Fix computation of hash codes for Listing, Duration, DataSize (#1922)

These are currently breaking the principle of: if two objects are
`equals`, then they have the same hash code.

pkl-core/src/main/java/org/pkl/core/runtime/VmDataSize.java

@@ -152,7 +152,8 @@ public final class VmDataSize extends VmValue implements Comparable<VmDataSize>
 
   @Override
   public int hashCode() {
-    return Double.hashCode(convertValueTo(DataSizeUnit.BYTES));
+    // adding 0.0 normalizes -0.0 to 0.0, because -0.0 == 0.0 but their hash codes differ
+    return Double.hashCode(convertValueTo(DataSizeUnit.BYTES) + 0.0);
   }
 
   @Override

pkl-core/src/main/java/org/pkl/core/runtime/VmDuration.java

@@ -149,7 +149,8 @@ public final class VmDuration extends VmValue implements Comparable<VmDuration>
 
   @Override
   public int hashCode() {
-    return Double.hashCode(getValue(DurationUnit.NANOS));
+    // adding 0.0 normalizes -0.0 to 0.0, because -0.0 == 0.0 but their hash codes differ
+    return Double.hashCode(getValue(DurationUnit.NANOS) + 0.0);
   }
 
   @Override

pkl-core/src/main/java/org/pkl/core/runtime/VmListing.java

@@ -212,18 +212,10 @@ public final class VmListing extends VmListingOrMapping {
 
     force(false);
     var result = 0;
-    var cursor = cachedValues.getEntries();
-
-    while (cursor.advance()) {
-      var key = cursor.getKey();
-      if (key instanceof Identifier) continue;
-
-      var value = cursor.getValue();
-      //noinspection ConstantValue
-      assert value != null;
+    for (var cursor = elements(); cursor.advance(); ) {
+      var value = cursor.cachedValue();
       result = 31 * result + value.hashCode();
     }
-
     cachedHash = result;
     return result;
   }

pkl-core/src/test/files/LanguageSnippetTests/input/basic/set2.pkl

@@ -0,0 +1,38 @@
+local l1: Listing = new {
+  new { x = 1 }
+  new { x = 2 }
+}
+
+local l2: Listing = new {
+  new { x = 1 }
+  new { x = 2 }
+}
+
+local m1: Mapping = new {
+  ["a"] { x = 1 }
+  ["b"] { x = 2 }
+}
+
+local m2: Mapping = new {
+  ["a"] { x = 1 }
+  ["b"] { x = 2 }
+}
+
+res1 {
+  first = l2[1]
+  // https://github.com/apple/pkl/issues/1920
+  size = Set(l1, l2).length
+}
+
+res2 {
+  first = m2["b"]
+  size = Set(m1, m2).length
+}
+
+local bigList = IntSeq(1, 200).toList().map((i) -> i.b)
+
+// https://github.com/apple/pkl/issues/1921
+res3 = (bigList + List(0.b, -0.b)).toSet().length - bigList.length
+
+// https://github.com/apple/pkl/issues/1921
+res4 = (bigList + List(0.ms, -0.ms)).toSet().length - bigList.length

pkl-core/src/test/files/LanguageSnippetTests/output/basic/set2.pcf

@@ -0,0 +1,14 @@
+res1 {
+  first {
+    x = 2
+  }
+  size = 1
+}
+res2 {
+  first {
+    x = 2
+  }
+  size = 1
+}
+res3 = 1
+res4 = 1