Regression while building Deno 2.6.0

[Lucy-dot-dot]

Example

I tried this code:

cargo install deno --locked

I expected to see this happen: installation success

Instead, this happened: a borrow checker error at the end of compilation in the deno crate

error[E0716]: temporary value dropped while borrowed
   --> /home/user/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/deno-2.6.0/tools/pm/audit.rs:507:16
    |
507 |               &format!("@{}", target)
    |               -^^^^^^^^^^^^^^^^^^^^^-
    |               ||                    |
    |               ||                    temporary value is freed at the end of this statement
    |               |creates a temporary value which is freed while still in use
    |               borrow later used here
    |
    = note: consider using a `let` binding to create a longer lived value
    = note: this error originates in the macro `format` (in Nightly builds, run with -Z macro-backtrace for more info)

For more information about this error, try `rustc --explain E0716`.
error: could not compile `deno` (bin "deno") due to 1 previous error

Version it worked on

It most recently worked on: 1.91.0

Version with regression

rustc --version --verbose:

rustc 1.92.0 (ded5c06cf 2025-12-08)
binary: rustc
commit-hash: ded5c06cf21d2b93bffd5d884aa6e96934ee4234
commit-date: 2025-12-08
host: x86_64-unknown-linux-gnu
release: 1.92.0
LLVM version: 21.1.3

[cyrgani]

reduction:

fn find_actions(action: &AuditAction) -> String {
    format!(
        "{} {}",
        action.action,
        if let Some(target) = &action.target {
            &format!("@{}", target)
        } else {
            ""
        },
    )
}
pub struct AuditAction {
    pub action: String,
    pub target: Option<String>,
}

in 1.91, this emitted the FCW warning: temporary lifetime will be shortened in Rust 1.92. I believe this is the intended breakage from #145838? (@dianne)

[dianne]

This is indeed intended breakage from #145838; it being accepted by the compiler was a bug in earlier Rust versions.

I'd recommend filing an issue with Deno instead, but looking at the Deno repository, it seems they only support building with a specific Rust toolchain version¹; at the moment it's 1.90.0².

Footnotes

1. https://github.com/denoland/deno/blob/main/.github/CONTRIBUTING.md#rust ↩

2. https://github.com/denoland/deno/blob/e8a725f5e9d9237824e79e58984ead0ba534497d/rust-toolchain.toml ↩