Include trailing colon in RBS keyword parameter offset

Align RBS keyword parameter offsets with Ruby indexer behavior.
The RBS indexer now includes the trailing colon in the offset for
required and optional keyword parameters (e.g. `name:` instead of `name`).

Adds `Offset::extend_end` helper to adjust byte ranges.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: soutaro

rust/rubydex/src/indexing/rbs_indexer.rs

@@ -271,14 +271,16 @@ impl<'a> RBSIndexer<'a> {
 
         for (key, _value) in function_node.required_keywords().iter() {
             let name = self.source_at(&key.location());
-            let offset = Offset::from_rbs_location(&key.location());
+            // Extend offset by 1 to include the trailing colon, matching Ruby indexer behavior
+            let offset = Offset::from_rbs_location(&key.location()).extend_end(1);
             let str_id = self.local_graph.intern_string(name);
             parameters.push(Parameter::RequiredKeyword(ParameterStruct::new(offset, str_id)));
         }
 
         for (key, _value) in function_node.optional_keywords().iter() {
             let name = self.source_at(&key.location());
-            let offset = Offset::from_rbs_location(&key.location());
+            // Extend offset by 1 to include the trailing colon, matching Ruby indexer behavior
+            let offset = Offset::from_rbs_location(&key.location()).extend_end(1);
             let str_id = self.local_graph.intern_string(name);
             parameters.push(Parameter::OptionalKeyword(ParameterStruct::new(offset, str_id)));
         }
@@ -1257,12 +1259,12 @@ mod tests {
 
             assert_parameter!(&def.signatures().as_slice()[0][4], RequiredKeyword, |param| {
                 assert_string_eq!(context, param.str(), "name");
-                assert_offset_string!(context, param.offset(), "name");
+                assert_offset_string!(context, param.offset(), "name:");
             });
 
             assert_parameter!(&def.signatures().as_slice()[0][5], OptionalKeyword, |param| {
                 assert_string_eq!(context, param.str(), "age");
-                assert_offset_string!(context, param.offset(), "age");
+                assert_offset_string!(context, param.offset(), "age:");
             });
 
             assert_parameter!(&def.signatures().as_slice()[0][6], RestKeyword, |param| {
@@ -1298,12 +1300,12 @@ mod tests {
 
             assert_parameter!(&def.signatures().as_slice()[0][4], RequiredKeyword, |param| {
                 assert_string_eq!(context, param.str(), "name");
-                assert_offset_string!(context, param.offset(), "name");
+                assert_offset_string!(context, param.offset(), "name:");
             });
 
             assert_parameter!(&def.signatures().as_slice()[0][5], OptionalKeyword, |param| {
                 assert_string_eq!(context, param.str(), "age");
-                assert_offset_string!(context, param.offset(), "age");
+                assert_offset_string!(context, param.offset(), "age:");
             });
 
             assert_parameter!(&def.signatures().as_slice()[0][6], RestKeyword, |param| {

rust/rubydex/src/offset.rs

@@ -74,6 +74,15 @@ impl Offset {
         self.end
     }
 
+    /// Returns a new offset with the end extended by the given number of bytes.
+    #[must_use]
+    pub const fn extend_end(self, bytes: u32) -> Self {
+        Self {
+            start: self.start,
+            end: self.end + bytes,
+        }
+    }
+
     /// Converts an offset to a display range like `1:1-1:5`
     #[must_use]
     pub fn to_display_range(&self, document: &Document) -> String {