Merge url query with exportPathMap (#4678)

This PR fixes #4615

From the issue :
> One thing we might consider is merging and showing a warning for keys not defined in exportPathMap

The behaviour after this PR is the following :

```js
// next.config.js
module.exports = {
  exportPathMap: () => ({
    '/': { page: '/', query: { a: 'blue' } }
  })
}
```

| url called | `ctx.query` | warning ? |
|-|-|-|
| `/` | `{ a: 'blue' }` | |
| `/?a=red` | `{ a: 'blue' }` | |
| `/?b=green` | `{ a: 'blue', b: 'green' }` | `... parameter 'b' missing in exportPathMap` |

Is that the expected behaviour ? If not, I'll update the PR to shape the expected behavior.

server/index.js

@@ -254,7 +254,15 @@ export default class Server {
         for (const path in exportPathMap) {
           const {page, query = {}} = exportPathMap[path]
           routes[path] = async (req, res, params, parsedUrl) => {
-            await this.render(req, res, page, query, parsedUrl)
+            const { query: urlQuery } = parsedUrl
+
+            Object.keys(urlQuery)
+              .filter(key => query[key] === undefined)
+              .forEach(key => console.warn(`Url defines a query parameter '${key}' that is missing in exportPathMap`))
+
+            const mergedQuery = {...urlQuery, ...query}
+
+            await this.render(req, res, page, mergedQuery, parsedUrl)
           }
         }
       }

test/integration/static/next.config.js

@@ -15,7 +15,8 @@ module.exports = (phase) => {
         '/dynamic': { page: '/dynamic', query: { text: 'cool dynamic text' } },
         '/dynamic/one': { page: '/dynamic', query: { text: 'next export is nice' } },
         '/dynamic/two': { page: '/dynamic', query: { text: 'zeit is awesome' } },
-        '/file-name.md': { page: '/dynamic', query: { text: 'this file has an extension' } }
+        '/file-name.md': { page: '/dynamic', query: { text: 'this file has an extension' } },
+        '/query': { page: '/query', query: { a: 'blue' } }
       }
     }
   }

test/integration/static/pages/query.js

@@ -0,0 +1,12 @@
+import { Component } from 'react'
+
+class Page extends Component {
+  static getInitialProps ({ query }) {
+    return { query }
+  }
+  render () {
+    return JSON.stringify(this.props.query, null, 2)
+  }
+}
+
+export default Page

test/integration/static/test/dev.js

@@ -1,5 +1,12 @@
 /* global describe, it, expect */
 import webdriver from 'next-webdriver'
+import { renderViaHTTP } from 'next-test-utils'
+import cheerio from 'cheerio'
+
+const loadJSONInPage = pageContent => {
+  const page = cheerio.load(pageContent)
+  return JSON.parse(page('#__next').text())
+}
 
 export default function (context) {
   describe('Render in development mode', () => {
@@ -21,4 +28,24 @@ export default function (context) {
       browser.close()
     })
   })
+
+  describe(`ExportPathMap's query in development mode`, () => {
+    it('should be present in ctx.query', async () => {
+      const pageContent = await renderViaHTTP(context.port, '/query')
+      const json = loadJSONInPage(pageContent)
+      expect(json).toEqual({ a: 'blue' })
+    })
+
+    it('should replace url query params in ctx.query when conflicting', async () => {
+      const pageContent = await renderViaHTTP(context.port, '/query?a=red')
+      const json = loadJSONInPage(pageContent)
+      expect(json).toEqual({ a: 'blue' })
+    })
+
+    it('should be merged with url query params in ctx.query', async () => {
+      const pageContent = await renderViaHTTP(context.port, '/query?b=green')
+      const json = loadJSONInPage(pageContent)
+      expect(json).toEqual({ a: 'blue', b: 'green' })
+    })
+  })
 }