Add the ability to see inherited envs on Command

library/std/src/process.rs

@@ -116,6 +116,8 @@ use crate::path::Path;
 use crate::str;
 use crate::sys::pipe::{read2, AnonPipe};
 use crate::sys::process as imp;
+#[unstable(feature = "command_captured_envs_access", issue = "none")]
+pub use crate::sys_common::process::CapturedEnvs;
 #[stable(feature = "command_access", since = "1.57.0")]
 pub use crate::sys_common::process::CommandEnvs;
 use crate::sys_common::{AsInner, AsInnerMut, FromInner, IntoInner};
@@ -1048,8 +1050,9 @@ impl Command {
     /// Environment variables explicitly set using [`Command::env`], [`Command::envs`], and
     /// [`Command::env_remove`] can be retrieved with this method.
     ///
-    /// Note that this output does not include environment variables inherited from the parent
-    /// process.
+    /// Note that this output does not include environment variables inherited
+    /// from the parent process. To get the variables that will be set
+    /// when the child spawns use [`Command::capture_envs`].
     ///
     /// Each element is a tuple key/value pair `(&OsStr, Option<&OsStr>)`. A [`None`] value
     /// indicates its key was explicitly removed via [`Command::env_remove`]. The associated key for
@@ -1078,6 +1081,43 @@ impl Command {
         self.inner.get_envs()
     }
 
+    /// Captures a snapshot of all environment variables, inherited and explicitly set, that would
+    /// have been passed to the child process.
+    ///
+    /// Return value is an iterator where each element is a tuple `(OsString, OsString)`. The first
+    /// value is the environment variable key, and the second is its value. Unlike
+    /// [`Command::get_envs`], this method includes inherited and explicitly set environment
+    /// variables.
+    ///
+    /// Note that this method does not prevent time-of-check to time-of-use (TOCTOU) bugs. You
+    /// should only use it when those bugs are not an issue. If no changes occur between when this
+    /// method is called and when the command is spawned, the values returned will be the same as
+    /// those of the spawned child process.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::ffi::OsString;
+    /// use std::process::Command;
+    /// use std::collections::HashMap;
+    ///
+    /// let mut cmd = Command::new("ls");
+    /// cmd.env("TERM", "dumb");
+    /// cmd.env_remove("TZ");
+    ///
+    /// let envs: HashMap<OsString, OsString> = cmd.capture_envs().collect();
+    /// // Inherited environment variable(s)
+    /// assert!(envs.contains_key(&OsString::from("PATH")));
+    ///
+    /// // Explicitly set environment variable(s)
+    /// assert!(envs.contains_key(&OsString::from("TERM")));
+    /// assert!(!envs.contains_key(&OsString::from("TZ")));
+    /// ```
+    #[unstable(feature = "command_captured_envs_access", issue = "none")]
+    pub fn capture_envs(&self) -> CapturedEnvs {
+        self.inner.capture_envs()
+    }
+
     /// Returns the working directory for the child process.
     ///
     /// This returns [`None`] if the working directory will not be changed.

library/std/src/sys/unix/process/process_common.rs

@@ -12,7 +12,7 @@ use crate::ptr;
 use crate::sys::fd::FileDesc;
 use crate::sys::fs::File;
 use crate::sys::pipe::{self, AnonPipe};
-use crate::sys_common::process::{CommandEnv, CommandEnvs};
+use crate::sys_common::process::{CapturedEnvs, CommandEnv, CommandEnvs};
 use crate::sys_common::{FromInner, IntoInner};
 
 #[cfg(not(target_os = "fuchsia"))]
@@ -302,6 +302,10 @@ impl Command {
         self.env.iter()
     }
 
+    pub fn capture_envs(&self) -> CapturedEnvs {
+        self.env.capture_iter()
+    }
+
     pub fn get_current_dir(&self) -> Option<&Path> {
         self.cwd.as_ref().map(|cs| Path::new(OsStr::from_bytes(cs.as_bytes())))
     }

library/std/src/sys/windows/process.rs

@@ -26,7 +26,7 @@ use crate::sys::handle::Handle;
 use crate::sys::path;
 use crate::sys::pipe::{self, AnonPipe};
 use crate::sys::stdio;
-use crate::sys_common::process::{CommandEnv, CommandEnvs};
+use crate::sys_common::process::{CapturedEnvs, CommandEnv, CommandEnvs};
 use crate::sys_common::IntoInner;
 
 use core::ffi::c_void;
@@ -244,6 +244,10 @@ impl Command {
         self.env.iter()
     }
 
+    pub fn capture_envs(&self) -> CapturedEnvs {
+        self.env.capture_iter()
+    }
+
     pub fn get_current_dir(&self) -> Option<&Path> {
         self.cwd.as_ref().map(|cwd| Path::new(cwd))
     }

library/std/src/sys_common/process.rs

@@ -98,9 +98,46 @@ impl CommandEnv {
         let iter = self.vars.iter();
         CommandEnvs { iter }
     }
+
+    pub fn capture_iter(&self) -> CapturedEnvs {
+        let iter = self.capture().into_iter();
+
+        CapturedEnvs { iter }
+    }
+}
+
+/// An iterator over captured [`Command`][crate::process::Command] environment variables.
+///
+/// This struct is created by
+/// [`Command::capture_envs`][crate::process::Command::capture_envs]. It includes inherited and
+/// explicitly set environment variables.
+///
+/// See [`Command::capture_envs`][crate::process::Command::capture_envs] documentation for more.
+pub struct CapturedEnvs {
+    iter: crate::collections::btree_map::IntoIter<EnvKey, OsString>,
 }
 
-/// An iterator over the command environment variables.
+impl Iterator for CapturedEnvs {
+    type Item = (OsString, OsString);
+
+    fn next(&mut self) -> Option<Self::Item> {
+        self.iter.next().into()
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.iter.size_hint()
+    }
+}
+
+/// An iterator over the explicitly set [`Command`][crate::process::Command] environment variables.
+///
+/// Each element is a tuple key/value pair `(&OsStr, Option<&OsStr>)`. A [`None`] value
+/// indicates its key was explicitly removed. The associated key for the [`None`] value will no
+/// longer inherit from its parent process.
+///
+/// Note that this output does not include environment variables inherited from the parent process.
+/// To get the variables that will be set when the child spawns use
+/// [`Command::captured_envs`][crate::process::Command::captured_envs].
 ///
 /// This struct is created by
 /// [`Command::get_envs`][crate::process::Command::get_envs]. See its