Add mockable home fn and Env trait

CHANGELOG.md

@@ -5,6 +5,9 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 <!-- ## [Unreleased] -->
+- Add `_with_env` variants of functions to support in-process threaded tests for
+  rustup.
+
 ## [0.5.3] - 2020-01-07
 
 Use Rust 1.36.0 as minimum Rust version.

src/env.rs

@@ -0,0 +1,106 @@
+//! 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")),
+    }
+}

src/lib.rs

@@ -28,10 +28,11 @@
 #![doc(html_root_url = "https://docs.rs/home/0.5.3")]
 #![deny(rust_2018_idioms)]
 
+pub mod env;
+
 #[cfg(windows)]
 mod windows;
 
-use std::env;
 use std::io;
 use std::path::{Path, PathBuf};
 
@@ -61,7 +62,7 @@ use std::path::{Path, PathBuf};
 /// }
 /// ```
 pub fn home_dir() -> Option<PathBuf> {
-    home_dir_inner()
+    env::home_dir_with_env(&env::OS_ENV)
 }
 
 #[cfg(windows)]
@@ -70,7 +71,7 @@ use windows::home_dir_inner;
 #[cfg(any(unix, target_os = "redox"))]
 fn home_dir_inner() -> Option<PathBuf> {
     #[allow(deprecated)]
-    env::home_dir()
+    std::env::home_dir()
 }
 
 /// Returns the storage directory used by Cargo, often knowns as
@@ -101,26 +102,13 @@ fn home_dir_inner() -> Option<PathBuf> {
 /// }
 /// ```
 pub fn cargo_home() -> io::Result<PathBuf> {
-    let cwd = env::current_dir()?;
-    cargo_home_with_cwd(&cwd)
+    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> {
-    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()
-            .map(|p| p.join(".cargo"))
-            .ok_or_else(|| io::Error::new(io::ErrorKind::Other, "could not find cargo home dir")),
-    }
+    env::cargo_home_with_cwd_env(&env::OS_ENV, cwd)
 }
 
 /// Returns the storage directory used by rustup, often knowns as
@@ -151,24 +139,11 @@ pub fn cargo_home_with_cwd(cwd: &Path) -> io::Result<PathBuf> {
 /// }
 /// ```
 pub fn rustup_home() -> io::Result<PathBuf> {
-    let cwd = env::current_dir()?;
-    rustup_home_with_cwd(&cwd)
+    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> {
-    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()
-            .map(|d| d.join(".rustup"))
-            .ok_or_else(|| io::Error::new(io::ErrorKind::Other, "could not find rustup home dir")),
-    }
+    env::rustup_home_with_cwd_env(&env::OS_ENV, cwd)
 }