Fix command name lookup for known externals (nushell#7830)

Fixes nushell#7822

crates/nu-parser/src/known_external.rs

@@ -51,7 +51,15 @@ impl Command for KnownExternal {
 
         let mut extern_call = Call::new(head_span);
 
-        let extern_name = engine_state.get_decl(call.decl_id).name();
+        let extern_name = if let Some(name_bytes) = engine_state.find_decl_name(call.decl_id, &[]) {
+            String::from_utf8_lossy(name_bytes)
+        } else {
+            return Err(ShellError::NushellFailedSpanned(
+                "known external name not found".to_string(),
+                "could not find name for this command".to_string(),
+                call.head,
+            ));
+        };
 
         let extern_name: Vec<_> = extern_name.split(' ').collect();
 

crates/nu-protocol/src/engine/engine_state.rs

@@ -585,6 +585,24 @@ impl EngineState {
         None
     }
 
+    pub fn find_decl_name(&self, decl_id: DeclId, removed_overlays: &[Vec<u8>]) -> Option<&[u8]> {
+        let mut visibility: Visibility = Visibility::new();
+
+        for overlay_frame in self.active_overlays(removed_overlays).iter().rev() {
+            visibility.append(&overlay_frame.visibility);
+
+            if visibility.is_decl_id_visible(&decl_id) {
+                for ((name, _), id) in overlay_frame.decls.iter() {
+                    if id == &decl_id {
+                        return Some(name);
+                    }
+                }
+            }
+        }
+
+        None
+    }
+
     pub fn find_alias(&self, name: &[u8], removed_overlays: &[Vec<u8>]) -> Option<AliasId> {
         let mut visibility: Visibility = Visibility::new();
 

src/tests/test_known_external.rs

@@ -76,3 +76,34 @@ fn known_external_misc_values() -> TestResult {
         "abc a b c",
     )
 }
+
+/// GitHub issue #7822
+#[test]
+fn known_external_subcommand_from_module() -> TestResult {
+    run_test_contains(
+        r#"
+            module cargo {
+                export extern check []
+            };
+            use cargo;
+            cargo check -h
+        "#,
+        "cargo check",
+    )
+}
+
+/// GitHub issue #7822
+#[test]
+fn known_external_aliased_subcommand_from_module() -> TestResult {
+    run_test_contains(
+        r#"
+            module cargo {
+                export extern check []
+            };
+            use cargo;
+            alias cc = cargo check;
+            cc -h
+        "#,
+        "cargo check",
+    )
+}