feat(gatsby-remark-code-repls): include matching css option (CodePen) (#12110)

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## Description

Currently it's possible to upload multiple files only by using CodeSandbox.

This PR adds an option that allows adding CSS files to CodePen examples by setting the `css` property in the `payload` object. 

Ref: https://blog.codepen.io/documentation/api/prefill/

Matching CSS means that if the user is linking to `example.js` and the option is set to true, if `example.css` is present in the same directory, its content is sent to CodePen.

- The default behaviour is left untouched
- If the option is set to `true` and the matched file doesn't exist, nothing changes
- tests included

## Related Issues

<!--
  Link to the issue that is fixed by this PR (if there is one)
  e.g. Fixes #1234, Addresses #1234, Related to #1234, etc.
-->

Author: deblasis

packages/gatsby-remark-code-repls/README.md

@@ -163,6 +163,13 @@ specified examples directory. (This will avoid broken links at runtime.)
     // Note that if a target is specified, "noreferrer" will also be added.
     // eg <a href="..." target="_blank" rel="noreferrer">...</a>
     target: '_blank',
+
+    // Include CSS with matching name.
+    // This option only applies to REPLs that support it (eg Codepen).
+    // If set to `true`, when specifying `file1.js` as example file,
+    // it will try to inject the CSS in `file1.css` if the file exists,
+    // otherwise the default behaviour is preserved
+    includeMatchingCSS: false,
   },
 },
 ```

packages/gatsby-remark-code-repls/src/__tests__/gatsby-node.js

@@ -30,6 +30,12 @@ const createPagesParams = {
   reporter,
 }
 
+const throwFileNotFoundErr = path => {
+  const err = new Error(`no such file or directory '${path}'`)
+  err.code = `ENOENT`
+  throw err
+}
+
 describe(`gatsby-remark-code-repls`, () => {
   beforeEach(() => {
     fs.existsSync.mockReset()
@@ -198,5 +204,105 @@ describe(`gatsby-remark-code-repls`, () => {
 
       expect(html).toBe(`<span id="foo"></span>`)
     })
+
+    it(`should support includeMatchingCSS = "true" when matching file exists`, async () => {
+      readdir.mockResolvedValue([`file.js`, `file.css`])
+      fs.readFileSync.mockReset()
+      fs.readFileSync.mockImplementation((path, options) => {
+        if (path === `file.js`) {
+          return `const foo = "bar";`
+        } else if (path === `file.css`) {
+          return `html { color: red; }`
+        } else {
+          throwFileNotFoundErr(path)
+        }
+        return null
+      })
+
+      await createPages(createPagesParams, {
+        includeMatchingCSS: true,
+      })
+
+      const { css, js } = JSON.parse(
+        createPage.mock.calls[0][0].context.payload
+      )
+
+      expect(js).toBe(`const foo = "bar";`)
+      expect(css).toBe(`html { color: red; }`)
+    })
+
+    it(`should support includeMatchingCSS = "false" when matching file exists`, async () => {
+      readdir.mockResolvedValue([`file.js`, `file.css`])
+      fs.readFileSync.mockReset()
+      fs.readFileSync.mockImplementation((path, options) => {
+        if (path === `file.js`) {
+          return `const foo = "bar";`
+        } else if (path === `file.css`) {
+          return `html { color: red; }`
+        } else {
+          throwFileNotFoundErr(path)
+        }
+        return null
+      })
+
+      await createPages(createPagesParams, {
+        includeMatchingCSS: false,
+      })
+
+      const { css, js } = JSON.parse(
+        createPage.mock.calls[0][0].context.payload
+      )
+
+      expect(js).toBe(`const foo = "bar";`)
+      expect(css).toBe(undefined)
+    })
+
+    it(`should support includeMatchingCSS = "true" when matching file doesn't exist`, async () => {
+      readdir.mockResolvedValue([`file.js`])
+      fs.readFileSync.mockReset()
+      fs.readFileSync.mockImplementation((path, options) => {
+        if (path === `file.js`) {
+          return `const foo = "bar";`
+        } else {
+          throwFileNotFoundErr(path)
+        }
+        return null
+      })
+
+      await createPages(createPagesParams, {
+        includeMatchingCSS: true,
+      })
+
+      const { css, js } = JSON.parse(
+        createPage.mock.calls[0][0].context.payload
+      )
+
+      expect(js).toBe(`const foo = "bar";`)
+      expect(css).toBe(undefined)
+    })
+
+    it(`should support includeMatchingCSS = "false" when matching file doesn't exist`, async () => {
+      readdir.mockResolvedValue([`file.js`])
+      fs.readFileSync.mockReset()
+      fs.readFileSync.mockImplementation((path, options) => {
+        if (path === `file.js`) {
+          return `const foo = "bar";`
+        } else {
+          throwFileNotFoundErr(path)
+        }
+        return null
+      })
+
+      await createPages(createPagesParams, {
+        includeMatchingCSS: false,
+      })
+
+      const { css, js } = JSON.parse(
+        createPage.mock.calls[0][0].context.payload
+      )
+
+      expect(js).toBe(`const foo = "bar";`)
+      expect(css).toBe(undefined)
+    })
   })
 })

packages/gatsby-remark-code-repls/src/__tests__/index.js

@@ -141,6 +141,21 @@ describe(`gatsby-remark-code-repls`, () => {
         }
       })
 
+      it(`supports includeMatchingCSS`, () => {
+        const markdownAST = remark.parse(
+          `[](${protocol}path/to/nested/file.js)`
+        )
+        const runPlugin = () =>
+          plugin(
+            { markdownAST },
+            {
+              directory: `examples`,
+              includeMatchingCSS: true,
+            }
+          )
+        expect(runPlugin).not.toThrow()
+      })
+
       if (protocol === PROTOCOL_CODE_SANDBOX) {
         it(`supports custom html config option for index html`, () => {
           const markdownAST = remark.parse(

packages/gatsby-remark-code-repls/src/constants.js

@@ -9,6 +9,7 @@ module.exports = {
   OPTION_DEFAULT_REDIRECT_TEMPLATE_PATH: normalizePath(
     join(__dirname, `default-redirect-template.js`)
   ),
+  OPTION_DEFAULT_INCLUDE_MATCHING_CSS: false,
   PROTOCOL_BABEL: `babel://`,
   PROTOCOL_CODEPEN: `codepen://`,
   PROTOCOL_CODE_SANDBOX: `codesandbox://`,

packages/gatsby-remark-code-repls/src/gatsby-node.js

@@ -9,6 +9,7 @@ const {
   OPTION_DEFAULT_LINK_TEXT,
   OPTION_DEFAULT_HTML,
   OPTION_DEFAULT_REDIRECT_TEMPLATE_PATH,
+  OPTION_DEFAULT_INCLUDE_MATCHING_CSS,
 } = require(`./constants`)
 
 exports.createPages = async (
@@ -18,6 +19,7 @@ exports.createPages = async (
     externals = [],
     html = OPTION_DEFAULT_HTML,
     redirectTemplate = OPTION_DEFAULT_REDIRECT_TEMPLATE_PATH,
+    includeMatchingCSS = OPTION_DEFAULT_INCLUDE_MATCHING_CSS,
   } = {}
 ) => {
   if (!directory.endsWith(`/`)) {
@@ -51,6 +53,18 @@ exports.createPages = async (
           .replace(new RegExp(`^${directory}`), `redirect-to-codepen/`)
         const code = fs.readFileSync(file, `utf8`)
 
+        let css
+        if (includeMatchingCSS === true) {
+          try {
+            css = fs.readFileSync(file.replace(extname(file), `.css`), `utf8`)
+          } catch (err) {
+            // If the file doesn't exist, we gracefully ignore the error
+            if (err.code !== `ENOENT`) {
+              throw err
+            }
+          }
+        }
+
         // Codepen configuration.
         // https://blog.codepen.io/documentation/api/prefill/
         const action = `https://codepen.io/pen/define`
@@ -61,6 +75,7 @@ exports.createPages = async (
           js_external: externals.join(`;`),
           js_pre_processor: `babel`,
           layout: `left`,
+          css,
         })
 
         createPage({