rust-lang/cargo · error

rustc load ok

Error message

rustc load ok

What it means

`BuildContext::get_sysroot` re-invokes `gctx.load_global_rustc(Some(self.ws)).expect("rustc load ok")`. The rustc used to compute target info has already been loaded successfully earlier in the build, and the result is cached on the `GlobalContext`, so a second call is expected to return the cached value. Failure indicates the cached rustc was cleared, the toolchain changed under the build, or `load_global_rustc` is non-deterministic for the environment.

Source

Thrown at src/compiler/build_context/mod.rs:176

    }

    /// Extra compiler args for either `rustc` or `rustdoc`.
    ///
    /// As of now, these flags come from the trailing args of either
    /// `cargo rustc` or `cargo rustdoc`.
    pub fn extra_args_for(&self, unit: &Unit) -> Option<&Vec<String>> {
        self.extra_compiler_args.get(unit)
    }

    /// Gets the path to the sysroot.
    ///
    /// Helper function that uses GlobalContext.
    pub fn get_sysroot(&self) -> &'gctx Path {
        // cfg::bad_cfg_discovery tests that these panics aren't reachable
        let rustc = self
            .gctx
            .load_global_rustc(Some(self.ws))
            .expect("rustc load ok");
        self.gctx.get_sysroot(&rustc).expect("sysroot fetch ok")
    }
}

#[derive(Copy, Clone, Default, Debug)]
pub struct DepKindSet {
    pub build: bool,
    pub normal: bool,
    pub dev: bool,
}

impl DepKindSet {
    pub fn contains(&self, kind: DepKind) -> bool {
        match kind {
            DepKind::Build => self.build,
            DepKind::Normal => self.normal,
            DepKind::Development => self.dev,
        }

View on GitHub (pinned to 0e07a15537)

Solutions

1. Pin the toolchain with `rustup override set <channel>` or a `rust-toolchain.toml` file before building.
2. Avoid changing `RUSTC`/`RUSTC_WRAPPER`/`RUSTUP_TOOLCHAIN` while a build runs.
3. Run `cargo clean` after switching toolchains, then rebuild.

Example fix

// before
let rustc = self
    .gctx
    .load_global_rustc(Some(self.ws))
    .expect("rustc load ok");
// after (propagate as an error; callers of get_sysroot are rare and can surface it)
let rustc = self.gctx.load_global_rustc(Some(self.ws))?;

// Verify the rustc binary is stable before building:
use std::process::Command;
fn rustc_invocable() -> bool {
    Command::new("rustc").arg("--version").output().map(|o| o.status.success()).unwrap_or(false)
}

When it happens

Trigger: `rustup override`/default toolchain changing while a build is in progress; `RUSTC`/`RUSTC_WRAPPER` env vars mutated mid-build; sysroot relocation between the initial probe and `get_sysroot`; a concurrent `rustup toolchain uninstall`.

Common situations: Long-running builds under `rustup` while the active toolchain is swapped; CI that re-points `RUSTUP_TOOLCHAIN` between steps sharing a `target/` dir; editor integrations that change `RUSTC` env.

Related errors

• able to invoke rustc
• able to invoke rustc
• malformed output when learning about crate-type {} informati
• output of --print={request} missing when learning about targ
• must be a host tuple

AI-assisted analysis of rust-lang/cargo@0e07a15537 (2026-08-06). Data as JSON: /data/errors/6097e400ac6b61b7.json. Report an issue: GitHub.