Add the ability to see inherited envs on Command

[schneems]

Add the ability to see inherited envs on Command

This is a reference implementation for one of the solution "sketches" in rust-lang/libs-team#194.

Problem statement(s)

• Problem 1: Cannot observe effects of Command::env_clear
• Problem 2: The "capture" logic has no exposed single source of truth

Problem 1 is a capability problem (I can't work around this). Problem 2 is a usability and stability problem.

Problem 1: Cannot observe effects of Command::env_clear

As documented in my merged PR, calling env_clear will cause the "capture" logic to skip inheriting from the parent process. While a developer can set this value, they cannot programmatically observe if it has been set (though they can manually observe it via "alternative" debug formatting {:#?}).

The end goals of programmatically observing that effect is listed below in "Motivation".

This problem prevents me from reproducing the capture logic in a library where I cannot observe if env_clear has been called. Even if this problem is solved, a related problem is detailed below.

Problem 2: The "capture" logic has no exposed single source of truth

Even if we could directly observe the effects of calling env_clear, every developer who needed this information would need to reproduce this "capture" logic

rust/library/std/src/sys_common/process.rs

Lines 36 to 51 in 3a5c8e9

	pub fn capture(&self) -> BTreeMap<EnvKey, OsString> {
	let mut result = BTreeMap::<EnvKey, OsString>::new();
	if !self.clear {
	for (k, v) in env::vars_os() {
	result.insert(k.into(), v);
	}
	}
	for (k, maybe_v) in &self.vars {
	if let &Some(ref v) = maybe_v {
	result.insert(k.clone(), v.clone());
	} else {
	result.remove(k);
	}
	}
	result
	}

and hope that it does not change or that their implementation does not diverge.

If the outcome of this logic is exposed, then it will:

• Solve problem 1
• Prevent divergent reimplementation of "capture" logic

[sketch] Expose captured env logic via a new capture_envs method on Command

We could add a method that exposes that information directly:

let command = Command::new("ls");

let envs: HashMap<OsString, OsString> = command.capture_envs().collect();

The name capture matches internal naming concepts and helps to reinforce that the value method will return a point in time value.

This sketch would solve problems 1 and 2. I'm open to name suggestions.

[rustbot]

r? @thomcc

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[bors]

☔ The latest upstream changes (presumably #110331) made this pull request unmergeable. Please resolve the merge conflicts.

[bors]

☔ The latest upstream changes (presumably #114590) made this pull request unmergeable. Please resolve the merge conflicts.

[rust-log-analyzer]

The job mingw-check failed! Check out the build log: (web) (plain)

Click to see the possible cause of the failure (guessed by this bot)

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---
    Checking miniz_oxide v0.7.1
    Checking object v0.32.0
    Checking hashbrown v0.14.2
    Checking addr2line v0.21.0
error[E0277]: the trait bound `core::option::Option<(OsString, OsString)>: core::convert::From<core::option::Option<(EnvKey, OsString)>>` is not satisfied
    |
    |
124 |         self.iter.next().into()
    |                          ^^^^ the trait `core::convert::From<core::option::Option<(EnvKey, OsString)>>` is not implemented for `core::option::Option<(OsString, OsString)>`
    = help: the following other types implement trait `core::convert::From<T>`:
    = help: the following other types implement trait `core::convert::From<T>`:
              <core::option::Option<&'a T> as core::convert::From<&'a core::option::Option<T>>>
              <core::option::Option<&'a mut T> as core::convert::From<&'a mut core::option::Option<T>>>
              <core::option::Option<T> as core::convert::From<T>>
    = note: required for `core::option::Option<(EnvKey, OsString)>` to implement `core::convert::Into<core::option::Option<(OsString, OsString)>>`
For more information about this error, try `rustc --explain E0277`.
error: could not compile `std` (lib) due to previous error
Build completed unsuccessfully in 0:00:14
  local time: Mon Nov 13 15:34:11 UTC 2023

[bors]

☔ The latest upstream changes (presumably #117285) made this pull request unmergeable. Please resolve the merge conflicts.