try to invoke rustup directly

crates/compiler/build/src/link.rs

@@ -3,8 +3,8 @@ use libloading::{Error, Library};
 use roc_builtins::bitcode;
 use roc_error_macros::internal_error;
 use roc_mono::ir::OptLevel;
-use roc_utils::get_lib_path;
 use roc_utils::{cargo, clang, zig};
+use roc_utils::{get_lib_path, rustup};
 use std::collections::HashMap;
 use std::env;
 use std::io;
@@ -632,11 +632,11 @@ pub fn rebuild_host(
             },
         );
 
-        let mut cargo_cmd = cargo();
+        let mut cargo_cmd = if cfg!(windows) { rustup() } else { cargo() };
 
         if cfg!(windows) {
             // on windows, we need the `+nightly` toolchain so we can use `-Z export-executable-symbols`
-            cargo_cmd.arg("+nightly");
+            cargo_cmd.args(["run", "nightly", "cargo"]);
         }
 
         cargo_cmd.arg("build").current_dir(cargo_dir);

crates/utils/src/lib.rs

@@ -127,9 +127,6 @@ pub fn get_lib_path() -> Option<PathBuf> {
 /// Also makes it easy to track where we use cargo in the codebase.
 pub fn cargo() -> Command {
     let command_str = if cfg!(windows) {
-        // on windows, we need the version of cargo installed by rustup. The meaning of `cargo` is
-        // different within a process that runs rust. So we need to explicitly refer to where
-        // rustup put the binary
         r"%HOMEPATH%\.cargo\bin\cargo.exe"
     } else {
         "cargo"
@@ -142,6 +139,21 @@ pub fn cargo() -> Command {
     }
 }
 
+/// Gives a friendly error if cargo is not installed.
+/// Also makes it easy to track where we use cargo in the codebase.
+pub fn rustup() -> Command {
+    // on windows, we need the version of cargo installed by rustup. The meaning of `cargo` is
+    // different within a process that runs rust. So we need to explicitly refer to where
+    // rustup put the binary
+    let command_str = "rustup";
+
+    if check_command_available(command_str) {
+        Command::new(command_str)
+    } else {
+        panic!("I could not find the rustup command.\nVisit https://rustup.rs/ to install cargo.",)
+    }
+}
+
 /// Gives a friendly error if clang is not installed.
 /// Also makes it easy to track where we use clang in the codebase.
 pub fn clang() -> Command {