#
cargo/util/context/
environment.rs

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    //! Encapsulates snapshotting of environment variables.

    use std::collections::HashMap;
    use std::ffi::{OsStr, OsString};

    use crate::util::errors::CargoResult;
    use anyhow::{anyhow, bail};

    /// Generate `case_insensitive_env` and `normalized_env` from the `env`.
    fn make_case_insensitive_and_normalized_env(
        env: &HashMap<OsString, OsString>,
    ) -> (HashMap<String, String>, HashMap<String, String>) {
        let case_insensitive_env: HashMap<_, _> = env
            .keys()
            .filter_map(|k| k.to_str())
            .map(|k| (k.to_uppercase(), k.to_owned()))
            .collect();

        let normalized_env = env
            .iter()
            // Only keep entries where both the key and value are valid UTF-8,
            // since the config env vars only support UTF-8 keys and values.
            // Otherwise, the normalized map warning could incorrectly warn about entries that can't be
            // read by the config system.
            // Please see the docs for `Env` for more context.
            .filter_map(|(k, v)| Some((k.to_str()?, v.to_str()?)))
            .map(|(k, _)| (k.to_uppercase().replace("-", "_"), k.to_owned()))
            .collect();
        (case_insensitive_env, normalized_env)
    }

    /// A snapshot of the environment variables available to [`GlobalContext`].
    ///
    /// Currently, the [`GlobalContext`] supports lookup of environment variables
    /// through two different means:
    ///
    /// - [`GlobalContext::get_env`](super::GlobalContext::get_env)
    ///   and [`GlobalContext::get_env_os`](super::GlobalContext::get_env_os)
    ///   for process environment variables (similar to [`std::env::var`] and [`std::env::var_os`]),
    /// - Typed Config Value API via [`GlobalContext::get`](super::GlobalContext::get).
    ///   This is only available for `CARGO_` prefixed environment keys.
    ///
    /// This type contains the env var snapshot and helper methods for both APIs.
    ///
    /// [`GlobalContext`]: super::GlobalContext
    #[derive(Debug)]
    pub struct Env {
        /// A snapshot of the process's environment variables.
        env: HashMap<OsString, OsString>,
        /// Used in the typed Config value API for warning messages when config keys are
        /// given in the wrong format.
        ///
        /// Maps from "normalized" (upper case and with "-" replaced by "_") env keys
        /// to the actual keys in the environment.
        /// The normalized format is the one expected by Cargo.
        ///
        /// This only holds env keys that are valid UTF-8, since [`super::ConfigKey`] only supports UTF-8 keys.
        /// In addition, this only holds env keys whose value in the environment is also valid UTF-8,
        /// since the typed Config value API only supports UTF-8 values.
        normalized_env: HashMap<String, String>,
        /// Used to implement `get_env` and `get_env_os` on Windows, where env keys are case-insensitive.
        ///
        /// Maps from uppercased env keys to the actual key in the environment.
        /// For example, this might hold a pair `("PATH", "Path")`.
        /// Currently only supports UTF-8 keys and values.
        case_insensitive_env: HashMap<String, String>,
    }

    impl Env {
        /// Create a new `Env` from process's environment variables.
        pub fn new() -> Self {
            // ALLOWED: This is the only permissible usage of `std::env::vars{_os}`
            // within cargo. If you do need access to individual variables without
            // interacting with the config system in [`GlobalContext`], please use
            // `std::env::var{_os}` and justify the validity of the usage.
            #[allow(clippy::disallowed_methods)]
            let env: HashMap<_, _> = std::env::vars_os().collect();
            let (case_insensitive_env, normalized_env) = make_case_insensitive_and_normalized_env(&env);
            Self {
                env,
                case_insensitive_env,
                normalized_env,
            }
        }

        /// Set the env directly from a `HashMap`.
        /// This should be used for debugging purposes only.
        pub(super) fn from_map(env: HashMap<String, String>) -> Self {
            let env = env.into_iter().map(|(k, v)| (k.into(), v.into())).collect();
            let (case_insensitive_env, normalized_env) = make_case_insensitive_and_normalized_env(&env);
            Self {
                env,
                case_insensitive_env,
                normalized_env,
            }
        }

        /// Returns all environment variables as an iterator,
        /// keeping only entries where both the key and value are valid UTF-8.
        pub fn iter_str(&self) -> impl Iterator<Item = (&str, &str)> {
            self.env
                .iter()
                .filter_map(|(k, v)| Some((k.to_str()?, v.to_str()?)))
        }

        /// Returns all environment variable keys, filtering out keys that are not valid UTF-8.
        pub fn keys_str(&self) -> impl Iterator<Item = &str> {
            self.env.keys().filter_map(|k| k.to_str())
        }

        /// Get the value of environment variable `key` through the snapshot in
        /// [`GlobalContext`](super::GlobalContext).
        ///
        /// This can be used similarly to [`std::env::var_os`].
        /// On Windows, we check for case mismatch since environment keys are case-insensitive.
        pub fn get_env_os(&self, key: impl AsRef<OsStr>) -> Option<&OsStr> {
            match self.env.get(key.as_ref()) {
                Some(s) => Some(s),
                None => {
                    if cfg!(windows) {
                        self.get_env_case_insensitive(key)
                    } else {
                        None
                    }
                }
            }
        }

        /// Get the value of environment variable `key` through the `self.env` snapshot.
        ///
        /// This can be used similarly to `std::env::var`.
        /// On Windows, we check for case mismatch since environment keys are case-insensitive.
        pub fn get_env(&self, key: impl AsRef<OsStr>) -> CargoResult<&str> {
            let key = key.as_ref();
            let s = self
                .get_env_os(key)
                .ok_or_else(|| anyhow!("{key:?} could not be found in the environment snapshot"))?;

            match s.to_str() {
                Some(s) => Ok(s),
                None => bail!("environment variable value is not valid unicode: {s:?}"),
            }
        }

        /// Performs a case-insensitive lookup of `key` in the environment.
        ///
        /// This is relevant on Windows, where environment variables are case-insensitive.
        /// Note that this only works on keys that are valid UTF-8 and it uses Unicode uppercase,
        /// which may differ from the OS's notion of uppercase.
        fn get_env_case_insensitive(&self, key: impl AsRef<OsStr>) -> Option<&OsStr> {
            let upper_case_key = key.as_ref().to_str()?.to_uppercase();
            let env_key: &OsStr = self.case_insensitive_env.get(&upper_case_key)?.as_ref();
            self.env.get(env_key).map(|v| v.as_ref())
        }

        /// Get the value of environment variable `key` as a `&str`.
        /// Returns `None` if `key` is not in `self.env` or if the value is not valid UTF-8.
        ///
        /// This is intended for use in private methods of [`GlobalContext`](super::GlobalContext),
        /// and does not check for env key case mismatch.
        ///
        /// This is case-sensitive on Windows (even though environment keys on Windows are usually
        /// case-insensitive) due to an unintended regression in 1.28 (via #5552).
        /// This should only affect keys used for cargo's config-system env variables (`CARGO_`
        /// prefixed ones), which are currently all uppercase.
        /// We may want to consider rectifying it if users report issues.
        /// One thing that adds a wrinkle here is the unstable advanced-env option that *requires*
        /// case-sensitive keys.
        ///
        /// Do not use this for any other purposes.
        /// Use [`Env::get_env_os`] or [`Env::get_env`] instead, which properly handle case
        /// insensitivity on Windows.
        pub(super) fn get_str(&self, key: impl AsRef<OsStr>) -> Option<&str> {
            self.env.get(key.as_ref()).and_then(|s| s.to_str())
        }

        /// Check if the environment contains `key`.
        ///
        /// This is intended for use in private methods of [`GlobalContext`](super::GlobalContext),
        /// and does not check for env key case mismatch.
        /// See the docstring of [`Env::get_str`] for more context.
        pub(super) fn contains_key(&self, key: impl AsRef<OsStr>) -> bool {
            self.env.contains_key(key.as_ref())
        }

        /// Looks up a normalized `key` in the `normalized_env`.
        /// Returns the corresponding (non-normalized) env key if it exists, else `None`.
        ///
        /// This is used by [`super::GlobalContext::check_environment_key_case_mismatch`].
        pub(super) fn get_normalized(&self, key: &str) -> Option<&str> {
            self.normalized_env.get(key).map(|s| s.as_ref())
        }
    }