Treat leading #{ in Engine::parse_json.

RELEASES.md

@@ -9,6 +9,7 @@ New features
 
 * Adds `Engine::register_get_result`, `Engine::register_set_result`, `Engine::register_indexer_get_result`, `Engine::register_indexer_set_result` API.
 * Adds `Module::combine` to combine two modules.
+* `Engine::parse_json` now also accepts a JSON object starting with `#{`.
 
 
 Version 0.18.1

doc/src/language/json.md

@@ -7,7 +7,7 @@ The syntax for an [object map] is extremely similar to JSON, with the exception
 technically be mapped to [`()`].  A valid JSON string does not start with a hash character `#` while a
 Rhai [object map] does - that's the major difference!
 
-Use the `Engine::parse_json` method to parse a piece of JSON into an object map:
+Use the `Engine::parse_json` method to parse a piece of _simple_ JSON into an object map:
 
 ```rust
 // JSON string - notice that JSON property names are always quoted
@@ -26,7 +26,7 @@ let json = r#"{
 // Set the second boolean parameter to true in order to map 'null' to '()'
 let map = engine.parse_json(json, true)?;
 
-map.len() == 6;                         // 'map' contains all properties in the JSON string
+map.len() == 6;       // 'map' contains all properties in the JSON string
 
 // Put the object map into a 'Scope'
 let mut scope = Scope::new();
@@ -34,7 +34,7 @@ scope.push("map", map);
 
 let result = engine.eval_with_scope::<INT>(r#"map["^^^!!!"].len()"#)?;
 
-result == 3;                            // the object map is successfully used in the script
+result == 3;          // the object map is successfully used in the script
 ```
 
 Representation of Numbers
@@ -45,3 +45,28 @@ the [`no_float`] feature is not used.  Most common generators of JSON data disti
 integer and floating-point values by always serializing a floating-point number with a decimal point
 (i.e. `123.0` instead of `123` which is assumed to be an integer).  This style can be used successfully
 with Rhai [object maps].
+
+
+Parse JSON with Sub-Objects
+--------------------------
+
+`Engine::parse_json` depends on the fact that the [object map] literal syntax in Rhai is _almost_
+the same as a JSON object.  However, it is _almost_ because the syntax for a sub-object in JSON
+(i.e. "`{ ... }`") is different from a Rhai [object map] literal (i.e. "`#{ ... }`").
+
+When `Engine::parse_json` encounters JSON with sub-objects, it fails with a syntax error.
+
+If it is certain that no text string in the JSON will ever contain the character '`{`',
+then it is possible to parse it by first replacing all occupance of '`{`' with "`#{`".
+
+```rust
+// JSON with sub-object 'b'.
+let json = r#"{"a":1, "b":{"x":true, "y":false}}"#;
+
+let new_json = json.replace("{" "#{");
+
+// The leading '{' will also be replaced to '#{', but parse_json can handle this.
+let map = engine.parse_json(&new_json, false)?;
+
+map.len() == 2;       // 'map' contains two properties: 'a' and 'b'
+```

src/api.rs

@@ -898,21 +898,34 @@ impl Engine {
     /// Set `has_null` to `true` in order to map `null` values to `()`.
     /// Setting it to `false` will cause a _variable not found_ error during parsing.
     ///
+    /// # JSON With Sub-Objects
+    ///
+    /// This method assumes no sub-objects in the JSON string.  That is because the syntax
+    /// of a JSON sub-object (or object hash), `{ .. }`, is different from Rhai's syntax, `#{ .. }`.
+    /// Parsing a JSON string with sub-objects will cause a syntax error.
+    ///
+    /// If it is certain that the character `{` never appears in any text string within the JSON object,
+    /// then globally replace `{` with `#{` before calling this method.
+    ///
     /// # Example
     ///
     /// ```
     /// # fn main() -> Result<(), Box<rhai::EvalAltResult>> {
-    /// use rhai::Engine;
+    /// use rhai::{Engine, Map};
     ///
     /// let engine = Engine::new();
     ///
-    /// let map = engine.parse_json(r#"{"a":123, "b":42, "c":false, "d":null}"#, true)?;
+    /// let map = engine.parse_json(
+    ///     r#"{"a":123, "b":42, "c":{"x":false, "y":true}, "d":null}"#
+    ///         .replace("{", "#{").as_str(), true)?;
     ///
     /// assert_eq!(map.len(), 4);
-    /// assert_eq!(map.get("a").cloned().unwrap().cast::<i64>(), 123);
-    /// assert_eq!(map.get("b").cloned().unwrap().cast::<i64>(), 42);
-    /// assert_eq!(map.get("c").cloned().unwrap().cast::<bool>(), false);
-    /// assert_eq!(map.get("d").cloned().unwrap().cast::<()>(), ());
+    /// assert_eq!(map["a"].as_int().unwrap(), 123);
+    /// assert_eq!(map["b"].as_int().unwrap(), 42);
+    /// assert!(map["d"].is::<()>());
+    ///
+    /// let c = map["c"].read_lock::<Map>().unwrap();
+    /// assert_eq!(c["x"].as_bool().unwrap(), false);
     /// # Ok(())
     /// # }
     /// ```
@@ -921,7 +934,12 @@ impl Engine {
         let mut scope = Scope::new();
 
         // Trims the JSON string and add a '#' in front
-        let scripts = ["#", json.trim()];
+        let json = json.trim();
+        let scripts = if json.starts_with(Token::MapStart.syntax().as_ref()) {
+            [json, ""]
+        } else {
+            ["#", json]
+        };
         let stream = lex(
             &scripts,
             if has_null {