Tell user if override is set in the environment after rustup default

src/rustup-cli/rustup_mode.rs

@@ -591,6 +591,15 @@ fn default_(cfg: &Cfg, m: &ArgMatches<'_>) -> Result<()> {
             println!();
             common::show_channel_update(cfg, toolchain.name(), Ok(status))?;
         }
+
+        let cwd = utils::current_dir()?;
+        if let Some((toolchain, reason)) = cfg.find_override(&cwd)? {
+            info!(
+                "note that the toolchain '{}' is currently in use ({})",
+                toolchain.name(),
+                reason
+            );
+        }
     } else {
         let installed_toolchains = cfg.list_toolchains()?;
         if installed_toolchains.len() > 0 {

tests/cli-rustup.rs

@@ -249,6 +249,24 @@ info: default toolchain set to 'nightly-{0}'
     });
 }
 
+#[test]
+fn default_override() {
+    setup(&|config| {
+        expect_ok(config, &["rustup", "update", "nightly", "--no-self-update"]);
+        expect_ok(config, &["rustup", "default", "stable"]);
+        expect_ok(config, &["rustup", "override", "set", "nightly"]);
+        expect_stderr_ok(
+            config,
+            &["rustup", "default", "stable"],
+            for_host!(
+                r"info: using existing install for 'stable-{0}'
+info: default toolchain set to 'stable-{0}'
+info: note that the toolchain 'nightly-{0}' is currently in use (directory override for"
+            ),
+        );
+    });
+}
+
 #[test]
 fn rustup_xz() {
     setup(&|config| {