slint-ui/slint · error

Missing field

Error message

Missing {} field

What it means

check_and_fix_package_string_field throws this when the Cargo.toml [package] table has no entry for the checked field at all and the check is not in fix mode. The xtask license-headers check requires certain package metadata fields (license, homepage, repository, ...) on every crate.

Solutions

1. Run `cargo xtask check --fix` to insert the expected field value automatically
2. Add the missing field manually with the expected value from xtask/src/license_headers_check.rs (e.g. repository = "https://github.com/slint-ui/slint")
3. If the crate is not meant to be checked, verify it is not unexpectedly part of the workspace

Example fix

// before
[package]
name = "my-crate"
version = "0.1.0"
// after
[package]
name = "my-crate"
version = "0.1.0"
repository = "https://github.com/slint-ui/slint"

let t: toml::Value = toml::from_str(&std::fs::read_to_string("Cargo.toml")?)?;
for field in ["license", "description", "repository", "homepage"] {
    assert!(t["package"].get(field).is_some(), "missing [package].{field}");
}

fn has_package_field(doc: &toml::Value, field: &str) -> bool {
    doc["package"].get(field).map_or(false, |v| !v.is_none())
}

When it happens

Trigger: Running `cargo xtask check` (no --fix) on a crate whose [package] section is missing e.g. `license`, `homepage`, or `repository`.

Common situations: Creating a new crate with cargo init and forgetting required metadata; a crate intentionally kept minimal; deleting a field during refactoring.

Understand the failure class

Background: "is required", "must be set", "missing required field": configuration validation errors across open-source libraries — this error's family across 36 libraries.

Related errors

• Missing description field
• Incorrect . Found expected
• cargo failed
• dev-dependencies cannot be from the workspace because…
• field is not a string

AI-assisted analysis of slint-ui/slint@3a7e700487 (2026-09-16). Data as JSON: /api/errors/d687a4a3aab2f084. Report an issue: GitHub.

Appendix: source

Thrown at xtask/src/license_headers_check.rs:911

                                        "Incorrect {}. Found {} expected {}",
                                        field,
                                        text,
                                        expected_str
                                    ));
                                }
                            }
                        }
                        None => return Err(anyhow!("{} field is not a string", field)),
                    },
                };
            }
            None => {
                if fix_it {
                    eprintln!("Fixing up {:?} as instructed. It has no {field}.", self.path);
                    self.doc["package"][field] = toml_edit::value(expected_str);
                    self.edited = true;
                } else {
                    return Err(anyhow!("Missing {} field", field));
                }
            }
        };
        Ok(())
    }

    fn published(&self) -> Result<bool> {
        Ok(self.package()?.get("publish").map(|v| v.as_bool().unwrap()).unwrap_or(true))
    }

    fn save_if_changed(&self) -> Result<()> {
        if self.edited {
            std::fs::write(&self.path, self.doc.to_string()).context("Error writing new Cargo.toml")
        } else {
            Ok(())
        }
    }
}

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