Fix VmDynamicCursor (#1948)

This fixes an issue where it fails to iterate over this entry:
`new Dynamic { [-1] = 2 }`

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

@@ -102,7 +102,7 @@ final class VmDynamicCursors {
 
     @Override
     protected boolean shouldVisit(Object key) {
-      return key instanceof Long l && l < iteratee.getLength();
+      return key instanceof Long l && l >= 0 && l < iteratee.getLength();
     }
 
     @Override
@@ -121,7 +121,7 @@ final class VmDynamicCursors {
       if (member.isProp()) {
         return false;
       }
-      return !(key() instanceof Long l) || l >= iteratee.getLength();
+      return !(key() instanceof Long l) || l < 0 || l >= iteratee.getLength();
     }
 
     @Override
@@ -140,7 +140,7 @@ final class VmDynamicCursors {
       if (member.isProp()) {
         return false;
       }
-      return !(key() instanceof Long l) || l >= iteratee.getLength();
+      return !(key() instanceof Long l) || l < 0 || l >= iteratee.getLength();
     }
 
     @Override
@@ -157,7 +157,7 @@ final class VmDynamicCursors {
     @Override
     protected boolean shouldVisit(Object key) {
       if (key instanceof Identifier) return false;
-      if (key instanceof Long l) return l >= iteratee.getLength();
+      if (key instanceof Long l) return l < 0 || l >= iteratee.getLength();
       return true;
     }
 
@@ -184,7 +184,7 @@ final class VmDynamicCursors {
 
     @Override
     public boolean isElement() {
-      return key() instanceof Long l && l < iteratee.getLength();
+      return key() instanceof Long l && l >= 0 && l < iteratee.getLength();
     }
 
     @Override
@@ -210,7 +210,7 @@ final class VmDynamicCursors {
 
     @Override
     public boolean isElement() {
-      return key() instanceof Long l && l < iteratee.getLength();
+      return key() instanceof Long l && l >= 0 && l < iteratee.getLength();
     }
 
     @Override

pkl-core/src/test/files/LanguageSnippetTests/input/api/map.pkl

@@ -115,6 +115,12 @@ examples {
     map1.toDynamic()
   }
 
+  ["toDynamic() round-trip"] {
+    Map(-1, 2).toDynamic().toMap()
+    Map(0, 2).toDynamic().toMap()
+    Map(1, 2).toDynamic().toMap()
+  }
+
   ["toMapping()"] {
     Map().toMapping()
     map1.toMapping()

pkl-core/src/test/files/LanguageSnippetTests/output/api/map.pcf

@@ -96,6 +96,11 @@ examples {
       three = 3
     }
   }
+  ["toDynamic() round-trip"] {
+    Map(-1, 2)
+    Map(0, 2)
+    Map(1, 2)
+  }
   ["toMapping()"] {
     new {}
     new {