feat(@angular-devkit/core): allow trailing commas in loose JSON

Author: thorn0

packages/angular_devkit/core/src/json/parser.ts

@@ -378,7 +378,11 @@ function _readArray(context: JsonParserContext, comments = _readBlanks(context))
   while (_peek(context) != ']') {
     _token(context, ',');
 
-    const node = _readValue(context);
+    const valueComments = _readBlanks(context);
+    if ((context.mode & JsonParseMode.TrailingCommasAllowed) !== 0 && _peek(context) === ']') {
+      break;
+    }
+    const node = _readValue(context, valueComments);
     elements.push(node);
     value.push(node.value);
   }
@@ -505,7 +509,11 @@ function _readObject(context: JsonParserContext,
     while (_peek(context) != '}') {
       _token(context, ',');
 
-      const property = _readProperty(context);
+      const propertyComments = _readBlanks(context);
+      if ((context.mode & JsonParseMode.TrailingCommasAllowed) !== 0 && _peek(context) === '}') {
+        break;
+      }
+      const property = _readProperty(context, propertyComments);
       value[property.key.value] = property.value.value;
       properties.push(property);
     }
@@ -607,11 +615,10 @@ function _readBlanks(context: JsonParserContext): (JsonAstComment | JsonAstMulti
  * Read a JSON value from the context, which can be any form of JSON value.
  * @private
  */
-function _readValue(context: JsonParserContext): JsonAstNode {
+function _readValue(context: JsonParserContext, comments = _readBlanks(context)): JsonAstNode {
   let result: JsonAstNode;
 
   // Clean up before.
-  const comments = _readBlanks(context);
   const char = _peek(context);
   switch (char) {
     case undefined:
@@ -673,9 +680,11 @@ export enum JsonParseMode {
   CommentsAllowed           = 1 << 0,  // Allows comments, both single or multi lines.
   SingleQuotesAllowed       = 1 << 1,  // Allow single quoted strings.
   IdentifierKeyNamesAllowed = 1 << 2,  // Allow identifiers as objectp properties.
+  TrailingCommasAllowed     = 1 << 3,
 
   Default                   = Strict,
-  Loose                     = CommentsAllowed | SingleQuotesAllowed | IdentifierKeyNamesAllowed,
+  Loose                     = CommentsAllowed | SingleQuotesAllowed |
+                              IdentifierKeyNamesAllowed | TrailingCommasAllowed,
 }
 
 

packages/angular_devkit/core/src/json/parser_spec.ts

@@ -240,6 +240,13 @@ describe('parseJson and parseJsonAst', () => {
       '{\n/* hello\n*/ }': [[0, 0, 0], [15, 2, 4], {}],
       '{}//  ': [[0, 0, 0], [2, 0, 2], {}, '{}'],
       '{}//': [[0, 0, 0], [2, 0, 2], {}, '{}'],
+      '{hello:0,}': [[0, 0, 0], [10, 0, 10], {hello: 0}],
+      '{hello:0/**/,}': [[0, 0, 0], [14, 0, 14], {hello: 0}],
+      '{hello:0,/**/}': [[0, 0, 0], [14, 0, 14], {hello: 0}],
+      '{hi:["hello",]}': [[0, 0, 0], [15, 0, 15], {hi: ['hello']}],
+      '{hi:["hello",/* */]}': [[0, 0, 0], [20, 0, 20], {hi: ['hello']}],
+      '{hi:["hello"/* */,]}': [[0, 0, 0], [20, 0, 20], {hi: ['hello']}],
+      '{hi:["hello" , ] , }': [[0, 0, 0], [20, 0, 20], {hi: ['hello']}],
     };
     const errors = [
       '{1b: 0}',