fix: warn if publish is "out" (#978)

Co-authored-by: kodiakhq[bot] <49736102+kodiakhq[bot]@users.noreply.github.com>

Author: ascorbic

src/helpers/verification.ts

@@ -61,12 +61,17 @@ export const checkNextSiteHasBuilt = ({
   failBuild: FailBuild
 }): void | never => {
   if (!existsSync(path.join(publish, 'BUILD_ID'))) {
+    const outWarning =
+      path.basename(publish) === 'out'
+        ? `Your publish directory is set to "out", but in most cases it should be ".next".`
+        : `In most cases it should be set to ".next", unless you have chosen a custom "distDir" in your Next config.`
+
     return failBuild(outdent`
       The directory "${path.relative(
         process.cwd(),
         publish,
-      )}" does not contain a Next.js production build. Perhaps the build command was not run, or you specified the wrong publish directory. 
-      In most cases it should be set to the site's ".next" directory path, unless you have chosen a custom "distDir" in your Next config. 
+      )}" does not contain a Next.js production build. Perhaps the build command was not run, or you specified the wrong publish directory.
+      ${outWarning}
       If you are using "next export" then the Essential Next.js plugin should be removed. See https://ntl.fyi/remove-plugin for details.
     `)
   }

test/index.js

@@ -208,11 +208,26 @@ describe('onBuild()', () => {
   test("fails if BUILD_ID doesn't exist", async () => {
     await moveNextDist()
     await unlink(path.join(process.cwd(), '.next/BUILD_ID'))
-    const failBuild = jest.fn().mockImplementation(() => {
-      throw new Error('BUILD_ID does not exist')
+    const failBuild = jest.fn().mockImplementation((err) => {
+      throw new Error(err)
     })
+    expect(() => plugin.onBuild({ ...defaultArgs, utils: { ...utils, build: { failBuild } } })).rejects.toThrow(
+      `In most cases it should be set to ".next", unless you have chosen a custom "distDir" in your Next config.`,
+    )
+    expect(failBuild).toHaveBeenCalled()
+  })
+
+  test("fails with helpful warning if BUILD_ID doesn't exist and publish is 'out'", async () => {
+    await moveNextDist()
+    await unlink(path.join(process.cwd(), '.next/BUILD_ID'))
+    const failBuild = jest.fn().mockImplementation((err) => {
+      throw new Error(err)
+    })
+    netlifyConfig.build.publish = path.resolve('out')
 
-    expect(() => plugin.onBuild({ ...defaultArgs, utils: { ...utils, build: { failBuild } } })).rejects.toThrow()
+    expect(() => plugin.onBuild({ ...defaultArgs, utils: { ...utils, build: { failBuild } } })).rejects.toThrow(
+      `Your publish directory is set to "out", but in most cases it should be ".next".`,
+    )
     expect(failBuild).toHaveBeenCalled()
   })