From e35c29fe4670c779e8b96133450959eddf2dae5e Mon Sep 17 00:00:00 2001
From: Ivo List <ilist@google.com>
Date: Mon, 4 Dec 2023 19:44:30 +0100
Subject: [PATCH] [7.0.0] Experimental extend rule and subrule functionality
 (#20429)

Following commits were cleanly cherry-picked:

e4c7cb6ecb ilist@google.com Support incoming configuration transition in
extended rules
faa2f3d6a1  ilist@google.com	 Support subrules in extended rules
d70d198e92 ilist@google.com Add an escape hatch for any type attributes
in the initializer
c00c272097 ilist@google.com Cleanup incoming configuration transitions
on Starlark rules
82a469ffc0 ilist@google.com Copy and lift labels in arguments of
initializers
6733c1844b  ilist@google.com	 Remove unused OBJECT_LIST type
e7a3dabfb6  ilist@google.com	 Remove unused FILESET_ENTRY label class
c95999046a ilist@google.com Implement type checks and label conversion
for Starlark values
c4f4073aa8 ilist@google.com Move convertFromBuildLangType into BuildType
class

Additional commit "Define function_transition_allowlist in
StarlarkRuleClassFunctionsTest" just fixes the mocking of the the tests.
---
 .../analysis/RuleConfiguredTargetBuilder.java |   4 -
 .../starlark/StarlarkRuleClassFunctions.java  | 108 ++++---
 .../starlark/StarlarkRuleContext.java         |   6 +-
 .../analysis/starlark/StarlarkSubrule.java    |   2 +-
 .../build/lib/packages/BuildType.java         | 152 ++++++++-
 .../build/lib/packages/RuleClass.java         | 120 ++-----
 .../build/lib/packages/RuleFactory.java       |   7 +-
 .../devtools/build/lib/packages/Type.java     |  49 ++-
 .../StarlarkRuleFunctionsApi.java             |   4 +-
 .../transitions/NoConfigTransitionTest.java   |   3 +-
 .../starlark/StarlarkSubruleTest.java         | 115 +++++++
 .../build/lib/packages/BuildTypeTest.java     |  75 ++++-
 .../build/lib/packages/RuleClassTest.java     |   1 +
 .../ConfiguredTargetQuerySemanticsTest.java   |   3 +-
 .../TransitionsOutputFormatterTest.java       |   2 +-
 .../testutil/PostAnalysisQueryTest.java       |   5 +-
 .../google/devtools/build/lib/starlark/BUILD  |   1 +
 .../StarlarkRuleClassFunctionsTest.java       | 303 +++++++++++++++++-
 .../starlark_configurations_test.sh           |   2 +-
 19 files changed, 794 insertions(+), 168 deletions(-)

diff --git a/src/main/java/com/google/devtools/build/lib/analysis/RuleConfiguredTargetBuilder.java b/src/main/java/com/google/devtools/build/lib/analysis/RuleConfiguredTargetBuilder.java
index 7365330045a37a..6031a709d5ba94 100644
--- a/src/main/java/com/google/devtools/build/lib/analysis/RuleConfiguredTargetBuilder.java
+++ b/src/main/java/com/google/devtools/build/lib/analysis/RuleConfiguredTargetBuilder.java
@@ -338,10 +338,6 @@ private NestedSet<Label> transitiveLabels() {
    *
    * <p>This is done within {@link RuleConfiguredTargetBuilder} so that every rule always and
    * automatically propagates the validation action output group.
-   *
-   * <p>Note that in addition to {@link LabelClass#DEPENDENCY}, there is also {@link
-   * LabelClass#FILESET_ENTRY}, however the fileset implementation takes care of propagating the
-   * validation action output group itself.
    */
   private void propagateTransitiveValidationOutputGroups() {
     if (outputGroupBuilders.containsKey(OutputGroupInfo.VALIDATION_TRANSITIVE)) {
diff --git a/src/main/java/com/google/devtools/build/lib/analysis/starlark/StarlarkRuleClassFunctions.java b/src/main/java/com/google/devtools/build/lib/analysis/starlark/StarlarkRuleClassFunctions.java
index ee8039b5967b2d..4d5d2ebfa57c8d 100644
--- a/src/main/java/com/google/devtools/build/lib/analysis/starlark/StarlarkRuleClassFunctions.java
+++ b/src/main/java/com/google/devtools/build/lib/analysis/starlark/StarlarkRuleClassFunctions.java
@@ -15,6 +15,7 @@
 package com.google.devtools.build.lib.analysis.starlark;
 
 import static com.google.common.base.Preconditions.checkState;
+import static com.google.common.collect.ImmutableList.toImmutableList;
 import static com.google.devtools.build.lib.analysis.BaseRuleClasses.RUN_UNDER;
 import static com.google.devtools.build.lib.analysis.BaseRuleClasses.TIMEOUT_DEFAULT;
 import static com.google.devtools.build.lib.analysis.BaseRuleClasses.getTestRuntimeLabelList;
@@ -43,11 +44,10 @@
 import com.google.devtools.build.lib.analysis.config.ExecutionTransitionFactory;
 import com.google.devtools.build.lib.analysis.config.StarlarkDefinedConfigTransition;
 import com.google.devtools.build.lib.analysis.config.ToolchainTypeRequirement;
+import com.google.devtools.build.lib.analysis.config.transitions.ComposingTransitionFactory;
 import com.google.devtools.build.lib.analysis.config.transitions.NoTransition;
-import com.google.devtools.build.lib.analysis.config.transitions.PatchTransition;
 import com.google.devtools.build.lib.analysis.config.transitions.StarlarkExposedRuleTransitionFactory;
 import com.google.devtools.build.lib.analysis.config.transitions.TransitionFactory;
-import com.google.devtools.build.lib.analysis.config.transitions.TransitionFactory.TransitionType;
 import com.google.devtools.build.lib.analysis.platform.ConstraintValueInfo;
 import com.google.devtools.build.lib.analysis.starlark.StarlarkAttrModule.Descriptor;
 import com.google.devtools.build.lib.analysis.test.TestConfiguration;
@@ -101,6 +101,7 @@
 import com.google.devtools.build.lib.util.Pair;
 import com.google.errorprone.annotations.FormatMethod;
 import java.util.HashMap;
+import java.util.List;
 import java.util.Map;
 import java.util.Map.Entry;
 import java.util.Objects;
@@ -380,10 +381,6 @@ public StarlarkRuleFunction rule(
           executableUnchecked != Starlark.UNBOUND,
           "Omit executable parameter when extending rules.");
       failIf(testUnchecked != Starlark.UNBOUND, "Omit test parameter when extending rules.");
-      // TODO b/300201845 - add cfg support
-      failIf(cfg != Starlark.NONE, "cfg is not supported in extended rules yet.");
-      // TODO b/300201845 - add subrules support
-      failIf(!subrules.isEmpty(), "subrules are not supported in extended rules yet.");
       failIf(
           implicitOutputs != Starlark.NONE,
           "implicit_outputs is not supported when extending rules (deprecated).");
@@ -496,7 +493,7 @@ public static StarlarkRuleFunction createRule(
       builder = new RuleClass.Builder("", type, true, baseParent);
     }
 
-    builder.initializer(initializer);
+    builder.initializer(initializer, labelConverter);
 
     builder.setDefaultExtendableAllowlist(
         ruleDefinitionEnvironment.getToolsLabel("//tools/allowlists/extend_rule_allowlist"));
@@ -646,38 +643,38 @@ public static StarlarkRuleFunction createRule(
     if (!buildSetting.equals(Starlark.NONE)) {
       builder.setBuildSetting((BuildSetting) buildSetting);
     }
+
+    TransitionFactory<RuleTransitionData> transitionFactory = null;
     if (!cfg.equals(Starlark.NONE)) {
       if (cfg instanceof StarlarkDefinedConfigTransition) {
+        // defined in Starlark via, cfg = transition
         StarlarkDefinedConfigTransition starlarkDefinedConfigTransition =
             (StarlarkDefinedConfigTransition) cfg;
-        builder.cfg(new StarlarkRuleTransitionProvider(starlarkDefinedConfigTransition));
+        transitionFactory = new StarlarkRuleTransitionProvider(starlarkDefinedConfigTransition);
         hasStarlarkDefinedTransition = true;
-      } else if (cfg instanceof PatchTransition) {
-        builder.cfg((PatchTransition) cfg);
       } else if (cfg instanceof StarlarkExposedRuleTransitionFactory) {
+        // only used for native Android transitions (platforms and feature flags)
         StarlarkExposedRuleTransitionFactory transition =
             (StarlarkExposedRuleTransitionFactory) cfg;
-        builder.cfg(transition);
         transition.addToStarlarkRule(ruleDefinitionEnvironment, builder);
-      } else if (cfg instanceof TransitionFactory) {
-        // This may be redundant with StarlarkExposedRuleTransitionFactory infra
-        TransitionFactory<? extends TransitionFactory.Data> transitionFactory =
-            (TransitionFactory<? extends TransitionFactory.Data>) cfg;
-        if (transitionFactory.transitionType().isCompatibleWith(TransitionType.RULE)) {
-          @SuppressWarnings("unchecked") // Actually checked due to above isCompatibleWith call.
-          TransitionFactory<RuleTransitionData> ruleTransitionFactory =
-              (TransitionFactory<RuleTransitionData>) transitionFactory;
-          builder.cfg(ruleTransitionFactory);
-        } else {
-          throw Starlark.errorf(
-              "`cfg` must be set to a transition appropriate for a rule, not an attribute-specific"
-                  + " transition.");
-        }
+        transitionFactory = transition;
       } else {
         throw Starlark.errorf(
             "`cfg` must be set to a transition object initialized by the transition() function.");
       }
     }
+    if (parent != null && parent.getTransitionFactory() != null) {
+      if (transitionFactory == null) {
+        transitionFactory = parent.getTransitionFactory();
+      } else {
+        transitionFactory =
+            ComposingTransitionFactory.of(transitionFactory, parent.getTransitionFactory());
+      }
+      hasStarlarkDefinedTransition = true;
+    }
+    if (transitionFactory != null) {
+      builder.cfg(transitionFactory);
+    }
 
     boolean hasFunctionTransitionAllowlist = false;
     // Check for existence of the function transition allowlist attribute.
@@ -964,6 +961,16 @@ public StarlarkAspect aspect(
         ImmutableSet.copyOf(subrules));
   }
 
+  private static ImmutableSet<String> getLegacyAnyTypeAttrs(RuleClass ruleClass) {
+    Attribute attr = ruleClass.getAttributeByNameMaybe("$legacy_any_type_attrs");
+    if (attr == null
+        || attr.getType() != STRING_LIST
+        || !(attr.getDefaultValueUnchecked() instanceof List<?>)) {
+      return ImmutableSet.of();
+    }
+    return ImmutableSet.copyOf(STRING_LIST.cast(attr.getDefaultValueUnchecked()));
+  }
+
   /**
    * The implementation for the magic function "rule" that creates Starlark rule classes.
    *
@@ -1028,9 +1035,17 @@ public Object call(StarlarkThread thread, Tuple args, Dict<String, Object> kwarg
       if (ruleClass == null) {
         throw new EvalException("Invalid rule class hasn't been exported by a bzl file");
       }
+      PackageContext pkgContext = thread.getThreadLocal(PackageContext.class);
+      if (pkgContext == null) {
+        throw new EvalException(
+            "Cannot instantiate a rule when loading a .bzl file. "
+                + "Rules may be instantiated only in a BUILD thread.");
+      }
 
       validateRulePropagatedAspects(ruleClass);
 
+      ImmutableSet<String> legacyAnyTypeAttrs = getLegacyAnyTypeAttrs(ruleClass);
+
       // Remove {@link BazelStarlarkContext} to prevent calls to load and analysis time functions.
       // Mutating values in initializers is mostly not a problem, because the attribute values are
       // copied before calling the initializers (<-TODO) and before they are set on the target.
@@ -1050,8 +1065,6 @@ public Object call(StarlarkThread thread, Tuple args, Dict<String, Object> kwarg
             continue;
           }
 
-          // TODO: b/298561048 - lift parameters to more accurate type - for example strings to
-          // Labels
           // You might feel tempted to inspect the signature of the initializer function. The
           // temptation might come from handling default values, making them work for better for the
           // users.
@@ -1060,7 +1073,19 @@ public Object call(StarlarkThread thread, Tuple args, Dict<String, Object> kwarg
           for (var attr : currentRuleClass.getAttributes()) {
             if (attr.isPublic() && attr.starlarkDefined()) {
               if (kwargs.containsKey(attr.getName())) {
-                initializerKwargs.put(attr.getName(), kwargs.get(attr.getName()));
+                Object value = kwargs.get(attr.getName());
+                if (value == Starlark.NONE) {
+                  continue;
+                }
+                Object reifiedValue =
+                    legacyAnyTypeAttrs.contains(attr.getName())
+                        ? value
+                        : BuildType.copyAndLiftStarlarkValue(
+                            currentRuleClass.getName(),
+                            attr,
+                            value,
+                            pkgContext.getBuilder().getLabelConverter());
+                initializerKwargs.put(attr.getName(), reifiedValue);
               }
             }
           }
@@ -1091,7 +1116,19 @@ public Object call(StarlarkThread thread, Tuple args, Dict<String, Object> kwarg
               throw Starlark.errorf(
                   "Initializer can only set Starlark defined attributes, not '%s'", arg);
             }
-            kwargs.putEntry(nativeName, newKwargs.get(arg));
+            Object value = newKwargs.get(arg);
+            Object reifiedValue =
+                attr == null
+                        || value == Starlark.NONE
+                        || legacyAnyTypeAttrs.contains(attr.getName())
+                    ? value
+                    : BuildType.copyAndLiftStarlarkValue(
+                        currentRuleClass.getName(),
+                        attr,
+                        value,
+                        // Reify to the location of the initializer definition
+                        currentRuleClass.getLabelConverterForInitializer());
+            kwargs.putEntry(nativeName, reifiedValue);
           }
         }
       } finally {
@@ -1101,12 +1138,6 @@ public Object call(StarlarkThread thread, Tuple args, Dict<String, Object> kwarg
       BuildLangTypedAttributeValuesMap attributeValues =
           new BuildLangTypedAttributeValuesMap(kwargs);
       try {
-        PackageContext pkgContext = thread.getThreadLocal(PackageContext.class);
-        if (pkgContext == null) {
-          throw new EvalException(
-              "Cannot instantiate a rule when loading a .bzl file. "
-                  + "Rules may be instantiated only in a BUILD thread.");
-        }
         RuleFactory.createAndAddRule(
             pkgContext.getBuilder(),
             ruleClass,
@@ -1146,7 +1177,12 @@ public void export(EventHandler handler, Label starlarkLabel, String ruleClassNa
       // exploit dependency resolution for "free"
       ImmutableList<Pair<String, Descriptor>> subruleAttributes;
       try {
-        subruleAttributes = StarlarkSubrule.discoverAttributes(builder.getSubrules());
+        var parentSubrules = builder.getParentSubrules();
+        ImmutableList<StarlarkSubruleApi> subrulesNotInParents =
+            builder.getSubrules().stream()
+                .filter(subrule -> !parentSubrules.contains(subrule))
+                .collect(toImmutableList());
+        subruleAttributes = StarlarkSubrule.discoverAttributes(subrulesNotInParents);
       } catch (EvalException e) {
         errorf(handler, "%s", e.getMessage());
         return;
diff --git a/src/main/java/com/google/devtools/build/lib/analysis/starlark/StarlarkRuleContext.java b/src/main/java/com/google/devtools/build/lib/analysis/starlark/StarlarkRuleContext.java
index 6b2e611eac1ae9..3168c814de7431 100644
--- a/src/main/java/com/google/devtools/build/lib/analysis/starlark/StarlarkRuleContext.java
+++ b/src/main/java/com/google/devtools/build/lib/analysis/starlark/StarlarkRuleContext.java
@@ -326,10 +326,14 @@ ImmutableSet<? extends StarlarkSubruleApi> getSubrules() {
     if (isForAspect()) {
       return getRuleContext().getMainAspect().getDefinition().getSubrules();
     } else {
-      return getRuleContext().getRule().getRuleClassObject().getSubrules();
+      return getRuleClassUnderEvaluation().getSubrules();
     }
   }
 
+  public RuleClass getRuleClassUnderEvaluation() {
+    return ruleClassUnderEvaluation;
+  }
+
   void setLockedForSubrule(@Nullable SubruleContext lockedBy) {
     this.lockedForSubruleEvaluation = lockedBy;
   }
diff --git a/src/main/java/com/google/devtools/build/lib/analysis/starlark/StarlarkSubrule.java b/src/main/java/com/google/devtools/build/lib/analysis/starlark/StarlarkSubrule.java
index a9fca48acde462..9024f12bce73b4 100644
--- a/src/main/java/com/google/devtools/build/lib/analysis/starlark/StarlarkSubrule.java
+++ b/src/main/java/com/google/devtools/build/lib/analysis/starlark/StarlarkSubrule.java
@@ -192,7 +192,7 @@ private EvalException getUndeclaredSubruleError(StarlarkRuleContext starlarkRule
     } else {
       return Starlark.errorf(
           "rule '%s' must declare '%s' in 'subrules'",
-          starlarkRuleContext.getRuleContext().getRule().getRuleClass(), this.getName());
+          starlarkRuleContext.getRuleClassUnderEvaluation(), this.getName());
     }
   }
 
diff --git a/src/main/java/com/google/devtools/build/lib/packages/BuildType.java b/src/main/java/com/google/devtools/build/lib/packages/BuildType.java
index 91bc1fed655c17..6a9d0d15f08391 100644
--- a/src/main/java/com/google/devtools/build/lib/packages/BuildType.java
+++ b/src/main/java/com/google/devtools/build/lib/packages/BuildType.java
@@ -18,8 +18,10 @@
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableMap;
 import com.google.common.collect.ImmutableSet;
+import com.google.common.collect.Interner;
 import com.google.common.collect.Lists;
 import com.google.common.collect.Maps;
+import com.google.common.collect.Ordering;
 import com.google.devtools.build.lib.cmdline.Label;
 import com.google.devtools.build.lib.cmdline.LabelSyntaxException;
 import com.google.devtools.build.lib.packages.License.DistributionType;
@@ -163,8 +165,8 @@ public static boolean isLabelType(Type<?> type) {
    *
    * <p>The caller is responsible for casting the returned value appropriately.
    */
-  public static <T> Object selectableConvert(
-      Type<T> type, Object x, Object what, LabelConverter context) throws ConversionException {
+  static <T> Object selectableConvert(Type<T> type, Object x, Object what, LabelConverter context)
+      throws ConversionException {
     if (x instanceof com.google.devtools.build.lib.packages.SelectorList) {
       return new SelectorList<>(
           ((com.google.devtools.build.lib.packages.SelectorList) x).getElements(),
@@ -176,6 +178,146 @@ public static <T> Object selectableConvert(
     }
   }
 
+  /**
+   * Converts the build-language-typed {@code buildLangValue} to a native value via {@link
+   * BuildType#selectableConvert}. Canonicalizes the value's order if it is a {@link List} type and
+   * {@code attr.isOrderIndependent()} returns {@code true}.
+   *
+   * <p>Throws {@link ConversionException} if the conversion fails, or if {@code buildLangValue} is
+   * a selector expression but {@code attr.isConfigurable()} is {@code false}.
+   */
+  public static Object convertFromBuildLangType(
+      String ruleClass,
+      Attribute attr,
+      Object buildLangValue,
+      LabelConverter labelConverter,
+      Interner<ImmutableList<?>> listInterner)
+      throws ConversionException {
+    Object converted =
+        BuildType.selectableConvert(
+            attr.getType(),
+            buildLangValue,
+            new AttributeConversionContext(attr.getName(), ruleClass),
+            labelConverter);
+
+    if ((converted instanceof SelectorList<?>) && !attr.isConfigurable()) {
+      throw new ConversionException(
+          String.format("attribute \"%s\" is not configurable", attr.getName()));
+    }
+
+    if (converted instanceof List<?>) {
+      if (attr.isOrderIndependent()) {
+        @SuppressWarnings("unchecked")
+        List<? extends Comparable<?>> list = (List<? extends Comparable<?>>) converted;
+        converted = Ordering.natural().sortedCopy(list);
+      }
+      // It's common for multiple rule instances in the same package to have the same value for some
+      // attributes. As a concrete example, consider a package having several 'java_test' instances,
+      // each with the same exact 'tags' attribute value.
+      converted = listInterner.intern(ImmutableList.copyOf((List<?>) converted));
+    }
+
+    return converted;
+  }
+
+  /** Copies a Starlark SelectorList converting label strings to Label objects. */
+  private static <T> Object copyAndLiftSelectorList(
+      Type<T> type,
+      com.google.devtools.build.lib.packages.SelectorList x,
+      Object what,
+      LabelConverter context)
+      throws ConversionException {
+    List<Object> elements = x.getElements();
+    try {
+      if (elements.size() > 1 && type.concat(ImmutableList.of()) == null) {
+        throw new ConversionException(
+            String.format("type '%s' doesn't support select concatenation", type));
+      }
+
+      ImmutableList.Builder<Object> builder = ImmutableList.builder();
+      for (Object elem : elements) {
+        ImmutableMap.Builder<Label, Object> newMap = ImmutableMap.builder();
+        if (elem instanceof SelectorValue) {
+          for (var entry : ((SelectorValue) elem).getDictionary().entrySet()) {
+            Label key = LABEL.convert(entry.getKey(), what, context);
+            newMap.put(
+                key,
+                entry.getValue() == Starlark.NONE
+                    ? Starlark.NONE
+                    : type.copyAndLiftStarlarkValue(
+                        entry.getValue(), new SelectBranchMessage(what, key), context));
+          }
+          builder.add(
+              new SelectorValue(
+                  newMap.buildKeepingLast(), ((SelectorValue) elem).getNoMatchError()));
+        } else {
+          Object directValue = type.copyAndLiftStarlarkValue(elem, what, context);
+          builder.add(directValue);
+        }
+      }
+      return com.google.devtools.build.lib.packages.SelectorList.of(builder.build());
+    } catch (EvalException e) {
+      throw new ConversionException(e.getMessage());
+    }
+  }
+
+  /**
+   * Copies a Starlark value to immutable ones and converts label strings to Label objects.
+   *
+   * <p>All Starlark values are also type checked.
+   *
+   * <p>In comparison to {@link #convertFromBuildLangType} unordered attributes are not
+   * canonicalized or interned.
+   *
+   * <p>Use the function before passing the values to initializers.
+   *
+   * @throws ConversionException if the {@code starlarkValue} doesn't match the type of attr or if
+   *     {@code starlarkValue} is a selector expression but {@code attr.isConfigurable()} is {@code
+   *     false}.
+   */
+  public static Object copyAndLiftStarlarkValue(
+      String ruleClass, Attribute attr, Object starlarkValue, LabelConverter labelConverter)
+      throws ConversionException {
+    if (starlarkValue instanceof com.google.devtools.build.lib.packages.SelectorList) {
+      if (!attr.isConfigurable()) {
+        throw new ConversionException(
+            String.format("attribute \"%s\" is not configurable", attr.getName()));
+      }
+      return copyAndLiftSelectorList(
+          attr.getType(),
+          (com.google.devtools.build.lib.packages.SelectorList) starlarkValue,
+          new AttributeConversionContext(attr.getName(), ruleClass),
+          labelConverter);
+    } else {
+      return attr.getType()
+          .copyAndLiftStarlarkValue(
+              starlarkValue,
+              new AttributeConversionContext(attr.getName(), ruleClass),
+              labelConverter);
+    }
+  }
+
+  /**
+   * Provides a {@link #toString()} description of the attribute being converted for {@link
+   * BuildType#selectableConvert}. This is preferred over a raw string to avoid uselessly
+   * constructing strings which are never used. A separate class instead of inline to avoid
+   * accidental memory leaks.
+   */
+  private static class AttributeConversionContext {
+    private final String attrName;
+    private final String ruleClass;
+
+    AttributeConversionContext(String attrName, String ruleClass) {
+      this.attrName = attrName;
+      this.ruleClass = ruleClass;
+    }
+
+    @Override
+    public String toString() {
+      return "attribute '" + attrName + "' in '" + ruleClass + "' rule";
+    }
+  }
+
   private static class LabelType extends Type<Label> {
     private final LabelClass labelClass;
 
@@ -311,6 +453,12 @@ public License convert(Object x, Object what, LabelConverter labelConverter)
       }
     }
 
+    @Override
+    public Object copyAndLiftStarlarkValue(
+        Object x, Object what, @Nullable LabelConverter labelConverter) throws ConversionException {
+      return STRING_LIST.copyAndLiftStarlarkValue(x, what, labelConverter);
+    }
+
     @Override
     public License getDefaultValue() {
       return License.NO_LICENSE;
diff --git a/src/main/java/com/google/devtools/build/lib/packages/RuleClass.java b/src/main/java/com/google/devtools/build/lib/packages/RuleClass.java
index 24877adceeebef..3b447a65b332a2 100644
--- a/src/main/java/com/google/devtools/build/lib/packages/RuleClass.java
+++ b/src/main/java/com/google/devtools/build/lib/packages/RuleClass.java
@@ -33,11 +33,8 @@
 import com.google.common.collect.Iterables;
 import com.google.common.collect.Lists;
 import com.google.common.collect.Maps;
-import com.google.common.collect.Ordering;
 import com.google.devtools.build.lib.analysis.config.Fragment;
 import com.google.devtools.build.lib.analysis.config.ToolchainTypeRequirement;
-import com.google.devtools.build.lib.analysis.config.transitions.PatchTransition;
-import com.google.devtools.build.lib.analysis.config.transitions.SplitTransition;
 import com.google.devtools.build.lib.analysis.config.transitions.TransitionFactory;
 import com.google.devtools.build.lib.cmdline.Label;
 import com.google.devtools.build.lib.cmdline.LabelSyntaxException;
@@ -60,7 +57,6 @@
 import com.google.devtools.build.lib.vfs.PathFragment;
 import com.google.errorprone.annotations.CanIgnoreReturnValue;
 import com.google.errorprone.annotations.FormatMethod;
-import java.io.Serializable;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.BitSet;
@@ -754,6 +750,8 @@ public String toString() {
     private final RuleClassType type;
     @Nullable private RuleClass starlarkParent = null;
     @Nullable private StarlarkFunction initializer = null;
+    @Nullable private LabelConverter labelConverterForInitializer = null;
+
     // The extendable may take 3 value, null means that the default allowlist should be use when
     // rule is extendable in practice.
     @Nullable private Boolean extendable = null;
@@ -771,7 +769,7 @@ public String toString() {
         ImmutableList.builder();
     private boolean ignoreLicenses = false;
     private ImplicitOutputsFunction implicitOutputsFunction = ImplicitOutputsFunction.NONE;
-    private TransitionFactory<RuleTransitionData> transitionFactory;
+    @Nullable private TransitionFactory<RuleTransitionData> transitionFactory;
     private ConfiguredTargetFactory<?, ?, ?> configuredTargetFactory = null;
     private PredicateWithMessage<Rule> validityPredicate = PredicatesWithMessage.alwaysTrue();
     private final AdvertisedProviderSet.Builder advertisedProviders =
@@ -962,6 +960,7 @@ public RuleClass build(String name, String key) {
           type,
           starlarkParent,
           initializer,
+          labelConverterForInitializer,
           starlark,
           extendable,
           extendableAllowlist,
@@ -1042,8 +1041,10 @@ private void assertStarlarkRuleClassHasEnvironmentLabel() {
     }
 
     @CanIgnoreReturnValue
-    public Builder initializer(StarlarkFunction initializer) {
+    public Builder initializer(
+        StarlarkFunction initializer, LabelConverter labelConverterForInitializer) {
       this.initializer = initializer;
+      this.labelConverterForInitializer = labelConverterForInitializer;
       return this;
     }
 
@@ -1167,26 +1168,8 @@ public Builder setImplicitOutputsFunction(ImplicitOutputsFunction implicitOutput
       return this;
     }
 
-    /**
-     * Applies the given transition to all incoming edges for this rule class.
-     *
-     * <p>This cannot be a {@link SplitTransition} because that requires coordination with the
-     * rule's parent: use {@link Attribute.Builder#cfg(TransitionFactory)} on the parent to declare
-     * splits.
-     *
-     * <p>If you need the transition to depend on the rule it's being applied to, use {@link
-     * #cfg(TransitionFactory)}.
-     */
-    public Builder cfg(PatchTransition transition) {
-      // Make sure this is cast to Serializable to avoid autocodec serialization errors.
-      return cfg((TransitionFactory<RuleTransitionData> & Serializable) unused -> transition);
-    }
-
     /**
      * Applies the given transition factory to all incoming edges for this rule class.
-     *
-     * <p>Unlike {@link #cfg(PatchTransition)}, the factory can examine the rule when deciding what
-     * transition to use.
      */
     @CanIgnoreReturnValue
     public Builder cfg(TransitionFactory<RuleTransitionData> transitionFactory) {
@@ -1390,6 +1373,16 @@ public ImmutableList<? extends StarlarkSubruleApi> getSubrules() {
       return subrules;
     }
 
+    public ImmutableSet<? extends StarlarkSubruleApi> getParentSubrules() {
+      ImmutableSet.Builder<StarlarkSubruleApi> builder = ImmutableSet.builder();
+      RuleClass currentParent = starlarkParent;
+      while (currentParent != null) {
+        builder.addAll(starlarkParent.getSubrules());
+        currentParent = currentParent.starlarkParent;
+      }
+      return builder.build();
+    }
+
     @CanIgnoreReturnValue
     public Builder setExternalBindingsFunction(Function<? super Rule, Map<String, Label>> func) {
       this.externalBindingsFunction = func;
@@ -1680,6 +1673,7 @@ public Attribute.Builder<?> copy(String name) {
   private final RuleClassType type;
   @Nullable private final RuleClass starlarkParent;
   @Nullable private final StarlarkFunction initializer;
+  @Nullable private final LabelConverter labelConverterForInitializer;
   private final boolean isStarlark;
   private final boolean extendable;
   @Nullable private final Label extendableAllowlist;
@@ -1719,7 +1713,7 @@ public Attribute.Builder<?> copy(String name) {
    * A factory which will produce a configuration transition that should be applied on any edge of
    * the configured target graph that leads into a target of this rule class.
    */
-  private final TransitionFactory<RuleTransitionData> transitionFactory;
+  @Nullable private final TransitionFactory<RuleTransitionData> transitionFactory;
 
   /** The factory that creates configured targets from this rule. */
   private final ConfiguredTargetFactory<?, ?, ?> configuredTargetFactory;
@@ -1817,6 +1811,7 @@ public Attribute.Builder<?> copy(String name) {
       RuleClassType type,
       RuleClass starlarkParent,
       @Nullable StarlarkFunction initializer,
+      @Nullable LabelConverter labelConverterForInitializer,
       boolean isStarlark,
       boolean extendable,
       @Nullable Label extendableAllowlist,
@@ -1830,7 +1825,7 @@ public Attribute.Builder<?> copy(String name) {
       ImmutableList<AllowlistChecker> allowlistCheckers,
       boolean ignoreLicenses,
       ImplicitOutputsFunction implicitOutputsFunction,
-      TransitionFactory<RuleTransitionData> transitionFactory,
+      @Nullable TransitionFactory<RuleTransitionData> transitionFactory,
       ConfiguredTargetFactory<?, ?, ?> configuredTargetFactory,
       PredicateWithMessage<Rule> validityPredicate,
       AdvertisedProviderSet advertisedProviders,
@@ -1856,6 +1851,7 @@ public Attribute.Builder<?> copy(String name) {
     this.type = type;
     this.starlarkParent = starlarkParent;
     this.initializer = initializer;
+    this.labelConverterForInitializer = labelConverterForInitializer;
     this.isStarlark = isStarlark;
     this.extendable = extendable;
     this.extendableAllowlist = extendableAllowlist;
@@ -1938,6 +1934,7 @@ public ImplicitOutputsFunction getDefaultImplicitOutputsFunction() {
     return implicitOutputsFunction;
   }
 
+  @Nullable
   public TransitionFactory<RuleTransitionData> getTransitionFactory() {
     return transitionFactory;
   }
@@ -1961,6 +1958,11 @@ public StarlarkFunction getInitializer() {
     return initializer;
   }
 
+  @Nullable
+  public LabelConverter getLabelConverterForInitializer() {
+    return labelConverterForInitializer;
+  }
+
   /**
    * Returns the stack of Starlark active function calls at the moment this rule class was created.
    * Entries appear outermost first, and exclude the built-in itself ('rule' or 'repository_rule').
@@ -2238,7 +2240,8 @@ private <T> BitSet populateDefinedRuleAttributeValues(
       if (attributeValues.valuesAreBuildLanguageTyped()) {
         try {
           nativeAttributeValue =
-              convertFromBuildLangType(rule, attr, attributeValue, labelConverter, listInterner);
+              BuildType.convertFromBuildLangType(
+                  rule.getRuleClass(), attr, attributeValue, labelConverter, listInterner);
         } catch (ConversionException e) {
           rule.reportError(String.format("%s: %s", rule.getLabel(), e.getMessage()), eventHandler);
           continue;
@@ -2477,69 +2480,6 @@ private static void checkForValidSizeAndTimeoutValues(Rule rule, EventHandler ev
     }
   }
 
-  /**
-   * Converts the build-language-typed {@code buildLangValue} to a native value via {@link
-   * BuildType#selectableConvert}. Canonicalizes the value's order if it is a {@link List} type and
-   * {@code attr.isOrderIndependent()} returns {@code true}.
-   *
-   * <p>Throws {@link ConversionException} if the conversion fails, or if {@code buildLangValue} is
-   * a selector expression but {@code attr.isConfigurable()} is {@code false}.
-   */
-  private static Object convertFromBuildLangType(
-      Rule rule,
-      Attribute attr,
-      Object buildLangValue,
-      LabelConverter labelConverter,
-      Interner<ImmutableList<?>> listInterner)
-      throws ConversionException {
-    Object converted =
-        BuildType.selectableConvert(
-            attr.getType(),
-            buildLangValue,
-            new AttributeConversionContext(attr.getName(), rule.getRuleClass()),
-            labelConverter);
-
-    if ((converted instanceof SelectorList<?>) && !attr.isConfigurable()) {
-      throw new ConversionException(
-          String.format("attribute \"%s\" is not configurable", attr.getName()));
-    }
-
-    if (converted instanceof List<?>) {
-      if (attr.isOrderIndependent()) {
-        @SuppressWarnings("unchecked")
-        List<? extends Comparable<?>> list = (List<? extends Comparable<?>>) converted;
-        converted = Ordering.natural().sortedCopy(list);
-      }
-      // It's common for multiple rule instances in the same package to have the same value for some
-      // attributes. As a concrete example, consider a package having several 'java_test' instances,
-      // each with the same exact 'tags' attribute value.
-      converted = listInterner.intern(ImmutableList.copyOf((List<?>) converted));
-    }
-
-    return converted;
-  }
-
-  /**
-   * Provides a {@link #toString()} description of the attribute being converted for
-   * {@link BuildType#selectableConvert}. This is preferred over a raw string to avoid uselessly
-   * constructing strings which are never used. A separate class instead of inline to avoid
-   * accidental memory leaks.
-   */
-  private static class AttributeConversionContext {
-    private final String attrName;
-    private final String ruleClass;
-
-    AttributeConversionContext(String attrName, String ruleClass) {
-      this.attrName = attrName;
-      this.ruleClass = ruleClass;
-    }
-
-    @Override
-    public String toString() {
-      return "attribute '" + attrName + "' in '" + ruleClass + "' rule";
-    }
-  }
-
   /**
    * Verifies that the rule has a valid value for the attribute according to its allowed values.
    *
diff --git a/src/main/java/com/google/devtools/build/lib/packages/RuleFactory.java b/src/main/java/com/google/devtools/build/lib/packages/RuleFactory.java
index 67cfb62fe2cc44..d6fa64d51edc25 100644
--- a/src/main/java/com/google/devtools/build/lib/packages/RuleFactory.java
+++ b/src/main/java/com/google/devtools/build/lib/packages/RuleFactory.java
@@ -109,8 +109,8 @@ public static Rule createRule(
    * @param attributeValues a {@link BuildLangTypedAttributeValuesMap} mapping attribute names to
    *     attribute values of build-language type. Each attribute must be defined for this class of
    *     rule, and have a build-language-typed value which can be converted to the appropriate
-   *     native type of the attribute (i.e. via {@link BuildType#selectableConvert}). There must be
-   *     a map entry for each non-optional attribute of this class of rule.
+   *     native type of the attribute (i.e. via {@link BuildType#convertFromBuildLangType}). There
+   *     must be a map entry for each non-optional attribute of this class of rule.
    * @param eventHandler a eventHandler on which errors and warnings are reported during rule
    *     creation
    * @param callstack the stack of active calls in the Starlark thread
@@ -159,7 +159,8 @@ public interface AttributeValues<T> {
     /**
      * Returns {@code true} if all the map's values are "build-language typed", i.e., resulting from
      * the evaluation of an expression in the build language. Returns {@code false} if all the map's
-     * values are "natively typed", i.e. of a type returned by {@link BuildType#selectableConvert}.
+     * values are "natively typed", i.e. of a type returned by {@link
+     * BuildType#convertFromBuildLangType}.
      */
     boolean valuesAreBuildLanguageTyped();
 
diff --git a/src/main/java/com/google/devtools/build/lib/packages/Type.java b/src/main/java/com/google/devtools/build/lib/packages/Type.java
index 0e2c3f81ea3a48..54577d36082d7e 100644
--- a/src/main/java/com/google/devtools/build/lib/packages/Type.java
+++ b/src/main/java/com/google/devtools/build/lib/packages/Type.java
@@ -40,6 +40,7 @@
 import net.starlark.java.eval.Sequence;
 import net.starlark.java.eval.Starlark;
 import net.starlark.java.eval.StarlarkInt;
+import net.starlark.java.eval.StarlarkList;
 
 /**
  * Root of Type symbol hierarchy for values in the build language.
@@ -95,12 +96,12 @@ public abstract class Type<T> {
    * <p>x must be directly convertible to this type. This therefore disqualifies "selector
    * expressions" of the form "{ config1: 'value1_of_orig_type', config2: 'value2_of_orig_type; }"
    * (which support configurable attributes). To handle those expressions, see {@link
-   * com.google.devtools.build.lib.packages.BuildType#selectableConvert}.
+   * com.google.devtools.build.lib.packages.BuildType#convertFromBuildLangType}.
    *
    * @param x The Starlark value to convert.
    * @param what An object whose toString method returns a description of the purpose of x.
-   *     Typically it is the name of a function parameter or struct field. The method is called only
-   *     in case of error.
+   *     Typically, it is the name of a function parameter or struct field. The method is called
+   *     only in case of error.
    * @param labelConverter the converter to use to convert label literals to Label objects; must be
    *     non-null if parsing non-canonical label strings is required
    * @throws ConversionException if there was a problem performing the type conversion
@@ -108,6 +109,25 @@ public abstract class Type<T> {
    */
   public abstract T convert(Object x, Object what, @Nullable LabelConverter labelConverter)
       throws ConversionException;
+
+  /**
+   * Copies a Starlark value to an immutable ones and converts label strings to Label objects.
+   *
+   * <p>All Starlark values are also type checked.
+   *
+   * @param x The Starlark value to copy.
+   * @param what An object whose toString method returns a description of the purpose of x.
+   *     Typically, it is the name of a function parameter or struct field. The method is called
+   *     only in case of error.
+   * @param labelConverter the converter to use to convert label literals to Label objects; must be
+   *     non-null if parsing non-canonical label strings is required
+   * @throws ConversionException if the Starlark value doesn't match the type
+   */
+  public Object copyAndLiftStarlarkValue(
+      Object x, Object what, @Nullable LabelConverter labelConverter) throws ConversionException {
+    return convert(x, what, labelConverter);
+  }
+
   // TODO(bazel-team): Check external calls (e.g. in PackageFactory), verify they always want
   // this over selectableConvert.
 
@@ -200,11 +220,6 @@ public enum LabelClass {
     GENQUERY_SCOPE_REFERENCE,
     /** Used for types which use labels to declare an output path. */
     OUTPUT,
-    /**
-     * Used for types which contain Fileset entries, which contain labels but do not produce normal
-     * dependencies.
-     */
-    FILESET_ENTRY
   }
 
   /** Returns the class of labels contained by this type, if any. */
@@ -261,9 +276,6 @@ public Set<String> toTagSet(Object value, String name) {
   /** The type of a boolean. */
   @SerializationConstant public static final Type<Boolean> BOOLEAN = new BooleanType();
 
-  /** The type of a list of not-yet-typed objects. */
-  @SerializationConstant public static final ObjectListType OBJECT_LIST = new ObjectListType();
-
   /** The type of a list of strings. */
   @SerializationConstant public static final ListType<String> STRING_LIST = ListType.create(STRING);
 
@@ -591,6 +603,12 @@ public Map<KeyT, ValueT> convert(Object x, Object what, LabelConverter labelConv
       return ImmutableMap.copyOf(result);
     }
 
+    @Override
+    public Object copyAndLiftStarlarkValue(
+        Object x, Object what, @Nullable LabelConverter labelConverter) throws ConversionException {
+      return Dict.immutableCopyOf(convert(x, what, labelConverter));
+    }
+
     @Override
     public Map<KeyT, ValueT> concat(Iterable<Map<KeyT, ValueT>> iterable) {
       Dict.Builder<KeyT, ValueT> output = new Dict.Builder<>();
@@ -697,14 +715,19 @@ public List<ElemT> convert(Object x, Object what, LabelConverter labelConverter)
                   + what
                   + " in "
                   + labelConverter;
-          LoggingUtil.logToRemote(Level.WARNING, message,
-              new ConversionException(message));
+          LoggingUtil.logToRemote(Level.WARNING, message, new ConversionException(message));
         }
         ++index;
       }
       return result;
     }
 
+    @Override
+    public Object copyAndLiftStarlarkValue(
+        Object x, Object what, @Nullable LabelConverter labelConverter) throws ConversionException {
+      return StarlarkList.immutableCopyOf(convert(x, what, labelConverter));
+    }
+
     @Override
     public List<ElemT> concat(Iterable<List<ElemT>> elements) {
       ImmutableList.Builder<ElemT> builder = ImmutableList.builder();
diff --git a/src/main/java/com/google/devtools/build/lib/starlarkbuildapi/StarlarkRuleFunctionsApi.java b/src/main/java/com/google/devtools/build/lib/starlarkbuildapi/StarlarkRuleFunctionsApi.java
index 5d0b05c9cea7a3..1e402377349296 100644
--- a/src/main/java/com/google/devtools/build/lib/starlarkbuildapi/StarlarkRuleFunctionsApi.java
+++ b/src/main/java/com/google/devtools/build/lib/starlarkbuildapi/StarlarkRuleFunctionsApi.java
@@ -495,7 +495,9 @@ Object provider(Object doc, Object fields, Object init, StarlarkThread thread)
                     + " <code>executable</code> and <code>test</code> from the parent. Values of"
                     + " <code>fragments</code>, <code>toolchains</code>,"
                     + " <code>exec_compatible_with</code>, and <code>exec_groups</code> are"
-                    + " merged. Legacy or deprecated parameters may not be set."),
+                    + " merged. Legacy or deprecated parameters may not be set. Incoming "
+                    + "configuration transition <code>cfg</code> of parent is applied after this"
+                    + "rule's incoming configuration."),
         @Param(
             name = "extendable",
             named = true,
diff --git a/src/test/java/com/google/devtools/build/lib/analysis/config/transitions/NoConfigTransitionTest.java b/src/test/java/com/google/devtools/build/lib/analysis/config/transitions/NoConfigTransitionTest.java
index b9a443f6f0dc4d..3ec8e2e99d5da1 100644
--- a/src/test/java/com/google/devtools/build/lib/analysis/config/transitions/NoConfigTransitionTest.java
+++ b/src/test/java/com/google/devtools/build/lib/analysis/config/transitions/NoConfigTransitionTest.java
@@ -32,7 +32,8 @@ public class NoConfigTransitionTest extends BuildViewTestCase {
   private static final MockRule NO_CONFIG_RULE =
       () ->
           MockRule.define(
-              "no_config_rule", (builder, env) -> builder.cfg(NoConfigTransition.INSTANCE));
+              "no_config_rule",
+              (builder, env) -> builder.cfg(unused -> NoConfigTransition.INSTANCE));
 
   @Override
   protected ConfiguredRuleClassProvider createRuleClassProvider() {
diff --git a/src/test/java/com/google/devtools/build/lib/analysis/starlark/StarlarkSubruleTest.java b/src/test/java/com/google/devtools/build/lib/analysis/starlark/StarlarkSubruleTest.java
index 98e806ed21f0dc..d30b6789284015 100644
--- a/src/test/java/com/google/devtools/build/lib/analysis/starlark/StarlarkSubruleTest.java
+++ b/src/test/java/com/google/devtools/build/lib/analysis/starlark/StarlarkSubruleTest.java
@@ -119,6 +119,121 @@ public void testSubrule_ruleMustDeclareSubrule() throws Exception {
             "Error in _my_subrule: rule 'my_rule' must declare '_my_subrule' in" + " 'subrules'");
   }
 
+  @Test
+  public void testSubrule_childAndParentSubrules() throws Exception {
+    scratch.file(
+        "subrule_testing/parent.bzl",
+        "_parent_subrule = subrule(implementation = lambda ctx: None)",
+        "def _rule_impl(ctx):",
+        "  _parent_subrule()",
+        "parent_rule = rule(implementation = _rule_impl, extendable = True, subrules ="
+            + " [_parent_subrule])");
+    scratch.file(
+        "subrule_testing/child.bzl",
+        "load('parent.bzl', 'parent_rule')",
+        "_child_subrule = subrule(implementation = lambda ctx: None)",
+        "def _rule_impl(ctx):",
+        "  ctx.super()",
+        "  _child_subrule()",
+        "child_rule = rule(implementation = _rule_impl, parent = parent_rule, subrules ="
+            + " [_child_subrule])");
+    scratch.file(
+        "subrule_testing/BUILD", "load('child.bzl', 'child_rule')", "child_rule(name = 'foo')");
+
+    getConfiguredTarget("//subrule_testing:foo");
+
+    assertNoEvents();
+  }
+
+  @Test
+  public void testSubrule_childAndParent_canUseTheSameSubrule() throws Exception {
+    scratch.file(
+        "subrule_testing/parent.bzl",
+        "parent_subrule = subrule(",
+        "  implementation = lambda ctx, _tool: None,",
+        "  attrs = {'_tool': attr.label(default = ':tool')}",
+        ")",
+        "def _rule_impl(ctx):",
+        "  parent_subrule()",
+        "parent_rule = rule(implementation = _rule_impl, extendable = True, subrules ="
+            + " [parent_subrule])");
+    scratch.file(
+        "subrule_testing/child.bzl",
+        "load('parent.bzl', 'parent_rule', 'parent_subrule')",
+        "def _rule_impl(ctx):",
+        "  ctx.super()",
+        "  parent_subrule()",
+        "child_rule = rule(implementation = _rule_impl, parent = parent_rule, subrules ="
+            + " [parent_subrule])");
+    scratch.file(
+        "subrule_testing/BUILD",
+        "load('child.bzl', 'child_rule')",
+        "child_rule(name = 'foo')",
+        "filegroup(name = 'tool')");
+
+    getConfiguredTarget("//subrule_testing:foo");
+
+    assertNoEvents();
+  }
+
+  @Test
+  public void testSubrule_childCantUseParentsSubrule() throws Exception {
+    scratch.file(
+        "subrule_testing/parent.bzl",
+        "parent_subrule = subrule(implementation = lambda ctx: None)",
+        "def _rule_impl(ctx):",
+        "  parent_subrule()",
+        "parent_rule = rule(implementation = _rule_impl, extendable = True, subrules ="
+            + " [parent_subrule])");
+    scratch.file(
+        "subrule_testing/child.bzl",
+        "load('parent.bzl', 'parent_rule', 'parent_subrule')",
+        "_child_subrule = subrule(implementation = lambda ctx: None)",
+        "def _rule_impl(ctx):",
+        "  ctx.super()",
+        "  parent_subrule()",
+        "child_rule = rule(implementation = _rule_impl, parent = parent_rule)");
+    scratch.file(
+        "subrule_testing/BUILD", "load('child.bzl', 'child_rule')", "child_rule(name = 'foo')");
+
+    AssertionError error =
+        assertThrows(AssertionError.class, () -> getConfiguredTarget("//subrule_testing:foo"));
+
+    assertThat(error)
+        .hasMessageThat()
+        .contains(
+            "Error in parent_subrule: rule 'child_rule' must declare 'parent_subrule' in"
+                + " 'subrules'");
+  }
+
+  @Test
+  public void testSubrule_parentCantUseChildsSubrule() throws Exception {
+    scratch.file(
+        "subrule_testing/parent.bzl",
+        "my_subrule = subrule(implementation = lambda ctx: None)",
+        "def _rule_impl(ctx):",
+        "  my_subrule()",
+        "parent_rule = rule(implementation = _rule_impl, extendable = True)");
+    scratch.file(
+        "subrule_testing/child.bzl",
+        "load('parent.bzl', 'parent_rule', 'my_subrule')",
+        "def _rule_impl(ctx):",
+        "  ctx.super()",
+        "  my_subrule()",
+        "child_rule = rule(implementation = _rule_impl, parent = parent_rule, subrules ="
+            + " [my_subrule])");
+    scratch.file(
+        "subrule_testing/BUILD", "load('child.bzl', 'child_rule')", "child_rule(name = 'foo')");
+
+    AssertionError error =
+        assertThrows(AssertionError.class, () -> getConfiguredTarget("//subrule_testing:foo"));
+
+    assertThat(error)
+        .hasMessageThat()
+        .contains(
+            "Error in my_subrule: rule 'parent_rule' must declare 'my_subrule' in 'subrules'");
+  }
+
   @Test
   public void testSubrule_aspectMustDeclareSubrule() throws Exception {
     scratch.file(
diff --git a/src/test/java/com/google/devtools/build/lib/packages/BuildTypeTest.java b/src/test/java/com/google/devtools/build/lib/packages/BuildTypeTest.java
index bea02188051f4c..79fe7d925d0c7c 100644
--- a/src/test/java/com/google/devtools/build/lib/packages/BuildTypeTest.java
+++ b/src/test/java/com/google/devtools/build/lib/packages/BuildTypeTest.java
@@ -27,9 +27,11 @@
 import java.util.Arrays;
 import java.util.List;
 import java.util.Map;
+import net.starlark.java.eval.Dict;
 import net.starlark.java.eval.EvalException;
 import net.starlark.java.eval.Starlark;
 import net.starlark.java.eval.StarlarkInt;
+import net.starlark.java.eval.StarlarkList;
 import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.junit.runners.JUnit4;
@@ -513,15 +515,82 @@ public void testSelectableConvert() throws Exception {
             expectedLabels);
   }
 
+  @Test
+  @SuppressWarnings({"unchecked"})
+  public void testCopyAndLiftStarlarkList() throws Exception {
+    Object starlarkList = StarlarkList.immutableOf("//a:a1", "//a:a2");
+    ImmutableList<Label> expectedLabels =
+        ImmutableList.of(Label.create("@//a", "a1"), Label.create("@//a", "a2"));
+
+    Object converted =
+        BuildType.copyAndLiftStarlarkValue(
+            "ruleClass",
+            Attribute.attr("attrName", BuildType.LABEL_LIST).allowedFileTypes().build(),
+            starlarkList,
+            labelConverter);
+
+    assertThat(converted instanceof StarlarkList<?>).isTrue();
+    assertThat((List<Label>) converted).containsExactlyElementsIn(expectedLabels);
+  }
+
+  @Test
+  public void testCopyAndLiftStarlarkDict() throws Exception {
+    Object inputDict = Dict.immutableCopyOf(ImmutableMap.of("a", "b", "c", "d"));
+
+    Object converted =
+        BuildType.copyAndLiftStarlarkValue(
+            "ruleClass",
+            Attribute.attr("attrName", Type.STRING_DICT).build(),
+            inputDict,
+            labelConverter);
+
+    assertThat(converted instanceof Dict).isTrue();
+    assertThat(converted).isEqualTo(inputDict);
+    assertThat(converted).isNotSameInstanceAs(inputDict);
+  }
+
+  @Test
+  public void testCopyAndLiftSelectableStarlarkValue() throws Exception {
+    Object starlarkList = StarlarkList.immutableOf("//a:a1", "//a:a2");
+    Object selectableInput =
+        SelectorList.of(
+            new SelectorValue(
+                ImmutableMap.of(
+                    "//conditions:a",
+                    starlarkList,
+                    BuildType.Selector.DEFAULT_CONDITION_KEY,
+                    starlarkList),
+                ""));
+    StarlarkList<Label> expectedLabels =
+        StarlarkList.immutableOf(Label.create("@//a", "a1"), Label.create("@//a", "a2"));
+
+    Object converted =
+        BuildType.copyAndLiftStarlarkValue(
+            "ruleClass",
+            Attribute.attr("attrName", BuildType.LABEL_LIST).allowedFileTypes().build(),
+            selectableInput,
+            labelConverter);
+
+    assertThat(converted instanceof SelectorList).isTrue();
+    SelectorList selectorList = (SelectorList) converted;
+    assertThat(((SelectorValue) selectorList.getElements().get(0)).getDictionary())
+        .containsExactly(
+            Label.parseCanonical("//conditions:a"),
+            expectedLabels,
+            Label.parseCanonical(Selector.DEFAULT_CONDITION_KEY),
+            expectedLabels);
+  }
+
   /**
    * Tests that {@link com.google.devtools.build.lib.packages.Type#convert} fails on selector
    * inputs.
    */
   @Test
   public void testConvertDoesNotAcceptSelectables() throws Exception {
-    Object selectableInput = SelectorList.of(
-        new SelectorValue(
-            ImmutableMap.of("//conditions:a", Arrays.asList("//a:a1", "//a:a2")), ""));
+    Object selectableInput =
+        SelectorList.of(
+            new SelectorValue(
+                ImmutableMap.of("//conditions:a", Arrays.asList("//a:a1", "//a:a2")), ""));
     ConversionException e =
         assertThrows(
             ConversionException.class,
diff --git a/src/test/java/com/google/devtools/build/lib/packages/RuleClassTest.java b/src/test/java/com/google/devtools/build/lib/packages/RuleClassTest.java
index d22a893bc01ba8..fe2796cbcdd728 100644
--- a/src/test/java/com/google/devtools/build/lib/packages/RuleClassTest.java
+++ b/src/test/java/com/google/devtools/build/lib/packages/RuleClassTest.java
@@ -1026,6 +1026,7 @@ private static RuleClass newRuleClass(
         RuleClassType.NORMAL,
         /* starlarkParent= */ null,
         /* initializer= */ null,
+        /* labelConverterForInitializer= */ null,
         /* isStarlark= */ starlarkExecutable,
         /* extendable= */ false,
         /* extendableAllowlist= */ null,
diff --git a/src/test/java/com/google/devtools/build/lib/query2/cquery/ConfiguredTargetQuerySemanticsTest.java b/src/test/java/com/google/devtools/build/lib/query2/cquery/ConfiguredTargetQuerySemanticsTest.java
index 2fb6bedc1eeb77..c81f3e5453bec9 100644
--- a/src/test/java/com/google/devtools/build/lib/query2/cquery/ConfiguredTargetQuerySemanticsTest.java
+++ b/src/test/java/com/google/devtools/build/lib/query2/cquery/ConfiguredTargetQuerySemanticsTest.java
@@ -241,7 +241,8 @@ public void testTopLevelTransition() throws Exception {
         () ->
             MockRule.define(
                 "rule_class_transition",
-                (builder, env) -> builder.cfg(new FooPatchTransition("SET BY PATCH")).build());
+                (builder, env) ->
+                    builder.cfg(unused -> new FooPatchTransition("SET BY PATCH")).build());
 
     helper.useRuleClassProvider(setRuleClassProviders(ruleClassTransition).build());
     helper.setUniverseScope("//test:rule_class");
diff --git a/src/test/java/com/google/devtools/build/lib/query2/cquery/TransitionsOutputFormatterTest.java b/src/test/java/com/google/devtools/build/lib/query2/cquery/TransitionsOutputFormatterTest.java
index d831f6cdba7bf6..6876b3530df418 100644
--- a/src/test/java/com/google/devtools/build/lib/query2/cquery/TransitionsOutputFormatterTest.java
+++ b/src/test/java/com/google/devtools/build/lib/query2/cquery/TransitionsOutputFormatterTest.java
@@ -205,7 +205,7 @@ private void setUpRules() throws Exception {
                 "my_rule",
                 (builder, env) ->
                     builder
-                        .cfg(ruleClassTransition)
+                        .cfg(unused -> ruleClassTransition)
                         .add(
                             attr("patched", LABEL_LIST)
                                 .allowedFileTypes(FileTypeSet.ANY_FILE)
diff --git a/src/test/java/com/google/devtools/build/lib/query2/testutil/PostAnalysisQueryTest.java b/src/test/java/com/google/devtools/build/lib/query2/testutil/PostAnalysisQueryTest.java
index e681cbbc9be97c..748cb5f9cb495d 100644
--- a/src/test/java/com/google/devtools/build/lib/query2/testutil/PostAnalysisQueryTest.java
+++ b/src/test/java/com/google/devtools/build/lib/query2/testutil/PostAnalysisQueryTest.java
@@ -555,7 +555,8 @@ public void testMultipleTopLevelConfigurations() throws Exception {
         () ->
             MockRule.define(
                 "transitioned_rule",
-                (builder, env) -> builder.cfg(new FooPatchTransition("SET BY PATCH")).build());
+                (builder, env) ->
+                    builder.cfg(unused -> new FooPatchTransition("SET BY PATCH")).build());
 
     MockRule untransitionedRule = () -> MockRule.define("untransitioned_rule");
 
@@ -587,7 +588,7 @@ public void testMultipleTopLevelConfigurations_multipleConfigsPrefersTopLevel()
                 "rule_with_transition_and_dep",
                 (builder, env) ->
                     builder
-                        .cfg(new FooPatchTransition("SET BY PATCH"))
+                        .cfg(unused -> new FooPatchTransition("SET BY PATCH"))
                         .addAttribute(
                             attr("dep", LABEL).allowedFileTypes(FileTypeSet.ANY_FILE).build())
                         .build());
diff --git a/src/test/java/com/google/devtools/build/lib/starlark/BUILD b/src/test/java/com/google/devtools/build/lib/starlark/BUILD
index 952d10cae81308..7a887cabfdd05f 100644
--- a/src/test/java/com/google/devtools/build/lib/starlark/BUILD
+++ b/src/test/java/com/google/devtools/build/lib/starlark/BUILD
@@ -41,6 +41,7 @@ java_test(
         "//src/main/java/com/google/devtools/build/lib/analysis:actions/template_expansion_action",
         "//src/main/java/com/google/devtools/build/lib/analysis:actions_provider",
         "//src/main/java/com/google/devtools/build/lib/analysis:analysis_cluster",
+        "//src/main/java/com/google/devtools/build/lib/analysis:config/build_configuration",
         "//src/main/java/com/google/devtools/build/lib/analysis:config/starlark_defined_config_transition",
         "//src/main/java/com/google/devtools/build/lib/analysis:config/toolchain_type_requirement",
         "//src/main/java/com/google/devtools/build/lib/analysis:config/transitions/no_transition",
diff --git a/src/test/java/com/google/devtools/build/lib/starlark/StarlarkRuleClassFunctionsTest.java b/src/test/java/com/google/devtools/build/lib/starlark/StarlarkRuleClassFunctionsTest.java
index 267915a617592e..d12add6d7f643b 100644
--- a/src/test/java/com/google/devtools/build/lib/starlark/StarlarkRuleClassFunctionsTest.java
+++ b/src/test/java/com/google/devtools/build/lib/starlark/StarlarkRuleClassFunctionsTest.java
@@ -30,6 +30,7 @@
 import com.google.devtools.build.lib.analysis.ConfiguredRuleClassProvider;
 import com.google.devtools.build.lib.analysis.ConfiguredTarget;
 import com.google.devtools.build.lib.analysis.RuleContext;
+import com.google.devtools.build.lib.analysis.config.BuildConfigurationValue;
 import com.google.devtools.build.lib.analysis.config.ToolchainTypeRequirement;
 import com.google.devtools.build.lib.analysis.config.transitions.NoTransition;
 import com.google.devtools.build.lib.analysis.starlark.StarlarkAttrModule;
@@ -102,7 +103,6 @@
 import org.junit.Test;
 import org.junit.rules.ExpectedException;
 import org.junit.runner.RunWith;
-
 /** Tests for StarlarkRuleClassFunctions. */
 @RunWith(TestParameterInjector.class)
 public final class StarlarkRuleClassFunctionsTest extends BuildViewTestCase {
@@ -2821,6 +2821,97 @@ public void initializer_basic() throws Exception {
     assertThat((List<String>) info.getValue("deps")).containsExactly("@@//:initial", "@@//:added");
   }
 
+  @Test
+  public void initializer_legacyAnyType() throws Exception {
+    scratch.file(
+        "initializer_testing/b.bzl",
+        "MyInfo = provider()",
+        "def initializer(tristate = -1):",
+        "  return {'tristate': int(tristate)}",
+        "def impl(ctx): ",
+        "  return [MyInfo(tristate = ctx.attr.tristate)]",
+        "my_rule = rule(impl,",
+        "  initializer = initializer,",
+        "  attrs = {",
+        "    'tristate': attr.int(),",
+        "    '_legacy_any_type_attrs': attr.string_list(default = ['tristate']),",
+        "  })");
+    scratch.file(
+        "initializer_testing/BUILD", //
+        "load(':b.bzl','my_rule')",
+        "my_rule(name = 'my_target', tristate = True)");
+
+    ConfiguredTarget myTarget = getConfiguredTarget("//initializer_testing:my_target");
+    StructImpl info =
+        (StructImpl)
+            myTarget.get(
+                new StarlarkProvider.Key(
+                    Label.parseCanonical("//initializer_testing:b.bzl"), "MyInfo"));
+
+    assertThat((StarlarkInt) info.getValue("tristate")).isEqualTo(StarlarkInt.of(1));
+  }
+
+  @Test
+  public void initializer_wrongType() throws Exception {
+    scratch.file(
+        "initializer_testing/b.bzl",
+        "MyInfo = provider()",
+        "def initializer(srcs = []):",
+        "  return {'srcs': ['a.ml']}",
+        "def impl(ctx): ",
+        "  return [MyInfo(",
+        "    srcs = [s.short_path for s in ctx.files.srcs])]",
+        "my_rule = rule(impl,",
+        "  initializer = initializer,",
+        "  attrs = {",
+        "    'srcs': attr.label_list(allow_files = ['ml']),",
+        "  })");
+    scratch.file(
+        "initializer_testing/BUILD", //
+        "load(':b.bzl','my_rule')",
+        "my_rule(name = 'my_target', srcs = 'default_files')");
+
+    reporter.removeHandler(failFastHandler);
+    reporter.addHandler(ev.getEventCollector());
+    getConfiguredTarget("//initializer_testing:my_target");
+
+    ev.assertContainsError(
+        "expected value of type 'list(label)' for attribute 'srcs' in 'my_rule' rule, but got"
+            + " \"default_files\" (string)");
+  }
+
+  @Test
+  @SuppressWarnings("unchecked")
+  public void initializer_withSelect() throws Exception {
+    scratch.file(
+        "initializer_testing/b.bzl",
+        "MyInfo = provider()",
+        "def initializer(srcs = []):",
+        "  return {'srcs': srcs + ['b.ml']}",
+        "def impl(ctx): ",
+        "  return [MyInfo(",
+        "    srcs = [s.short_path for s in ctx.files.srcs])]",
+        "my_rule = rule(impl,",
+        "  initializer = initializer,",
+        "  attrs = {",
+        "    'srcs': attr.label_list(allow_files = ['ml']),",
+        "  })");
+    scratch.file(
+        "initializer_testing/BUILD", //
+        "load(':b.bzl','my_rule')",
+        "my_rule(name = 'my_target', srcs = select({'//conditions:default': ['a.ml']}))");
+
+    ConfiguredTarget myTarget = getConfiguredTarget("//initializer_testing:my_target");
+    StructImpl info =
+        (StructImpl)
+            myTarget.get(
+                new StarlarkProvider.Key(
+                    Label.parseCanonical("//initializer_testing:b.bzl"), "MyInfo"));
+
+    assertThat((List<String>) info.getValue("srcs"))
+        .containsExactly("initializer_testing/a.ml", "initializer_testing/b.ml");
+  }
+
   @Test
   public void initializer_passThrough() throws Exception {
     scratch.file(
@@ -2923,8 +3014,7 @@ public void initializer_omittedValueIsNotPassed() throws Exception {
         "def initializer(srcs):",
         "  return {'srcs': srcs}",
         "def impl(ctx): ",
-        "  return [MyInfo(",
-        "    deps = [str(d.label) for d in ctx.attr.deps])]",
+        "  pass",
         "my_rule = rule(impl,",
         "  initializer = initializer,",
         "  attrs = {",
@@ -2934,8 +3024,6 @@ public void initializer_omittedValueIsNotPassed() throws Exception {
         "initializer_testing/BUILD", //
         "load(':b.bzl','my_rule')",
         "my_rule(name = 'my_target')");
-    // TODO: b/298561048 - Behavior with `srcs=[]` or `srcs=None` is different. Fix that when
-    // lifting parameters types.
 
     reporter.removeHandler(failFastHandler);
     reporter.addHandler(ev.getEventCollector());
@@ -2945,6 +3033,32 @@ public void initializer_omittedValueIsNotPassed() throws Exception {
     ev.assertContainsError("initializer() missing 1 required positional argument: srcs");
   }
 
+  @Test
+  public void initializer_noneValueIsNotPassed() throws Exception {
+    scratch.file(
+        "initializer_testing/b.bzl",
+        "MyInfo = provider()",
+        "def initializer(srcs):",
+        "  return {'srcs': srcs}",
+        "def impl(ctx): ",
+        "  pass",
+        "my_rule = rule(impl,",
+        "  initializer = initializer,",
+        "  attrs = {",
+        "    'srcs': attr.label_list(),",
+        "  })");
+    scratch.file(
+        "initializer_testing/BUILD", //
+        "load(':b.bzl','my_rule')",
+        "my_rule(name = 'my_target', srcs = None)");
+
+    reporter.removeHandler(failFastHandler);
+    reporter.addHandler(ev.getEventCollector());
+    getConfiguredTarget("//initializer_testing:my_target");
+
+    ev.assertContainsError("initializer() missing 1 required positional argument: srcs");
+  }
+
   @Test
   public void initializer_incorrectReturnType() throws Exception {
     scratch.file(
@@ -3052,7 +3166,10 @@ public void initializer_failsSettingPrivateAttribute_outsideBuiltins() throws Ex
 
   @Test
   public void initializer_settingPrivateAttribute_insideBuiltins() throws Exception {
-    scratch.file("initializer_testing/builtins/BUILD");
+    // Because it's hard to test something that needs to be in builtins,
+    // this is also allowed in a special testing location: {@link
+    // StarlarkRuleClassFunctions.ALLOWLIST_RULE_EXTENSION_API_EXPERIMENTAL}
+    scratch.file("initializer_testing/builtins/BUILD", "filegroup(name='my_tool')");
     scratch.file(
         "initializer_testing/builtins/b.bzl",
         "def initializer(srcs = [], deps = []):",
@@ -3069,7 +3186,6 @@ public void initializer_settingPrivateAttribute_insideBuiltins() throws Exceptio
     scratch.file(
         "initializer_testing/BUILD", //
         "load('//initializer_testing/builtins:b.bzl','my_rule')",
-        "filegroup(name='my_tool')",
         "my_rule(name = 'my_target', srcs = ['a.ml'])");
 
     ConfiguredTarget myTarget = getConfiguredTarget("//initializer_testing:my_target");
@@ -3079,7 +3195,8 @@ public void initializer_settingPrivateAttribute_insideBuiltins() throws Exceptio
                 new StarlarkProvider.Key(
                     Label.parseCanonical("//initializer_testing/builtins:b.bzl"), "MyInfo"));
 
-    assertThat(info.getValue("_tool").toString()).isEqualTo("@@//initializer_testing:my_tool");
+    assertThat(info.getValue("_tool").toString())
+        .isEqualTo("@@//initializer_testing/builtins:my_tool");
   }
 
   @Test
@@ -4222,6 +4339,176 @@ public void extendRule_execGroups_merged() throws Exception {
         .containsExactly("parent_exec_group", "child_exec_group");
   }
 
+  private void scratchStarlarkTransition() throws IOException {
+    scratch.overwriteFile(
+        TestConstants.TOOLS_REPOSITORY_SCRATCH
+            + "tools/allowlists/function_transition_allowlist/BUILD",
+        "package_group(",
+        "    name = 'function_transition_allowlist',",
+        "    packages = [",
+        "        'public',",
+        "    ],",
+        ")");
+    scratch.file(
+        "test/build_settings.bzl",
+        "def _impl(ctx):",
+        "  return []",
+        "string_flag = rule(implementation = _impl, build_setting = config.string(flag=True))");
+    scratch.file(
+        "test/BUILD",
+        "load('//test:build_settings.bzl', 'string_flag')",
+        "string_flag(",
+        "  name = 'parent-flag',",
+        "  build_setting_default = 'default-parent'",
+        ")",
+        "string_flag(",
+        "  name = 'parent-child-flag',",
+        "  build_setting_default = 'default-parent-child'",
+        ")",
+        "string_flag(",
+        "  name = 'child-flag',",
+        "  build_setting_default = 'child-default'",
+        ")");
+    scratch.file(
+        "test/transitions.bzl",
+        "def _parent_trans_impl(settings, attr):",
+        "  return {'//test:parent-flag': 'parent-changed',",
+        "          '//test:parent-child-flag': 'parent-child-changed-in-parent'}",
+        "parent_transition = transition(",
+        "  implementation = _parent_trans_impl,",
+        "  inputs = [],",
+        "  outputs = ['//test:parent-flag', '//test:parent-child-flag']",
+        ")",
+        "def _child_trans_impl(settings, attr):",
+        "  return {'//test:child-flag': 'child-changed',",
+        "          '//test:parent-child-flag': 'parent-child-changed-in-child'}",
+        "child_transition = transition(",
+        "  implementation = _child_trans_impl,",
+        "  inputs = [],",
+        "  outputs = ['//test:child-flag', '//test:parent-child-flag']",
+        ")");
+  }
+
+  @Test
+  public void extendRule_cfg_fromParent() throws Exception {
+    scratchStarlarkTransition();
+    scratch.file("extend_rule_testing/parent/BUILD");
+    scratch.file(
+        "extend_rule_testing/parent/parent.bzl",
+        "load('//test:transitions.bzl', 'parent_transition')",
+        "def _impl(ctx):",
+        "  pass",
+        "parent_rule = rule(",
+        "  implementation = _impl,",
+        "  extendable = True,",
+        "  cfg = parent_transition",
+        ")");
+    scratch.file(
+        "extend_rule_testing/child.bzl",
+        "load('//extend_rule_testing/parent:parent.bzl', 'parent_rule')",
+        "def _impl(ctx):",
+        "  ctx.super()",
+        "my_library = rule(",
+        "  implementation = _impl,",
+        "  parent = parent_rule,",
+        ")");
+    scratch.file(
+        "extend_rule_testing/BUILD",
+        "load(':child.bzl', 'my_library')",
+        "my_library(name = 'my_target')");
+
+    BuildConfigurationValue configuration =
+        getConfiguration(getConfiguredTarget("//extend_rule_testing:my_target"));
+
+    var options = configuration.getOptions().getStarlarkOptions();
+    assertThat(options.get(Label.parseCanonicalUnchecked("//test:parent-flag")))
+        .isEqualTo("parent-changed");
+    assertThat(options.get(Label.parseCanonicalUnchecked("//test:parent-child-flag")))
+        .isEqualTo("parent-child-changed-in-parent");
+    assertThat(options.get(Label.parseCanonicalUnchecked("//test:child-flag"))).isNull();
+  }
+
+  @Test
+  public void extendRule_cfg_onChild() throws Exception {
+    scratchStarlarkTransition();
+    scratch.file("extend_rule_testing/parent/BUILD");
+    scratch.file(
+        "extend_rule_testing/parent/parent.bzl",
+        "def _impl(ctx):",
+        "  pass",
+        "parent_rule = rule(",
+        "  implementation = _impl,",
+        "  extendable = True,",
+        ")");
+    scratch.file(
+        "extend_rule_testing/child.bzl",
+        "load('//extend_rule_testing/parent:parent.bzl', 'parent_rule')",
+        "load('//test:transitions.bzl', 'child_transition')",
+        "def _impl(ctx):",
+        "  ctx.super()",
+        "my_library = rule(",
+        "  implementation = _impl,",
+        "  parent = parent_rule,",
+        "  cfg = child_transition",
+        ")");
+    scratch.file(
+        "extend_rule_testing/BUILD",
+        "load(':child.bzl', 'my_library')",
+        "my_library(name = 'my_target')");
+
+    BuildConfigurationValue configuration =
+        getConfiguration(getConfiguredTarget("//extend_rule_testing:my_target"));
+
+    var options = configuration.getOptions().getStarlarkOptions();
+    assertThat(options.get(Label.parseCanonicalUnchecked("//test:parent-flag"))).isNull();
+    assertThat(options.get(Label.parseCanonicalUnchecked("//test:parent-child-flag")))
+        .isEqualTo("parent-child-changed-in-child");
+    assertThat(options.get(Label.parseCanonicalUnchecked("//test:child-flag")))
+        .isEqualTo("child-changed");
+  }
+
+  @Test
+  public void extendRule_cfg_onChildAndFromParent() throws Exception {
+    scratchStarlarkTransition();
+    scratch.file("extend_rule_testing/parent/BUILD");
+    scratch.file(
+        "extend_rule_testing/parent/parent.bzl",
+        "load('//test:transitions.bzl', 'parent_transition')",
+        "def _impl(ctx):",
+        "  pass",
+        "parent_rule = rule(",
+        "  implementation = _impl,",
+        "  extendable = True,",
+        "  cfg = parent_transition",
+        ")");
+    scratch.file(
+        "extend_rule_testing/child.bzl",
+        "load('//extend_rule_testing/parent:parent.bzl', 'parent_rule')",
+        "load('//test:transitions.bzl', 'child_transition')",
+        "def _impl(ctx):",
+        "  ctx.super()",
+        "my_library = rule(",
+        "  implementation = _impl,",
+        "  parent = parent_rule,",
+        "  cfg = child_transition",
+        ")");
+    scratch.file(
+        "extend_rule_testing/BUILD",
+        "load(':child.bzl', 'my_library')",
+        "my_library(name = 'my_target')");
+
+    BuildConfigurationValue configuration =
+        getConfiguration(getConfiguredTarget("//extend_rule_testing:my_target"));
+
+    var options = configuration.getOptions().getStarlarkOptions();
+    assertThat(options.get(Label.parseCanonicalUnchecked("//test:parent-flag")))
+        .isEqualTo("parent-changed");
+    assertThat(options.get(Label.parseCanonicalUnchecked("//test:parent-child-flag")))
+        .isEqualTo("parent-child-changed-in-parent");
+    assertThat(options.get(Label.parseCanonicalUnchecked("//test:child-flag")))
+        .isEqualTo("child-changed");
+  }
+
   @Test
   public void testAnalysisTest() throws Exception {
     scratch.file(
diff --git a/src/test/shell/integration/starlark_configurations_test.sh b/src/test/shell/integration/starlark_configurations_test.sh
index 3cad6b08857c01..1191d7f2fdeb7c 100755
--- a/src/test/shell/integration/starlark_configurations_test.sh
+++ b/src/test/shell/integration/starlark_configurations_test.sh
@@ -740,7 +740,7 @@ EOF
 
   bazel build //$pkg:demo >& "$TEST_log" && fail "Expected failure"
   expect_not_log "crashed due to an internal error"
-  expect_log "`cfg` must be set to a transition appropriate for a rule"
+  expect_log "`cfg` must be set to a transition object initialized by the transition() function"
 }
 
 run_suite "${PRODUCT_NAME} starlark configurations tests"