Fix no_std builds.

CHANGELOG.md

@@ -31,6 +31,7 @@ New features
 ------------
 
 * Added support for integer _ranges_ via the `..` and `..=` operators.
+* Added `EvalAltResult::ErrorCustomSyntax` to catch errors in custom syntax, which should not happen unless an `AST` is compiled on one `Engine` but evaluated on another unrelated `Engine`.
 
 Enhancements
 ------------

src/eval/expr.rs

@@ -416,14 +416,16 @@ impl Engine {
                 .into())
             }
 
-            Expr::Custom(custom, _) => {
+            Expr::Custom(custom, pos) => {
                 let expressions: StaticVec<_> = custom.inputs.iter().map(Into::into).collect();
+                // The first token acts as the custom syntax's key
                 let key_token = custom.tokens.first().unwrap();
+                // The key should exist, unless the AST is compiled in a different Engine
                 let custom_def = self.custom_syntax.get(key_token).ok_or_else(|| {
-                    let code: Vec<_> = custom.tokens.iter().map(|s| s.as_str()).collect();
+                    Box::new(ERR::ErrorCustomSyntax(
-                    Box::new(ERR::ErrorSystem(
                         format!("Invalid custom syntax prefix: {}", key_token),
-                        code.join(" ").into(),
+                        custom.tokens.iter().map(|s| s.to_string()).collect(),
+                        *pos,
                     ))
                 })?;
                 let mut context = EvalContext {

src/types/error.rs

@@ -71,6 +71,7 @@ pub enum EvalAltResult {
     ErrorDotExpr(String, Position),
     /// Arithmetic error encountered. Wrapped value is the error message.
     ErrorArithmetic(String, Position),
+
     /// Number of operations over maximum limit.
     ErrorTooManyOperations(Position),
     /// [Modules][crate::Module] over maximum limit.
@@ -81,6 +82,14 @@ pub enum EvalAltResult {
     ErrorDataTooLarge(String, Position),
     /// The script is prematurely terminated. Wrapped value is the termination token.
     ErrorTerminated(Dynamic, Position),
+
+    /// Error encountered for a custom syntax. Wrapped values are the error message and
+    /// custom syntax symbols stream.
+    ///
+    /// Normally this should never happen, unless an [`AST`][crate::AST] is compiled on one
+    /// [`Engine`][crate::Engine] but evaluated on another unrelated [`Engine`][crate::Engine].
+    ErrorCustomSyntax(String, Vec<String>, Position),
+
     /// Run-time error encountered. Wrapped value is the error token.
     ErrorRuntime(Dynamic, Position),
 
@@ -204,6 +213,8 @@ impl fmt::Display for EvalAltResult {
                 index, max
             )?,
             Self::ErrorDataTooLarge(typ, _) => write!(f, "{} exceeds maximum limit", typ)?,
+
+            Self::ErrorCustomSyntax(s, tokens, _) => write!(f, "{}: {}", s, tokens.join(" "))?,
         }
 
         // Do not write any position if None
@@ -266,7 +277,8 @@ impl EvalAltResult {
             | Self::ErrorArithmetic(_, _)
             | Self::ErrorRuntime(_, _) => true,
 
-            Self::ErrorTooManyOperations(_)
+            Self::ErrorCustomSyntax(_, _, _)
+            | Self::ErrorTooManyOperations(_)
             | Self::ErrorTooManyModules(_)
             | Self::ErrorStackOverflow(_)
             | Self::ErrorDataTooLarge(_, _)
@@ -282,7 +294,8 @@ impl EvalAltResult {
             Self::ErrorSystem(_, _) => true,
             Self::ErrorParsing(_, _) => true,
 
-            Self::ErrorTooManyOperations(_)
+            Self::ErrorCustomSyntax(_, _, _)
+            | Self::ErrorTooManyOperations(_)
             | Self::ErrorTooManyModules(_)
             | Self::ErrorStackOverflow(_)
             | Self::ErrorDataTooLarge(_, _) => true,
@@ -295,6 +308,8 @@ impl EvalAltResult {
     /// Get the [position][Position] of this error.
     #[cfg(not(feature = "no_object"))]
     pub(crate) fn dump_fields(&self, map: &mut crate::Map) {
+        use std::str::FromStr;
+
         map.insert(
             "error".into(),
             format!("{:?}", self)
@@ -358,6 +373,17 @@ impl EvalAltResult {
             Self::ErrorTerminated(t, _) => {
                 map.insert("token".into(), t.clone());
             }
+            Self::ErrorCustomSyntax(_, tokens, _) => {
+                map.insert(
+                    "tokens".into(),
+                    Dynamic::from_array(
+                        tokens
+                            .iter()
+                            .map(|s| Dynamic::from_str(s).unwrap())
+                            .collect(),
+                    ),
+                );
+            }
         };
     }
     /// Get the [position][Position] of this error.
@@ -389,6 +415,7 @@ impl EvalAltResult {
             | Self::ErrorStackOverflow(pos)
             | Self::ErrorDataTooLarge(_, pos)
             | Self::ErrorTerminated(_, pos)
+            | Self::ErrorCustomSyntax(_, _, pos)
             | Self::ErrorRuntime(_, pos)
             | Self::LoopBreak(_, pos)
             | Self::Return(_, pos) => *pos,
@@ -436,6 +463,7 @@ impl EvalAltResult {
             | Self::ErrorStackOverflow(pos)
             | Self::ErrorDataTooLarge(_, pos)
             | Self::ErrorTerminated(_, pos)
+            | Self::ErrorCustomSyntax(_, _, pos)
             | Self::ErrorRuntime(_, pos)
             | Self::LoopBreak(_, pos)
             | Self::Return(_, pos) => *pos = new_position,