feat(cli): add feature to disable downloads (#3465)

* feat(cli): add feature to disable downloads

---------

Co-authored-by: Jonathan Kelley <jkelleyrtp@gmail.com>

packages/cli/src/rustc.rs

@@ -0,0 +1,31 @@
+use crate::Result;
+use anyhow::Context;
+use std::path::PathBuf;
+use tokio::process::Command;
+
+#[derive(Debug, Default)]
+pub struct RustcDetails {
+    pub sysroot: PathBuf,
+}
+
+impl RustcDetails {
+    /// Find the current sysroot location using the CLI
+    pub async fn from_cli() -> Result<RustcDetails> {
+        let output = Command::new("rustc")
+            .args(["--print", "sysroot"])
+            .output()
+            .await?;
+
+        let stdout =
+            String::from_utf8(output.stdout).context("Failed to extract rustc sysroot output")?;
+
+        let sysroot = PathBuf::from(stdout.trim());
+        Ok(Self { sysroot })
+    }
+
+    pub fn has_wasm32_unknown_unknown(&self) -> bool {
+        self.sysroot
+            .join("lib/rustlib/wasm32-unknown-unknown")
+            .exists()
+    }
+}