parse exception: duplicate export name

[Madoshakalaka]

Some of Yew's example crates (but not all) fail to build in our binary size comparison CI because of wasm-opt

https://github.com/yewstack/yew/actions/runs/19726188911/job/56517994922?pr=3949#step:9:676

  [parse exception: duplicate export name (at 0:8529)]
  Fatal: error parsing wasm (try --debug for more info)
  2025-11-27T05:32:21.251418Z ERROR ❌ error
  error from build pipeline
  
  Caused by:
      0: HTML build pipeline failed (1 errors), showing first
      1: error from asset pipeline
      2: running wasm-opt
      3: wasm-opt call to executable '/home/runner/.cache/trunk/wasm-opt-version_125/bin/wasm-opt' with args: '["--output=/home/runner/work/yew/yew/target/wasm-opt/release/function_router_bg.wasm", "-O", "/home/runner/work/yew/yew/dist/function_router/.stage/function_router-93f56f6c1d2b72c_bg.wasm"]' returned a bad status: exit status: 1
  2025-11-27T05:32:21.251443Z ERROR error from build pipeline
  2025-11-27T05:32:21.251452Z  INFO   1: HTML build pipeline failed (1 errors), showing first
  2025-11-27T05:32:21.251454Z  INFO   2: error from asset pipeline
  2025-11-27T05:32:21.251455Z  INFO   3: running wasm-opt
  2025-11-27T05:32:21.251456Z  INFO   4: wasm-opt call to executable '/home/runner/.cache/trunk/wasm-opt-version_125/bin/wasm-opt' with args: '["--output=/home/runner/work/yew/yew/target/wasm-opt/release/function_router_bg.wasm", "-O", "/home/runner/work/yew/yew/dist/function_router/.stage/function_router-93f56f6c1d2b72c_bg.wasm"]' returned a bad status: exit status: 1

[kripken]

Please provide a wasm file to reproduce this issue.

[tlively]

Is it possible that wasm-opt is correct and there actually are duplicate export names? If so, this would be working as intended because duplicate export names are disallowed by the Wasm spec.

[Madoshakalaka]

here is the file
wasm-bindgen version 0.2.105
wasm-opt 125 fails to process it

https://drive.google.com/file/d/16EDQBi9VgWljtqevKAwmukXBh7z3WlJg/view?usp=sharing

alternatively this can be generate by

gh repo clone yewstack/yew
cd yew/examples/function_router
trunk build --release

The wasm will be generated to function_router/dist/.stage

Is it possible that wasm-opt is correct and there actually are duplicate export names?

Not sure how I check that... the failing PR yewstack/yew#3949 bumps the versions of some deps and consolidated some deps as workspace dependencies. Other later commits to the yew repo don't trigger the issue. I can try to isolate the minimum change to trigger the error if it's helpful.

[tlively]

There is indeed at least one duplicate export: wasm_bindgen_b6b266dc1a4d1fd9___convert__closures________invoke___web_sys_cd0631b8eb5639e2___features__gen_Event__Event_____. The bug must be in something that runs before wasm-opt.

[Madoshakalaka]

oof, that sounds like really bad news. Can I get more pointers on where to look at or ask for help?

[kripken]

The function name mentions wasm_bindgen, so I would guess the bug is there. To confirm, you can try the wasm file before running wasm-bindgen and after.

[Madoshakalaka]

thanks!

[cormacrelf]

For linkage I believe this is the issue wasm-bindgen/wasm-bindgen#4820 which was ultimately fixed by wasm-bindgen/wasm-bindgen#4822 (wbg 0.2.106)