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    //! Platform definition used by Cargo.
    //!
    //! This defines a [`Platform`] type which is used in Cargo to specify a target platform.
    //! There are two kinds, a named target like `x86_64-apple-darwin`, and a "cfg expression"
    //! like `cfg(any(target_os = "macos", target_os = "ios"))`.
    //!
    //! See `examples/matches.rs` for an example of how to match against a `Platform`.
    //!
    //! [`Platform`]: enum.Platform.html

    use std::fmt;
    use std::str::FromStr;

    mod cfg;
    mod error;

    pub use cfg::{Cfg, CfgExpr};
    pub use error::{ParseError, ParseErrorKind};

    /// Platform definition.
    #[derive(Eq, PartialEq, Hash, Ord, PartialOrd, Clone, Debug)]
    pub enum Platform {
        /// A named platform, like `x86_64-apple-darwin`.
        Name(String),
        /// A cfg expression, like `cfg(windows)`.
        Cfg(CfgExpr),
    }

    impl Platform {
        /// Returns whether the Platform matches the given target and cfg.
        ///
        /// The named target and cfg values should be obtained from `rustc`.
        pub fn matches(&self, name: &str, cfg: &[Cfg]) -> bool {
            match *self {
                Platform::Name(ref p) => p == name,
                Platform::Cfg(ref p) => p.matches(cfg),
            }
        }

        fn validate_named_platform(name: &str) -> Result<(), ParseError> {
            if let Some(ch) = name
                .chars()
                .find(|&c| !(c.is_alphanumeric() || c == '_' || c == '-' || c == '.'))
            {
                if name.chars().any(|c| c == '(') {
                    return Err(ParseError::new(
                        name,
                        ParseErrorKind::InvalidTarget(
                            "unexpected `(` character, cfg expressions must start with `cfg(`"
                                .to_string(),
                        ),
                    ));
                }
                return Err(ParseError::new(
                    name,
                    ParseErrorKind::InvalidTarget(format!(
                        "unexpected character {} in target name",
                        ch
                    )),
                ));
            }
            Ok(())
        }

        pub fn check_cfg_attributes(&self, warnings: &mut Vec<String>) {
            fn check_cfg_expr(expr: &CfgExpr, warnings: &mut Vec<String>) {
                match *expr {
                    CfgExpr::Not(ref e) => check_cfg_expr(e, warnings),
                    CfgExpr::All(ref e) | CfgExpr::Any(ref e) => {
                        for e in e {
                            check_cfg_expr(e, warnings);
                        }
                    }
                    CfgExpr::Value(ref e) => match e {
                        Cfg::Name(name) => match name.as_str() {
                            "test" | "debug_assertions" | "proc_macro" =>
                                warnings.push(format!(
                                    "Found `{}` in `target.'cfg(...)'.dependencies`. \
                                     This value is not supported for selecting dependencies \
                                     and will not work as expected. \
                                     To learn more visit \
                                     https://doc.rust-lang.org/cargo/reference/specifying-dependencies.html#platform-specific-dependencies",
                                     name
                                )),
                            _ => (),
                        },
                        Cfg::KeyPair(name, _) => if name.as_str() == "feature" {
                            warnings.push(String::from(
                                "Found `feature = ...` in `target.'cfg(...)'.dependencies`. \
                                 This key is not supported for selecting dependencies \
                                 and will not work as expected. \
                                 Use the [features] section instead: \
                                 https://doc.rust-lang.org/cargo/reference/features.html"
                            ))
                        },
                    }
                }
            }

            if let Platform::Cfg(cfg) = self {
                check_cfg_expr(cfg, warnings);
            }
        }
    }

    impl serde::Serialize for Platform {
        fn serialize<S>(&self, s: S) -> Result<S::Ok, S::Error>
        where
            S: serde::Serializer,
        {
            self.to_string().serialize(s)
        }
    }

    impl<'de> serde::Deserialize<'de> for Platform {
        fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
        where
            D: serde::Deserializer<'de>,
        {
            let s = String::deserialize(deserializer)?;
            FromStr::from_str(&s).map_err(serde::de::Error::custom)
        }
    }

    impl FromStr for Platform {
        type Err = ParseError;

        fn from_str(s: &str) -> Result<Platform, ParseError> {
            if s.starts_with("cfg(") && s.ends_with(')') {
                let s = &s[4..s.len() - 1];
                s.parse().map(Platform::Cfg)
            } else {
                Platform::validate_named_platform(s)?;
                Ok(Platform::Name(s.to_string()))
            }
        }
    }

    impl fmt::Display for Platform {
        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
            match *self {
                Platform::Name(ref n) => n.fmt(f),
                Platform::Cfg(ref e) => write!(f, "cfg({})", e),
            }
        }
    }