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Emscripten linker stderr: deprecated -sWASM_BIGINT #163441

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#162839
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Emscripten linker stderr: deprecated -sWASM_BIGINT#163441
#162839
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C-bugCategory: This is a bug.L-linker_messagesLint: linker_messagesO-emscriptenTarget: 50% off wasm32-unknown-musl. the savings come out of stdio.h, but hey, you get SDL!P-lowLow priorityT-compilerRelevant to the compiler team, which will review and decide on the PR/issue.

Description

@madsmtm
madsmtm
opened on Sep 28, 2026

Doing a simple rustc +1.98.1 --target wasm32-unknown-emscripten foo.rs gives the following warning:

warning: linker stderr: emcc: WASM_BIGINT is deprecated (no longer needed. Should only ever be implicitly disabled by -sWASM=0). Please open a bug if you have a continuing need for this setting [-Wdeprecated]
  |
  = note: `#[warn(linker_messages)]` on by default

warning: 1 warning emitted

I can see two options for resolving this:

  1. Remove -sWASM_BIGINT from the default linker arguments. This would be simplest, but might drop support for older emsdk versions though, I'm unsure whether this is a problem? Which versions of emsdk we support?
  2. Tweak the linker_messages lint to filter out this warning. This is a bit more involved, but it's done for loads of other messages, so it wouldn't be a big issue.

CC target maintainers @hoodmane @juntyr, WDYT we should do here?

Activity

  1. madsmtm
    added
    P-lowLow priority
    T-compilerRelevant to the compiler team, which will review and decide on the PR/issue.
    C-bugCategory: This is a bug.
    O-emscriptenTarget: 50% off wasm32-unknown-musl. the savings come out of stdio.h, but hey, you get SDL!
    L-linker_messagesLint: linker_messages
    on Sep 28, 2026
  2. rustbot
    added
    needs-triageThis issue may need triage. Remove when done. See docs forge.rust-lang.org/release/issue-triaging
    on Sep 28, 2026

  3. hoodmane commented on Sep 28, 2026

    @hoodmane
    hoodmane
    on Sep 28, 2026
    Contributor

    I think we can remove it. Old versions of Emscripten can pass -Clink-arg=-sWASM_BIGINT explicitly but they aren't all that well supported. It's been on by default since 5.0.

  4. bjorn3 commented on Sep 29, 2026

    @bjorn3
    bjorn3
    on Sep 29, 2026
    Member

    Will be fixed by #162839

  5. madsmtm
    linked a pull request that will close this issueBump min Emscripten version to 4.0, drop deprecated -sWASM_BIGINT for wasm32-unknown-emscripten #162839on Sep 29, 2026
  6. madsmtm
    removed
    needs-triageThis issue may need triage. Remove when done. See docs forge.rust-lang.org/release/issue-triaging
    on Sep 29, 2026
  7. rust-bors
    closed this as completedin #162839on Sep 29, 2026
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    C-bugCategory: This is a bug.L-linker_messagesLint: linker_messagesO-emscriptenTarget: 50% off wasm32-unknown-musl. the savings come out of stdio.h, but hey, you get SDL!P-lowLow priorityT-compilerRelevant to the compiler team, which will review and decide on the PR/issue.

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