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    //! Helpers for validating and checking names like package and crate names.

    use anyhow::bail;
    use anyhow::Result;

    /// Check the base requirements for a package name.
    ///
    /// This can be used for other things than package names, to enforce some
    /// level of sanity. Note that package names have other restrictions
    /// elsewhere. `cargo new` has a few restrictions, such as checking for
    /// reserved names. crates.io has even more restrictions.
    pub fn validate_package_name(name: &str, what: &str, help: &str) -> Result<()> {
        if name.is_empty() {
            bail!("{what} cannot be empty");
        }

        let mut chars = name.chars();
        if let Some(ch) = chars.next() {
            if ch.is_digit(10) {
                // A specific error for a potentially common case.
                bail!(
                    "the name `{}` cannot be used as a {}, \
                    the name cannot start with a digit{}",
                    name,
                    what,
                    help
                );
            }
            if !(unicode_xid::UnicodeXID::is_xid_start(ch) || ch == '_') {
                bail!(
                    "invalid character `{}` in {}: `{}`, \
                    the first character must be a Unicode XID start character \
                    (most letters or `_`){}",
                    ch,
                    what,
                    name,
                    help
                );
            }
        }
        for ch in chars {
            if !(unicode_xid::UnicodeXID::is_xid_continue(ch) || ch == '-') {
                bail!(
                    "invalid character `{}` in {}: `{}`, \
                    characters must be Unicode XID characters \
                    (numbers, `-`, `_`, or most letters){}",
                    ch,
                    what,
                    name,
                    help
                );
            }
        }
        Ok(())
    }

    /// Ensure a package name is [valid][validate_package_name]
    pub fn sanitize_package_name(name: &str, placeholder: char) -> String {
        let mut slug = String::new();
        let mut chars = name.chars();
        while let Some(ch) = chars.next() {
            if (unicode_xid::UnicodeXID::is_xid_start(ch) || ch == '_') && !ch.is_digit(10) {
                slug.push(ch);
                break;
            }
        }
        while let Some(ch) = chars.next() {
            if unicode_xid::UnicodeXID::is_xid_continue(ch) || ch == '-' {
                slug.push(ch);
            } else {
                slug.push(placeholder);
            }
        }
        if slug.is_empty() {
            slug.push_str("package");
        }
        slug
    }

    /// Validate dir-names and profile names according to RFC 2678.
    pub fn validate_profile_name(name: &str) -> Result<()> {
        if let Some(ch) = name
            .chars()
            .find(|ch| !ch.is_alphanumeric() && *ch != '_' && *ch != '-')
        {
            bail!(
                "invalid character `{}` in profile name `{}`\n\
                    Allowed characters are letters, numbers, underscore, and hyphen.",
                ch,
                name
            );
        }

        const SEE_DOCS: &str = "See https://doc.rust-lang.org/cargo/reference/profiles.html \
                for more on configuring profiles.";

        let lower_name = name.to_lowercase();
        if lower_name == "debug" {
            bail!(
                "profile name `{}` is reserved\n\
                     To configure the default development profile, use the name `dev` \
                     as in [profile.dev]\n\
                    {}",
                name,
                SEE_DOCS
            );
        }
        if lower_name == "build-override" {
            bail!(
                "profile name `{}` is reserved\n\
                     To configure build dependency settings, use [profile.dev.build-override] \
                     and [profile.release.build-override]\n\
                     {}",
                name,
                SEE_DOCS
            );
        }

        // These are some arbitrary reservations. We have no plans to use
        // these, but it seems safer to reserve a few just in case we want to
        // add more built-in profiles in the future. We can also uses special
        // syntax like cargo:foo if needed. But it is unlikely these will ever
        // be used.
        if matches!(
            lower_name.as_str(),
            "build"
                | "check"
                | "clean"
                | "config"
                | "fetch"
                | "fix"
                | "install"
                | "metadata"
                | "package"
                | "publish"
                | "report"
                | "root"
                | "run"
                | "rust"
                | "rustc"
                | "rustdoc"
                | "target"
                | "tmp"
                | "uninstall"
        ) || lower_name.starts_with("cargo")
        {
            bail!(
                "profile name `{}` is reserved\n\
                     Please choose a different name.\n\
                     {}",
                name,
                SEE_DOCS
            );
        }

        Ok(())
    }

    pub fn validate_feature_name(name: &str) -> Result<()> {
        if name.is_empty() {
            bail!("feature name cannot be empty");
        }

        if name.starts_with("dep:") {
            bail!("feature named `{name}` is not allowed to start with `dep:`",);
        }
        if name.contains('/') {
            bail!("feature named `{name}` is not allowed to contain slashes",);
        }
        let mut chars = name.chars();
        if let Some(ch) = chars.next() {
            if !(unicode_xid::UnicodeXID::is_xid_start(ch) || ch == '_' || ch.is_digit(10)) {
                bail!(
                    "invalid character `{ch}` in feature `{name}`, \
                    the first character must be a Unicode XID start character or digit \
                    (most letters or `_` or `0` to `9`)",
                );
            }
        }
        for ch in chars {
            if !(unicode_xid::UnicodeXID::is_xid_continue(ch) || ch == '-' || ch == '+' || ch == '.') {
                bail!(
                    "invalid character `{ch}` in feature `{name}`, \
                    characters must be Unicode XID characters, '-', `+`, or `.` \
                    (numbers, `+`, `-`, `_`, `.`, or most letters)",
                );
            }
        }
        Ok(())
    }

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

        #[test]
        fn valid_feature_names() {
            assert!(validate_feature_name("c++17").is_ok());
            assert!(validate_feature_name("128bit").is_ok());
            assert!(validate_feature_name("_foo").is_ok());
            assert!(validate_feature_name("feat-name").is_ok());
            assert!(validate_feature_name("feat_name").is_ok());
            assert!(validate_feature_name("foo.bar").is_ok());

            assert!(validate_feature_name("").is_err());
            assert!(validate_feature_name("+foo").is_err());
            assert!(validate_feature_name("-foo").is_err());
            assert!(validate_feature_name(".foo").is_err());
            assert!(validate_feature_name("dep:bar").is_err());
            assert!(validate_feature_name("foo/bar").is_err());
            assert!(validate_feature_name("foo:bar").is_err());
            assert!(validate_feature_name("foo?").is_err());
            assert!(validate_feature_name("?foo").is_err());
            assert!(validate_feature_name("ⒶⒷⒸ").is_err());
            assert!(validate_feature_name("a¼").is_err());
            assert!(validate_feature_name("").is_err());
        }
    }