Bring back previous optimization

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

@@ -16,12 +16,14 @@
 package org.pkl.core.runtime;
 
 import com.oracle.truffle.api.CompilerDirectives;
+import com.oracle.truffle.api.CompilerDirectives.TruffleBoundary;
 import com.oracle.truffle.api.frame.MaterializedFrame;
 import com.oracle.truffle.api.nodes.IndirectCallNode;
 import org.graalvm.collections.UnmodifiableEconomicMap;
 import org.pkl.core.ast.member.ListingOrMappingTypeCastNode;
 import org.pkl.core.ast.member.ObjectMember;
 import org.pkl.core.ast.type.TypeNode;
+import org.pkl.core.util.EconomicMaps;
 import org.pkl.core.util.Nullable;
 
 public abstract class VmListingOrMapping extends VmObject {
@@ -51,7 +53,7 @@ public final Object doTypeCast(
     var result =
         this == owner
             ? value
-            : ((VmListingOrMapping) this.parent)
+            : ((VmListingOrMapping) parent)
                 .doTypeCast(value, owner, callNode, member, newNextTypeCastNode);
     if (typeCastNode == null || typeCastNode == nextTypeCastNode) return result;
     var callTarget = typeCastNode.getCallTarget();
@@ -66,6 +68,34 @@ public final Object doTypeCast(
     }
   }
 
+  @Override
+  @TruffleBoundary
+  public final @Nullable Object getCachedValue(Object key) {
+    var result = EconomicMaps.get(cachedValues, key);
+    if (result != null || !members.isEmpty()) return result;
+
+    // optimization: steal value from parent cache to avoid computing it multiple times
+
+    assert parent != null; // VmListingOrMapping always has a parent
+    result = parent.getCachedValue(key);
+    if (result == null) return null;
+
+    if (typeCastNode != null) {
+      var callNode = IndirectCallNode.getUncached();
+      var callTarget = typeCastNode.getCallTarget();
+      try {
+        result = callNode.call(callTarget, getEnclosingReceiver(), getEnclosingOwner(), result);
+      } catch (VmException e) {
+        var member = VmUtils.findMember(parent, key);
+        assert member != null; // already found the member's cached value
+        VmUtils.insertStackFrame(member, callTarget, e);
+        throw e;
+      }
+    }
+    setCachedValue(key, result);
+    return result;
+  }
+
   /**
    * Tells whether the reified element/value type of this listing/mapping is known to be a subtype
    * of {@code typeNode}. (If {@code true}, it is redundant to check that elements/values have type

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

@@ -82,7 +82,7 @@ public final UnmodifiableEconomicMap<Object, ObjectMember> getMembers() {
   }
 
   @Override
-  public @Nullable final Object getCachedValue(Object key) {
+  public @Nullable Object getCachedValue(Object key) {
     return EconomicMaps.get(cachedValues, key);
   }
 

pkl-core/src/test/files/LanguageSnippetTests/input/listings/listing7.pkl

@@ -0,0 +1,10 @@
+// ensure that these members are only evaluated once (trace should only be emitted once)
+listing = new Listing { trace(1) }
+
+listing2: Listing<Int> = listing
+
+listing3 = new Listing {
+  new Listing { trace(2) }
+}
+
+listing4: Listing<Listing<Int>> = listing3

pkl-core/src/test/files/LanguageSnippetTests/output/listings/listing7.err

@@ -0,0 +1,18 @@
+listing {
+  1
+}
+listing2 {
+  1
+}
+listing3 {
+  new {
+    2
+  }
+}
+listing4 {
+  new {
+    2
+  }
+}
+pkl: TRACE: 1 = 1 (file:///$snippetsDir/input/listings/listing7.pkl)
+pkl: TRACE: 2 = 2 (file:///$snippetsDir/input/listings/listing7.pkl)