Fix path issues for running rustup wrapper on Windows.

Cargo likes to modify PATH, which circumvents the ability to choose the
correct "cargo" executable to run on Windows (because Windows uses PATH
for both binary and shared library searching).

crates/cargo-test-macro/src/lib.rs

@@ -1,4 +1,5 @@
 use proc_macro::*;
+use std::path::Path;
 use std::process::Command;
 use std::sync::Once;
 
@@ -210,8 +211,9 @@ fn version() -> (u32, bool) {
     unsafe { VERSION }
 }
 
-fn check_command(command_name: &str, args: &[&str]) -> bool {
-    let mut command = Command::new(command_name);
+fn check_command(command_path: &Path, args: &[&str]) -> bool {
+    let mut command = Command::new(command_path);
+    let command_name = command.get_program().to_str().unwrap().to_owned();
     command.args(args);
     let output = match command.output() {
         Ok(output) => output,
@@ -220,7 +222,7 @@ fn check_command(command_name: &str, args: &[&str]) -> bool {
             //   environments like Docker. Consider installing it if Cargo
             //   gains more hg support, but otherwise it isn't critical.
             // * lldb is not pre-installed on Ubuntu and Windows, so skip.
-            if is_ci() && !matches!(command_name, "hg" | "lldb") {
+            if is_ci() && !matches!(command_name.as_str(), "hg" | "lldb") {
                 panic!("expected command `{command_name}` to be somewhere in PATH: {e}",);
             }
             return false;
@@ -240,7 +242,7 @@ fn check_command(command_name: &str, args: &[&str]) -> bool {
 }
 
 fn has_command(command: &str) -> bool {
-    check_command(command, &["--version"])
+    check_command(Path::new(command), &["--version"])
 }
 
 fn has_rustup_stable() -> bool {
@@ -255,7 +257,16 @@ fn has_rustup_stable() -> bool {
         // https://github.com/rust-lang/rustup/issues/3036 is resolved.
         return false;
     }
-    check_command("cargo", &["+stable", "--version"])
+    // Cargo mucks with PATH on Windows, adding sysroot host libdir, which is
+    // "bin", which circumvents the rustup wrapper. Use the path directly from
+    // CARGO_HOME.
+    let home = match option_env!("CARGO_HOME") {
+        Some(home) => home,
+        None if is_ci() => panic!("expected to run under rustup"),
+        None => return false,
+    };
+    let cargo = Path::new(home).join("bin/cargo");
+    check_command(&cargo, &["+stable", "--version"])
 }
 
 /// Whether or not this running in a Continuous Integration environment.

tests/testsuite/global_cache_tracker.rs

@@ -14,11 +14,12 @@ use cargo::GlobalContext;
 use cargo_test_support::paths::{self, CargoPathExt};
 use cargo_test_support::registry::{Package, RegistryBuilder};
 use cargo_test_support::{
-    basic_manifest, cargo_process, execs, git, project, retry, sleep_ms, thread_wait_timeout,
-    Project,
+    basic_manifest, cargo_process, execs, git, process, project, retry, sleep_ms,
+    thread_wait_timeout, Execs, Project,
 };
 use itertools::Itertools;
 use std::fmt::Write;
+use std::path::Path;
 use std::path::PathBuf;
 use std::process::Stdio;
 use std::time::{Duration, SystemTime};
@@ -153,6 +154,14 @@ fn populate_cache(
     (cache_dir, src_dir)
 }
 
+fn rustup_cargo() -> Execs {
+    // Get the path to the rustup cargo wrapper. This is necessary because
+    // cargo adds the "deps" directory into PATH on Windows, which points to
+    // the wrong cargo.
+    let rustup_cargo = Path::new(&std::env::var_os("CARGO_HOME").unwrap()).join("bin/cargo");
+    execs().with_process_builder(process(rustup_cargo))
+}
+
 #[cargo_test]
 fn auto_gc_gated() {
     // Requires -Zgc to both track last-use data and to run auto-gc.
@@ -1915,12 +1924,11 @@ fn compatible_with_older_cargo() {
             middle = "1.0"
         "#,
     );
-    p.process("cargo")
+    rustup_cargo()
         .args(&["+stable", "check", "-Zgc"])
+        .cwd(p.root())
         .masquerade_as_nightly_cargo(&["gc"])
         .env("__CARGO_TEST_LAST_USE_NOW", months_ago_unix(2))
-        // Necessary since `process` removes rustup.
-        .env("PATH", std::env::var_os("PATH").unwrap())
         .run();
     assert_eq!(get_registry_names("src"), ["middle-1.0.0", "new-1.0.0"]);
     assert_eq!(
@@ -1978,11 +1986,10 @@ fn forward_compatible() {
         .file("src/lib.rs", "")
         .build();
 
-    p.process("cargo")
+    rustup_cargo()
         .args(&["+stable", "check", "-Zgc"])
+        .cwd(p.root())
         .masquerade_as_nightly_cargo(&["gc"])
-        // Necessary since `process` removes rustup.
-        .env("PATH", std::env::var_os("PATH").unwrap())
         .run();
 
     let config = GlobalContextBuilder::new().unstable_flag("gc").build();