rust-lang/cargo · error · anyhow::Error

no library targets found in package `{}`

Error message

no library targets found in package `{}`

What it means

Thrown in proposals_to_units (src/ops/cargo_compile/unit_generator.rs:445-458) when a single selected package is required to provide a library target (LibRule::True) and not in all-targets mode, but the package has no [lib] target. The single-package branch formats the package name.

Source

Thrown at src/ops/cargo_compile/unit_generator.rs:452

                            let types = target.rustc_crate_types();
                            let types_str: Vec<&str> = types.iter().map(|t| t.as_str()).collect();
                            self.ws.gctx().shell().warn(format!(
                                "doc tests are not supported for crate type(s) `{}` in package `{}`",
                                types_str.join(", "),
                                pkg.name()
                            ))?;
                        } else {
                            libs.push(proposal)
                        }
                    }
                    if !all_targets && libs.is_empty() && *lib == LibRule::True {
                        let names = self
                            .packages
                            .iter()
                            .map(|pkg| pkg.name())
                            .collect::<Vec<_>>();
                        if names.len() == 1 {
                            anyhow::bail!("no library targets found in package `{}`", names[0]);
                        } else {
                            anyhow::bail!(
                                "no library targets found in packages: {}",
                                names.join(", ")
                            );
                        }
                    }
                    proposals.extend(libs);
                }

                let default_mode = to_compile_mode(self.intent);

                // If `--tests` was specified, add all targets that would be
                // generated by `cargo test`.
                let test_filter = match tests {
                    FilterRule::All => Target::tested,
                    FilterRule::Just(_) => Target::is_test,
                };

View on GitHub (pinned to 0e07a15537)

Solutions

1. Add a [lib] section (or ensure src/lib.rs exists) if the crate should be a library.
2. Drop the --lib flag and build the intended target (e.g. --bin).
3. Verify you targeted the right package with -p.

Example fix

# before: binary-only crate, `cargo build --lib` fails
src/main.rs

# after: add a library target
touch src/lib.rs
# Cargo.toml auto-detects src/lib.rs as the lib target

// Ensure the single package has a library target before --lib builds.
fn has_lib(pkg: &cargo::core::Package) -> bool {
    pkg.targets().iter().any(|t| t.is_lib())
}

fn is_library_pkg(pkg: &cargo::core::Package) -> bool {
    pkg.targets().iter().any(|t| t.is_lib())
}

if let Err(e) = ops::compile(ws, &opts) {
    if e.to_string().contains("no library targets found") {
        eprintln!("add a [lib] target or drop --lib");
    }
    return Err(e);
}

When it happens

Trigger: `cargo build --lib` (or any lib-requiring intent like doc/check on the lib) on a package whose Cargo.toml has no [lib] section and no default src/lib.rs. LibRule::True with libs.is_empty() triggers the bail.

Common situations: A binary-only crate (src/main.rs only) where someone runs `cargo doc --lib` or `cargo build --lib`. A crate renamed to drop its lib. Missing src/lib.rs file in a crate that was expected to be a library.

Related errors

• crate types can only be specified for libraries and example
• no library targets found in packages: {}
• extra arguments to `{}` can only be passed to one target, co
• could not compile due to {error_count} previous target resol
• crate types to rustc can only be passed to one target, consi

AI-assisted analysis of rust-lang/cargo@0e07a15537 (2026-08-06). Data as JSON: /data/errors/93534b855b834bc8.json. Report an issue: GitHub.