feat: write granular info into skip file

src/__tests__/gatsby-node.ts

@@ -1,3 +1,4 @@
+/* eslint-disable max-lines-per-function */
 jest.mock('../plugin-data', () => ({
   __esModule: true,
   default: jest.fn().mockReturnValue({
@@ -14,10 +15,12 @@ jest.mock('fs-extra', () => ({
   existsSync: jest.fn(),
   readFile: jest.fn(),
   writeFile: jest.fn(),
+  writeJson: jest.fn(),
+  remove: jest.fn(),
 }))
 
 // Importing writeFile here gives us access to the mocked method to assert the correct content is written to the file within test cases
-import { writeFile } from 'fs-extra'
+import { writeFile, writeJson, remove } from 'fs-extra'
 import { testPluginOptionsSchema } from 'gatsby-plugin-utils'
 
 import { pluginOptionsSchema, onPostBuild } from '../gatsby-node'
@@ -67,12 +70,12 @@ describe(`gatsby-node.js`, () => {
   })
 
   describe('onPostBuild', () => {
-    let store = {}
     const reporter = {
       info: jest.fn(),
     }
-    beforeEach(() => {
-      store = {
+
+    it('creates redirects for SSR and DSG pages in format Netlify expects', async () => {
+      const store = {
         getState: jest.fn().mockReturnValue({
           redirects: [],
           pages: [
@@ -89,13 +92,6 @@ describe(`gatsby-node.js`, () => {
           program: { directory: '' },
         }),
       }
-    })
-
-    afterEach(() => {
-      jest.resetAllMocks()
-    })
-
-    it('creates redirects for SSR and DSG pages in format Netlify expects', async () => {
       const expectedValue = [
         '',
         '## Created with gatsby-plugin-netlify',
@@ -106,7 +102,55 @@ describe(`gatsby-node.js`, () => {
       ].join(`\n`)
 
       await onPostBuild({ store, pathPrefix: '', reporter }, {})
-      expect(writeFile).toHaveBeenCalledWith('mock-file-path', expectedValue)
+      expect(writeFile).toHaveBeenLastCalledWith('mock-file-path', expectedValue)
+    })
+
+    it('creates skip file for unneeded function bundles', async () => {
+      const store = {
+        getState: jest.fn().mockReturnValue({
+          redirects: [],
+          pages: [
+            {
+              mode: 'DSG',
+              path: 'some/other/path',
+            },
+          ],
+          functions: [],
+          program: { directory: '' },
+        }),
+      }
+      const expectedValue = {
+        API: false,
+        SSR: false,
+        DSG: true,
+      }
+
+      await onPostBuild({ store, pathPrefix: '', reporter }, {})
+      expect(writeJson).toHaveBeenLastCalledWith('.cache/.nf-skip-gatsby-functions', expectedValue)
+    })
+
+    it('removes skip file when all function bundles needed', async () => {
+      const store = {
+        getState: jest.fn().mockReturnValue({
+          redirects: [],
+          pages: [
+            {
+              mode: 'SSR',
+              path: 'some/path',
+            },
+            {
+              mode: 'DSG',
+              path: 'some/other/path',
+            },
+          ],
+          functions: [true],
+          program: { directory: '' },
+        }),
+      }
+
+      await onPostBuild({ store, pathPrefix: '', reporter }, {})
+      expect(remove).toHaveBeenCalled()
     })
   })
 })
+/* eslint-enable max-lines-per-function */

src/gatsby-node.ts

@@ -1,7 +1,7 @@
 // https://www.netlify.com/docs/headers-and-basic-auth/
 import { join } from 'path'
 
-import { writeFile } from 'fs-extra'
+import { writeJson, remove } from 'fs-extra'
 import { generatePageDataPath } from 'gatsby-core-utils'
 import WebpackAssetsManifest from 'webpack-assets-manifest'
 
@@ -72,15 +72,19 @@ export const onPostBuild = async ({ store, pathPrefix, reporter }: any, userPlug
   let count = 0
   const rewrites: any = []
 
-  let needsFunctions = functions.length !== 0
+  const neededFunctions = {
+    API: functions.length !== 0,
+    SSR: false,
+    DSG: false,
+  }
 
   ;[...pages.values()].forEach((page) => {
     const { mode, matchPath, path } = page
     const matchPathClean = matchPath && matchPath.replace(/\*.*/, '*')
     const matchPathIsNotPath = matchPath && matchPath !== path
 
     if (mode === `SSR` || mode === `DSG`) {
-      needsFunctions = true
+      neededFunctions[mode] = true
       const fromPath = matchPathClean ?? path
       const toPath = mode === `SSR` ? `/.netlify/functions/__ssr` : `/.netlify/functions/__dsg`
       count++
@@ -103,12 +107,13 @@ export const onPostBuild = async ({ store, pathPrefix, reporter }: any, userPlug
   })
   reporter.info(`[gatsby-plugin-netlify] Created ${count} SSR/DSG redirect${count === 1 ? `` : `s`}...`)
 
-  if (!needsFunctions) {
-    reporter.info(`[gatsby-plugin-netlify] No Netlify functions needed. Skipping...`)
-    await writeFile(join(program.directory, `.cache`, `.nf-skip-gatsby-functions`), ``)
-  }
+  const skipFilePath = join(program.directory, `.cache`, `.nf-skip-gatsby-functions`)
+  const generateSkipFile = Object.values(neededFunctions).includes(false)
+    ? writeJson(skipFilePath, neededFunctions)
+    : remove(skipFilePath)
 
   await Promise.all([
+    generateSkipFile,
     buildHeadersProgram(pluginData, pluginOptions, reporter),
     createRedirects(pluginData, redirects, rewrites),
   ])