weren't using the right separator

* Make chunk graph more accurate

* Include shared files in every page

Previously this didn't work properly with nested pages.

* Add a build all but specified pages mode

* Always include reserved pages in build

* Add tests for ignore pages

* Output a more correct message for debug builds

* Adjust wording

* Add ** page globbing support

* Update check

* Generate two versions of pages

* Add code VSCode deleted

* Add dynamicBuildId option to __NEXT_DATA__

* Reduce amount of diff

* Make getPageFile code easier to read

* Minimize diff

* minimize diff

* Fix default value for dynamicBuildId

* Fix weird bug

* Fetch the head build id on client

* Move __selectivePageBuilding

* Add tests

* Remove _this

* Add console warning

* Set buildId to a fixed value during debug build

* __debug => debug

* Add a debug mode to webpack configuration

* Undo debug change for dist dir

* [wip] individual page builds

* Make flag experimental and remove from main bin

* Do not split chunks when using shared runtime

When overriding `config.resolve.alias` incorrectly webpack will throw an error because private-next-pages is not defined. This adds a more descriptive error explaining the error better.

Fixes: #6681

When compiling the serverless target there is no need for having an array of configs.

* await config

* update config-promise-error test

* Actually update test

We don't use a lot of the features of `glob`, so let's remove it in favor of a leaner approach using regex.

It's failing on windows and I have no idea why and don't own a windows machine 🤦🏼‍♂️

(Ignore some of the commits in here, I forgot to create the new branch before I started working)

Currently, `getBaseWebpackConfig` is marked async, but it doesn't await anything or otherwise return a Promise.  Please correct me if I am wrong, but it looks like it can be made synchronous.

Success:
![image](https://user-images.githubusercontent.com/616428/52907314-5e636480-322d-11e9-9420-b348663a3a7a.png)

Error:
![image](https://user-images.githubusercontent.com/616428/52907318-6c18ea00-322d-11e9-848d-e615d6af747d.png)

Warnings:
![image](https://user-images.githubusercontent.com/616428/52907353-2d376400-322e-11e9-9778-370f36912491.png)

---

We can still make build error output friendlier, but this is a good start.

Introduce env to next.config.js for build-time configuration

This reverts commit 9112f63e.

* show pages created when building

* fix types

* Move phases back to next/constants

* Fix typescript error

* Remove unused argument

* Replace pages-plugin with loader

* Add loader-utils types

* Remove logs

* Bring back previous deposal behavior

* Remove console.log

* Remove webpack/utils as it’s no longer in use

* Remove hot-self-accept-loader

* Error Recovery tests

* Make hotSelfAccept a noop default loader

* Fix windows deleted/added

* Remove logging

* Remove unused variables

* Remove log

* Simplify entrypoint generation

* Don’t return the function

* Fix _app test

* Remove code that’s always true

* Move aliases to constants

* Use alias

* Join pages alias in reduce

* Default pages differently

* Loop over pages instead of manually defining

* Move entry generation into common function

* Update packages/next/build/webpack/loaders/next-client-pages-loader.ts
Co-Authored-By: Ntimneutkens <tim@timneutkens.nl>

* Update packages/next/build/webpack/loaders/next-client-pages-loader.ts

**This does not change existing behavior.**

building to serverless is completely opt-in.

- Implements `target: 'serverless'` in `next.config.js`
- Removes `next build --lambdas` (was only available on next@canary so far)

This implements the concept of build targets. Currently there will be 2 build targets:

- server (This is the target that already existed / the default, no changes here)
- serverless (New target aimed at compiling pages to serverless handlers)

The serverless target will output a single file per `page` in the `pages` directory:

- `pages/index.js` => `.next/serverless/index.js`
- `pages/about.js` => `.next/serverless/about.js`

So what is inside `.next/serverless/about.js`? All the code needed to render that specific page. It has the Node.js `http.Server` request handler function signature:

```ts
(req: http.IncomingMessage, res: http.ServerResponse) => void
```

So how do you use it? Generally you **don't** want to use the below example, but for illustration purposes it's shown how the handler is called using a plain `http.Server`:

```js
const http = require('http')
// Note that `.default` is needed because the exported module is an esmodule
const handler = require('./.next/serverless/about.js').default
const server = new http.Server((req, res) => handler(req, res))
server.listen(3000, () => console.log('Listening on http://localhost:3000'))
```

Generally you'll upload this handler function to an external service like [Now v2](https://zeit.co/now-2), the `@now/next` builder will be updated to reflect these changes. This means that it'll be no longer neccesary for `@now/next` to do some of the guesswork in creating smaller handler functions. As Next.js will output the smallest possible serverless handler function automatically.

The function has 0 dependencies so no node_modules are required to run it, and is generally very small. 45Kb zipped is the baseline, but I'm sure we can make it even smaller in the future.

One important thing to note is that the function won't try to load `next.config.js`, so `publicRuntimeConfig` / `serverRuntimeConfig` are not supported. Reasons are outlined here: #5846

So to summarize:

- every page becomes a serverless function
- the serverless function has 0 dependencies (they're all inlined)
- "just" uses the `req` and `res` coming from Node.js
- opt-in using `target: 'serverless'` in `next.config.js`
- Does not load next.config.js when executing the function

TODO:

- [x] Compile next/dynamic / `import()` into the function file, so that no extra files have to be uploaded.
- [x] Setting `assetPrefix` at build time for serverless target
- [x] Support custom /_app
- [x] Support custom /_document
- [x] Support custom /_error
- [x] Add `next.config.js` property for `target`

Need discussion:
- [ ] Since the serverless target won't support `publicRuntimeConfig` / `serverRuntimeConfig` as they're runtime values. I think we should support build-time env var replacement with webpack.DefinePlugin or similar.
- [ ] Serving static files with the correct cache-control, as there is no static file serving in the serverless target