feat(install): warn if default linker (cc) is missing; add respective test case

Author: cachebag

src/cli/self_update.rs

@@ -610,6 +610,9 @@ pub(crate) async fn install(
     };
     md(&mut term, msg);
 
+    #[cfg(unix)]
+    warn_if_default_linker_missing(process);
+
     #[cfg(windows)]
     if !no_prompt {
         // On windows, where installation happens in a console
@@ -742,6 +745,24 @@ fn current_install_opts(opts: &InstallOpts<'_>, process: &Process) -> String {
     )
 }
 
+#[cfg(unix)]
+fn warn_if_default_linker_missing(process: &Process) {
+    // Search for `cc` in PATH
+    if let Some(path) = process.var_os("PATH") {
+        let cc_binary = format!("cc{}", env::consts::EXE_SUFFIX);
+
+        for mut p in env::split_paths(&path) {
+            p.push(&cc_binary);
+            if p.is_file() {
+                return;
+            }
+        }
+    }
+
+    warn!("no default linker (`cc`) was found in your PATH");
+    warn!("many Rust crates require a system C toolchain to build");
+}
+
 fn install_bins(process: &Process) -> Result<()> {
     let bin_path = process.cargo_home()?.join("bin");
     let this_exe_path = utils::current_exe()?;

tests/suite/cli_inst_interactive.rs

@@ -626,3 +626,29 @@ warn: It looks like you have an existing rustup settings file at:
 ...
 "#]]);
 }
+
+#[cfg(unix)]
+#[tokio::test]
+async fn install_warns_if_default_linker_missing() {
+    // Fake PATH pointing to an empty directory so `cc` cannot be found
+    let temp_dir = tempfile::Builder::new()
+        .prefix("emptybin")
+        .tempdir()
+        .unwrap();
+    let temp_dir_path = temp_dir.path().to_str().unwrap();
+
+    let cx = CliTestContext::new(Scenario::SimpleV2).await;
+    cx.config
+        .expect_with_env(
+            ["rustup-init", "-y", "--no-modify-path"],
+            [("PATH", temp_dir_path)], // override PATH to hide system `cc`
+        )
+        .await
+        .is_ok()
+        .with_stderr(snapbox::str![[r#"
+...
+warn: no default linker (`cc`) was found in your PATH
+warn: many Rust crates require a system C toolchain to build
+...
+"#]]);
+}