Fix Java comparator symmetry. #114

Java sort enforces compare symmetry:
sgn(compare(x, y)) == -sgn(compare(y, x))

This is not mandatory for the Jsonata comparator, and produces the error ("violates general contract") if it doesn't.

This change ensures Java compare symmetry. Runtime complexity remains O(2) == O(1).

Fixes original unit tests (2 test overrides removed) and the sorting test data provided.

Author: uw4

src/main/java/com/dashjoin/jsonata/Functions.java

@@ -1959,15 +1959,17 @@ public static List sort(List arr, Object comparator) {
                 public int compare(Object o1, Object o2) {
                     try {
                         Boolean swap = toBoolean(funcApply(comparator, Arrays.asList(o1, o2)));
+                        // Symmetry/equality: if Jsonata comp(o1,o2)==comp(o2,o1) means Java o1==o2 (return 0)
+                        Boolean swapSym = toBoolean(funcApply(comparator, Arrays.asList(o2, o1)));
+                        if (swap != null && swap.equals(swapSym))
+                          return 0;
                         if (swap == null)
                           return 0;
                         if (swap)
                           return 1;
                         else
                           return -1;
                     } catch (Throwable e) {
-                        // TODO Auto-generated catch block
-                        //e.printStackTrace();
                         throw new RuntimeException(e);
                     }
                 }

test/test-overrides.json

@@ -130,16 +130,6 @@
             "alternateResult": "1e+20",
             "reason": "toString precision should be 15, handled differently by Java Bigdecimal(..., new MathContext(15)"
         },
-        { 
-            "name": "function-sort/case009.json",
-            "alternateResult": ["0406634348", "040657863", "0406654608", "0406654603"],
-            "reason": "the sort expression is evaluated correctly - however the sort algorithm seems to behave slightly different for equality - jsonata expects the native order to be preserved"
-        },
-        { 
-            "name": "function-sort/case010.json",
-            "alternateResult": ["0406634348", "0406654608", "040657863", "0406654603"],
-            "reason": "same as above, works if the condition is changed to >="
-        },
         { 
             "name": "function-applications/case008.json",
             "ignoreError": true,