fix(mysql): generate index COMMENT clause and enable index_comment capability

crates/dbx-core/src/table_structure_sql/dialect.rs

@@ -78,6 +78,7 @@ pub(super) fn capabilities_for(database_type: Option<DatabaseType>) -> TableStru
             drop_index: true,
             rebuild_index: true,
             index_type: true,
+            index_comment: true,
             alter_primary_key: true,
             ..base
         },

crates/dbx-core/src/table_structure_sql/indexes.rs

@@ -169,6 +169,12 @@ pub(super) fn build_create_index_statements(
     } else {
         String::new()
     };
+    let comment = clean(&index.comment);
+    let comment_clause = if !comment.is_empty() && capabilities.index_comment && dialect == StructureDialect::Mysql {
+        format!(" COMMENT {}", quote_string(&comment))
+    } else {
+        String::new()
+    };
     let filter = clean(&index.filter);
     let supports_where = capabilities.index_filter
         && matches!(dialect, StructureDialect::Postgres | StructureDialect::SqlServer | StructureDialect::Sqlite);
@@ -180,17 +186,18 @@ pub(super) fn build_create_index_statements(
         )
     } else {
         format!(
-            "CREATE {unique}{type_prefix}INDEX {}{using_clause} ON {table} ({cols}){include_clause}{where_clause};",
+            "CREATE {unique}{type_prefix}INDEX {}{using_clause} ON {table} ({cols}){include_clause}{where_clause}{comment_clause};",
             quote_ident(dialect, &name)
         )
     };
     let mut statements = vec![create_sql];
 
-    let comment = clean(&index.comment);
     if !comment.is_empty() && capabilities.index_comment && dialect == StructureDialect::Postgres {
         statements.push(format!("COMMENT ON INDEX {} IS {};", quote_ident(dialect, &name), quote_string(&comment)));
     } else if !comment.is_empty() && capabilities.index_comment && dialect == StructureDialect::SqlServer {
         statements.extend(build_sqlserver_index_comment_sql(table, schema, table_name, &name, &comment));
+    } else if !comment.is_empty() && capabilities.index_comment && dialect == StructureDialect::Mysql {
+        // MySQL comment is embedded inline in the CREATE INDEX statement above
     } else if !comment.is_empty() && capabilities.index_comment {
         warnings.push(format!("Index comments are not supported for {} from this editor.", dialect_label(dialect)));
     }

crates/dbx-core/src/table_structure_sql/tests.rs

@@ -117,6 +117,61 @@ fn builds_mysql_column_and_index_changes() {
         );
 }
 
+#[test]
+fn mysql_create_index_with_comment() {
+    let mut col = column("name");
+    col.data_type = "varchar(120)".to_string();
+    let mut idx = index("idx_users_name", &["name"]);
+    idx.comment = "Search index".to_string();
+
+    let result = build_table_structure_change_sql(TableStructureSqlOptions {
+        database_type: Some(DatabaseType::Mysql),
+        schema: None,
+        table_name: "users".to_string(),
+        columns: vec![col],
+        indexes: vec![idx],
+        foreign_keys: Vec::new(),
+        triggers: Vec::new(),
+        table_comment: None,
+        original_table_comment: None,
+    });
+
+    assert_eq!(result.warnings, Vec::<String>::new());
+    assert_eq!(
+        result.statements,
+        vec![
+            "ALTER TABLE `users` ADD COLUMN `name` varchar(120);",
+            "CREATE INDEX `idx_users_name` ON `users` (`name`) COMMENT 'Search index';",
+        ]
+    );
+}
+
+#[test]
+fn mysql_create_unique_index_with_comment_and_btree() {
+    let mut idx = index("uniq_users_email", &["email"]);
+    idx.is_unique = true;
+    idx.index_type = "BTREE".to_string();
+    idx.comment = "Unique email index".to_string();
+
+    let result = build_table_structure_change_sql(TableStructureSqlOptions {
+        database_type: Some(DatabaseType::Mysql),
+        schema: None,
+        table_name: "users".to_string(),
+        columns: Vec::new(),
+        indexes: vec![idx],
+        foreign_keys: Vec::new(),
+        triggers: Vec::new(),
+        table_comment: None,
+        original_table_comment: None,
+    });
+
+    assert_eq!(result.warnings, Vec::<String>::new());
+    assert_eq!(
+        result.statements,
+        vec!["CREATE UNIQUE INDEX `uniq_users_email` USING BTREE ON `users` (`email`) COMMENT 'Unique email index';",]
+    );
+}
+
 #[test]
 fn mysql_add_timestamp_column_drops_invalid_precision() {
     let mut created_at = column("created_at");