What causes "no library targets found in packages: {}" in rust-lang/cargo?

Inspect the listed package names; whichever should be a library needs a [lib] (src/lib.rs).

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

no library targets found in packages: {}

Error message

no library targets found in packages: {}

What it means

Same condition as error 89 but the multi-package branch (src/ops/cargo_compile/unit_generator.rs:454-457): multiple selected packages collectively lack any library target while LibRule::True is required. The names of all offending packages are joined.

Source

Thrown at src/ops/cargo_compile/unit_generator.rs:454

                            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,
                };
                let test_mode = match self.intent {
                    UserIntent::Build => CompileMode::Test,

View on GitHub (pinned to 0e07a15537)

Solutions

Inspect the listed package names; whichever should be a library needs a [lib] (src/lib.rs).
Remove --lib and target binaries/tests explicitly.
Narrow -p to the single package that actually has a lib.

Example fix

# before
cargo build --lib -p app-a -p app-b   # neither has a [lib]

# after
cargo build --lib -p shared-core      # the crate that actually has a lib

Defensive patterns

Strategy: validation

Validate before calling

// For a multi-package --lib selection, ensure at least one member has a lib.
fn any_lib_among(ws: &Workspace, names: &[String]) -> bool {
    ws.members()
        .filter(|m| names.iter().any(|n| n == m.name().as_str()))
        .any(|m| m.targets().iter().any(|t| t.is_lib()))
}

Type guard

fn selection_has_lib(pkgs: &[&cargo::core::Package]) -> bool {
    pkgs.iter().flat_map(|p| p.targets()).any(|t| t.is_lib())
}

Try / catch

if let Err(e) = ops::compile(ws, &opts) {
    if e.to_string().contains("no library targets found in packages") {
        eprintln!("none of the selected packages has a [lib]; drop --lib or pick a lib crate");
    }
    return Err(e);
}

Prevention

For --workspace --lib, ensure at least one crate exposes a library.
Narrow -p to the crate that owns the lib.

When it happens

Trigger: `cargo build --lib --workspace` (or -p across several crates) where none of the selected packages expose a [lib]. libs stays empty across all packages and LibRule::True holds.

Common situations: A workspace of binary-only crates where `--lib` was passed by mistake. Selecting several app crates expecting a shared lib that was moved or deleted.

Related errors

AI-assisted analysis of rust-lang/cargo@0e07a15537 (2026-08-06). Data as JSON: /data/errors/14ae698d639d0108.json. Report an issue: GitHub.