feat(parser): implement object spread syntax support

Add JSObjectSpread constructor to JSObjectProperty type and implement
grammar rules to parse spread expressions in object literals.

- Add JSObjectSpread constructor with annotation and expression fields
- Update ShowStripped instance for JSObjectProperty to handle spreads
- Add SpreadExpression support to PropertyAssignment grammar rule
- Add spreadExpressionToProperty helper function for AST conversion

Enables parsing of object spread syntax like {...obj} according to
ECMAScript specification for object literal spread expressions.

Resolves: Object spread syntax parsing for PR #118

Author: quintenkasteel

src/Language/JavaScript/Parser/AST.hs

@@ -308,6 +308,7 @@ data JSObjectProperty
     = JSPropertyNameandValue !JSPropertyName !JSAnnot ![JSExpression] -- ^name, colon, value
     | JSPropertyIdentRef !JSAnnot !String
     | JSObjectMethod !JSMethodDefinition
+    | JSObjectSpread !JSAnnot !JSExpression -- ^..., expression
     deriving (Data, Eq, Show, Typeable)
 
 data JSMethodDefinition
@@ -531,6 +532,7 @@ instance ShowStripped JSObjectProperty where
     ss (JSPropertyNameandValue x1 _colon x2s) = "JSPropertyNameandValue (" ++ ss x1 ++ ") " ++ ss x2s
     ss (JSPropertyIdentRef _ s) = "JSPropertyIdentRef " ++ singleQuote s
     ss (JSObjectMethod m) = ss m
+    ss (JSObjectSpread _ expr) = "JSObjectSpread (" ++ ss expr ++ ")"
 
 instance ShowStripped JSMethodDefinition where
     ss (JSMethodDefinition x1 _lb1 x2s _rb1 x3) = "JSMethodDefinition (" ++ ss x1 ++ ") " ++ ss x2s ++ " (" ++ ss x3 ++ ")"

src/Language/JavaScript/Parser/Grammar7.y

@@ -622,6 +622,7 @@ PropertyAssignment :: { AST.JSObjectProperty }
 PropertyAssignment : PropertyName Colon AssignmentExpression { AST.JSPropertyNameandValue $1 $2 [$3] }
                    | IdentifierName { identifierToProperty $1 }
                    | MethodDefinition { AST.JSObjectMethod $1 }
+                   | SpreadExpression { spreadExpressionToProperty $1 }
 
 -- TODO: not clear if get/set are keywords, or just used in a specific context. Puzzling.
 MethodDefinition :: { AST.JSMethodDefinition }
@@ -1610,6 +1611,10 @@ identifierToProperty :: AST.JSExpression -> AST.JSObjectProperty
 identifierToProperty (AST.JSIdentifier a s) = AST.JSPropertyIdentRef a s
 identifierToProperty x = error $ "Cannot convert '" ++ show x ++ "' to a JSObjectProperty."
 
+spreadExpressionToProperty :: AST.JSExpression -> AST.JSObjectProperty
+spreadExpressionToProperty (AST.JSSpreadExpression a expr) = AST.JSObjectSpread a expr
+spreadExpressionToProperty x = error $ "Cannot convert '" ++ show x ++ "' to a JSObjectSpread."
+
 toArrowParameterList :: AST.JSExpression -> Token -> Alex AST.JSArrowParameterList
 toArrowParameterList (AST.JSIdentifier a s)          = const . return $ AST.JSUnparenthesizedArrowParameter (AST.JSIdentName a s)
 toArrowParameterList (AST.JSExpressionParen lb x rb) = const . return $ AST.JSParenthesizedArrowParameterList lb (commasToCommaList x) rb