feat(gatsby-plugin-feed): add match plugin option (#13827)

docs/docs/adding-an-rss-feed.md

@@ -130,6 +130,8 @@ This snippet contains a custom `gatsby-plugin-feed` setup in `gatsby-config.js`
 
 The `output` field in your feed object allows you to customize the filename for your RSS feed, and `title` for the name of your site's RSS feed.
 
+By default, feed is referenced in every page. You can customize this behavior by providing an extra field `match` of type `string`. This string will be used to build a `RegExp`, and this regular expression will be used to test the `pathname` of current page. Only pages that satisfied the regular expression will have feed reference included.
+
 To see your feed in action, run `gatsby build && gatsby serve` and you can then inspect the content and URLs in your RSS file at `http://localhost:9000/rss.xml`.
 
 > NOTE: if your blog has custom permalinks, such as links with or without dates in them, you may need to [customize `gatsby-node.js`](https://github.com/gatsbyjs/gatsby-starter-blog/blob/master/gatsby-node.js#L57) to output the correct URLs in your RSS feed. [Get in touch with us](/contributing/how-to-contribute/) if you need any help!

packages/gatsby-plugin-feed/README.md

@@ -61,6 +61,11 @@ module.exports = {
             `,
             output: "/rss.xml",
             title: "Your Site's RSS Feed",
+            // optional configuration to insert feed reference in pages:
+            // if `string` is used, it will be used to create RegExp and then test if pathname of
+            // current page satisfied this regular expression;
+            // if not provided or `undefined`, all pages will have feed reference inserted
+            match: "^/blog/",
           },
         ],
       },
@@ -71,6 +76,8 @@ module.exports = {
 
 Each feed must include `output`, `query`, and `title`. Additionally, it is strongly recommended to pass a custom `serialize` function, otherwise an internal serialize function will be used which may not exactly match your particular use case.
 
+`match` is an optional configuration, indicating which pages will have feed reference included. The accepted types of `match` are `string` or `undefined`. By default, when `match` is not configured, all pages will have feed reference inserted. If `string` is provided, it will be used to build a RegExp and then to test whether `pathname` of current page satisifed this regular expression. Only pages that satisifed this rule will have feed reference included.
+
 All additional options are passed through to the [`rss`][rss] utillity. For more info on those additional options, [explore the `itemOptions` section of the `rss` package](https://www.npmjs.com/package/rss#itemoptions).
 
 Check out an example of [how you could implement](https://www.gatsbyjs.org/docs/adding-an-rss-feed/) to your own site, with a custom `serialize` function, and additional functionality.

packages/gatsby-plugin-feed/src/__tests__/__snapshots__/gatsby-ssr.js.snap

@@ -49,6 +49,29 @@ exports[`Adds <Link> for feed to head creates Link if feeds does exist 1`] = `
 }
 `;
 
+exports[`Adds <Link> for feed to head creates Link only if pathname satisfied match 1`] = `
+[MockFunction] {
+  "calls": Array [
+    Array [
+      Array [
+        <link
+          href="/gryffindor/feed.xml"
+          rel="alternate"
+          title="Gryffindor's RSS Feed"
+          type="application/rss+xml"
+        />,
+      ],
+    ],
+  ],
+  "results": Array [
+    Object {
+      "type": "return",
+      "value": undefined,
+    },
+  ],
+}
+`;
+
 exports[`Adds <Link> for feed to head creates Link with a title if it does exist 1`] = `
 [MockFunction] {
   "calls": Array [

packages/gatsby-plugin-feed/src/__tests__/gatsby-ssr.js

@@ -105,4 +105,33 @@ describe(`Adds <Link> for feed to head`, () => {
     expect(setHeadComponents).toMatchSnapshot()
     expect(setHeadComponents).toHaveBeenCalledTimes(1)
   })
+
+  it(`creates Link only if pathname satisfied match`, async () => {
+    const pluginOptions = {
+      feeds: [
+        {
+          output: `gryffindor/feed.xml`,
+          title: `Gryffindor's RSS Feed`,
+          match: `^/gryffindor/`,
+        },
+        {
+          output: `ravenclaw/feed.xml`,
+          title: `Ravenclaw's RSS Feed`,
+          match: `^/ravenclaw/`,
+        },
+      ],
+    }
+    const setHeadComponents = jest.fn()
+
+    await onRenderBody(
+      {
+        setHeadComponents,
+        pathname: `/gryffindor/welcome`,
+      },
+      pluginOptions
+    )
+
+    expect(setHeadComponents).toMatchSnapshot()
+    expect(setHeadComponents).toHaveBeenCalledTimes(1)
+  })
 })

packages/gatsby-plugin-feed/src/gatsby-ssr.js

@@ -5,27 +5,32 @@ import { defaultOptions } from "./internals"
 // TODO: remove for v3
 const withPrefix = withAssetPrefix || fallbackWithPrefix
 
-exports.onRenderBody = ({ setHeadComponents }, pluginOptions) => {
+exports.onRenderBody = ({ setHeadComponents, pathname }, pluginOptions) => {
   const { feeds } = {
     ...defaultOptions,
     ...pluginOptions,
   }
 
-  const links = feeds.map(({ output, title }, i) => {
-    if (output.charAt(0) !== `/`) {
-      output = `/` + output
-    }
+  const links = feeds
+    .filter(({ match }) => {
+      if (typeof match === `string`) return new RegExp(match).exec(pathname)
+      return true
+    })
+    .map(({ output, title }, i) => {
+      if (output.charAt(0) !== `/`) {
+        output = `/` + output
+      }
 
-    return (
-      <link
-        key={`gatsby-plugin-feed-${i}`}
-        rel="alternate"
-        type="application/rss+xml"
-        title={title}
-        href={withPrefix(output)}
-      />
-    )
-  })
+      return (
+        <link
+          key={`gatsby-plugin-feed-${i}`}
+          rel="alternate"
+          type="application/rss+xml"
+          title={title}
+          href={withPrefix(output)}
+        />
+      )
+    })
 
   setHeadComponents(links)
 }

packages/gatsby-plugin-feed/src/plugin-options.js

@@ -6,6 +6,7 @@ const feed = Joi.object({
   query: Joi.string().required(),
   title: Joi.string(),
   serialize: Joi.func(),
+  match: Joi.string(),
 }).unknown(true)
 
 // TODO: make feeds required in next major version bump