xtask: Fix channel of cargo operations

Starting in rustup 1.25.0, the environment is modified during `cargo`
invocations in a way that breaks setting the channel arg
(e.g. "+nightly") in a subprocess.

Fix by unsetting those variables in the child cargo's env.

See rust-lang/rustup#3031

xtask/src/cargo.rs

@@ -1,5 +1,7 @@
 use crate::arch::UefiArch;
 use anyhow::{bail, Result};
+use std::env;
+use std::ffi::OsString;
 use std::process::Command;
 
 #[derive(Clone, Copy, Debug)]
@@ -86,6 +88,32 @@ pub enum CargoAction {
     Test,
 }
 
+/// Get a modified PATH to remove entries added by rustup. This is
+/// necessary on Windows, see
+/// https://github.com/rust-lang/rustup/issues/3031.
+fn sanitized_path(orig_path: OsString) -> OsString {
+    // Modify the PATH to remove entries added by rustup. This is
+    // necessary on Windows, see https://github.com/rust-lang/rustup/issues/3031.
+    let paths = env::split_paths(&orig_path);
+    let sanitized_paths = paths.filter(|path| {
+        !path
+            .components()
+            .any(|component| component.as_os_str() == ".rustup")
+    });
+
+    env::join_paths(sanitized_paths).expect("invalid PATH")
+}
+
+/// Cargo automatically sets some env vars that can prevent the
+/// channel arg (e.g. "+nightly") from working. Unset them in the
+/// child's environment.
+pub fn fix_nested_cargo_env(cmd: &mut Command) {
+    cmd.env_remove("RUSTC");
+    cmd.env_remove("RUSTDOC");
+    let orig_path = env::var_os("PATH").unwrap_or_default();
+    cmd.env("PATH", sanitized_path(orig_path));
+}
+
 #[derive(Debug)]
 pub struct Cargo {
     pub action: CargoAction,
@@ -101,6 +129,8 @@ impl Cargo {
     pub fn command(&self) -> Result<Command> {
         let mut cmd = Command::new("cargo");
 
+        fix_nested_cargo_env(&mut cmd);
+
         if let Some(toolchain) = &self.toolchain {
             cmd.arg(&format!("+{}", toolchain));
         }
@@ -193,6 +223,17 @@ mod tests {
         );
     }
 
+    #[test]
+    fn test_sanitize_path() {
+        let (input, expected) = match env::consts::FAMILY {
+            "unix" => ("Abc:/path/.rustup/cargo:Xyz", "Abc:Xyz"),
+            "windows" => ("Abc;/path/.rustup/cargo;Xyz", "Abc;Xyz"),
+            _ => unimplemented!(),
+        };
+
+        assert_eq!(sanitized_path(input.into()), expected);
+    }
+
     #[test]
     fn test_cargo_command() {
         let cargo = Cargo {

xtask/src/main.rs

@@ -7,7 +7,7 @@ mod qemu;
 mod util;
 
 use anyhow::Result;
-use cargo::{Cargo, CargoAction, Feature, Package};
+use cargo::{fix_nested_cargo_env, Cargo, CargoAction, Feature, Package};
 use cfg_if::cfg_if;
 use clap::Parser;
 use opt::{Action, BuildOpt, ClippyOpt, DocOpt, MiriOpt, Opt, QemuOpt};
@@ -172,6 +172,7 @@ fn test_latest_release() -> Result<()> {
     // Create cargo build command, not using the `cargo` module to make
     // it explicit that it matches the command in `BUILDING.md`.
     let mut build_cmd = Command::new("cargo");
+    fix_nested_cargo_env(&mut build_cmd);
     build_cmd
         .args(&["+nightly", "build", "--target", "x86_64-unknown-uefi"])
         .current_dir(tmp_dir.join("template"));

xtask/src/util.rs

@@ -6,8 +6,12 @@ use std::process::Command;
 /// Example: "VAR=val program --arg1 arg2".
 pub fn command_to_string(cmd: &Command) -> String {
     // Format env vars as "name=val".
+    let ignore_var = ["PATH", "RUSTC", "RUSTDOC"];
     let mut parts = cmd
         .get_envs()
+        // Filter out some internally-set variables that would just
+        // clutter the output.
+        .filter(|(name, _)| !ignore_var.contains(&name.to_str().unwrap_or_default()))
         .map(|(name, val)| {
             format!(
                 "{}={}",
@@ -47,8 +51,13 @@ mod tests {
     #[test]
     fn test_command_to_string() {
         let mut cmd = Command::new("MyCommand");
-        cmd.args(&["abc", "123"])
-            .envs([("VAR1", "val1"), ("VAR2", "val2")]);
+        cmd.args(&["abc", "123"]).envs([
+            ("VAR1", "val1"),
+            ("VAR2", "val2"),
+            ("PATH", "pathval"),
+            ("RUSTC", "rustcval"),
+            ("RUSTDOC", "rustdocval"),
+        ]);
         assert_eq!(
             command_to_string(&cmd),
             "VAR1=val1 VAR2=val2 MyCommand abc 123"