Add features info in docs.

src/any.rs

@@ -7,9 +7,15 @@ use crate::stdlib::{
 };
 
 /// An raw value of any type.
+///
+/// Currently, `Variant` is not `Send` nor `Sync`, so it can practically be any type.
+/// Turn on the `sync` feature to restrict it to only types that implement `Send + Sync`.
 pub type Variant = dyn Any;
 
 /// A boxed dynamic type containing any value.
+///
+/// Currently, `Dynamic` is not `Send` nor `Sync`, so it can practically be any type.
+/// Turn on the `sync` feature to restrict it to only types that implement `Send + Sync`.
 pub type Dynamic = Box<Variant>;
 
 /// A trait covering any type.
@@ -48,6 +54,7 @@ impl<T: crate::stdlib::any::Any + Clone + Send + Sync + ?Sized> Any for T {
     }
 }
 
+/// A trait covering any type.
 #[cfg(not(feature = "sync"))]
 pub trait Any: crate::stdlib::any::Any {
     /// Get the `TypeId` of this type.

src/engine.rs

@@ -23,10 +23,14 @@ use crate::stdlib::{
 };
 
 /// An dynamic array of `Dynamic` values.
+///
+/// Not available under the `no_index` feature.
 #[cfg(not(feature = "no_index"))]
 pub type Array = Vec<Dynamic>;
 
-/// An dynamic hash map of `Dynamic` values.
+/// An dynamic hash map of `Dynamic` values with `String` keys.
+///
+/// Not available under the `no_object` feature.
 #[cfg(not(feature = "no_object"))]
 pub type Map = HashMap<String, Dynamic>;
 
@@ -188,6 +192,8 @@ impl FunctionsLib {
 /// # Ok(())
 /// # }
 /// ```
+///
+/// Currently, `Engine` is neither `Send` nor `Sync`. Turn on the `sync` feature to make it `Send + Sync`.
 pub struct Engine<'e> {
     /// A hashmap containing all compiled functions known to the engine.
     pub(crate) functions: HashMap<FnSpec<'e>, Box<FnAny>>,
@@ -302,6 +308,8 @@ impl Engine<'_> {
     }
 
     /// Control whether and how the `Engine` will optimize an AST after compilation
+    ///
+    /// Not available under the `no_optimize` feature.
     #[cfg(not(feature = "no_optimize"))]
     pub fn set_optimization_level(&mut self, optimization_level: OptimizationLevel) {
         self.optimization_level = optimization_level

src/error.rs

@@ -30,9 +30,7 @@ impl fmt::Display for LexError {
             Self::MalformedEscapeSequence(s) => write!(f, "Invalid escape sequence: '{}'", s),
             Self::MalformedNumber(s) => write!(f, "Invalid number: '{}'", s),
             Self::MalformedChar(s) => write!(f, "Invalid character: '{}'", s),
-            Self::MalformedIdentifier(s) => {
+            Self::MalformedIdentifier(s) => write!(f, "Variable name is not proper: '{}'", s),
-                write!(f, "Variable name is not in a legal format: '{}'", s)
-            }
             Self::UnterminatedString => write!(f, "Open string is not terminated"),
         }
     }
@@ -47,37 +45,51 @@ pub enum ParseErrorType {
     UnexpectedEOF,
     /// An unknown operator is encountered. Wrapped value is the operator.
     UnknownOperator(String),
-    /// Expecting a particular token but not finding one. Wrapped values are the token and usage.
+    /// Expecting a particular token but not finding one. Wrapped values are the token and description.
     MissingToken(String, String),
-    /// An expression in function call arguments `()` has syntax error.
+    /// An expression in function call arguments `()` has syntax error. Wrapped value is the error description (if any).
     MalformedCallExpr(String),
-    /// An expression in indexing brackets `[]` has syntax error.
+    /// An expression in indexing brackets `[]` has syntax error. Wrapped value is the error description (if any).
+    ///
+    /// Not available under the `no_index` feature.
     #[cfg(not(feature = "no_index"))]
     MalformedIndexExpr(String),
-    /// A map definition has duplicated property names. Wrapped is the property name.
+    /// A map definition has duplicated property names. Wrapped value is the property name.
+    ///
+    /// Not available under the `no_object` feature.
     #[cfg(not(feature = "no_object"))]
     DuplicatedProperty(String),
-    /// Invalid expression assigned to constant.
+    /// Invalid expression assigned to constant. Wrapped value is the name of the constant.
     ForbiddenConstantExpr(String),
     /// Missing a property name for custom types and maps.
     PropertyExpected,
     /// Missing a variable name after the `let`, `const` or `for` keywords.
     VariableExpected,
-    /// Missing an expression.
+    /// Missing an expression. Wrapped value is the expression type.
     ExprExpected(String),
     /// Defining a function `fn` in an appropriate place (e.g. inside another function).
+    ///
+    /// Not available under the `no_function` feature.
     #[cfg(not(feature = "no_function"))]
     WrongFnDefinition,
     /// Missing a function name after the `fn` keyword.
+    ///
+    /// Not available under the `no_function` feature.
     #[cfg(not(feature = "no_function"))]
     FnMissingName,
     /// A function definition is missing the parameters list. Wrapped value is the function name.
+    ///
+    /// Not available under the `no_function` feature.
     #[cfg(not(feature = "no_function"))]
     FnMissingParams(String),
     /// A function definition has duplicated parameters. Wrapped values are the function name and parameter name.
+    ///
+    /// Not available under the `no_function` feature.
     #[cfg(not(feature = "no_function"))]
     FnDuplicatedParam(String, String),
     /// A function definition is missing the body. Wrapped value is the function name.
+    ///
+    /// Not available under the `no_function` feature.
     #[cfg(not(feature = "no_function"))]
     FnMissingBody(String),
     /// Assignment to an inappropriate LHS (left-hand-side) expression.

src/lib.rs

@@ -36,7 +36,23 @@
 //! }
 //! ```
 //!
-//! [Check out the README on GitHub for more information!](https://github.com/jonathandturner/rhai)
+//! ## Optional features
+//!
+//! | Feature       | Description                                                                                                                                              |
+//! | ------------- | -------------------------------------------------------------------------------------------------------------------------------------------------------- |
+//! | `no_stdlib`   | Exclude the standard library of utility functions in the build, and only include the minimum necessary functionalities. Standard types are not affected. |
+//! | `unchecked`   | Exclude arithmetic checking (such as overflows and division by zero). Beware that a bad script may panic the entire system!                              |
+//! | `no_function` | Disable script-defined functions if not needed.                                                                                                          |
+//! | `no_index`    | Disable arrays and indexing features if not needed.                                                                                                      |
+//! | `no_object`   | Disable support for custom types and objects.                                                                                                            |
+//! | `no_float`    | Disable floating-point numbers and math if not needed.                                                                                                   |
+//! | `no_optimize` | Disable the script optimizer.                                                                                                                            |
+//! | `only_i32`    | Set the system integer type to `i32` and disable all other integer types. `INT` is set to `i32`.                                                         |
+//! | `only_i64`    | Set the system integer type to `i64` and disable all other integer types. `INT` is set to `i64`.                                                         |
+//! | `no_std`      | Build for `no-std`. Notice that additional dependencies will be pulled in to replace `std` features.                                                     |
+//! | `sync`        | Restrict all values types to those that are `Send + Sync`. Under this feature, `Engine`, `Scope` and `AST` are all `Send + Sync`.                        |
+//!
+//! [Check out the README on GitHub for details on the Rhai language!](https://github.com/jonathandturner/rhai)
 
 #![cfg_attr(feature = "no_std", no_std)]
 

src/optimize.rs

@@ -16,6 +16,8 @@ use crate::stdlib::{
 };
 
 /// Level of optimization performed.
+///
+/// Not available under the `no_optimize` feature.
 #[derive(Debug, Eq, PartialEq, Hash, Clone, Copy)]
 pub enum OptimizationLevel {
     /// No optimization performed.

src/parser.rs

@@ -37,6 +37,8 @@ pub type INT = i64;
 pub type INT = i32;
 
 /// The system floating-point type.
+///
+/// Not available under the `no_float` feature.
 #[cfg(not(feature = "no_float"))]
 pub type FLOAT = f64;
 
@@ -160,6 +162,8 @@ impl fmt::Debug for Position {
 }
 
 /// Compiled AST (abstract syntax tree) of a Rhai script.
+///
+/// Currently, `AST` is neither `Send` nor `Sync`. Turn on the `sync` feature to make it `Send + Sync`.
 #[derive(Debug, Clone)]
 pub struct AST(pub(crate) Vec<Stmt>, pub(crate) Vec<Arc<FnDef>>);
 

src/result.rs

@@ -22,6 +22,8 @@ pub enum EvalAltResult {
     ErrorParsing(ParseError),
 
     /// Error reading from a script file. Wrapped value is the path of the script file.
+    ///
+    /// Not available under the `no_std` feature.
     #[cfg(not(feature = "no_std"))]
     ErrorReadingScriptFile(PathBuf, std::io::Error),
 

src/scope.rs

@@ -61,6 +61,8 @@ pub(crate) struct EntryRef<'a> {
 ///
 /// When searching for entries, newly-added entries are found before similarly-named but older entries,
 /// allowing for automatic _shadowing_.
+///
+/// Currently, `Scope` is neither `Send` nor `Sync`. Turn on the `sync` feature to make it `Send + Sync`.
 pub struct Scope<'a>(Vec<Entry<'a>>);
 
 impl<'a> Scope<'a> {