Handle #{ in Engine::parse_json, restrict to object hashes only.

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

@@ -3,11 +3,14 @@ Parse an Object Map from JSON
 
 {{#include ../links.md}}
 
-The syntax for an [object map] is extremely similar to JSON, with the exception of `null` values which can
+The syntax for an [object map] is extremely similar to the JSON representation of a object hash,
-technically be mapped to [`()`].  A valid JSON string does not start with a hash character `#` while a
+with the exception of `null` values which can technically be mapped to [`()`].
-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:
+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.
+The JSON text must represent a single object hash (i.e. must be wrapped within "`{ .. }`")
+otherwise it returns a syntax error.
 
 ```rust
 // JSON string - notice that JSON property names are always quoted
@@ -45,3 +48,30 @@ 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 "`#{`".
+
+A JSON object hash starting with `#{` is handled transparently by `Engine::parse_json`.
+
+```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

@@ -2,7 +2,7 @@
 
 use crate::any::{Dynamic, Variant};
 use crate::engine::{Engine, Imports, State};
-use crate::error::ParseError;
+use crate::error::{ParseError, ParseErrorType};
 use crate::fn_native::{IteratorFn, SendSync};
 use crate::module::{FuncReturn, Module};
 use crate::optimize::OptimizationLevel;
@@ -895,24 +895,39 @@ impl Engine {
 
     /// Parse a JSON string into a map.
     ///
+    /// The JSON string must be an object hash.  It cannot be a simple JavaScript primitive.
+    ///
     /// 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["a"].as_int().unwrap(), 123);
-    /// assert_eq!(map.get("b").cloned().unwrap().cast::<i64>(), 42);
+    /// assert_eq!(map["b"].as_int().unwrap(), 42);
-    /// assert_eq!(map.get("c").cloned().unwrap().cast::<bool>(), false);
+    /// assert!(map["d"].is::<()>());
-    /// assert_eq!(map.get("d").cloned().unwrap().cast::<()>(), ());
+    ///
+    /// let c = map["c"].read_lock::<Map>().unwrap();
+    /// assert_eq!(c["x"].as_bool().unwrap(), false);
     /// # Ok(())
     /// # }
     /// ```
@@ -921,7 +936,20 @@ impl Engine {
         let mut scope = Scope::new();
 
         // Trims the JSON string and add a '#' in front
-        let scripts = ["#", json.trim()];
+        let json_text = json.trim_start();
+        let scripts = if json_text.starts_with(Token::MapStart.syntax().as_ref()) {
+            [json_text, ""]
+        } else if json_text.starts_with(Token::LeftBrace.syntax().as_ref()) {
+            ["#", json_text]
+        } else {
+            return Err(ParseErrorType::MissingToken(
+                Token::LeftBrace.syntax().to_string(),
+                "to start a JSON object hash".to_string(),
+            )
+            .into_err(Position::new(1, (json.len() - json_text.len() + 1) as u16))
+            .into());
+        };
+
         let stream = lex(
             &scripts,
             if has_null {

tests/maps.rs

@@ -1,6 +1,6 @@
 #![cfg(not(feature = "no_object"))]
 
-use rhai::{Engine, EvalAltResult, Map, Scope, INT};
+use rhai::{Engine, EvalAltResult, Map, ParseErrorType, Scope, INT};
 
 #[test]
 fn test_map_indexing() -> Result<(), Box<EvalAltResult>> {
@@ -182,6 +182,14 @@ fn test_map_json() -> Result<(), Box<EvalAltResult>> {
         );
     }
 
+    engine.parse_json(&format!("#{}", json), true)?;
+
+    assert!(matches!(
+        *engine.parse_json("   123", true).expect_err("should error"),
+        EvalAltResult::ErrorParsing(ParseErrorType::MissingToken(token, _), pos)
+            if token == "{" && pos.position() == Some(4)
+    ));
+
     Ok(())
 }