diff --git a/src/main/java/com/google/devtools/build/lib/bazel/repository/skylark/SkylarkRepositoryFunction.java b/src/main/java/com/google/devtools/build/lib/bazel/repository/skylark/SkylarkRepositoryFunction.java
index ec1c2fd..904e177 100644
--- a/src/main/java/com/google/devtools/build/lib/bazel/repository/skylark/SkylarkRepositoryFunction.java
+++ b/src/main/java/com/google/devtools/build/lib/bazel/repository/skylark/SkylarkRepositoryFunction.java
@@ -36,9 +36,9 @@
 import com.google.devtools.build.lib.runtime.RepositoryRemoteExecutor;
 import com.google.devtools.build.lib.skyframe.BlacklistedPackagePrefixesValue;
 import com.google.devtools.build.lib.skyframe.PrecomputedValue;
-import com.google.devtools.build.lib.syntax.BaseFunction;
 import com.google.devtools.build.lib.syntax.EvalException;
 import com.google.devtools.build.lib.syntax.Mutability;
+import com.google.devtools.build.lib.syntax.StarlarkFunction;
 import com.google.devtools.build.lib.syntax.StarlarkSemantics;
 import com.google.devtools.build.lib.syntax.StarlarkThread;
 import com.google.devtools.build.lib.vfs.Path;
@@ -84,7 +84,7 @@
               new SkylarkRepositoryDefinitionLocationEvent(
                   rule.getName(), rule.getDefinitionInformation()));
     }
-    BaseFunction function = rule.getRuleClassObject().getConfiguredTargetFunction();
+    StarlarkFunction function = rule.getRuleClassObject().getConfiguredTargetFunction();
     if (declareEnvironmentDependencies(markerData, env, getEnviron(rule)) == null) {
       return null;
     }
diff --git a/src/main/java/com/google/devtools/build/lib/bazel/repository/skylark/SkylarkRepositoryModule.java b/src/main/java/com/google/devtools/build/lib/bazel/repository/skylark/SkylarkRepositoryModule.java
index 4fdc01c..fdf1b9e 100644
--- a/src/main/java/com/google/devtools/build/lib/bazel/repository/skylark/SkylarkRepositoryModule.java
+++ b/src/main/java/com/google/devtools/build/lib/bazel/repository/skylark/SkylarkRepositoryModule.java
@@ -49,6 +49,7 @@
 import com.google.devtools.build.lib.syntax.Sequence;
 import com.google.devtools.build.lib.syntax.SkylarkUtils;
 import com.google.devtools.build.lib.syntax.Starlark;
+import com.google.devtools.build.lib.syntax.StarlarkFunction;
 import com.google.devtools.build.lib.syntax.StarlarkSemantics;
 import com.google.devtools.build.lib.syntax.StarlarkThread;
 import java.util.Map;
@@ -61,7 +62,7 @@
 
   @Override
   public BaseFunction repositoryRule(
-      BaseFunction implementation,
+      StarlarkFunction implementation,
       Object attrs,
       Boolean local,
       Sequence<?> environ, // <String> expected
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 f087893..29a0e35 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
@@ -55,10 +55,10 @@
 import com.google.devtools.build.lib.packages.Type.ConversionException;
 import com.google.devtools.build.lib.skyframe.serialization.autocodec.AutoCodec;
 import com.google.devtools.build.lib.skyframe.serialization.autocodec.AutoCodec.VisibleForSerialization;
-import com.google.devtools.build.lib.syntax.BaseFunction;
 import com.google.devtools.build.lib.syntax.EvalException;
 import com.google.devtools.build.lib.syntax.Sequence;
 import com.google.devtools.build.lib.syntax.Starlark;
+import com.google.devtools.build.lib.syntax.StarlarkFunction;
 import com.google.devtools.build.lib.util.FileTypeSet;
 import com.google.devtools.build.lib.util.StringUtil;
 import com.google.devtools.build.lib.vfs.PathFragment;
@@ -640,7 +640,7 @@
         PredicatesWithMessage.<Rule>alwaysTrue();
     private Predicate<String> preferredDependencyPredicate = Predicates.alwaysFalse();
     private AdvertisedProviderSet.Builder advertisedProviders = AdvertisedProviderSet.builder();
-    private BaseFunction configuredTargetFunction = null;
+    private StarlarkFunction configuredTargetFunction = null;
     private BuildSetting buildSetting = null;
     private Function<? super Rule, Map<String, Label>> externalBindingsFunction =
         NO_EXTERNAL_BINDINGS;
@@ -1150,10 +1150,8 @@
       return attributes.containsKey(name);
     }
 
-    /**
-     * Sets the rule implementation function. Meant for Skylark usage.
-     */
-    public Builder setConfiguredTargetFunction(BaseFunction func) {
+    /** Sets the rule implementation function. Meant for Skylark usage. */
+    public Builder setConfiguredTargetFunction(StarlarkFunction func) {
       this.configuredTargetFunction = func;
       return this;
     }
@@ -1443,7 +1441,7 @@
   /**
    * The Skylark rule implementation of this RuleClass. Null for non Skylark executable RuleClasses.
    */
-  @Nullable private final BaseFunction configuredTargetFunction;
+  @Nullable private final StarlarkFunction configuredTargetFunction;
 
   /**
    * The BuildSetting associated with this rule. Null for all RuleClasses except Skylark-defined
@@ -1530,7 +1528,7 @@
       PredicateWithMessage<Rule> validityPredicate,
       Predicate<String> preferredDependencyPredicate,
       AdvertisedProviderSet advertisedProviders,
-      @Nullable BaseFunction configuredTargetFunction,
+      @Nullable StarlarkFunction configuredTargetFunction,
       Function<? super Rule, Map<String, Label>> externalBindingsFunction,
       Function<? super Rule, ? extends Set<String>> optionReferenceFunction,
       @Nullable Label ruleDefinitionEnvironmentLabel,
@@ -2369,10 +2367,9 @@
     return binaryOutput;
   }
 
-  /**
-   * Returns this RuleClass's custom Skylark rule implementation.
-   */
-  @Nullable public BaseFunction getConfiguredTargetFunction() {
+  /** Returns this RuleClass's custom Skylark rule implementation. */
+  @Nullable
+  public StarlarkFunction getConfiguredTargetFunction() {
     return configuredTargetFunction;
   }
 
diff --git a/src/main/java/com/google/devtools/build/lib/skylarkbuildapi/repository/RepositoryModuleApi.java b/src/main/java/com/google/devtools/build/lib/skylarkbuildapi/repository/RepositoryModuleApi.java
index 33afe11..8f7840c 100644
--- a/src/main/java/com/google/devtools/build/lib/skylarkbuildapi/repository/RepositoryModuleApi.java
+++ b/src/main/java/com/google/devtools/build/lib/skylarkbuildapi/repository/RepositoryModuleApi.java
@@ -23,6 +23,7 @@
 import com.google.devtools.build.lib.syntax.EvalException;
 import com.google.devtools.build.lib.syntax.FuncallExpression;
 import com.google.devtools.build.lib.syntax.Sequence;
+import com.google.devtools.build.lib.syntax.StarlarkFunction;
 import com.google.devtools.build.lib.syntax.StarlarkSemantics.FlagIdentifier;
 import com.google.devtools.build.lib.syntax.StarlarkThread;
 
@@ -41,12 +42,13 @@
       parameters = {
         @Param(
             name = "implementation",
-            type = BaseFunction.class,
+            type = StarlarkFunction.class,
             named = true,
             doc =
-                "the function implementing this rule, has to have exactly one parameter: <code><a"
-                    + " href=\"repository_ctx.html\">repository_ctx</a></code>. The function is"
-                    + " called during loading phase for each instance of the rule."),
+                "the Starlark function that implements this rule. Must have a single parameter,"
+                    + " <code><a href=\"repository_ctx.html\">repository_ctx</a></code>. The"
+                    + " function is called during the loading phase for each instance of the"
+                    + " rule."),
         @Param(
             name = "attrs",
             type = Dict.class,
@@ -110,7 +112,7 @@
       useAst = true,
       useStarlarkThread = true)
   BaseFunction repositoryRule(
-      BaseFunction implementation,
+      StarlarkFunction implementation,
       Object attrs,
       Boolean local,
       Sequence<?> environ, // <String> expected
diff --git a/src/main/java/com/google/devtools/build/lib/syntax/BaseFunction.java b/src/main/java/com/google/devtools/build/lib/syntax/BaseFunction.java
index 90325f0..a248503 100644
--- a/src/main/java/com/google/devtools/build/lib/syntax/BaseFunction.java
+++ b/src/main/java/com/google/devtools/build/lib/syntax/BaseFunction.java
@@ -277,6 +277,7 @@
    * @return the value resulting from evaluating the function with the given arguments
    * @throws EvalException-s containing source information.
    */
+  @Override
   public Object call(
       List<Object> args,
       @Nullable Map<String, Object> kwargs,
@@ -358,9 +359,4 @@
   public void repr(Printer printer) {
     printer.append("<function " + getName() + ">");
   }
-
-  @Override
-  public Location getLocation() {
-    return Location.BUILTIN;
-  }
 }
diff --git a/src/main/java/com/google/devtools/build/lib/syntax/BuiltinCallable.java b/src/main/java/com/google/devtools/build/lib/syntax/BuiltinCallable.java
index 8faf014..0cdd461 100644
--- a/src/main/java/com/google/devtools/build/lib/syntax/BuiltinCallable.java
+++ b/src/main/java/com/google/devtools/build/lib/syntax/BuiltinCallable.java
@@ -13,7 +13,6 @@
 // limitations under the License.
 package com.google.devtools.build.lib.syntax;
 
-import com.google.devtools.build.lib.events.Location;
 import com.google.devtools.build.lib.profiler.Profiler;
 import com.google.devtools.build.lib.profiler.ProfilerTask;
 import com.google.devtools.build.lib.profiler.SilentCloseable;
@@ -104,11 +103,6 @@
   }
 
   @Override
-  public Location getLocation() {
-    return Location.BUILTIN;
-  }
-
-  @Override
   public String getName() {
     return methodName;
   }
diff --git a/src/main/java/com/google/devtools/build/lib/syntax/StarlarkCallable.java b/src/main/java/com/google/devtools/build/lib/syntax/StarlarkCallable.java
index b4d488d..a8372d1 100644
--- a/src/main/java/com/google/devtools/build/lib/syntax/StarlarkCallable.java
+++ b/src/main/java/com/google/devtools/build/lib/syntax/StarlarkCallable.java
@@ -55,5 +55,7 @@
    * Returns the location of the definition of this callable value, or BUILTIN if it was not defined
    * in Starlark code.
    */
-  Location getLocation();
+  default Location getLocation() {
+    return Location.BUILTIN;
+  }
 }
diff --git a/src/main/java/com/google/devtools/build/skydoc/fakebuildapi/repository/FakeRepositoryModule.java b/src/main/java/com/google/devtools/build/skydoc/fakebuildapi/repository/FakeRepositoryModule.java
index 4486139..773fab5 100644
--- a/src/main/java/com/google/devtools/build/skydoc/fakebuildapi/repository/FakeRepositoryModule.java
+++ b/src/main/java/com/google/devtools/build/skydoc/fakebuildapi/repository/FakeRepositoryModule.java
@@ -25,6 +25,7 @@
 import com.google.devtools.build.lib.syntax.FunctionSignature;
 import com.google.devtools.build.lib.syntax.Sequence;
 import com.google.devtools.build.lib.syntax.Starlark;
+import com.google.devtools.build.lib.syntax.StarlarkFunction;
 import com.google.devtools.build.lib.syntax.StarlarkThread;
 import com.google.devtools.build.skydoc.fakebuildapi.FakeDescriptor;
 import com.google.devtools.build.skydoc.fakebuildapi.FakeSkylarkRuleFunctionsApi.AttributeNameComparator;
@@ -51,7 +52,7 @@
 
   @Override
   public BaseFunction repositoryRule(
-      BaseFunction implementation,
+      StarlarkFunction implementation,
       Object attrs,
       Boolean local,
       Sequence<?> environ, // <String> expected