Vendor dependencies

Let's see how I like this workflow.

vendor/home/src/env.rs

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+//! Lower-level utilities for mocking the process environment.
+
+use std::{
+    ffi::OsString,
+    io,
+    path::{Path, PathBuf},
+};
+
+/// Permits parameterizing the home functions via the _from variants - used for
+/// in-process unit testing by rustup.
+pub trait Env {
+    /// Return the path to the the users home dir, or None if any error occurs:
+    /// see home_inner.
+    fn home_dir(&self) -> Option<PathBuf>;
+    /// Return the current working directory.
+    fn current_dir(&self) -> io::Result<PathBuf>;
+    /// Get an environment variable, as per std::env::var_os.
+    fn var_os(&self, key: &str) -> Option<OsString>;
+}
+
+/// Implements Env for the OS context, both Unix style and Windows.
+///
+/// This is trait permits in-process testing by providing a control point to
+/// allow in-process divergence on what is normally process wide state.
+///
+/// Implementations should be provided by whatever testing framework the caller
+/// is using. Code that is not performing in-process threaded testing requiring
+/// isolated rustup/cargo directories does not need this trait or the _from
+/// functions.
+pub struct OsEnv;
+impl Env for OsEnv {
+    fn home_dir(&self) -> Option<PathBuf> {
+        crate::home_dir_inner()
+    }
+    fn current_dir(&self) -> io::Result<PathBuf> {
+        std::env::current_dir()
+    }
+    fn var_os(&self, key: &str) -> Option<OsString> {
+        std::env::var_os(key)
+    }
+}
+
+pub const OS_ENV: OsEnv = OsEnv {};
+
+/// Returns the path of the current user's home directory from [`Env::home_dir`].
+pub fn home_dir_with_env(env: &dyn Env) -> Option<PathBuf> {
+    env.home_dir()
+}
+
+/// Variant of cargo_home where the environment source is parameterized. This is
+/// specifically to support in-process testing scenarios as environment
+/// variables and user home metadata are normally process global state. See the
+/// [`Env`] trait.
+pub fn cargo_home_with_env(env: &dyn Env) -> io::Result<PathBuf> {
+    let cwd = env.current_dir()?;
+    cargo_home_with_cwd_env(env, &cwd)
+}
+
+/// Variant of cargo_home_with_cwd where the environment source is
+/// parameterized. This is specifically to support in-process testing scenarios
+/// as environment variables and user home metadata are normally process global
+/// state. See the OsEnv trait.
+pub fn cargo_home_with_cwd_env(env: &dyn Env, cwd: &Path) -> io::Result<PathBuf> {
+    match env.var_os("CARGO_HOME").filter(|h| !h.is_empty()) {
+        Some(home) => {
+            let home = PathBuf::from(home);
+            if home.is_absolute() {
+                Ok(home)
+            } else {
+                Ok(cwd.join(&home))
+            }
+        }
+        _ => home_dir_with_env(env)
+            .map(|p| p.join(".cargo"))
+            .ok_or_else(|| io::Error::new(io::ErrorKind::Other, "could not find cargo home dir")),
+    }
+}
+
+/// Variant of cargo_home_with_cwd where the environment source is
+/// parameterized. This is specifically to support in-process testing scenarios
+/// as environment variables and user home metadata are normally process global
+/// state. See the OsEnv trait.
+pub fn rustup_home_with_env(env: &dyn Env) -> io::Result<PathBuf> {
+    let cwd = env.current_dir()?;
+    rustup_home_with_cwd_env(env, &cwd)
+}
+
+/// Variant of cargo_home_with_cwd where the environment source is
+/// parameterized. This is specifically to support in-process testing scenarios
+/// as environment variables and user home metadata are normally process global
+/// state. See the OsEnv trait.
+pub fn rustup_home_with_cwd_env(env: &dyn Env, cwd: &Path) -> io::Result<PathBuf> {
+    match env.var_os("RUSTUP_HOME").filter(|h| !h.is_empty()) {
+        Some(home) => {
+            let home = PathBuf::from(home);
+            if home.is_absolute() {
+                Ok(home)
+            } else {
+                Ok(cwd.join(&home))
+            }
+        }
+        _ => home_dir_with_env(env)
+            .map(|d| d.join(".rustup"))
+            .ok_or_else(|| io::Error::new(io::ErrorKind::Other, "could not find rustup home dir")),
+    }
+}

vendor/home/src/lib.rs

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+//! Canonical definitions of `home_dir`, `cargo_home`, and `rustup_home`.
+//!
+//! This provides the definition of `home_dir` used by Cargo and
+//! rustup, as well functions to find the correct value of
+//! `CARGO_HOME` and `RUSTUP_HOME`.
+//!
+//! See also the [`dirs`](https://docs.rs/dirs) crate.
+//!
+//! _Note that as of 2019/08/06 it appears that cargo uses this crate. And
+//! rustup has used this crate since 2019/08/21._
+//!
+//! The definition of `home_dir` provided by the standard library is
+//! incorrect because it considers the `HOME` environment variable on
+//! Windows. This causes surprising situations where a Rust program
+//! will behave differently depending on whether it is run under a
+//! Unix emulation environment like Cygwin or MinGW. Neither Cargo nor
+//! rustup use the standard libraries definition - they use the
+//! definition here.
+//!
+//! This crate further provides two functions, `cargo_home` and
+//! `rustup_home`, which are the canonical way to determine the
+//! location that Cargo and rustup store their data.
+//!
+//! See also this [discussion].
+//!
+//! [discussion]: https://github.com/rust-lang/rust/pull/46799#issuecomment-361156935
+
+#![doc(html_root_url = "https://docs.rs/home/0.5.4")]
+#![deny(rust_2018_idioms)]
+
+pub mod env;
+
+#[cfg(windows)]
+mod windows;
+
+use std::io;
+use std::path::{Path, PathBuf};
+
+/// 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 `USERPROFILE` environment variable if it
+/// is set and not equal to the empty string. If both do not exist,
+/// [`SHGetFolderPathW`][msdn] is used to return the appropriate path.
+///
+/// [msdn]: https://docs.microsoft.com/en-us/windows/win32/api/shlobj_core/nf-shlobj_core-shgetfolderpathw
+///
+/// # Examples
+///
+/// ```
+/// match home::home_dir() {
+///     Some(path) => println!("{}", path.display()),
+///     None => println!("Impossible to get your home dir!"),
+/// }
+/// ```
+pub fn home_dir() -> Option<PathBuf> {
+    env::home_dir_with_env(&env::OS_ENV)
+}
+
+#[cfg(windows)]
+use windows::home_dir_inner;
+
+#[cfg(any(unix, target_os = "redox"))]
+fn home_dir_inner() -> Option<PathBuf> {
+    #[allow(deprecated)]
+    std::env::home_dir()
+}
+
+/// Returns the storage directory used by Cargo, often knowns as
+/// `.cargo` or `CARGO_HOME`.
+///
+/// It returns one of the following values, in this order of
+/// preference:
+///
+/// - The value of the `CARGO_HOME` environment variable, if it is
+///   an absolute path.
+/// - The value of the current working directory joined with the value
+///   of the `CARGO_HOME` environment variable, if `CARGO_HOME` is a
+///   relative directory.
+/// - The `.cargo` directory in the user's home directory, as reported
+///   by the `home_dir` function.
+///
+/// # Errors
+///
+/// This function fails if it fails to retrieve the current directory,
+/// or if the home directory cannot be determined.
+///
+/// # Examples
+///
+/// ```
+/// match home::cargo_home() {
+///     Ok(path) => println!("{}", path.display()),
+///     Err(err) => eprintln!("Cannot get your cargo home dir: {:?}", err),
+/// }
+/// ```
+pub fn cargo_home() -> io::Result<PathBuf> {
+    env::cargo_home_with_env(&env::OS_ENV)
+}
+
+/// Returns the storage directory used by Cargo within `cwd`.
+/// For more details, see [`cargo_home`](fn.cargo_home.html).
+pub fn cargo_home_with_cwd(cwd: &Path) -> io::Result<PathBuf> {
+    env::cargo_home_with_cwd_env(&env::OS_ENV, cwd)
+}
+
+/// Returns the storage directory used by rustup, often knowns as
+/// `.rustup` or `RUSTUP_HOME`.
+///
+/// It returns one of the following values, in this order of
+/// preference:
+///
+/// - The value of the `RUSTUP_HOME` environment variable, if it is
+///   an absolute path.
+/// - The value of the current working directory joined with the value
+///   of the `RUSTUP_HOME` environment variable, if `RUSTUP_HOME` is a
+///   relative directory.
+/// - The `.rustup` directory in the user's home directory, as reported
+///   by the `home_dir` function.
+///
+/// # Errors
+///
+/// This function fails if it fails to retrieve the current directory,
+/// or if the home directory cannot be determined.
+///
+/// # Examples
+///
+/// ```
+/// match home::rustup_home() {
+///     Ok(path) => println!("{}", path.display()),
+///     Err(err) => eprintln!("Cannot get your rustup home dir: {:?}", err),
+/// }
+/// ```
+pub fn rustup_home() -> io::Result<PathBuf> {
+    env::rustup_home_with_env(&env::OS_ENV)
+}
+
+/// Returns the storage directory used by rustup within `cwd`.
+/// For more details, see [`rustup_home`](fn.rustup_home.html).
+pub fn rustup_home_with_cwd(cwd: &Path) -> io::Result<PathBuf> {
+    env::rustup_home_with_cwd_env(&env::OS_ENV, cwd)
+}

vendor/home/src/windows.rs

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+use std::env;
+use std::ffi::OsString;
+use std::os::windows::ffi::OsStringExt;
+use std::path::PathBuf;
+use std::ptr;
+
+use winapi::shared::minwindef::MAX_PATH;
+use winapi::shared::winerror::S_OK;
+use winapi::um::shlobj::{SHGetFolderPathW, CSIDL_PROFILE};
+
+pub fn home_dir_inner() -> Option<PathBuf> {
+    env::var_os("USERPROFILE")
+        .filter(|s| !s.is_empty())
+        .map(PathBuf::from)
+        .or_else(home_dir_crt)
+}
+
+#[cfg(not(target_vendor = "uwp"))]
+fn home_dir_crt() -> Option<PathBuf> {
+    unsafe {
+        let mut path: Vec<u16> = Vec::with_capacity(MAX_PATH);
+        match SHGetFolderPathW(ptr::null_mut(), CSIDL_PROFILE, ptr::null_mut(), 0, path.as_mut_ptr()) {
+            S_OK => {
+                let len = wcslen(path.as_ptr());
+                path.set_len(len);
+                let s = OsString::from_wide(&path);
+                Some(PathBuf::from(s))
+            }
+            _ => None,
+        }
+    }
+}
+
+#[cfg(target_vendor = "uwp")]
+fn home_dir_crt() -> Option<PathBuf> {
+    None
+}
+
+extern "C" {
+    fn wcslen(buf: *const u16) -> usize;
+}
+
+#[cfg(not(target_vendor = "uwp"))]
+#[cfg(test)]
+mod tests {
+    use super::home_dir_inner;
+    use std::env;
+    use std::ops::Deref;
+    use std::path::{Path, PathBuf};
+
+    #[test]
+    fn test_with_without() {
+        let olduserprofile = env::var_os("USERPROFILE").unwrap();
+
+        env::remove_var("HOME");
+        env::remove_var("USERPROFILE");
+
+        assert_eq!(home_dir_inner(), Some(PathBuf::from(olduserprofile)));
+
+        let home = Path::new(r"C:\Users\foo tar baz");
+
+        env::set_var("HOME", home.as_os_str());
+        assert_ne!(home_dir_inner().as_ref().map(Deref::deref), Some(home));
+
+        env::set_var("USERPROFILE", home.as_os_str());
+        assert_eq!(home_dir_inner().as_ref().map(Deref::deref), Some(home));
+    }
+}