JS: Tolerate trailing comma in JSON array

Previously we'd fail to extract some tsconfig.json files because of this.

Author: asgerf

javascript/extractor/src/com/semmle/js/parser/JSONParser.java

@@ -205,9 +205,6 @@ private JSONArray readArray(int startoff, Position start) throws ParseError {
         char c = peek();
         switch (c) {
           case ']':
-            if (!needsComma) {
-              raise("Omitted elements are not allowed in JSON.");
-            }
             next();
             break out;
           case ',':

javascript/extractor/tests/json/output/trap/array-trailing-comma.json.trap

@@ -7,9 +7,27 @@ containerparent(#10001,#10000)
 locations_default(#10002,#10000,0,0,0,0)
 hasLocation(#10000,#10002)
 #20000=*
-json_errors(#20000,"Error: Omitted elements are not allowed in JSON.")
-#20001=@"loc,{#10000},5,4,5,4"
-locations_default(#20001,#10000,5,4,5,4)
-hasLocation(#20000,#20001)
+json(#20000,5,#10000,0,"{\n    "" ...     ]\n}")
+#20001=@"loc,{#10000},1,1,6,1"
+locations_default(#20001,#10000,1,1,6,1)
+json_locations(#20000,#20001)
+#20002=*
+json(#20002,4,#20000,0,"[\n      ... ,\n    ]")
+#20003=@"loc,{#10000},2,14,5,5"
+locations_default(#20003,#10000,2,14,5,5)
+json_locations(#20002,#20003)
+#20004=*
+json(#20004,3,#20002,0,"""foo""")
+#20005=@"loc,{#10000},3,9,3,13"
+locations_default(#20005,#10000,3,9,3,13)
+json_locations(#20004,#20005)
+json_literals("foo","""foo""",#20004)
+#20006=*
+json(#20006,3,#20002,1,"""bar""")
+#20007=@"loc,{#10000},4,9,4,13"
+locations_default(#20007,#10000,4,9,4,13)
+json_locations(#20006,#20007)
+json_literals("bar","""bar""",#20006)
+json_properties(#20000,"array",#20002)
 numlines(#10000,6,0,0)
 filetype(#10000,"json")