wasm-strip reduces bundle size inexplicably

[surma]

💡 Feature description

Building the default example project as a release build yields some rather big wasm modules, which might be deterring to some:

Command: wasm-pack build --release

• stable: 1.3M
• nightly: 771K

After running wasm-strip, the size goes down drastically:

• stable: 1.6K
• nightly: 1.6K

Anything speaking against running wasm-strip automatically, at least for --release?

wasm-pack 0.6.0
rustc 1.32.0 (9fda7c223 2019-01-16)
rustc 1.34.0-nightly (57d7cfc3c 2019-02-11)

[ashleygwilliams]

@surma yeah! i was actually thinking about this after our in person hack sesh at the meetup. the biggest blocker to adding tools to wasm-pack is the availability of a rust library and/or linux/macOS/windows binaries (the binaries are the preferred option). would you be willing to take a look into the availability of these binaries? if they exist, adding wasm-strip should be otherwise not too difficult.

also a side note- wasm-pack defaults to release so this is a feature that would be run by default and turned off for when wasm-pack runs in --dev mode.

[fitzgen]

I think we would only want to run wasm-strip for the release profile, not debug or profiling profiles, since it will remove debug info. But I'm also a little confused because I would assume that we are already not including any custom sections in release profile builds...

Either way -- if we add support for this, we would want to control it via the toml config.

[ashleygwilliams]

@fitzgen agree we'd only want it for --release, which is the "default" (i.e. not on --dev, or debug, or the others)

it certainly appears that wasm-strip does something here, perhaps it would help to figure out exactly what it does! (re: your comment re custom sections)

[surma]

As I mentioned in the title, I definitely meant wasm-strip to only be run for release builds!

I ran Twiggy real quick:

So it seems that custom sections do not get stripped.

(That being said, I think this might have been a change in 1.32 or something. I believe when I was on 1.30 the binary was way smaller)

[fitzgen]

Figured out why the DWARF isn't getting stripped: rustwasm/wasm-bindgen#1254

[ashleygwilliams]

@surma could you try the newest release of wasm-bindgen and confirm this is fixed? (i'd expect that wasm-strip would make a lot less of, if no, difference if the bug is indeed fixed!)

[surma]

I updated the wasm-bindgen dependency in my test project to 0.2.37, but sadly wasm-strip doesn’t seem to actually be invoked.

Invoking wasm-strip manually shaves off around 3k.

[ashleygwilliams]

@fitzgen circling back up on this - any idea what wasm-strip is stripping? @surma can you give any more details?

[fitzgen]

wasm-bindgen doesn't ever attempt to run wasm-strip -- I think there is some kind of misunderstanding here?

I think we need to be more concrete about examples, expectations, and actual behavior here, so it would be useful to have:

• steps to reproduce (clone this repo, run this command, etc)
• expected behavior (the generated wasm does not have any custom sections)
• actual behavior (the generated wasm has X and Y custom sections)

[ashleygwilliams]

@surma sorry for the Extreme Delay. any status update on this? if you have a way to repro that'd be great.

[surma]

Apologies! I lost track of this as well!

Here’s a repro repo: https://github.com/surma-dump/wasm-pack-issue-543

Repro steps:

1. Run wasm-pack build --release
2. Check file size of pkg/wasm_pack_issue_543_bg.wasm
3. Run wasm-strip pkg/wasm_pack_issue_543_bg.wasm
4. Check file size of pkg/wasm_pack_issue_543_bg.wasm again

Expected: File size remains the same

Currently observed: File size got smaller after running wasm-strip

[wdanilo]

I've got a different story to share:

1. Clone enso-org/ide@9d1b18d
2. Build with ./scripts/build.sh (wrapper for wasm-pack).
3. Check file size of target/web/basegl_bg.wasm
4. Run wasm-strip on the file.
5. Check the file size again.

Result: After running wasm-strip the size grows from 3.9Mb to 4.1Mb.
What is even more strange (to me) is that after running the 4.1Mb version via webpack optimizer, I got 3.83Mb output, smaller than running webpack without using wasm-strip.