`web_sys` fails to compile with `dx serve` on windows

[Himmelschmidt]

Problem

dx serve fails on Windows when building WASM projects that use web-sys with many features, due to
Windows' ~32,767 character command line length limit. The error manifests as rustc failing with exit code 101. Running dx build first is a temporary workaround.

Steps To Reproduce

Steps to reproduce the behavior:

• Create a Dioxus web project that uses web-sys with many features (or any project that results in
  hundreds of --cfg "feature=..." arguments)
• Run dx serve --platform web on Windows
• The build will fail during dx serve compilation when rustc is called directly with cached arguments

Expected behavior

dx serve should work on Windows just like dx build does, without hitting command line length limitations.

Screenshots

Environment:

• Dioxus version: main
• Rust version: 1.88
• OS info: Windows
• App platform: Web (Fullstack)

Questionnaire

I don't have time to fix this right now, but maybe later.

[Himmelschmidt]

I think the difference is that dx build uses cargo rustc which handles long argument lists internally, while dx serve bypasses cargo entirely for speed during hot reloads. This optimization works fine on Unix systems but hits Windows' CreateProcessW limitations.

For anyone looking to fix this, the relevant code is in /packages/cli/src/build/request.rs around line 2120 where BuildMode::Thin constructs the direct rustc command.

[Himmelschmidt]

Maybe we should use response files when compiling on windows?

[jkelleyrtp]

Maybe we should use response files when compiling on windows?

We do use response files when linking on windows, as of 0.7.0-alpha.3. We also only link when running with --hotpatch. Are you running with hotpatch?

Also make sure you're up to date with dioxus 0.7.0-alpha.3 since we added response file support recently

---

edit - oh, passing arguments to rustc, not the linker? we don't do that currently

Made a PR to address this - can you try out #4465 ?

[Himmelschmidt]

We do use response files when linking on windows, as of 0.7.0-alpha.3.

Hmm, I've only seen this issue recently after commit b257e7e8cec00c1b9f3f2017fc342f72aef31e87

We also only link when running with --hotpatch. Are you running with hotpatch?

I don't usually, but I did now and it didn't change anything, still the same issue.

Made a PR to address this - can you try out #4465 ?

Still errors out with a massive list of cfg flags

[jkelleyrtp]

Ah I think cargo might actually be assembling a command file and passing it to rustc. We currently interpret that as attempting to link when running our RUSTC_WRAPPER. I made a small PR that changes that behavior. I don't necessarily expect hotpatching to work on this branch, but do you mind testing it out to see if it fixes regular dx serve? I'll get around to opening my windows VM and testing it at some point

#4468

The real fix might be reading the command file if it exists and then looking for the .o args

[Himmelschmidt]

Yep that works now, I'll drop a pr to address the fix you mentioned