chore(gatsby-plugin-netlify): add pluginOptionsSchema export

packages/gatsby-plugin-netlify/package.json

@@ -23,7 +23,8 @@
     "@babel/cli": "^7.11.6",
     "@babel/core": "^7.11.6",
     "babel-preset-gatsby-package": "^0.5.3",
-    "cross-env": "^7.0.2"
+    "cross-env": "^7.0.2",
+    "gatsby-plugin-utils": "^0.2.27"
   },
   "homepage": "https://github.com/gatsbyjs/gatsby/tree/master/packages/gatsby-plugin-netlify#readme",
   "keywords": [

packages/gatsby-plugin-netlify/src/__tests__/gatsby-node.js

@@ -0,0 +1,45 @@
+import { testPluginOptionsSchema } from "gatsby-plugin-utils"
+import { pluginOptionsSchema } from "../gatsby-node"
+
+describe(`gatsby-node.js`, () => {
+  it(`should provide meaningful errors when fields are invalid`, () => {
+    const expectedErrors = [
+      `"headers" must be of type object`,
+      `"allPageHeaders" must be an array`,
+      `"mergeSecurityHeaders" must be a boolean`,
+      `"mergeLinkHeaders" must be a boolean`,
+      `"mergeCachingHeaders" must be a boolean`,
+      `"transformHeaders" must have an arity lesser or equal to 2`,
+      `"generateMatchPathRewrites" must be a boolean`,
+    ]
+
+    const { errors } = testPluginOptionsSchema(pluginOptionsSchema, {
+      headers: `this should be an object`,
+      allPageHeaders: `this should be an array`,
+      mergeSecurityHeaders: `this should be a boolean`,
+      mergeLinkHeaders: `this should be a boolean`,
+      mergeCachingHeaders: `this should be a boolean`,
+      transformHeaders: (too, many, args) => ``,
+      generateMatchPathRewrites: `this should be a boolean`,
+    })
+
+    expect(errors).toEqual(expectedErrors)
+  })
+
+  it(`should validate the schema`, () => {
+    const { isValid } = testPluginOptionsSchema(pluginOptionsSchema, {
+      headers: {
+        "/some-page": [`Bearer: Some-Magic-Token`],
+        "/some-other-page": [`some`, `great`, `headers`],
+      },
+      allPageHeaders: [`First header`, `Second header`],
+      mergeSecurityHeaders: true,
+      mergeLinkHeaders: false,
+      mergeCachingHeaders: true,
+      transformHeaders: () => null,
+      generateMatchPathRewrites: false,
+    })
+
+    expect(isValid).toBe(true)
+  })
+})

packages/gatsby-plugin-netlify/src/gatsby-node.js

@@ -52,3 +52,39 @@ exports.onPostBuild = async (
     createRedirects(pluginData, redirects, rewrites),
   ])
 }
+
+const MATH_ALL_KEYS = /^/
+const pluginOptionsSchema = function ({ Joi }) {
+  // headers is a specific type used by Netlify: https://www.gatsbyjs.com/plugins/gatsby-plugin-netlify/#headers
+  const headersSchema = Joi.object()
+    .pattern(MATH_ALL_KEYS, Joi.array().items(Joi.string()))
+    .description(`Add more Netlify headers to specific pages`)
+
+  return Joi.object({
+    headers: headersSchema,
+    allPageHeaders: Joi.array()
+      .items(Joi.string())
+      .description(`Add more headers to all the pages`),
+    mergeSecurityHeaders: Joi.boolean().description(
+      `When set to true, turns off the default security headers`
+    ),
+    mergeLinkHeaders: Joi.boolean().description(
+      `When set to true, turns off the default gatsby js headers`
+    ),
+    mergeCachingHeaders: Joi.boolean().description(
+      `When set to true, turns off the default caching headers`
+    ),
+    transformHeaders: Joi.function()
+      .maxArity(2)
+      .description(
+        `Transform function for manipulating headers under each path (e.g.sorting), etc. This should return an object of type: { key: Array<string> }`
+      ),
+    generateMatchPathRewrites: Joi.boolean().description(
+      `When set to true, turns off automatic creation of redirect rules for client only paths`
+    ),
+  })
+}
+
+if (process.env.GATSBY_EXPERIMENTAL_PLUGIN_OPTION_VALIDATION) {
+  exports.pluginOptionsSchema = pluginOptionsSchema
+}