Add no_custom_syntax.

src/api/custom_syntax.rs

@@ -1,4 +1,5 @@
 //! Module implementing custom syntax for [`Engine`].
+#![cfg(not(feature = "no_custom_syntax"))]
 
 use crate::ast::Expr;
 use crate::func::SendSync;
@@ -153,6 +154,8 @@ pub struct CustomSyntax {
 impl Engine {
     /// Register a custom syntax with the [`Engine`].
     ///
+    /// Not available under `no_custom_syntax`.
+    ///
     /// * `symbols` holds a slice of strings that define the custom syntax.  
     /// * `scope_may_be_changed` specifies variables _may_ be added/removed by this custom syntax.
     /// * `func` is the implementation function.
@@ -296,6 +299,8 @@ impl Engine {
     }
     /// Register a custom syntax with the [`Engine`].
     ///
+    /// Not available under `no_custom_syntax`.
+    ///
     /// # WARNING - Low Level API
     ///
     /// This function is very low level.

src/api/deprecated.rs

@@ -1,8 +1,8 @@
 //! Module containing all deprecated API that will be removed in the next major version.
 
 use crate::{
-    Dynamic, Engine, EvalAltResult, Expression, FnPtr, ImmutableString, NativeCallContext,
-    Position, RhaiResult, RhaiResultOf, Scope, AST,
+    Dynamic, Engine, EvalAltResult, FnPtr, ImmutableString, NativeCallContext, Position,
+    RhaiResult, RhaiResultOf, Scope, AST,
 };
 #[cfg(feature = "no_std")]
 use std::prelude::v1::*;
@@ -312,7 +312,8 @@ impl FnPtr {
     }
 }
 
-impl Expression<'_> {
+#[cfg(not(feature = "no_custom_syntax"))]
+impl crate::Expression<'_> {
     /// If this expression is a variable name, return it.  Otherwise [`None`].
     ///
     /// # Deprecated

src/api/mod.rs

@@ -28,10 +28,11 @@ pub mod custom_syntax;
 
 pub mod deprecated;
 
-use crate::engine::Precedence;
-use crate::tokenizer::Token;
 use crate::{Dynamic, Engine, Identifier};
 
+#[cfg(not(feature = "no_custom_syntax"))]
+use crate::{engine::Precedence, tokenizer::Token};
+
 #[cfg(feature = "no_std")]
 use std::prelude::v1::*;
 
@@ -121,6 +122,8 @@ impl Engine {
 
     /// Register a custom operator with a precedence into the language.
     ///
+    /// Not available under `no_custom_syntax`.
+    ///
     /// The operator can be a valid identifier, a reserved symbol, a disabled operator or a disabled keyword.
     ///
     /// The precedence cannot be zero.
@@ -147,6 +150,7 @@ impl Engine {
     /// # Ok(())
     /// # }
     /// ```
+    #[cfg(not(feature = "no_custom_syntax"))]
     pub fn register_custom_operator(
         &mut self,
         keyword: impl AsRef<str>,
@@ -161,8 +165,11 @@ impl Engine {
         let keyword = keyword.as_ref();
 
         match Token::lookup_from_syntax(keyword) {
-            // Standard identifiers, reserved keywords and custom keywords are OK
-            None | Some(Token::Reserved(..)) | Some(Token::Custom(..)) => (),
+            // Standard identifiers and reserved keywords are OK
+            None | Some(Token::Reserved(..)) => (),
+            // custom keywords are OK
+            #[cfg(not(feature = "no_custom_syntax"))]
+            Some(Token::Custom(..)) => (),
             // Active standard keywords cannot be made custom
             // Disabled keywords are OK
             Some(token) if token.is_standard_keyword() => {