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    // Copyright 2012-2015 The Rust Project Developers. See the COPYRIGHT
    // file at the top-level directory of this distribution and at
    // http://rust-lang.org/COPYRIGHT.
    //
    // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
    // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
    // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
    // option. This file may not be copied, modified, or distributed
    // except according to those terms.

    //! Inspection and manipulation of the process's environment.
    //!
    //! This module contains functions to inspect various aspects such as
    //! environment variables, process arguments, the current directory, and various
    //! other important directories.
    //!
    //! There are several functions and structs in this module that have a
    //! counterpart ending in `os`. Those ending in `os` will return an [`OsString`]
    //! and those without will be returning a [`String`].
    //!
    //! [`OsString`]: ../../std/ffi/struct.OsString.html
    //! [`String`]: ../string/struct.String.html

    #![stable(feature = "env", since = "1.0.0")]

    use error::Error;
    use ffi::{OsStr, OsString};
    use fmt;
    use io;
    use path::{Path, PathBuf};
    use sys;
    use sys::os as os_imp;

    /// Returns the current working directory as a [`PathBuf`].
    ///
    /// # Errors
    ///
    /// Returns an [`Err`] if the current working directory value is invalid.
    /// Possible cases:
    ///
    /// * Current directory does not exist.
    /// * There are insufficient permissions to access the current directory.
    ///
    /// [`PathBuf`]: ../../std/path/struct.PathBuf.html
    /// [`Err`]: ../../std/result/enum.Result.html#method.err
    ///
    /// # Examples
    ///
    /// ```
    /// use std::env;
    ///
    /// // We assume that we are in a valid directory.
    /// let path = env::current_dir().unwrap();
    /// println!("The current directory is {}", path.display());
    /// ```
    #[stable(feature = "env", since = "1.0.0")]
    pub fn current_dir() -> io::Result<PathBuf> {
        os_imp::getcwd()
    }

    /// Changes the current working directory to the specified path.
    ///
    /// Returns an [`Err`] if the operation fails.
    ///
    /// [`Err`]: ../../std/result/enum.Result.html#method.err
    ///
    /// # Examples
    ///
    /// ```
    /// use std::env;
    /// use std::path::Path;
    ///
    /// let root = Path::new("/");
    /// assert!(env::set_current_dir(&root).is_ok());
    /// println!("Successfully changed working directory to {}!", root.display());
    /// ```
    #[stable(feature = "env", since = "1.0.0")]
    pub fn set_current_dir<P: AsRef<Path>>(path: P) -> io::Result<()> {
        os_imp::chdir(path.as_ref())
    }

    /// An iterator over a snapshot of the environment variables of this process.
    ///
    /// This structure is created by the [`std::env::vars`] function. See its
    /// documentation for more.
    ///
    /// [`std::env::vars`]: fn.vars.html
    #[stable(feature = "env", since = "1.0.0")]
    pub struct Vars { inner: VarsOs }

    /// An iterator over a snapshot of the environment variables of this process.
    ///
    /// This structure is created by the [`std::env::vars_os`] function. See
    /// its documentation for more.
    ///
    /// [`std::env::vars_os`]: fn.vars_os.html
    #[stable(feature = "env", since = "1.0.0")]
    pub struct VarsOs { inner: os_imp::Env }

    /// Returns an iterator of (variable, value) pairs of strings, for all the
    /// environment variables of the current process.
    ///
    /// The returned iterator contains a snapshot of the process's environment
    /// variables at the time of this invocation. Modifications to environment
    /// variables afterwards will not be reflected in the returned iterator.
    ///
    /// # Panics
    ///
    /// While iterating, the returned iterator will panic if any key or value in the
    /// environment is not valid unicode. If this is not desired, consider using the
    /// [`env::vars_os`] function.
    ///
    /// [`env::vars_os`]: fn.vars_os.html
    ///
    /// # Examples
    ///
    /// ```
    /// use std::env;
    ///
    /// // We will iterate through the references to the element returned by
    /// // env::vars();
    /// for (key, value) in env::vars() {
    ///     println!("{}: {}", key, value);
    /// }
    /// ```
    #[stable(feature = "env", since = "1.0.0")]
    pub fn vars() -> Vars {
        Vars { inner: vars_os() }
    }

    /// Returns an iterator of (variable, value) pairs of OS strings, for all the
    /// environment variables of the current process.
    ///
    /// The returned iterator contains a snapshot of the process's environment
    /// variables at the time of this invocation. Modifications to environment
    /// variables afterwards will not be reflected in the returned iterator.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::env;
    ///
    /// // We will iterate through the references to the element returned by
    /// // env::vars_os();
    /// for (key, value) in env::vars_os() {
    ///     println!("{:?}: {:?}", key, value);
    /// }
    /// ```
    #[stable(feature = "env", since = "1.0.0")]
    pub fn vars_os() -> VarsOs {
        VarsOs { inner: os_imp::env() }
    }

    #[stable(feature = "env", since = "1.0.0")]
    impl Iterator for Vars {
        type Item = (String, String);
        fn next(&mut self) -> Option<(String, String)> {
            self.inner.next().map(|(a, b)| {
                (a.into_string().unwrap(), b.into_string().unwrap())
            })
        }
        fn size_hint(&self) -> (usize, Option<usize>) { self.inner.size_hint() }
    }

    #[stable(feature = "std_debug", since = "1.16.0")]
    impl fmt::Debug for Vars {
        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            f.pad("Vars { .. }")
        }
    }

    #[stable(feature = "env", since = "1.0.0")]
    impl Iterator for VarsOs {
        type Item = (OsString, OsString);
        fn next(&mut self) -> Option<(OsString, OsString)> { self.inner.next() }
        fn size_hint(&self) -> (usize, Option<usize>) { self.inner.size_hint() }
    }

    #[stable(feature = "std_debug", since = "1.16.0")]
    impl fmt::Debug for VarsOs {
        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            f.pad("VarsOs { .. }")
        }
    }

    /// Fetches the environment variable `key` from the current process.
    ///
    /// # Errors
    ///
    /// * Environment variable is not present
    /// * Environment variable is not valid unicode
    ///
    /// # Examples
    ///
    /// ```
    /// use std::env;
    ///
    /// let key = "HOME";
    /// match env::var(key) {
    ///     Ok(val) => println!("{}: {:?}", key, val),
    ///     Err(e) => println!("couldn't interpret {}: {}", key, e),
    /// }
    /// ```
    #[stable(feature = "env", since = "1.0.0")]
    pub fn var<K: AsRef<OsStr>>(key: K) -> Result<String, VarError> {
        _var(key.as_ref())
    }

    fn _var(key: &OsStr) -> Result<String, VarError> {
        match var_os(key) {
            Some(s) => s.into_string().map_err(VarError::NotUnicode),
            None => Err(VarError::NotPresent),
        }
    }

    /// Fetches the environment variable `key` from the current process, returning
    /// [`None`] if the variable isn't set.
    ///
    /// [`None`]: ../option/enum.Option.html#variant.None
    ///
    /// # Examples
    ///
    /// ```
    /// use std::env;
    ///
    /// let key = "HOME";
    /// match env::var_os(key) {
    ///     Some(val) => println!("{}: {:?}", key, val),
    ///     None => println!("{} is not defined in the environment.", key)
    /// }
    /// ```
    #[stable(feature = "env", since = "1.0.0")]
    pub fn var_os<K: AsRef<OsStr>>(key: K) -> Option<OsString> {
        _var_os(key.as_ref())
    }

    fn _var_os(key: &OsStr) -> Option<OsString> {
        os_imp::getenv(key).unwrap_or_else(|e| {
            panic!("failed to get environment variable `{:?}`: {}", key, e)
        })
    }

    /// The error type for operations interacting with environment variables.
    /// Possibly returned from the [`env::var`] function.
    ///
    /// [`env::var`]: fn.var.html
    #[derive(Debug, PartialEq, Eq, Clone)]
    #[stable(feature = "env", since = "1.0.0")]
    pub enum VarError {
        /// The specified environment variable was not present in the current
        /// process's environment.
        #[stable(feature = "env", since = "1.0.0")]
        NotPresent,

        /// The specified environment variable was found, but it did not contain
        /// valid unicode data. The found data is returned as a payload of this
        /// variant.
        #[stable(feature = "env", since = "1.0.0")]
        NotUnicode(#[stable(feature = "env", since = "1.0.0")] OsString),
    }

    #[stable(feature = "env", since = "1.0.0")]
    impl fmt::Display for VarError {
        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            match *self {
                VarError::NotPresent => write!(f, "environment variable not found"),
                VarError::NotUnicode(ref s) => {
                    write!(f, "environment variable was not valid unicode: {:?}", s)
                }
            }
        }
    }

    #[stable(feature = "env", since = "1.0.0")]
    impl Error for VarError {
        fn description(&self) -> &str {
            match *self {
                VarError::NotPresent => "environment variable not found",
                VarError::NotUnicode(..) => "environment variable was not valid unicode",
            }
        }
    }

    /// Sets the environment variable `k` to the value `v` for the currently running
    /// process.
    ///
    /// Note that while concurrent access to environment variables is safe in Rust,
    /// some platforms only expose inherently unsafe non-threadsafe APIs for
    /// inspecting the environment. As a result extra care needs to be taken when
    /// auditing calls to unsafe external FFI functions to ensure that any external
    /// environment accesses are properly synchronized with accesses in Rust.
    ///
    /// Discussion of this unsafety on Unix may be found in:
    ///
    ///  - [Austin Group Bugzilla](http://austingroupbugs.net/view.php?id=188)
    ///  - [GNU C library Bugzilla](https://sourceware.org/bugzilla/show_bug.cgi?id=15607#c2)
    ///
    /// # Panics
    ///
    /// This function may panic if `key` is empty, contains an ASCII equals sign
    /// `'='` or the NUL character `'\0'`, or when the value contains the NUL
    /// character.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::env;
    ///
    /// let key = "KEY";
    /// env::set_var(key, "VALUE");
    /// assert_eq!(env::var(key), Ok("VALUE".to_string()));
    /// ```
    #[stable(feature = "env", since = "1.0.0")]
    pub fn set_var<K: AsRef<OsStr>, V: AsRef<OsStr>>(k: K, v: V) {
        _set_var(k.as_ref(), v.as_ref())
    }

    fn _set_var(k: &OsStr, v: &OsStr) {
        os_imp::setenv(k, v).unwrap_or_else(|e| {
            panic!("failed to set environment variable `{:?}` to `{:?}`: {}",
                   k, v, e)
        })
    }

    /// Removes an environment variable from the environment of the currently running process.
    ///
    /// Note that while concurrent access to environment variables is safe in Rust,
    /// some platforms only expose inherently unsafe non-threadsafe APIs for
    /// inspecting the environment. As a result extra care needs to be taken when
    /// auditing calls to unsafe external FFI functions to ensure that any external
    /// environment accesses are properly synchronized with accesses in Rust.
    ///
    /// Discussion of this unsafety on Unix may be found in:
    ///
    ///  - [Austin Group Bugzilla](http://austingroupbugs.net/view.php?id=188)
    ///  - [GNU C library Bugzilla](https://sourceware.org/bugzilla/show_bug.cgi?id=15607#c2)
    ///
    /// # Panics
    ///
    /// This function may panic if `key` is empty, contains an ASCII equals sign
    /// `'='` or the NUL character `'\0'`, or when the value contains the NUL
    /// character.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::env;
    ///
    /// let key = "KEY";
    /// env::set_var(key, "VALUE");
    /// assert_eq!(env::var(key), Ok("VALUE".to_string()));
    ///
    /// env::remove_var(key);
    /// assert!(env::var(key).is_err());
    /// ```
    #[stable(feature = "env", since = "1.0.0")]
    pub fn remove_var<K: AsRef<OsStr>>(k: K) {
        _remove_var(k.as_ref())
    }

    fn _remove_var(k: &OsStr) {
        os_imp::unsetenv(k).unwrap_or_else(|e| {
            panic!("failed to remove environment variable `{:?}`: {}", k, e)
        })
    }

    /// An iterator that splits an environment variable into paths according to
    /// platform-specific conventions.
    ///
    /// This structure is created by the [`std::env::split_paths`] function. See its
    /// documentation for more.
    ///
    /// [`std::env::split_paths`]: fn.split_paths.html
    #[stable(feature = "env", since = "1.0.0")]
    pub struct SplitPaths<'a> { inner: os_imp::SplitPaths<'a> }

    /// Parses input according to platform conventions for the `PATH`
    /// environment variable.
    ///
    /// Returns an iterator over the paths contained in `unparsed`.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::env;
    ///
    /// let key = "PATH";
    /// match env::var_os(key) {
    ///     Some(paths) => {
    ///         for path in env::split_paths(&paths) {
    ///             println!("'{}'", path.display());
    ///         }
    ///     }
    ///     None => println!("{} is not defined in the environment.", key)
    /// }
    /// ```
    #[stable(feature = "env", since = "1.0.0")]
    pub fn split_paths<T: AsRef<OsStr> + ?Sized>(unparsed: &T) -> SplitPaths {
        SplitPaths { inner: os_imp::split_paths(unparsed.as_ref()) }
    }

    #[stable(feature = "env", since = "1.0.0")]
    impl<'a> Iterator for SplitPaths<'a> {
        type Item = PathBuf;
        fn next(&mut self) -> Option<PathBuf> { self.inner.next() }
        fn size_hint(&self) -> (usize, Option<usize>) { self.inner.size_hint() }
    }

    #[stable(feature = "std_debug", since = "1.16.0")]
    impl<'a> fmt::Debug for SplitPaths<'a> {
        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            f.pad("SplitPaths { .. }")
        }
    }

    /// The error type for operations on the `PATH` variable. Possibly returned from
    /// the [`env::join_paths`] function.
    ///
    /// [`env::join_paths`]: fn.join_paths.html
    #[derive(Debug)]
    #[stable(feature = "env", since = "1.0.0")]
    pub struct JoinPathsError {
        inner: os_imp::JoinPathsError
    }

    /// Joins a collection of [`Path`]s appropriately for the `PATH`
    /// environment variable.
    ///
    /// # Errors
    ///
    /// Returns an [`Err`][err] (containing an error message) if one of the input
    /// [`Path`]s contains an invalid character for constructing the `PATH`
    /// variable (a double quote on Windows or a colon on Unix).
    ///
    /// [`Path`]: ../../std/path/struct.Path.html
    /// [`OsString`]: ../../std/ffi/struct.OsString.html
    /// [err]: ../../std/result/enum.Result.html#variant.Err
    ///
    /// # Examples
    ///
    /// Joining paths on a Unix-like platform:
    ///
    /// ```
    /// # if cfg!(unix) {
    /// use std::env;
    /// use std::ffi::OsString;
    /// use std::path::Path;
    ///
    /// let paths = [Path::new("/bin"), Path::new("/usr/bin")];
    /// let path_os_string = env::join_paths(paths.iter()).unwrap();
    /// assert_eq!(path_os_string, OsString::from("/bin:/usr/bin"));
    /// # }
    /// ```
    ///
    /// Joining a path containing a colon on a Unix-like platform results in an error:
    ///
    /// ```
    /// # if cfg!(unix) {
    /// use std::env;
    /// use std::path::Path;
    ///
    /// let paths = [Path::new("/bin"), Path::new("/usr/bi:n")];
    /// assert!(env::join_paths(paths.iter()).is_err());
    /// # }
    /// ```
    ///
    /// Using `env::join_paths` with `env::spit_paths` to append an item to the `PATH` environment
    /// variable:
    ///
    /// ```
    /// use std::env;
    /// use std::path::PathBuf;
    ///
    /// if let Some(path) = env::var_os("PATH") {
    ///     let mut paths = env::split_paths(&path).collect::<Vec<_>>();
    ///     paths.push(PathBuf::from("/home/xyz/bin"));
    ///     let new_path = env::join_paths(paths).unwrap();
    ///     env::set_var("PATH", &new_path);
    /// }
    /// ```
    #[stable(feature = "env", since = "1.0.0")]
    pub fn join_paths<I, T>(paths: I) -> Result<OsString, JoinPathsError>
        where I: IntoIterator<Item=T>, T: AsRef<OsStr>
    {
        os_imp::join_paths(paths.into_iter()).map_err(|e| {
            JoinPathsError { inner: e }
        })
    }

    #[stable(feature = "env", since = "1.0.0")]
    impl fmt::Display for JoinPathsError {
        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            self.inner.fmt(f)
        }
    }

    #[stable(feature = "env", since = "1.0.0")]
    impl Error for JoinPathsError {
        fn description(&self) -> &str { self.inner.description() }
    }

    /// Returns the path of the current user's home directory if known.
    ///
    /// # Unix
    ///
    /// Returns the value of the 'HOME' environment variable if it is set
    /// and not equal to the empty string. Otherwise, it tries to determine the
    /// home directory by invoking the `getpwuid_r` function on the UID of the
    /// current user.
    ///
    /// # Windows
    ///
    /// Returns the value of the 'HOME' environment variable if it is
    /// set and not equal to the empty string. Otherwise, returns the value of the
    /// 'USERPROFILE' environment variable if it is set and not equal to the empty
    /// string. If both do not exist, [`GetUserProfileDirectory`][msdn] is used to
    /// return the appropriate path.
    ///
    /// [msdn]: https://msdn.microsoft.com/en-us/library/windows/desktop/bb762280(v=vs.85).aspx
    ///
    /// # Examples
    ///
    /// ```
    /// use std::env;
    ///
    /// match env::home_dir() {
    ///     Some(path) => println!("{}", path.display()),
    ///     None => println!("Impossible to get your home dir!"),
    /// }
    /// ```
    #[stable(feature = "env", since = "1.0.0")]
    pub fn home_dir() -> Option<PathBuf> {
        os_imp::home_dir()
    }

    /// Returns the path of a temporary directory.
    ///
    /// # Unix
    ///
    /// Returns the value of the `TMPDIR` environment variable if it is
    /// set, otherwise for non-Android it returns `/tmp`. If Android, since there
    /// is no global temporary folder (it is usually allocated per-app), it returns
    /// `/data/local/tmp`.
    ///
    /// # Windows
    ///
    /// Returns the value of, in order, the `TMP`, `TEMP`,
    /// `USERPROFILE` environment variable if any are set and not the empty
    /// string. Otherwise, `temp_dir` returns the path of the Windows directory.
    /// This behavior is identical to that of [`GetTempPath`][msdn], which this
    /// function uses internally.
    ///
    /// [msdn]: https://msdn.microsoft.com/en-us/library/windows/desktop/aa364992(v=vs.85).aspx
    ///
    /// ```
    /// use std::env;
    /// use std::fs::File;
    ///
    /// # fn foo() -> std::io::Result<()> {
    /// let mut dir = env::temp_dir();
    /// dir.push("foo.txt");
    ///
    /// let f = File::create(dir)?;
    /// # Ok(())
    /// # }
    /// ```
    #[stable(feature = "env", since = "1.0.0")]
    pub fn temp_dir() -> PathBuf {
        os_imp::temp_dir()
    }

    /// Returns the full filesystem path of the current running executable.
    ///
    /// The path returned is not necessarily a "real path" of the executable as
    /// there may be intermediate symlinks.
    ///
    /// # Errors
    ///
    /// Acquiring the path of the current executable is a platform-specific operation
    /// that can fail for a good number of reasons. Some errors can include, but not
    /// be limited to, filesystem operations failing or general syscall failures.
    ///
    /// # Security
    ///
    /// The output of this function should not be used in anything that might have
    /// security implications. For example:
    ///
    /// ```
    /// fn main() {
    ///     println!("{:?}", std::env::current_exe());
    /// }
    /// ```
    ///
    /// On Linux systems, if this is compiled as `foo`:
    ///
    /// ```bash
    /// $ rustc foo.rs
    /// $ ./foo
    /// Ok("/home/alex/foo")
    /// ```
    ///
    /// And you make a symbolic link of the program:
    ///
    /// ```bash
    /// $ ln foo bar
    /// ```
    ///
    /// When you run it, you won't get the original executable, you'll get the
    /// symlink:
    ///
    /// ```bash
    /// $ ./bar
    /// Ok("/home/alex/bar")
    /// ```
    ///
    /// This sort of behavior has been known to [lead to privilege escalation] when
    /// used incorrectly, for example.
    ///
    /// [lead to privilege escalation]: http://securityvulns.com/Wdocument183.html
    ///
    /// # Examples
    ///
    /// ```
    /// use std::env;
    ///
    /// match env::current_exe() {
    ///     Ok(exe_path) => println!("Path of this executable is: {}",
    ///                               exe_path.display()),
    ///     Err(e) => println!("failed to get current exe path: {}", e),
    /// };
    /// ```
    #[stable(feature = "env", since = "1.0.0")]
    pub fn current_exe() -> io::Result<PathBuf> {
        os_imp::current_exe()
    }

    /// An iterator over the arguments of a process, yielding a [`String`] value for
    /// each argument.
    ///
    /// This struct is created by the [`std::env::args`] function. See its
    /// documentation for more.
    ///
    /// The first element is traditionally the path of the executable, but it can be
    /// set to arbitrary text, and may not even exist. This means this property
    /// should not be relied upon for security purposes.
    ///
    /// [`String`]: ../string/struct.String.html
    /// [`std::env::args`]: ./fn.args.html
    #[stable(feature = "env", since = "1.0.0")]
    pub struct Args { inner: ArgsOs }

    /// An iterator over the arguments of a process, yielding an [`OsString`] value
    /// for each argument.
    ///
    /// This struct is created by the [`std::env::args_os`] function. See its
    /// documentation for more.
    ///
    /// The first element is traditionally the path of the executable, but it can be
    /// set to arbitrary text, and may not even exist. This means this property
    /// should not be relied upon for security purposes.
    ///
    /// [`OsString`]: ../ffi/struct.OsString.html
    /// [`std::env::args_os`]: ./fn.args_os.html
    #[stable(feature = "env", since = "1.0.0")]
    pub struct ArgsOs { inner: sys::args::Args }

    /// Returns the arguments which this program was started with (normally passed
    /// via the command line).
    ///
    /// The first element is traditionally the path of the executable, but it can be
    /// set to arbitrary text, and may not even exist. This means this property should
    /// not be relied upon for security purposes.
    ///
    /// On Unix systems shell usually expands unquoted arguments with glob patterns
    /// (such as `*` and `?`). On Windows this is not done, and such arguments are
    /// passed as-is.
    ///
    /// # Panics
    ///
    /// The returned iterator will panic during iteration if any argument to the
    /// process is not valid unicode. If this is not desired,
    /// use the [`args_os`] function instead.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::env;
    ///
    /// // Prints each argument on a separate line
    /// for argument in env::args() {
    ///     println!("{}", argument);
    /// }
    /// ```
    ///
    /// [`args_os`]: ./fn.args_os.html
    #[stable(feature = "env", since = "1.0.0")]
    pub fn args() -> Args {
        Args { inner: args_os() }
    }

    /// Returns the arguments which this program was started with (normally passed
    /// via the command line).
    ///
    /// The first element is traditionally the path of the executable, but it can be
    /// set to arbitrary text, and it may not even exist, so this property should
    /// not be relied upon for security purposes.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::env;
    ///
    /// // Prints each argument on a separate line
    /// for argument in env::args_os() {
    ///     println!("{:?}", argument);
    /// }
    /// ```
    #[stable(feature = "env", since = "1.0.0")]
    pub fn args_os() -> ArgsOs {
        ArgsOs { inner: sys::args::args() }
    }

    #[stable(feature = "env", since = "1.0.0")]
    impl Iterator for Args {
        type Item = String;
        fn next(&mut self) -> Option<String> {
            self.inner.next().map(|s| s.into_string().unwrap())
        }
        fn size_hint(&self) -> (usize, Option<usize>) { self.inner.size_hint() }
    }

    #[stable(feature = "env", since = "1.0.0")]
    impl ExactSizeIterator for Args {
        fn len(&self) -> usize { self.inner.len() }
        fn is_empty(&self) -> bool { self.inner.is_empty() }
    }

    #[stable(feature = "env_iterators", since = "1.12.0")]
    impl DoubleEndedIterator for Args {
        fn next_back(&mut self) -> Option<String> {
            self.inner.next_back().map(|s| s.into_string().unwrap())
        }
    }

    #[stable(feature = "std_debug", since = "1.16.0")]
    impl fmt::Debug for Args {
        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            f.debug_struct("Args")
                .field("inner", &self.inner.inner.inner_debug())
                .finish()
        }
    }

    #[stable(feature = "env", since = "1.0.0")]
    impl Iterator for ArgsOs {
        type Item = OsString;
        fn next(&mut self) -> Option<OsString> { self.inner.next() }
        fn size_hint(&self) -> (usize, Option<usize>) { self.inner.size_hint() }
    }

    #[stable(feature = "env", since = "1.0.0")]
    impl ExactSizeIterator for ArgsOs {
        fn len(&self) -> usize { self.inner.len() }
        fn is_empty(&self) -> bool { self.inner.is_empty() }
    }

    #[stable(feature = "env_iterators", since = "1.12.0")]
    impl DoubleEndedIterator for ArgsOs {
        fn next_back(&mut self) -> Option<OsString> { self.inner.next_back() }
    }

    #[stable(feature = "std_debug", since = "1.16.0")]
    impl fmt::Debug for ArgsOs {
        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            f.debug_struct("ArgsOs")
                .field("inner", &self.inner.inner_debug())
                .finish()
        }
    }

    /// Constants associated with the current target
    #[stable(feature = "env", since = "1.0.0")]
    pub mod consts {
        use sys::env::os;

        /// A string describing the architecture of the CPU that is currently
        /// in use.
        ///
        /// Some possible values:
        ///
        /// - x86
        /// - x86_64
        /// - arm
        /// - aarch64
        /// - mips
        /// - mips64
        /// - powerpc
        /// - powerpc64
        /// - s390x
        /// - sparc64
        #[stable(feature = "env", since = "1.0.0")]
        pub const ARCH: &'static str = super::arch::ARCH;

        /// The family of the operating system. Example value is `unix`.
        ///
        /// Some possible values:
        ///
        /// - unix
        /// - windows
        #[stable(feature = "env", since = "1.0.0")]
        pub const FAMILY: &'static str = os::FAMILY;

        /// A string describing the specific operating system in use.
        /// Example value is `linux`.
        ///
        /// Some possible values:
        ///
        /// - linux
        /// - macos
        /// - ios
        /// - freebsd
        /// - dragonfly
        /// - bitrig
        /// - netbsd
        /// - openbsd
        /// - solaris
        /// - android
        /// - windows
        #[stable(feature = "env", since = "1.0.0")]
        pub const OS: &'static str = os::OS;

        /// Specifies the filename prefix used for shared libraries on this
        /// platform. Example value is `lib`.
        ///
        /// Some possible values:
        ///
        /// - lib
        /// - `""` (an empty string)
        #[stable(feature = "env", since = "1.0.0")]
        pub const DLL_PREFIX: &'static str = os::DLL_PREFIX;

        /// Specifies the filename suffix used for shared libraries on this
        /// platform. Example value is `.so`.
        ///
        /// Some possible values:
        ///
        /// - .so
        /// - .dylib
        /// - .dll
        #[stable(feature = "env", since = "1.0.0")]
        pub const DLL_SUFFIX: &'static str = os::DLL_SUFFIX;

        /// Specifies the file extension used for shared libraries on this
        /// platform that goes after the dot. Example value is `so`.
        ///
        /// Some possible values:
        ///
        /// - so
        /// - dylib
        /// - dll
        #[stable(feature = "env", since = "1.0.0")]
        pub const DLL_EXTENSION: &'static str = os::DLL_EXTENSION;

        /// Specifies the filename suffix used for executable binaries on this
        /// platform. Example value is `.exe`.
        ///
        /// Some possible values:
        ///
        /// - .exe
        /// - .nexe
        /// - .pexe
        /// - `""` (an empty string)
        #[stable(feature = "env", since = "1.0.0")]
        pub const EXE_SUFFIX: &'static str = os::EXE_SUFFIX;

        /// Specifies the file extension, if any, used for executable binaries
        /// on this platform. Example value is `exe`.
        ///
        /// Some possible values:
        ///
        /// - exe
        /// - `""` (an empty string)
        #[stable(feature = "env", since = "1.0.0")]
        pub const EXE_EXTENSION: &'static str = os::EXE_EXTENSION;
    }

    #[cfg(target_arch = "x86")]
    mod arch {
        pub const ARCH: &'static str = "x86";
    }

    #[cfg(target_arch = "x86_64")]
    mod arch {
        pub const ARCH: &'static str = "x86_64";
    }

    #[cfg(target_arch = "arm")]
    mod arch {
        pub const ARCH: &'static str = "arm";
    }

    #[cfg(target_arch = "aarch64")]
    mod arch {
        pub const ARCH: &'static str = "aarch64";
    }

    #[cfg(target_arch = "mips")]
    mod arch {
        pub const ARCH: &'static str = "mips";
    }

    #[cfg(target_arch = "mips64")]
    mod arch {
        pub const ARCH: &'static str = "mips64";
    }

    #[cfg(target_arch = "powerpc")]
    mod arch {
        pub const ARCH: &'static str = "powerpc";
    }

    #[cfg(target_arch = "powerpc64")]
    mod arch {
        pub const ARCH: &'static str = "powerpc64";
    }

    #[cfg(target_arch = "s390x")]
    mod arch {
        pub const ARCH: &'static str = "s390x";
    }

    #[cfg(target_arch = "sparc64")]
    mod arch {
        pub const ARCH: &'static str = "sparc64";
    }

    #[cfg(target_arch = "le32")]
    mod arch {
        pub const ARCH: &'static str = "le32";
    }

    #[cfg(target_arch = "asmjs")]
    mod arch {
        pub const ARCH: &'static str = "asmjs";
    }

    #[cfg(target_arch = "wasm32")]
    mod arch {
        pub const ARCH: &'static str = "wasm32";
    }

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

        use ffi::OsStr;
        use path::{Path, PathBuf};

        #[test]
        #[cfg_attr(target_os = "emscripten", ignore)]
        fn test_self_exe_path() {
            let path = current_exe();
            assert!(path.is_ok());
            let path = path.unwrap();

            // Hard to test this function
            assert!(path.is_absolute());
        }

        #[test]
        fn test() {
            assert!((!Path::new("test-path").is_absolute()));

            current_dir().unwrap();
        }

        #[test]
        #[cfg(windows)]
        fn split_paths_windows() {
            fn check_parse(unparsed: &str, parsed: &[&str]) -> bool {
                split_paths(unparsed).collect::<Vec<_>>() ==
                    parsed.iter().map(|s| PathBuf::from(*s)).collect::<Vec<_>>()
            }

            assert!(check_parse("", &mut [""]));
            assert!(check_parse(r#""""#, &mut [""]));
            assert!(check_parse(";;", &mut ["", "", ""]));
            assert!(check_parse(r"c:\", &mut [r"c:\"]));
            assert!(check_parse(r"c:\;", &mut [r"c:\", ""]));
            assert!(check_parse(r"c:\;c:\Program Files\",
                                &mut [r"c:\", r"c:\Program Files\"]));
            assert!(check_parse(r#"c:\;c:\"foo"\"#, &mut [r"c:\", r"c:\foo\"]));
            assert!(check_parse(r#"c:\;c:\"foo;bar"\;c:\baz"#,
                                &mut [r"c:\", r"c:\foo;bar\", r"c:\baz"]));
        }

        #[test]
        #[cfg(unix)]
        fn split_paths_unix() {
            fn check_parse(unparsed: &str, parsed: &[&str]) -> bool {
                split_paths(unparsed).collect::<Vec<_>>() ==
                    parsed.iter().map(|s| PathBuf::from(*s)).collect::<Vec<_>>()
            }

            assert!(check_parse("", &mut [""]));
            assert!(check_parse("::", &mut ["", "", ""]));
            assert!(check_parse("/", &mut ["/"]));
            assert!(check_parse("/:", &mut ["/", ""]));
            assert!(check_parse("/:/usr/local", &mut ["/", "/usr/local"]));
        }

        #[test]
        #[cfg(unix)]
        fn join_paths_unix() {
            fn test_eq(input: &[&str], output: &str) -> bool {
                &*join_paths(input.iter().cloned()).unwrap() ==
                    OsStr::new(output)
            }

            assert!(test_eq(&[], ""));
            assert!(test_eq(&["/bin", "/usr/bin", "/usr/local/bin"],
                             "/bin:/usr/bin:/usr/local/bin"));
            assert!(test_eq(&["", "/bin", "", "", "/usr/bin", ""],
                             ":/bin:::/usr/bin:"));
            assert!(join_paths(["/te:st"].iter().cloned()).is_err());
        }

        #[test]
        #[cfg(windows)]
        fn join_paths_windows() {
            fn test_eq(input: &[&str], output: &str) -> bool {
                &*join_paths(input.iter().cloned()).unwrap() ==
                    OsStr::new(output)
            }

            assert!(test_eq(&[], ""));
            assert!(test_eq(&[r"c:\windows", r"c:\"],
                            r"c:\windows;c:\"));
            assert!(test_eq(&["", r"c:\windows", "", "", r"c:\", ""],
                            r";c:\windows;;;c:\;"));
            assert!(test_eq(&[r"c:\te;st", r"c:\"],
                            r#""c:\te;st";c:\"#));
            assert!(join_paths([r#"c:\te"st"#].iter().cloned()).is_err());
        }

        #[test]
        fn args_debug() {
            assert_eq!(
                format!("Args {{ inner: {:?} }}", args().collect::<Vec<_>>()),
                format!("{:?}", args()));
            assert_eq!(
                format!("ArgsOs {{ inner: {:?} }}", args_os().collect::<Vec<_>>()),
                format!("{:?}", args_os()));
        }
    }

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## Search Tricks

Prefix searches with a type followed by a colon (e.g. `fn:`) to restrict the search to a given type.

Accepted types are: `fn`, `mod`, `struct`, `enum`, `trait`, `type`, `macro`, and `const`.

Search functions by type signature (e.g. `vec -> usize` or `* -> vec`)