three required keys or if one of those keys is mistyped.

packages/astro-rss/src/index.ts

@@ -110,8 +110,21 @@ async function validateRssOptions(rssOptions: RSSOptions) {
 		[
 			`[RSS] Invalid or missing options:`,
 			...parsedResult.error.errors.map(
-				(zodError) => `${zodError.message} (${zodError.path.join('.')})`
-			),
+				(zodError) => {
+					const path = zodError.path.join('.');
+					const message = `${zodError.message} (${path})`;
+					const code = zodError.code;
+
+					if (path === 'items' && code === 'invalid_union') {
+						return [
+							message,
+						`The \`items\` property requires properly typed \`title\`, \`pubDate\`, and \`link\` keys.`,
+						`Check your collection's schema, and visit https://docs.astro.build/en/guides/rss/#generating-items for more info.`
+						].join('\n')
+					}
+
+					return message;
+				}),
 		].join('\n')
 	);
 	throw formattedError;