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    use semver::{Comparator, Op, Version, VersionReq};
    use std::fmt::{self, Display};

    #[derive(PartialEq, Eq, Hash, Clone, Debug)]
    pub enum OptVersionReq {
        Any,
        Req(VersionReq),
        /// The exact locked version and the original version requirement.
        Locked(Version, VersionReq),
    }

    pub trait VersionExt {
        fn is_prerelease(&self) -> bool;
    }

    pub trait VersionReqExt {
        fn exact(version: &Version) -> Self;
    }

    impl VersionExt for Version {
        fn is_prerelease(&self) -> bool {
            !self.pre.is_empty()
        }
    }

    impl VersionReqExt for VersionReq {
        fn exact(version: &Version) -> Self {
            VersionReq {
                comparators: vec![Comparator {
                    op: Op::Exact,
                    major: version.major,
                    minor: Some(version.minor),
                    patch: Some(version.patch),
                    pre: version.pre.clone(),
                }],
            }
        }
    }

    impl OptVersionReq {
        pub fn exact(version: &Version) -> Self {
            OptVersionReq::Req(VersionReq::exact(version))
        }

        pub fn is_exact(&self) -> bool {
            match self {
                OptVersionReq::Any => false,
                OptVersionReq::Req(req) => {
                    req.comparators.len() == 1 && {
                        let cmp = &req.comparators[0];
                        cmp.op == Op::Exact && cmp.minor.is_some() && cmp.patch.is_some()
                    }
                }
                OptVersionReq::Locked(..) => true,
            }
        }

        pub fn lock_to(&mut self, version: &Version) {
            assert!(self.matches(version), "cannot lock {} to {}", self, version);
            use OptVersionReq::*;
            let version = version.clone();
            *self = match self {
                Any => Locked(version, VersionReq::STAR),
                Req(req) => Locked(version, req.clone()),
                Locked(_, req) => Locked(version, req.clone()),
            };
        }

        pub fn is_locked(&self) -> bool {
            matches!(self, OptVersionReq::Locked(..))
        }

        /// Gets the version to which this req is locked, if any.
        pub fn locked_version(&self) -> Option<&Version> {
            match self {
                OptVersionReq::Locked(version, _) => Some(version),
                _ => None,
            }
        }

        pub fn matches(&self, version: &Version) -> bool {
            match self {
                OptVersionReq::Any => true,
                OptVersionReq::Req(req) => req.matches(version),
                OptVersionReq::Locked(v, _) => {
                    v.major == version.major
                        && v.minor == version.minor
                        && v.patch == version.patch
                        && v.pre == version.pre
                }
            }
        }
    }

    impl Display for OptVersionReq {
        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
            match self {
                OptVersionReq::Any => f.write_str("*"),
                OptVersionReq::Req(req) => Display::fmt(req, f),
                OptVersionReq::Locked(_, req) => Display::fmt(req, f),
            }
        }
    }

    impl From<VersionReq> for OptVersionReq {
        fn from(req: VersionReq) -> Self {
            OptVersionReq::Req(req)
        }
    }

    #[cfg(test)]
    mod tests {
        use super::*;

        #[test]
        fn locked_has_the_same_with_exact() {
            fn test_versions(target_ver: &str, vers: &[&str]) {
                let ver = Version::parse(target_ver).unwrap();
                let exact = OptVersionReq::exact(&ver);
                let mut locked = exact.clone();
                locked.lock_to(&ver);
                for v in vers {
                    let v = Version::parse(v).unwrap();
                    assert_eq!(exact.matches(&v), locked.matches(&v));
                }
            }

            test_versions(
                "1.0.0",
                &["1.0.0", "1.0.1", "0.9.9", "0.10.0", "0.1.0", "1.0.0-pre"],
            );
            test_versions("0.9.0", &["0.9.0", "0.9.1", "1.9.0", "0.0.9", "0.9.0-pre"]);
            test_versions("0.0.2", &["0.0.2", "0.0.1", "0.0.3", "0.0.2-pre"]);
            test_versions(
                "0.1.0-beta2.a",
                &[
                    "0.1.0-beta2.a",
                    "0.9.1",
                    "0.1.0",
                    "0.1.1-beta2.a",
                    "0.1.0-beta2",
                ],
            );
            test_versions("0.1.0+meta", &["0.1.0", "0.1.0+meta", "0.1.0+any"]);
        }
    }