Fix bug in optimizer.

RELEASES.md

@@ -8,6 +8,7 @@ Bug fixes
 ---------
 
 * Bug in `FileModuleResolver::clear_cache_for_path` path mapping fixed.
+* Some optimizer fringe cases is fixed - related to constants propagation when the evil `eval` is present.
 
 Breaking changes
 ----------------

src/ast.rs

@@ -1070,6 +1070,8 @@ pub struct CustomExpr {
     pub keywords: StaticVec<Expr>,
     /// List of tokens actually parsed.
     pub tokens: Vec<ImmutableString>,
+    /// Delta number of variables in the scope.
+    pub scope_delta: isize,
 }
 
 impl fmt::Debug for CustomExpr {

src/optimize.rs

@@ -58,6 +58,8 @@ struct State<'a> {
     changed: bool,
     /// Collection of constants to use for eager function evaluations.
     variables: Vec<(String, AccessMode, Expr)>,
+    /// Activate constants propagation?
+    propagate_constants: bool,
     /// An [`Engine`] instance for eager function evaluation.
     engine: &'a Engine,
     /// Collection of sub-modules.
@@ -75,6 +77,7 @@ impl<'a> State<'a> {
         Self {
             changed: false,
             variables: vec![],
+            propagate_constants: true,
             engine,
             mods: (&engine.global_sub_modules).into(),
             lib,
@@ -109,6 +112,10 @@ impl<'a> State<'a> {
     /// Look up a constant from the list.
     #[inline]
     pub fn find_constant(&self, name: &str) -> Option<&Expr> {
+        if !self.propagate_constants {
+            return None;
+        }
+
         for (n, access, expr) in self.variables.iter().rev() {
             if n == name {
                 return if access.is_read_only() {
@@ -160,18 +167,28 @@ fn optimize_stmt_block(
 ) -> Stmt {
     let orig_len = statements.len(); // Original number of statements in the block, for change detection
     let orig_constants_len = state.variables.len(); // Original number of constants in the state, for restore later
+    let orig_propagate_constants = state.propagate_constants;
 
     // Optimize each statement in the block
-    statements.iter_mut().for_each(|stmt| match stmt {
+    statements.iter_mut().for_each(|stmt| {
+        match stmt {
             // Add constant literals into the state
-        Stmt::Const(var_def, Some(expr), _, _) if expr.is_constant() => {
+            Stmt::Const(var_def, Some(value_expr), _, _) => {
-            state.push_var(&var_def.name, AccessMode::ReadOnly, mem::take(expr));
+                optimize_expr(value_expr, state);
+
+                if value_expr.is_constant() {
+                    state.push_var(&var_def.name, AccessMode::ReadOnly, value_expr.clone());
+                }
             }
             Stmt::Const(var_def, None, _, _) => {
                 state.push_var(&var_def.name, AccessMode::ReadOnly, Expr::Unit(var_def.pos));
             }
             // Add variables into the state
-        Stmt::Let(var_def, _, _, _) => {
+            Stmt::Let(var_def, expr, _, _) => {
+                if let Some(value_expr) = expr {
+                    optimize_expr(value_expr, state);
+                }
+
                 state.push_var(
                     &var_def.name,
                     AccessMode::ReadWrite,
@@ -180,6 +197,7 @@ fn optimize_stmt_block(
             }
             // Optimize the statement
             _ => optimize_stmt(stmt, state, preserve_result),
+        }
     });
 
     // Remove all raw expression statements that are pure except for the very last statement
@@ -251,6 +269,8 @@ fn optimize_stmt_block(
     // Pop the stack and remove all the local constants
     state.restore_var(orig_constants_len);
 
+    state.propagate_constants = orig_propagate_constants;
+
     match &statements[..] {
         // No statements in block - change to No-op
         [] => {
@@ -637,6 +657,10 @@ fn optimize_expr(expr: &mut Expr, state: &mut State) {
             (lhs, rhs) => { optimize_expr(lhs, state); optimize_expr(rhs, state); }
         },
 
+        // eval!
+        Expr::FnCall(x, _) if x.name == KEYWORD_EVAL => {
+            state.propagate_constants = false;
+        }
         // Do not call some special keywords
         Expr::FnCall(x, _) if DONT_EVAL_KEYWORDS.contains(&x.name.as_ref()) => {
             x.args.iter_mut().for_each(|a| optimize_expr(a, state));
@@ -726,7 +750,12 @@ fn optimize_expr(expr: &mut Expr, state: &mut State) {
         }
 
         // Custom syntax
-        Expr::Custom(x, _) => x.keywords.iter_mut().for_each(|expr| optimize_expr(expr, state)),
+        Expr::Custom(x, _) => {
+            if x.scope_delta != 0 {
+                state.propagate_constants = false;
+            }
+            x.keywords.iter_mut().for_each(|expr| optimize_expr(expr, state));
+        }
 
         // All other expressions - skip
         _ => (),
@@ -790,7 +819,11 @@ fn optimize_top_level(
                 Stmt::Const(var_def, None, _, _) => {
                     state.push_var(&var_def.name, AccessMode::ReadOnly, Expr::Unit(var_def.pos));
                 }
-                Stmt::Let(var_def, _, _, _) => {
+                Stmt::Let(var_def, expr, _, _) => {
+                    if let Some(value_expr) = expr {
+                        optimize_expr(value_expr, &mut state);
+                    }
+
                     state.push_var(
                         &var_def.name,
                         AccessMode::ReadWrite,

src/parser.rs

@@ -1995,7 +1995,14 @@ fn parse_custom_syntax(
         }
     }
 
-    Ok(Expr::Custom(Box::new(CustomExpr { keywords, tokens }), pos))
+    Ok(Expr::Custom(
+        Box::new(CustomExpr {
+            keywords,
+            tokens,
+            scope_delta: syntax.scope_delta,
+        }),
+        pos,
+    ))
 }
 
 /// Parse an expression.

tests/optimizer.rs

@@ -55,7 +55,7 @@ fn test_optimizer_parse() -> Result<(), Box<EvalAltResult>> {
 
     let ast = engine.compile("{ const DECISION = false; if DECISION { 42 } else { 123 } }")?;
 
-    assert!(format!("{:?}", ast).starts_with(r#"AST { source: None, statements: [Block([Const(Ident("DECISION" @ 1:9), Some(Unit(0:0)), false, 1:3), Expr(IntegerConstant(123, 1:53))], 1:1)]"#));
+    assert!(format!("{:?}", ast).starts_with(r#"AST { source: None, statements: [Block([Const(Ident("DECISION" @ 1:9), Some(BoolConstant(false, 1:20)), false, 1:3), Expr(IntegerConstant(123, 1:53))], 1:1)]"#));
 
     let ast = engine.compile("if 1 == 2 { 42 }")?;