9.0.5 Dynamic imports not extracted to chunks

[thebuilder]

Bug report

Describe the bug

After upgrading from 9.0.4 to 9.0.5, dynamic(() => import()) are now all merged into commons.js, and no chunks are exported. Before it would create a new chunk for each.

It only happens when building for prodution with target: serverless. Running in development, the chunks are still generated correctly

Example

I've created a simple Codesandbox that just adds a single import(). It correctly chunks and loads the chunk on 9.0.4.

• 9.0.4: https://csb-ybitp-7585dpimf.now.sh/
• 9.0.5: https://csb-ybitp-o12p4pxlm.now.sh/

See the Network Requests.

Expected behavior

When using the dynamic imports, they should be extracted into chunks by Webpack.

[Timer]

Traced this down:

5ad0ea8e5b426183601cc28e98f158bcf2d0c524 is the first bad commit
commit 5ad0ea8e5b426183601cc28e98f158bcf2d0c524
Author: Joe Haddad <timer150@gmail.com>
Date:   Tue Aug 20 12:38:14 2019 -0400

    Remove `__NEXT_REPLACE__BUILD_ID__` workaround (#8445)
    
    We no longer need this because we don't run terser on serverless bundles.
    
    ---
    
    Closes https://github.com/zeit/next.js/issues/8436

 packages/next/build/entries.ts                     |  1 +
 packages/next/build/webpack-config.ts              |  6 +-
 .../webpack/loaders/next-serverless-loader.ts      |  4 +-
 .../build/webpack/plugins/serverless-plugin.ts     | 96 +++-------------------
 4 files changed, 18 insertions(+), 89 deletions(-)

[balazsorban44]

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