feat(productions/default): support {} as a default value

lib/productions/default.js

@@ -10,11 +10,14 @@ export class Default extends Base {
     if (!assign) {
       return null;
     }
-    const def = const_value(tokeniser) || tokeniser.consume("string", "null", "[") || tokeniser.error("No value for default");
+    const def = const_value(tokeniser) || tokeniser.consume("string", "null", "[", "{") || tokeniser.error("No value for default");
     const expression = [def];
     if (def.type === "[") {
       const close = tokeniser.consume("]") || tokeniser.error("Default sequence value must be empty");
       expression.push(close);
+    } else if (def.type === "{") {
+      const close = tokeniser.consume("}") || tokeniser.error("Default dictionary value must be empty");
+      expression.push(close);
     }
     return new Default({ source: tokeniser.source, tokens: { assign }, expression });
   }

lib/productions/helpers.js

@@ -57,6 +57,8 @@ export function const_data({ type, value }) {
       return { type: "Infinity", negative: type.startsWith("-") };
     case "[":
       return { type: "sequence", value: [] };
+    case "{":
+      return { type: "dictionary" };
     case "decimal":
     case "integer":
         return { type: "number", value };

test/syntax/baseline/dictionary.json

@@ -95,6 +95,23 @@
                 },
                 "default": null,
                 "required": true
+            },
+            {
+                "type": "field",
+                "name": "dict",
+                "extAttrs": [],
+                "idlType": {
+                    "type": "dictionary-type",
+                    "extAttrs": [],
+                    "generic": "",
+                    "nullable": false,
+                    "union": false,
+                    "idlType": "Dictionary"
+                },
+                "default": {
+                    "type": "dictionary"
+                },
+                "required": false
             }
         ],
         "extAttrs": [],

test/syntax/idl/dictionary.widl

@@ -7,6 +7,7 @@ dictionary PaintOptions {
   sequence<long> seq = [];
   // https://heycam.github.io/webidl/#required-dictionary-member
   required long reqSeq;
+  Dictionary dict = {};
 };
 
 partial dictionary _A {