fix(lsp): find_id for custom def in custom def (#15289)

# Description

Enables hover/rename/references for:

```nushell
def foo [] {
  def bar [] { }
     # |____________ this custom command
}
```

# User-Facing Changes

# Tests + Formatting

+1

# After Submitting

crates/nu-lsp/src/ast.rs

@@ -74,7 +74,17 @@ fn try_find_id_in_def(
     }
     let span = strip_quotes(span?, working_set);
     let name = working_set.get_span_contents(span);
-    let decl_id = Id::Declaration(working_set.find_decl(name)?);
+    let decl_id = Id::Declaration(working_set.find_decl(name).or_else(|| {
+        // for defs inside def
+        // TODO: get scope by position
+        // https://github.com/nushell/nushell/issues/15291
+        (0..working_set.num_decls()).find_map(|id| {
+            let decl_id = nu_protocol::DeclId::new(id);
+            let decl = working_set.get_decl(decl_id);
+            let span = working_set.get_block(decl.block_id()?).span?;
+            call.span().contains_span(span).then_some(decl_id)
+        })
+    })?);
     id_ref
         .is_none_or(|id_r| decl_id == *id_r)
         .then_some((decl_id, span))

crates/nu-lsp/src/lib.rs

@@ -957,6 +957,30 @@ mod tests {
         );
     }
 
+    #[test]
+    fn hover_on_custom_in_custom() {
+        let (client_connection, _recv) = initialize_language_server(None, None);
+
+        let mut script = fixtures();
+        script.push("lsp");
+        script.push("hover");
+        script.push("command.nu");
+        let script = path_to_uri(&script);
+
+        open_unchecked(&client_connection, script.clone());
+        let resp = send_hover_request(&client_connection, script.clone(), 9, 7);
+
+        assert_json_eq!(
+            result_from_message(resp),
+            serde_json::json!({
+                    "contents": {
+                    "kind": "markdown",
+                    "value": "\n---\n### Usage \n```nu\n  bar {flags}\n```\n\n### Flags\n\n  `-h`, `--help` - Display the help message for this command\n\n"
+                }
+            })
+        );
+    }
+
     #[test]
     fn hover_on_external_command() {
         let (client_connection, _recv) = initialize_language_server(None, None);

tests/fixtures/lsp/hover/command.nu

@@ -5,3 +5,7 @@ hello
 
 [""] | str join
 ^sleep
+
+def foo [] {
+  def bar [] { }
+}