Add groups export.

- Prevent declaring subgroup without group.

Author: Yarwin

godot-macros/src/class/data_models/group_export.rs

@@ -6,7 +6,7 @@
  */
 
 use crate::class::data_models::fields::Fields;
-use crate::util::KvParser;
+use crate::util::{bail, KvParser};
 use crate::ParseResult;
 use std::cmp::Ordering;
 
@@ -45,9 +45,21 @@ impl FieldGroup {
         parser: &mut KvParser,
         groups: &mut Vec<String>,
     ) -> ParseResult<Self> {
+        let (group_name_index, subgroup_name_index) = (
+            Self::parse_group("group", parser, groups)?,
+            Self::parse_group("subgroup", parser, groups)?,
+        );
+
+        // Declaring only a subgroup for given property – with no group at all – is totally valid in Godot.
+        // Unfortunately it leads to a lot of very janky and not too ideal behaviours
+        // So it is better to treat it as a user error.
+        if subgroup_name_index.is_some() && group_name_index.is_none() {
+            return bail!(parser.span(), "Subgroups without groups are not supported.");
+        }
+
         Ok(Self {
-            group_name_index: Self::parse_group("group", parser, groups)?,
-            subgroup_name_index: Self::parse_group("subgroup", parser, groups)?,
+            group_name_index,
+            subgroup_name_index,
         })
     }
 }

itest/rust/src/object_tests/property_test.rs

@@ -242,7 +242,7 @@ struct CheckAllExports {
     #[export(group = "test_group")]
     grouped: i64,
 
-    #[export(subgroup = "test_subgroup")]
+    #[export(group = "another group")]
     subgrouped: i64,
 
     #[export(group = "test_group", subgroup = "test_subgroup")]