Add support for additional/custom Netlify redirect rule criteria

packages/gatsby-plugin-netlify/src/create-redirects.js

@@ -11,8 +11,36 @@ export default async function writeRedirectsFile(pluginData, redirects) {
   // Map redirect data to the format Netlify expects
   // https://www.netlify.com/docs/redirects/
   redirects = redirects.map(redirect => {
-    const status = redirect.isPermanent ? 301 : 302
-    return `${redirect.fromPath}  ${redirect.toPath}  ${status}`
+    const {
+      fromPath,
+      isPermanent,
+      redirectInBrowser, // eslint-disable-line no-unused-vars
+      toPath,
+      ...rest
+    } = redirect
+
+    // The order of the first 3 parameters is significant.
+    // The order for rest params (key-value pairs) is arbitrary.
+    const pieces = [
+      fromPath,
+      toPath,
+      isPermanent ? 301 : 302, // Status
+    ]
+
+    for (let key in rest) {
+      const value = rest[key]
+
+      if (typeof value === `string` && value.indexOf(` `) >= 0) {
+        console.warn(
+          `Invalid redirect value "${value}" specified for key "${key}". ` +
+            `Values should not contain spaces.`
+        )
+      } else {
+        pieces.push(`${key}=${value}`)
+      }
+    }
+
+    return pieces.join(`  `)
   })
 
   let appendToFile = false

packages/gatsby/src/redux/actions.js

@@ -712,12 +712,14 @@ actions.setPluginStatus = (
  * @param {string} redirect.redirectInBrowser Redirects are generally for redirecting legacy URLs to their new configuration. If you can't update your UI for some reason, set `redirectInBrowser` to true and Gatsby will handle redirecting in the client as well.
  * @example
  * createRedirect({ fromPath: '/old-url', toPath: '/new-url', isPermanent: true })
+ * createRedirect({ fromPath: '/url', toPath: '/zn-CH/url', Language: 'zn' })
  */
 actions.createRedirect = ({
   fromPath,
   isPermanent = false,
-  toPath,
   redirectInBrowser = false,
+  toPath,
+  ...rest
 }) => {
   let pathPrefix = ``
   if (store.getState().program.prefixPaths) {
@@ -729,8 +731,9 @@ actions.createRedirect = ({
     payload: {
       fromPath: `${pathPrefix}${fromPath}`,
       isPermanent,
-      toPath: `${pathPrefix}${toPath}`,
       redirectInBrowser,
+      toPath: `${pathPrefix}${toPath}`,
+      ...rest,
     },
   }
 }