Add custom state.

src/eval/debugger.rs

@@ -18,7 +18,7 @@ pub type OnDebuggingInit = dyn Fn() -> Dynamic + Send + Sync;
 /// Callback function for debugging.
 #[cfg(not(feature = "sync"))]
 pub type OnDebuggerCallback = dyn Fn(
-    &mut EvalContext,
+    EvalContext,
     DebuggerEvent,
     ASTNode,
     Option<&str>,
@@ -26,13 +26,7 @@ pub type OnDebuggerCallback = dyn Fn(
 ) -> RhaiResultOf<DebuggerCommand>;
 /// Callback function for debugging.
 #[cfg(feature = "sync")]
-pub type OnDebuggerCallback = dyn Fn(
-        &mut EvalContext,
-        DebuggerEvent,
-        ASTNode,
-        Option<&str>,
-        Position,
-    ) -> RhaiResultOf<DebuggerCommand>
+pub type OnDebuggerCallback = dyn Fn(EvalContext, DebuggerEvent, ASTNode, Option<&str>, Position) -> RhaiResultOf<DebuggerCommand>
     + Send
     + Sync;
 
@@ -525,7 +519,7 @@ impl Engine {
             Some(source.as_str())
         };
 
-        let mut context = crate::EvalContext {
+        let context = crate::EvalContext {
             engine: self,
             scope,
             global,
@@ -536,7 +530,7 @@ impl Engine {
         };
 
         if let Some((.., ref on_debugger)) = self.debugger {
-            let command = on_debugger(&mut context, event, node, source, node.position())?;
+            let command = on_debugger(context, event, node, source, node.position())?;
 
             match command {
                 DebuggerCommand::Continue => {
@@ -559,12 +553,12 @@ impl Engine {
                     // Bump a level if it is a function call
                     let level = match node {
                         ASTNode::Expr(Expr::FnCall(..)) | ASTNode::Stmt(Stmt::FnCall(..)) => {
-                            context.call_level() + 1
+                            level + 1
                         }
                         ASTNode::Stmt(Stmt::Expr(e)) if matches!(e.as_ref(), Expr::FnCall(..)) => {
-                            context.call_level() + 1
+                            level + 1
                         }
-                        _ => context.call_level(),
+                        _ => level,
                     };
                     global.debugger.status = DebuggerStatus::FunctionExit(level);
                     Ok(None)

src/eval/eval_context.rs

@@ -60,6 +60,18 @@ impl<'s, 'ps, 'm, 'pm, 'pt> EvalContext<'_, 's, 'ps, 'm, 'pm, '_, '_, 'pt> {
     pub fn iter_imports(&self) -> impl Iterator<Item = (&str, &Module)> {
         self.global.iter_imports()
     }
+    /// Custom state kept in a [`Dynamic`].
+    #[inline(always)]
+    #[must_use]
+    pub const fn tag(&self) -> &Dynamic {
+        &self.global.tag
+    }
+    /// Mutable reference to the custom state kept in a [`Dynamic`].
+    #[inline(always)]
+    #[must_use]
+    pub fn tag_mut(&mut self) -> &mut Dynamic {
+        &mut self.global.tag
+    }
     /// _(internals)_ The current [`GlobalRuntimeState`].
     /// Exported under the `internals` feature only.
     #[cfg(feature = "internals")]

src/eval/expr.rs

@@ -161,7 +161,7 @@ impl Engine {
                 level,
             };
             let var_name = expr.get_variable_name(true).expect("`Expr::Variable`");
-            match resolve_var(var_name, index, &context) {
+            match resolve_var(var_name, index, context) {
                 Ok(Some(mut result)) => {
                     result.set_access_mode(AccessMode::ReadOnly);
                     return Ok((result.into(), var_pos));

src/eval/global_state.rs

@@ -1,6 +1,6 @@
 //! Global runtime state.
 
-use crate::{Engine, Identifier};
+use crate::{Dynamic, Engine, Identifier};
 #[cfg(feature = "no_std")]
 use std::prelude::v1::*;
 use std::{fmt, marker::PhantomData};
@@ -9,7 +9,7 @@ use std::{fmt, marker::PhantomData};
 #[cfg(not(feature = "no_module"))]
 #[cfg(not(feature = "no_function"))]
 pub type GlobalConstants =
-    crate::Shared<crate::Locked<std::collections::BTreeMap<Identifier, crate::Dynamic>>>;
+    crate::Shared<crate::Locked<std::collections::BTreeMap<Identifier, Dynamic>>>;
 
 /// _(internals)_ Global runtime states.
 /// Exported under the `internals` feature only.
@@ -64,6 +64,8 @@ pub struct GlobalRuntimeState<'a> {
     #[cfg(not(feature = "no_module"))]
     #[cfg(not(feature = "no_function"))]
     pub constants: Option<GlobalConstants>,
+    /// Custom state that can be used by the external host.
+    pub tag: Dynamic,
     /// Debugging interface.
     #[cfg(feature = "debugging")]
     pub debugger: super::Debugger,
@@ -95,6 +97,7 @@ impl GlobalRuntimeState<'_> {
             #[cfg(not(feature = "no_module"))]
             #[cfg(not(feature = "no_function"))]
             constants: None,
+            tag: Dynamic::UNIT,
             #[cfg(feature = "debugging")]
             debugger: crate::eval::Debugger::new(_engine),
             dummy: PhantomData::default(),

src/eval/stmt.rs

@@ -841,7 +841,7 @@ impl Engine {
                         level,
                     };
 
-                    match filter(true, info, &context) {
+                    match filter(true, info, context) {
                         Ok(true) => None,
                         Ok(false) => {
                             Some(Err(