rust-lang/cargo · error

unexpected variable ` ` in resolver.lockfile-path

Error message

unexpected variable `{variable}` in resolver.lockfile-path `{raw_template}`

What it means

Cargo resolves `resolver.lockfile-path` (from config) as a templated path via `resolve_templated_path`. The replacements map is currently empty (`[(&str, &str); 0] = []`), so no variables are supported. If the template contains a `{variable}` token that is not in the (empty) replacement map, `ResolveTemplateError::UnexpectedVariable` is raised and wrapped into this anyhow error naming both the unknown variable and the raw template string.

Solutions

1. Use a literal, fully-specified file path for `resolver.lockfile-path` ending in `Cargo.lock` (the code later requires `path.ends_with(LOCKFILE_NAME)`).
2. Remove any `{...}` template tokens from the lockfile-path value, since no variables are currently substituted.
3. If you need path relativization across workspace roots, compute the absolute path externally and set the literal result.

Example fix

# before
[resolver]
lockfile-path = "{workspace}/Cargo.lock"

# after
[resolver]
lockfile-path = "./Cargo.lock"

use regex::Regex;
fn has_brace_token(s: &str) -> bool {
    Regex::new(r"\{[^}]*}").unwrap().is_match(s)
}
let lp: String = /* resolver.lockfile-path */;
assert!(!has_brace_token(&lp), "lockfile-path supports no variables");

When it happens

Trigger: Setting `resolver.lockfile-path` to a string containing a brace-delimited token such as `{workspace}` or `{target}` in `.cargo/config.toml`, then triggering workspace lockfile path resolution. Because the replacements array is empty, every brace-token is unexpected.

Common situations: Assuming lockfile-path supports the same template variables as `build.build-dir`; copying templating syntax from docs/examples that target a different Cargo feature; using `${...}`-style or `{...}`-style placeholders expecting expansion.

Related errors

• unexpected bracket ` ` in build.build-dir path
• can't find library ` `, rename file to `src/lib.rs` or…
• cannot mix `proc-macro` crate type with others
• cannot specify both `metabuild` and `build`
• config.json not found

AI-assisted analysis of rust-lang/cargo@98a09e7e7d (2026-08-11). Data as JSON: /api/errors/87d729603d997968. Report an issue: GitHub.

Appendix: source

Thrown at src/workspace/workspace.rs:366

                .feature_unification
                .unwrap_or(FeatureUnification::Selected);
        } else if config.feature_unification.is_some() {
            self.gctx()
                .shell()
                .warn("ignoring `resolver.feature-unification` without `-Zfeature-unification`")?;
        };

        if let Some(lockfile_path) = config.lockfile_path {
            // Reserve the ability to add templates in the future.
            let replacements: [(&str, &str); 0] = [];
            let path = lockfile_path
                    .resolve_templated_path(self.gctx(), replacements)
                    .map_err(|e| match e {
                        context::ResolveTemplateError::UnexpectedVariable {
                            variable,
                            raw_template,
                        } => {
                            anyhow!(
                                "unexpected variable `{variable}` in resolver.lockfile-path `{raw_template}`"
                            )
                        }
                        context::ResolveTemplateError::UnexpectedBracket { bracket_type, raw_template } => {
                            let (btype, literal) = match bracket_type {
                                context::BracketType::Opening => ("opening", "{"),
                                context::BracketType::Closing => ("closing", "}"),
                            };

                            anyhow!(
                                "unexpected {btype} bracket `{literal}` in build.build-dir path `{raw_template}`"
                            )
                        }
                    })?;
            if !path.ends_with(LOCKFILE_NAME) {
                bail!("the `resolver.lockfile-path` must be a path to a {LOCKFILE_NAME} file");
            }
            if path.is_dir() {

View on GitHub (pinned to 98a09e7e7d)