Cannot build in Rust 1.89 nightly

[clin1234]

    Updating git repository `https://github.com/spinframework/spin`
  Installing spin-cli v3.4.0-pre0 (https://github.com/spinframework/spin#92bb6c5d)
    Updating crates.io index
    Updating git repository `https://github.com/watchexec/watchexec.git`
    Updating git repository `https://github.com/fermyon/cargo-target-dep`
    Updating git repository `https://github.com/fermyon/dkregistry-rs`
    Updating git repository `https://github.com/fermyon/oci-distribution`
    Updating git repository `https://github.com/vdice/rust-jwt`
    Updating git repository `https://github.com/azure/azure-sdk-for-rust`
     Locking 960 packages to latest compatible versions
      Adding azure_core v0.21.0 (available: v0.25.0)
      Adding azure_data_cosmos v0.21.0 (available: v0.24.0)
      Adding azure_identity v0.21.0 (available: v0.25.0)
      Adding candle-core v0.8.4 (available: v0.9.1)
      Adding candle-nn v0.8.4 (available: v0.9.1)
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      Adding clap v3.2.25 (available: v4.5.40)
      Adding command-group v2.1.0 (available: v5.0.1)
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      Adding opentelemetry v0.28.0 (available: v0.30.0)
      Adding opentelemetry-appender-tracing v0.28.1 (available: v0.30.1)
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      Adding redis v0.25.4 (available: v0.32.2)
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      Adding wac-graph v0.6.1 (available: v0.7.0)
      Adding webpki-roots v0.26.11 (available: v1.0.1)
   Compiling wasmtime v34.0.0
warning: lifetime flowing from input to output with different syntax can be confusing
   --> crates/app/src/lib.rs:252:18
    |
252 |     pub fn files(&self) -> std::slice::Iter<ContentPath> {
    |                  ^^^^^     ----------------------------- the lifetime gets resolved as `'_`
    |                  |
    |                  this lifetime flows to the output
    |
    = note: `#[warn(mismatched_lifetime_syntaxes)]` on by default
help: one option is to remove the lifetime for references and use the anonymous lifetime for paths
    |
252 |     pub fn files(&self) -> std::slice::Iter<'_, ContentPath> {
    |                                             +++

warning: `spin-app` (lib) generated 1 warning (run `cargo fix --lib -p spin-app` to apply 1 suggestion)
warning: lifetime flowing from input to output with different syntax can be confusing
  --> crates/expressions/src/template.rs:49:25
   |
49 |     pub(crate) fn parts(&self) -> std::slice::Iter<Part> {
   |                         ^^^^^     ---------------------- the lifetime gets resolved as `'_`
   |                         |
   |                         this lifetime flows to the output
   |
   = note: `#[warn(mismatched_lifetime_syntaxes)]` on by default
help: one option is to remove the lifetime for references and use the anonymous lifetime for paths
   |
49 |     pub(crate) fn parts(&self) -> std::slice::Iter<'_, Part> {
   |                                                    +++

warning: `spin-expressions` (lib) generated 1 warning (run `cargo fix --lib -p spin-expressions` to apply 1 suggestion)
   Compiling spin-componentize v3.4.0-pre0 (/home/cc/.cargo/git/checkouts/spin-6133b75e3590288b/92bb6c5/crates/componentize)
   Compiling hashlink v0.8.4
   Compiling zbus_macros v4.4.0
   Compiling async-fs v2.1.2
   Compiling gix-path v0.7.3
   Compiling gix-validate v0.7.7
   Compiling libsql-sqlite3-parser v0.13.0
   Compiling serde_with_macros v3.13.0
   Compiling gix-utils v0.1.14
   Compiling async-broadcast v0.7.2
   Compiling azure_core v0.21.0
   Compiling azure_core v0.20.0 (https://github.com/azure/azure-sdk-for-rust?rev=8c4caa251c3903d5eae848b41bb1d02a4d65231c#8c4caa25)
   Compiling dirs-sys v0.4.1
   Compiling combine v4.6.7
   Compiling md-5 v0.10.6
   Compiling serde_path_to_error v0.1.17
   Compiling esaxx-rs v0.1.10
   Compiling cmake v0.1.54
   Compiling miette-derive v5.10.0
   Compiling bitmaps v2.1.0
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   Compiling xdg-home v1.3.0
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   Compiling im-rc v15.1.0
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   Compiling pathdiff v0.2.3
error: lifetime flowing from input to output with different syntax can be confusing
  --> crates/componentize/src/lib.rs:42:55
   |
42 | pub fn componentize_if_necessary(module_or_component: &[u8]) -> Result<Cow<[u8]>> {
   |                                                       ^^^^^            --------- the lifetime gets resolved as `'_`
   |                                                       |
   |                                                       this lifetime flows to the output
   |
note: the lint level is defined here
  --> crates/componentize/src/lib.rs:1:9
   |
1  | #![deny(warnings)]
   |         ^^^^^^^^
   = note: `#[deny(mismatched_lifetime_syntaxes)]` implied by `#[deny(warnings)]`
help: one option is to remove the lifetime for references and use the anonymous lifetime for paths
   |
42 | pub fn componentize_if_necessary(module_or_component: &[u8]) -> Result<Cow<'_, [u8]>> {
   |                                                                            +++

error: lifetime flowing from input to output with different syntax can be confusing
  --> crates/componentize/src/module_info.rs:86:31
   |
86 |     pub fn bindgen_processors(&self) -> Option<wasm_metadata::ProducersField> {
   |                               ^^^^^            ----------------------------- the lifetime gets resolved as `'_`
   |                               |
   |                               this lifetime flows to the output
   |
help: one option is to remove the lifetime for references and use the anonymous lifetime for paths
   |
86 |     pub fn bindgen_processors(&self) -> Option<wasm_metadata::ProducersField<'_>> {
   |                                                                             ++++

error: could not compile `spin-componentize` (lib) due to 2 previous errors
warning: build failed, waiting for other jobs to finish...
error: failed to compile `spin-cli v3.4.0-pre0 (https://github.com/spinframework/spin#92bb6c5d)`, intermediate artifacts can be found at `/tmp/cargo-installStqdR2`.
To reuse those artifacts with a future compilation, set the environment variable `CARGO_TARGET_DIR` to that path.

[lann]

Could you post the version of Rust (rustc --version) you are using?

[clin1234]

Could you post the version of Rust (rustc --version) you are using?

rustc 1.89.0-nightly (be19eda0d 2025-06-22)

[itowlson]

Thanks for flagging this. It looks like this is a new warning in nightly, and there's still discussion going on around it (https://rust-lang.zulipchat.com/#narrow/channel/213817-t-lang/topic/Feedback.20on.20mismatched_lifetime_syntaxes/with/524650475). Given that it's not yet stable, we'll likely wait until the warning stabilises to implement a fix.

That said, I don't know if anyone has yet built Spin with 1.88 stable: if you see the same error in stable, then we should definitely fix it!

[itowlson]

Okay I just tried 1.88 and it builds okay (from local, not from GitHub, but that shouldn't matter). I'll update the title to reflect that this appears to be a nightly-only issue so far, but please change it back if you're seeing something different!

[lann]

We'll leave this open for tracking until 1.89 stabilizes, scheduled for Aug 7.