Allow mismatching href and as when manually provided

packages/next/next-server/lib/router/router.ts

@@ -331,22 +331,34 @@ export default class Router implements BaseRouter {
 
       if (isDynamicRoute(route)) {
         const { pathname: asPathname } = parse(as)
-        const routeMatch = getRouteMatcher(getRouteRegex(route))(asPathname)
+        const routeRegex = getRouteRegex(route)
+        const routeMatch = getRouteMatcher(routeRegex)(asPathname)
         if (!routeMatch) {
-          const error =
-            `The provided \`as\` value (${asPathname}) is incompatible with the \`href\` value (${route}). ` +
-            `Read more: https://err.sh/zeit/next.js/incompatible-href-as`
-
-          if (process.env.NODE_ENV !== 'production') {
-            throw new Error(error)
-          } else {
-            console.error(error)
+          const missingParams = Object.keys(routeRegex.groups).filter(
+            param => !query[param]
+          )
+
+          if (missingParams.length > 0) {
+            if (process.env.NODE_ENV !== 'production') {
+              console.warn(
+                `Mismatching \`as\` and \`href\` failed to manually provide ` +
+                  `the params: ${missingParams.join(
+                    ', '
+                  )} in the \`href\`'s \`query\``
+              )
+            }
+
+            return reject(
+              new Error(
+                `The provided \`as\` value (${asPathname}) is incompatible with the \`href\` value (${route}). ` +
+                  `Read more: https://err.sh/zeit/next.js/incompatible-href-as`
+              )
+            )
           }
-          return resolve(false)
+        } else {
+          // Merge params into `query`, overwriting any specified in search
+          Object.assign(query, routeMatch)
         }
-
-        // Merge params into `query`, overwriting any specified in search
-        Object.assign(query, routeMatch)
       }
 
       Router.events.emit('routeChangeStart', as)

test/integration/invalid-href/pages/[post].js

@@ -0,0 +1 @@
+export default () => 'hi from post'

test/integration/invalid-href/pages/dynamic-route-mismatch-manual.js

@@ -0,0 +1,7 @@
+import Link from 'next/link'
+
+export default () => (
+  <Link href="/[post]?post=post-1" as="/blog/post-1">
+    <a>Click me</a>
+  </Link>
+)

test/integration/invalid-href/test/index.test.js

@@ -20,13 +20,45 @@ const appDir = join(__dirname, '..')
 const firstErrorRegex = /Invalid href passed to router: mailto:idk@idk.com.*invalid-href-passed/
 const secondErrorRegex = /Invalid href passed to router: .*google\.com.*invalid-href-passed/
 
-const showsError = async (pathname, regex, click = false) => {
+const showsError = async (
+  pathname,
+  regex,
+  click = false,
+  isWarn = false,
+  cb
+) => {
   const browser = await webdriver(appPort, pathname)
+  if (isWarn) {
+    await browser.eval(`(function() {
+      window.warnLogs = []
+      var origWarn = window.console.warn
+      window.console.warn = function() {
+        var warnStr = ''
+        for (var i = 0; i < arguments.length; i++) {
+          if (i > 0) warnStr += ' ';
+          warnStr += arguments[i]
+        }
+        window.warnLogs.push(warnStr)
+        origWarn.apply(undefined, arguments)
+      }
+    })()`)
+  }
+
   if (click) {
     await browser.elementByCss('a').click()
   }
-  const errorContent = await getReactErrorOverlayContent(browser)
-  expect(errorContent).toMatch(regex)
+  if (isWarn) {
+    await waitFor(2000)
+    const warnLogs = await browser.eval('window.warnLogs')
+    console.log(warnLogs)
+    expect(warnLogs.some(log => log.match(regex))).toBe(true)
+  } else {
+    const errorContent = await getReactErrorOverlayContent(browser)
+    expect(errorContent).toMatch(regex)
+  }
+
+  if (cb) await cb(browser)
+
   await browser.close()
 }
 
@@ -89,6 +121,16 @@ describe('Invalid hrefs', () => {
         /The provided `as` value \(\/blog\/post-1\) is incompatible with the `href` value \(\/\[post\]\)/,
         true
       )
+      await showsError(
+        '/dynamic-route-mismatch',
+        /Mismatching `as` and `href` failed to manually provide the params: post in the `href`'s `query`/,
+        true,
+        true
+      )
+    })
+
+    it('does not throw error when dynamic route mismatch is used on Link and params are manually provided', async () => {
+      await noError('/dynamic-route-mismatch-manual', true)
     })
   })
 
@@ -123,5 +165,25 @@ describe('Invalid hrefs', () => {
     it('does not show error in production when https://google.com is used as href on router.replace', async () => {
       await noError('/second?method=replace', true)
     })
+
+    it('shows error when dynamic route mismatch is used on Link', async () => {
+      const browser = await webdriver(appPort, '/dynamic-route-mismatch')
+      await browser.eval(`(function() {
+        window.caughtErrors = []
+        window.addEventListener('unhandledrejection', (error) => {
+          window.caughtErrors.push(error.reason.message)
+        })
+      })()`)
+      await browser.elementByCss('a').click()
+      await waitFor(500)
+      const errors = await browser.eval('window.caughtErrors')
+      expect(
+        errors.find(err =>
+          err.includes(
+            'The provided `as` value (/blog/post-1) is incompatible with the `href` value (/[post]). Read more: https://err.sh/zeit/next.js/incompatible-href-as'
+          )
+        )
+      ).toBeTruthy()
+    })
   })
 })