Revise on_def_var API.

src/eval/stmt.rs

@@ -1,6 +1,7 @@
 //! Module defining functions for evaluating a statement.
 
 use super::{EvalContext, EvalState, GlobalRuntimeState, Target};
+use crate::api::events::VarDefInfo;
 use crate::ast::{
     BinaryExpr, Expr, Ident, OpAssignment, Stmt, SwitchCases, TryCatchBlock, AST_OPTION_FLAGS::*,
 };
@@ -818,9 +819,15 @@ impl Engine {
                 let export = options.contains(AST_OPTION_EXPORTED);
 
                 let result = if let Some(ref filter) = self.def_var_filter {
-                    let shadowing = scope.contains(var_name);
-                    let scope_level = state.scope_level;
+                    let will_shadow = scope.contains(var_name);
+                    let nesting_level = state.scope_level;
                     let is_const = entry_type == AccessMode::ReadOnly;
+                    let info = VarDefInfo {
+                        name: var_name,
+                        is_const,
+                        nesting_level,
+                        will_shadow,
+                    };
                     let context = EvalContext {
                         engine: self,
                         scope,
@@ -828,10 +835,10 @@ impl Engine {
                         state,
                         lib,
                         this_ptr,
-                        level: level,
+                        level,
                     };
 
-                    match filter(var_name, true, is_const, scope_level, shadowing, &context) {
+                    match filter(true, info, &context) {
                         Ok(true) => None,
                         Ok(false) => {
                             Some(Err(