fix: std.format %f uses round-half-away-from-zero instead of HALF_EVEN

sjsonnet/src/sjsonnet/DecimalFormat.scala

@@ -64,22 +64,23 @@ object DecimalFormat {
       case None =>
         val precision = zeroes + hashes
         if (precision == 0) {
-          // No fractional digits needed - just round and format the integer part
-          val rounded = math.rint(number)
+          // Round half away from zero (matching go-jsonnet/jrsonnet behavior)
+          val rounded = if (number >= 0) math.floor(number + 0.5) else math.ceil(number - 0.5)
           val prefix =
             if (rounded.isInfinite || math.abs(rounded) > Long.MaxValue)
               BigDecimal(rounded).toBigInt.toString
             else rounded.toLong.toString
           if (alternate) prefix + "." else prefix
         } else {
           val denominator = BigDecimal(10).pow(precision)
-          val bd = BigDecimal(number)
+          val bd = BigDecimal(number).abs
           val scaled =
             (bd * denominator + BigDecimal("0.5")).setScale(0, BigDecimal.RoundingMode.FLOOR)
           val wholeBD = (scaled / denominator).setScale(0, BigDecimal.RoundingMode.FLOOR)
           val fracBD = (scaled - wholeBD * denominator).abs
 
-          val prefix = wholeBD.toBigInt.toString
+          val sign = if (number < 0) "-" else ""
+          val prefix = sign + wholeBD.toBigInt.toString
           val fracStr = fracBD.toBigInt.toString
 
           val frac =

sjsonnet/test/resources/new_test_suite/format_rounding_half_away_from_zero.jsonnet

@@ -0,0 +1,23 @@
+// Verify std.format uses round-half-away-from-zero (matching go-jsonnet/jrsonnet).
+// Previously used HALF_EVEN (banker's rounding) which gave wrong results for .5 values.
+
+std.assertEqual(std.format("%.0f", [0.5]), "1") &&
+std.assertEqual(std.format("%.0f", [1.5]), "2") &&
+std.assertEqual(std.format("%.0f", [2.5]), "3") &&
+std.assertEqual(std.format("%.0f", [3.5]), "4") &&
+std.assertEqual(std.format("%.0f", [4.5]), "5") &&
+std.assertEqual(std.format("%.0f", [-0.5]), "-1") &&
+std.assertEqual(std.format("%.0f", [-1.5]), "-2") &&
+std.assertEqual(std.format("%.0f", [-2.5]), "-3") &&
+// Higher precision
+std.assertEqual(std.format("%.1f", [0.25]), "0.3") &&
+std.assertEqual(std.format("%.1f", [0.35]), "0.4") &&
+std.assertEqual(std.format("%.1f", [-0.25]), "-0.3") &&
+std.assertEqual(std.format("%.2f", [0.005]), "0.01") &&
+std.assertEqual(std.format("%.2f", [0.015]), "0.02") &&
+std.assertEqual(std.format("%.2f", [-0.005]), "-0.01") &&
+// Carry case: rounding causes integer part to increment
+std.assertEqual(std.format("%.2f", [9.999]), "10.00") &&
+// Negative rounding to zero
+std.assertEqual(std.format("%.2f", [-0.001]), "-0.00") &&
+true

sjsonnet/test/resources/new_test_suite/format_rounding_half_away_from_zero.jsonnet.golden

@@ -0,0 +1 @@
+true