Implementation of delete (SPICE-0008)

docs/modules/language-reference/pages/index.adoc

@@ -3178,6 +3178,7 @@ pkl: TRACE: num1 * num2 = 672 (at file:///some/module.pkl, line 42)
 This section discusses language features that are generally more relevant to template and library authors than template consumers.
 
 <<meaning-of-new,Meaning of `new`>> +
+<<member-deletion,Deleting members with `delete`>> +
 <<let-expressions,Let Expressions>> +
 <<type-tests,Type Tests>> +
 <<type-casts,Type Casts>> +
@@ -3357,6 +3358,45 @@ swiftHatchlings = typedProperty.listHatchlings(new { "Poppy"; "Chirpy" }) // <8>
 <7> Admending the property default value `new Listing { new Bird { name = "Osprey" } }`; the result contains both birds.
 <8> Error: Cannot tell which parent to amend.
 
+[[member-deletions]]
+=== Deleting members with `delete`
+
+Members can be deleted when amending the object containing them.
+This is done using the `delete` keyword.
+By itself, `delete` is not an expression; it can be used only in specific places, namely in a member
+assignment.
+These are all the positions where `delete` can be used:
+
+[source,pkl]
+----
+foo {
+  bar = delete // <1>
+  ["baz"] = delete // <2>
+  [42] = delete // <3>
+  [[qux == 1337]] = delete // <4>
+}
+----
+<1> Property deletion.
+<2> Entry deletion.
+<3> Element deletion.
+<4> Member predicate deletion (can include both entries and elements).
+
+Properties can only be deleted from `Dynamic`s, because a `Typed` must have precisely the properties defined in its class.
+Since elements are contiguously indices, deleting elements effectively renames other elements.
+This means that the indices used in the definition of an object can differ from those used in subscripting.
+In the following, `result = true`:
+
+[source,pkl]
+----
+result = (new Listing {
+  /* [0] */ "foo"
+  /* [1] */ "bar"
+  /* [2] */ "baz"
+}) {
+  [1] = delete
+}[1] == "baz"
+----
+
 [[let-expressions]]
 === Let Expressions
 

pkl-core/src/main/antlr/PklParser.g4

@@ -217,14 +217,14 @@ objectBody
   ;
 
 objectMember
-  : modifier* Identifier (typeAnnotation? '=' expr | objectBody+)  # objectProperty
-  | methodHeader '=' expr                                          # objectMethod
-  | t='[[' k=expr err1=']'? err2=']'? ('=' v=expr | objectBody+)   # memberPredicate
-  | t='[' k=expr err1=']'? err2=']'? ('=' v=expr | objectBody+)    # objectEntry
-  | expr                                                           # objectElement
-  | ('...' | '...?') expr                                          # objectSpread
-  | 'when' '(' e=expr err=')'? (b1=objectBody ('else' b2=objectBody)?)   # whenGenerator
-  | 'for' '(' t1=parameter (',' t2=parameter)? 'in' e=expr err=')'? objectBody   # forGenerator
+  : modifier* Identifier (typeAnnotation? '=' (v=expr | d='delete') | objectBody+) # objectProperty
+  | methodHeader '=' expr                                                          # objectMethod
+  | t='[[' k=expr err1=']'? err2=']'? ('=' (v=expr | d='delete') | objectBody+)    # memberPredicate
+  | t='[' k=expr err1=']'? err2=']'? ('=' (v=expr | d='delete') | objectBody+)     # objectEntry
+  | expr                                                                           # objectElement
+  | ('...' | '...?') expr                                                          # objectSpread
+  | 'when' '(' e=expr err=')'? (b1=objectBody ('else' b2=objectBody)?)             # whenGenerator
+  | 'for' '(' t1=parameter (',' t2=parameter)? 'in' e=expr err=')'? objectBody     # forGenerator
   ;
 
 stringConstant
@@ -247,7 +247,6 @@ reservedKeyword
   : 'protected'
   | 'override'
   | 'record'
-  | 'delete'
   | 'case'
   | 'switch'
   | 'vararg'

pkl-core/src/main/java/org/pkl/core/ast/VmModifier.java

@@ -55,6 +55,8 @@ private VmModifier() {}
 
   public static final int GLOB = 0x1000;
 
+  public static final int DELETE = 0x2000;
+
   // modifier sets
 
   public static final int NONE = 0;
@@ -134,16 +136,20 @@ public static boolean isEntry(int modifiers) {
     return (modifiers & ENTRY) != 0;
   }
 
+  public static boolean isDelete(int modifiers) {
+    return (modifiers & DELETE) != 0;
+  }
+
   public static boolean isType(int modifiers) {
-    return (modifiers & (CLASS | TYPE_ALIAS | IMPORT)) != 0 && (modifiers & GLOB) == 0;
+    return (modifiers & (CLASS | TYPE_ALIAS | IMPORT)) != 0 && (modifiers & (GLOB | DELETE)) == 0;
   }
 
   public static boolean isLocalOrExternalOrHidden(int modifiers) {
     return (modifiers & (LOCAL | EXTERNAL | HIDDEN)) != 0;
   }
 
-  public static boolean isLocalOrExternalOrAbstract(int modifiers) {
-    return (modifiers & (LOCAL | EXTERNAL | ABSTRACT)) != 0;
+  public static boolean isLocalOrExternalOrAbstractOrDelete(int modifiers) {
+    return (modifiers & (LOCAL | EXTERNAL | ABSTRACT | DELETE)) != 0;
   }
 
   public static boolean isConstOrFixed(int modifiers) {

pkl-core/src/main/java/org/pkl/core/ast/builder/AstBuilder.java

@@ -651,7 +651,13 @@ private VmException missingLocalPropertyValue(TypeAnnotationContext typeAnnCtx)
 
   private ObjectMember doVisitObjectProperty(ObjectPropertyContext ctx) {
     return doVisitObjectProperty(
-        ctx, ctx.modifier(), ctx.Identifier(), ctx.typeAnnotation(), ctx.expr(), ctx.objectBody());
+        ctx,
+        ctx.modifier(),
+        ctx.Identifier(),
+        ctx.typeAnnotation(),
+        ctx.v,
+        ctx.d,
+        ctx.objectBody());
   }
 
   private ObjectMember doVisitObjectMethod(ObjectMethodContext ctx) {
@@ -720,6 +726,7 @@ private ObjectMember doVisitObjectProperty(
       TerminalNode propertyName,
       @Nullable TypeAnnotationContext typeAnnCtx,
       @Nullable ExprContext exprCtx,
+      @Nullable Token deleteToken,
       @Nullable List<? extends ObjectBodyContext> bodyCtx) {
 
     return doVisitObjectProperty(
@@ -730,18 +737,21 @@ private ObjectMember doVisitObjectProperty(
         propertyName.getText(),
         typeAnnCtx,
         exprCtx,
+        deleteToken,
         bodyCtx);
   }
 
   private ObjectMember doVisitObjectProperty(
       SourceSection sourceSection,
       SourceSection headerSection,
-      int modifiers,
+      int propertyModifiers,
       String propertyName,
       @Nullable TypeAnnotationContext typeAnnCtx,
       @Nullable ExprContext exprCtx,
+      @Nullable Token deleteToken,
       @Nullable List<? extends ObjectBodyContext> bodyCtx) {
 
+    var modifiers = propertyModifiers | (deleteToken == null ? 0 : VmModifier.DELETE);
     var isLocal = VmModifier.isLocal(modifiers);
     var identifier = Identifier.property(propertyName, isLocal);
 
@@ -783,6 +793,15 @@ private ObjectMember doVisitObjectProperty(
                         // 2. if in a const scope (i.e. `const bar = new { foo { ... } }`),
                         // `super.foo` does not reference something outside the scope.
                         false));
+          } else if (deleteToken != null) {
+            var deleteSourceSection = createSourceSection(deleteToken);
+            if (isLocal) {
+              throw exceptionBuilder()
+                  .evalError("cannotDeleteLocalProperty")
+                  .withSourceSection(deleteSourceSection)
+                  .build();
+            }
+            bodyNode = VmUtils.DELETE_MARKER;
           } else { // foo = ...
             assert exprCtx != null;
             bodyNode = visitExpr(exprCtx);
@@ -1218,7 +1237,8 @@ private Pair<ExpressionNode, ObjectMember> doVisitMemberPredicate(MemberPredicat
     var keyNode = symbolTable.enterCustomThisScope(scope -> visitExpr(ctx.k));
 
     return symbolTable.enterEntry(
-        keyNode, objectMemberInserter(createSourceSection(ctx), keyNode, ctx.v, ctx.objectBody()));
+        keyNode,
+        objectMemberInserter(createSourceSection(ctx), keyNode, ctx.v, ctx.d, ctx.objectBody()));
   }
 
   private Pair<ExpressionNode, ObjectMember> doVisitObjectEntry(ObjectEntryContext ctx) {
@@ -1232,20 +1252,22 @@ private Pair<ExpressionNode, ObjectMember> doVisitObjectEntry(ObjectEntryContext
     var keyNode = visitExpr(ctx.k);
 
     return symbolTable.enterEntry(
-        keyNode, objectMemberInserter(createSourceSection(ctx), keyNode, ctx.v, ctx.objectBody()));
+        keyNode,
+        objectMemberInserter(createSourceSection(ctx), keyNode, ctx.v, ctx.d, ctx.objectBody()));
   }
 
   private Function<EntryScope, Pair<ExpressionNode, ObjectMember>> objectMemberInserter(
       SourceSection sourceSection,
       ExpressionNode keyNode,
       @Nullable ExprContext valueCtx,
+      @Nullable Token deleteToken,
       List<? extends ObjectBodyContext> objectBodyCtxs) {
     return scope -> {
       var member =
           new ObjectMember(
               sourceSection,
               keyNode.getSourceSection(),
-              VmModifier.ENTRY,
+              VmModifier.ENTRY | (deleteToken == null ? 0 : VmModifier.DELETE),
               null,
               scope.getQualifiedName());
 
@@ -2610,6 +2632,7 @@ private EconomicMap<Object, ObjectMember> doVisitModuleProperties(
               ctx.Identifier(),
               ctx.typeAnnotation(),
               ctx.expr(),
+              null,
               ctx.objectBody());
 
       if (moduleInfo.isAmend() && !member.isLocal() && ctx.typeAnnotation() != null) {

pkl-core/src/main/java/org/pkl/core/ast/member/Member.java

@@ -119,6 +119,10 @@ public final boolean isType() {
     return VmModifier.isType(modifiers);
   }
 
+  public final boolean isDelete() {
+    return VmModifier.isDelete(modifiers);
+  }
+
   public final boolean isLocalOrExternalOrHidden() {
     return VmModifier.isLocalOrExternalOrHidden(modifiers);
   }
@@ -127,7 +131,7 @@ public final boolean isConstOrFixed() {
     return VmModifier.isConstOrFixed(modifiers);
   }
 
-  public final boolean isLocalOrExternalOrAbstract() {
-    return VmModifier.isLocalOrExternalOrAbstract(modifiers);
+  public final boolean isLocalOrExternalOrAbstractOrDelete() {
+    return VmModifier.isLocalOrExternalOrAbstractOrDelete(modifiers);
   }
 }

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

@@ -247,12 +247,13 @@ private void doRunAndValidateExamples(
             return true;
           }
           if (examples.getCachedValue(groupKey) == null) {
+            var key = String.valueOf(groupKey);
             allGroupsSucceeded.set(false);
             results
-                .newResult(String.valueOf(groupKey))
+                .newResult(key)
                 .addFailure(
                     Failure.buildExamplePropertyMismatchFailure(
-                        getDisplayUri(groupMember), String.valueOf(groupKey), false));
+                        getDisplayUri(groupMember), key, false));
           }
           return true;
         });

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

@@ -62,7 +62,7 @@ public int getLength() {
     return length;
   }
 
-  /** Tells whether this object has any elements. */
+  @Override
   public boolean hasElements() {
     return length != 0;
   }

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

@@ -19,7 +19,6 @@
 import com.oracle.truffle.api.CompilerDirectives.TruffleBoundary;
 import com.oracle.truffle.api.RootCallTarget;
 import com.oracle.truffle.api.frame.MaterializedFrame;
-import java.util.function.BiFunction;
 import org.graalvm.collections.UnmodifiableEconomicMap;
 import org.pkl.core.ast.PklRootNode;
 import org.pkl.core.ast.member.ObjectMember;
@@ -142,7 +141,7 @@ public boolean iterateAlreadyForcedMemberValues(ForcedMemberValueConsumer consum
   }
 
   @Override
-  public boolean iterateMembers(BiFunction<Object, ObjectMember, Boolean> consumer) {
+  public boolean iterateMembers(MemberConsumer consumer) {
     return true;
   }
 

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

@@ -77,6 +77,11 @@ public int getLength() {
     return length;
   }
 
+  @Override
+  public boolean hasElements() {
+    return !isEmpty();
+  }
+
   public boolean isEmpty() {
     return length == 0;
   }

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

@@ -79,6 +79,11 @@ public VmClass getVmClass() {
     return BaseModule.getMappingClass();
   }
 
+  @Override
+  public boolean hasElements() {
+    return false;
+  }
+
   @TruffleBoundary
   public VmSet getAllKeys() {
     synchronized (this) {