refactor: enhance config override at compile time.

kclvm/sema/src/pre_process/config.rs

@@ -293,7 +293,14 @@ fn unify_config_entries(
         };
         let entry = entry.clone();
         match bucket.get_mut(&name) {
-            Some(values) => values.push(entry),
+            Some(values) => {
+                // If the attribute operation is override, clear all previous entries and override
+                // with current entry.
+                if let ast::ConfigEntryOperation::Override = entry.node.operation {
+                    values.clear();
+                }
+                values.push(entry);
+            }
             None => {
                 let values = vec![entry];
                 bucket.insert(name, values);

kclvm/sema/src/pre_process/test_data/config_override.k

@@ -0,0 +1,17 @@
+schema ConfigMapping:
+    [str]: Config
+
+schema Config:
+    [str]: any
+
+configMapping: ConfigMapping {
+    key = Config {
+        data.key: "value"
+    }
+}
+
+configMapping: ConfigMapping {
+    key = Config {
+        data.key: "value1"
+    }
+}

kclvm/sema/src/pre_process/tests.rs

@@ -78,10 +78,15 @@ fn test_config_merge() {
     if let ast::Stmt::Unification(unification) = &module.body[0].node {
         let schema = &unification.value.node;
         if let ast::Expr::Config(config) = &schema.config.node {
-            // 2 contains `name` in `config1.k`, `age` in `config2.k` and `age` in `config2.k`
+            // 2 contains `name` in `config1.k`, `age` in `config2.k`.
+            // person: Person {
+            //     name = "Alice"
+            //     age = 18
+            // }
+            assert_eq!(config.items.len(), 2);
             assert_eq!(
                 get_attr_paths_from_config_expr(&config),
-                vec!["name".to_string(), "age".to_string(), "age".to_string(),]
+                vec!["name".to_string(), "age".to_string()]
             );
         } else {
             panic!(
@@ -96,3 +101,37 @@ fn test_config_merge() {
         )
     }
 }
+
+#[test]
+fn test_config_override() {
+    let mut program =
+        load_program(&["./src/pre_process/test_data/config_override.k"], None).unwrap();
+    merge_program(&mut program);
+    let modules = program.pkgs.get_mut(kclvm_ast::MAIN_PKG).unwrap();
+    assert_eq!(modules.len(), 1);
+    // Test the module merge result
+    let module = modules.first().unwrap();
+    if let ast::Stmt::Unification(unification) = &module.body[2].node {
+        let schema = &unification.value.node;
+        if let ast::Expr::Config(config) = &schema.config.node {
+            // key = Config {
+            //     data.key: "value1"
+            // }
+            assert_eq!(config.items.len(), 1);
+            assert_eq!(
+                get_attr_paths_from_config_expr(&config),
+                vec!["key".to_string(), "key.data.key".to_string()]
+            );
+        } else {
+            panic!(
+                "test failed, expect config expression, got {:?}",
+                schema.config
+            )
+        }
+    } else {
+        panic!(
+            "test failed, expect unification statement, got {:?}",
+            module.body[2]
+        )
+    }
+}