swcMinify adds considerably to the bundle size in version 13.0.3

[TheThirdRace]

Verify canary release

• I verified that the issue exists in the latest Next.js canary release

Provide environment information

Operating System:
Platform: win32
Arch: x64
Version: Windows 10 Pro
Binaries:
Node: 16.15.1
npm: N/A
Yarn: N/A
pnpm: N/A
Relevant packages:
next: 13.0.3
eslint-config-next: 13.0.3
react: 18.2.0
react-dom: 18.2.0

What browser are you using? (if relevant)

No response

How are you deploying your application? (if relevant)

No response

Describe the Bug

Short Story

When migrating from version 13.0.2 to 13.0.3, my bundle size jumped from 217 KB to 253 KB.

This is a 36 KB increase, there's clearly a problem...

Long Story

I just migrated my website from 12.3.3 to 13.0.3.

In 12.3.3, I never activated swcMinify because it always added 2 to 4 KB to my bundle size. Sure, it was faster to build by a whole 2 seconds, but I'd take that 4 KB before the build speed.

Now that 13.x has been released, swcMinify is the default and I activated it to see if I could finally get the same bundle size with faster builds.

To my surprise, my bundle size jumped 36 KB!!! I was already on the fence for 4 KB, 36 is simply unacceptable.

I did some testing:

Version	swcMinify = false	swcMinify = true
12.3.3	215 KB	217 KB
13.0.0	216 KB	217 KB
13.0.1	216 KB	217 KB
13.0.2	217 KB	218 KB
13.0.3	217 KB	253 KB

As you can see, somehow activating swcMinify always produced higher bundle size. But version 13.0.3 is simply abnormal.

I ran next-bundle-analyzer and I saw a weird difference with version 13.0.3.

While the Stat size values are pretty much the same across the board between 13.0.2 and 13.0.3, the Parsed size and Gzipped size have huge differences.

Parsed size (KB):

Package	13.0.2	13.0.3
@chakra-ui	134.33	188.25
framer-motion	94.96	156.44
@emotion	14.87	26.56

Gzipped size (KB):

Package	13.0.2	13.0.3
@chakra-ui	41.91	48.41
framer-motion	32.44	41.51
@emotion	5.98	7.63

This pattern repeats for all packages. This is where all those extra 36 KB are coming from.

I don't know what exactly changed in swc to have such an impact, but it seems it's not parsing the sources the same way anymore and it's producing way larger files in 13.0.3 as the result.

Going through the PRs for 13.0.3, maybe one of these is the culprit:

• feat: add --no-mangling to next build + fix --profile option
• Eagerly bundle external ESM dependencies for pages

Expected Behavior

Hopefully, swcMinify would minify as well as babel did.

But I'd settle with as well as it did in 13.0.2

Link to reproduction - Issues with a link to complete (but minimal) reproduction code will be addressed faster

https://github.com/TheThirdRace/thethirdrace.com.git

To Reproduce

I have a private repo I could give access to a contributor.

Just gives me a heads up in this ticket and I should give access within 12 hours.

The steps to reproduce are simple:

1. Clone the repo
2. Checkout branch develop
3. Run yarn to install dependencies
4. Run yarn build
5. You'll see 217 KB because swcMinify is set to false in next.config.js
6. Modify next.config.js to put swcMinify in comment (default value is true)
7. Run yarn build
8. You'll see 253 KB

[jakejarvis]

Looks like this was fixed in #42790 a couple days ago, hopefully there will be a patch release soon...

[kdy1]

Yes, it's fixed.
Closing as fixed

[TheThirdRace]

Ah, I see...

I filed the bug after it was fixed so I didn't see an open issue for it, but before any canary build was created so I didn't have the fix...

Talk about good timing 😅

[github-actions]

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