Properly handle commands defined inside of other commands (#2837)

* Fix function inner scopes

* tweak error

tests/shell/pipeline/commands/internal.rs

@@ -380,6 +380,30 @@ fn run_custom_subcommand() {
     assert_eq!(actual.out, "bobbob");
 }
 
+#[test]
+fn run_inner_custom_command() {
+    let actual = nu!(
+        cwd: ".",
+        r#"
+          def outer [x] { def inner [y] { echo $y }; inner $x }; outer 10
+        "#
+    );
+
+    assert_eq!(actual.out, "10");
+}
+
+#[test]
+fn run_broken_inner_custom_command() {
+    let actual = nu!(
+        cwd: ".",
+        r#"
+        def outer [x] { def inner [y] { echo $y }; inner $x }; inner 10
+        "#
+    );
+
+    assert!(actual.err.contains("not found"));
+}
+
 #[test]
 fn set_variable() {
     let actual = nu!(