Rollback of commit cdbad585187dfe7bbb4d69ad68a1baf852beb691.

*** Reason for rollback ***

Breaks Skylark aspects running over rules with LABEL_DICT_UNARY attributes.

*** Original change description ***

Refactoring: Types report what class of labels they contain.

Currently label-type attributes are detected in many places across the
codebase by simply reference-comparing against each of the label types.
This CL aims to generalize most of these cases, moving the encoding of
this logic into a single place (Type/BuildType itself). Not all of these
cases can be made general without further refactoring, and some perhaps
shouldn't be - serialization and Skylark rule context, for example, need
to do...

--
PiperOrigin-RevId: 147385072
MOS_MIGRATED_REVID=147385072

12 files changed, 81 insertions, 163 deletions

diff --git a/src/main/java/com/google/devtools/build/lib/analysis/RuleContext.java b/src/main/java/com/google/devtools/build/lib/analysis/RuleContext.java
index 656ca2595f..937cf74c45 100644
--- a/src/main/java/com/google/devtools/build/lib/analysis/RuleContext.java
+++ b/src/main/java/com/google/devtools/build/lib/analysis/RuleContext.java
@@ -81,7 +81,6 @@ import com.google.devtools.build.lib.rules.fileset.FilesetProvider;
 import com.google.devtools.build.lib.shell.ShellUtils;
 import com.google.devtools.build.lib.syntax.EvalException;
 import com.google.devtools.build.lib.syntax.Type;
-import com.google.devtools.build.lib.syntax.Type.LabelClass;
 import com.google.devtools.build.lib.util.FileTypeSet;
 import com.google.devtools.build.lib.util.OrderedSetMultimap;
 import com.google.devtools.build.lib.util.Preconditions;
@@ -1084,7 +1083,8 @@ public final class RuleContext extends TargetContext
       throw new IllegalStateException(getRule().getLocation() + ": " + getRuleClassNameForLogging()
         + " attribute " + attributeName + " is not defined");
     }
-    if (attributeDefinition.getType().getLabelClass() != LabelClass.DEPENDENCY) {
+    if (!(attributeDefinition.getType() == BuildType.LABEL
+        || attributeDefinition.getType() == BuildType.LABEL_LIST)) {
       throw new IllegalStateException(getRuleClassNameForLogging() + " attribute " + attributeName
         + " is not a label type attribute");
     }
@@ -1125,7 +1125,8 @@ public final class RuleContext extends TargetContext
       throw new IllegalStateException(getRule().getLocation() + ": " + getRuleClassNameForLogging()
         + " attribute " + attributeName + " is not defined");
     }
-    if (attributeDefinition.getType().getLabelClass() != LabelClass.DEPENDENCY) {
+    if (!(attributeDefinition.getType() == BuildType.LABEL
+        || attributeDefinition.getType() == BuildType.LABEL_LIST)) {
       throw new IllegalStateException(getRuleClassNameForLogging() + " attribute " + attributeName
         + " is not a label type attribute");
     }
diff --git a/src/main/java/com/google/devtools/build/lib/analysis/constraints/ConstraintSemantics.java b/src/main/java/com/google/devtools/build/lib/analysis/constraints/ConstraintSemantics.java
index 33f7d348f6..86d736d60a 100644
--- a/src/main/java/com/google/devtools/build/lib/analysis/constraints/ConstraintSemantics.java
+++ b/src/main/java/com/google/devtools/build/lib/analysis/constraints/ConstraintSemantics.java
@@ -36,8 +36,6 @@ import com.google.devtools.build.lib.packages.Rule;
 import com.google.devtools.build.lib.packages.RuleClass;
 import com.google.devtools.build.lib.packages.Target;
 import com.google.devtools.build.lib.syntax.Type;
-import com.google.devtools.build.lib.syntax.Type.LabelClass;
-import com.google.devtools.build.lib.syntax.Type.LabelVisitor;
 import com.google.devtools.build.lib.util.Preconditions;
 
 import java.util.Collection;
@@ -741,7 +739,7 @@ public class ConstraintSemantics {
     AttributeMap attributes = ruleContext.attributes();
     for (String attr : attributes.getAttributeNames()) {
       Attribute attrDef = attributes.getAttributeDefinition(attr);
-      if (attrDef.getType().getLabelClass() != LabelClass.DEPENDENCY
+      if ((attrDef.getType() != BuildType.LABEL && attrDef.getType() != BuildType.LABEL_LIST)
           || attrDef.skipConstraintsOverride()) {
         continue;
       }
@@ -821,22 +819,21 @@ public class ConstraintSemantics {
    * Adds all label values from the given select to the given set. Automatically handles different
    * value types (e.g. labels vs. label lists).
    */
-  private static void addSelectValuesToSet(BuildType.Selector<?> select, final Set<Label> set) {
+  private static void addSelectValuesToSet(BuildType.Selector<?> select, Set<Label> set) {
     Type<?> type = select.getOriginalType();
-    LabelVisitor visitor = new LabelVisitor() {
-      @Override
-      public void visit(Label label) {
-        set.add(label);
+    if (type == BuildType.LABEL || type == BuildType.NODEP_LABEL) {
+      set.addAll(((BuildType.Selector<Label>) select).getEntries().values());
+    } else if (type == BuildType.LABEL_LIST ||  type == BuildType.NODEP_LABEL_LIST) {
+      for (List<Label> labels : ((BuildType.Selector<List<Label>>) select).getEntries().values()) {
+        set.addAll(labels);
       }
-    };
-    for (Object value : select.getEntries().values()) {
-      try {
-        type.visitLabels(visitor, value);
-      } catch (InterruptedException ex) {
-        // Because the LabelVisitor does not throw InterruptedException, it should not be thrown
-        // by visitLabels here.
-        throw new AssertionError(ex);
+    } else if (type == BuildType.LABEL_DICT_UNARY) {
+      for (Map<String, Label> mapEntry :
+          ((BuildType.Selector<Map<String, Label>>) select).getEntries().values()) {
+        set.addAll(mapEntry.values());
       }
+    } else {
+      throw new IllegalStateException("Expected a label-based type for this select");
     }
   }
 }
diff --git a/src/main/java/com/google/devtools/build/lib/packages/AspectDefinition.java b/src/main/java/com/google/devtools/build/lib/packages/AspectDefinition.java
index a305e515d2..338d4bfce8 100644
--- a/src/main/java/com/google/devtools/build/lib/packages/AspectDefinition.java
+++ b/src/main/java/com/google/devtools/build/lib/packages/AspectDefinition.java
@@ -25,12 +25,11 @@ import com.google.devtools.build.lib.cmdline.Label;
 import com.google.devtools.build.lib.concurrent.ThreadSafety.Immutable;
 import com.google.devtools.build.lib.packages.ConfigurationFragmentPolicy.MissingFragmentPolicy;
 import com.google.devtools.build.lib.syntax.Type;
-import com.google.devtools.build.lib.syntax.Type.LabelClass;
-import com.google.devtools.build.lib.syntax.Type.LabelVisitor;
 import com.google.devtools.build.lib.util.Preconditions;
 import java.util.Collection;
 import java.util.LinkedHashMap;
 import java.util.LinkedHashSet;
+import java.util.List;
 import java.util.Map;
 import javax.annotation.Nullable;
 
@@ -191,36 +190,32 @@ public final class AspectDefinition {
    * Collects all attribute labels from the specified aspectDefinition.
    */
   public static void addAllAttributesOfAspect(
-      final Rule from,
-      final Multimap<Attribute, Label> labelBuilder,
+      Rule from,
+      Multimap<Attribute, Label> labelBuilder,
       Aspect aspect,
       DependencyFilter dependencyFilter) {
     ImmutableMap<String, Attribute> attributes = aspect.getDefinition().getAttributes();
-    for (final Attribute aspectAttribute : attributes.values()) {
+    for (Attribute aspectAttribute : attributes.values()) {
       if (!dependencyFilter.apply(aspect, aspectAttribute)) {
         continue;
       }
-      Type type = aspectAttribute.getType();
-      if (type.getLabelClass() != LabelClass.DEPENDENCY) {
-        continue;
-      }
-      try {
-        type.visitLabels(
-            new LabelVisitor() {
-              @Override
-              public void visit(Label label) {
-                Label repositoryRelative = maybeGetRepositoryRelativeLabel(from, label);
-                if (repositoryRelative == null) {
-                  return;
-                }
-                labelBuilder.put(aspectAttribute, repositoryRelative);
-              }
-            },
+      if (aspectAttribute.getType() == BuildType.LABEL) {
+        Label label = maybeGetRepositoryRelativeLabel(
+            from, BuildType.LABEL.cast(aspectAttribute.getDefaultValue(from)));
+        if (label != null) {
+          labelBuilder.put(aspectAttribute, label);
+        }
+      } else if (aspectAttribute.getType() == BuildType.LABEL_LIST) {
+        List<Label> defaultLabels = BuildType.LABEL_LIST.cast(
             aspectAttribute.getDefaultValue(from));
-      } catch (InterruptedException ex) {
-        // Because the LabelVisitor does not throw InterruptedException, it should not be thrown
-        // by visitLabels here.
-        throw new AssertionError(ex);
+        if (defaultLabels != null) {
+          for (Label defaultLabel : defaultLabels) {
+            Label label = maybeGetRepositoryRelativeLabel(from, defaultLabel);
+            if (label != null) {
+              labelBuilder.put(aspectAttribute, label);
+            }
+          }
+        }
       }
     }
   }
diff --git a/src/main/java/com/google/devtools/build/lib/packages/Attribute.java b/src/main/java/com/google/devtools/build/lib/packages/Attribute.java
index f5e9b95eb9..2288a76210 100644
--- a/src/main/java/com/google/devtools/build/lib/packages/Attribute.java
+++ b/src/main/java/com/google/devtools/build/lib/packages/Attribute.java
@@ -36,7 +36,6 @@ import com.google.devtools.build.lib.syntax.Runtime;
 import com.google.devtools.build.lib.syntax.SkylarkCallbackFunction;
 import com.google.devtools.build.lib.syntax.Type;
 import com.google.devtools.build.lib.syntax.Type.ConversionException;
-import com.google.devtools.build.lib.syntax.Type.LabelClass;
 import com.google.devtools.build.lib.util.FileType;
 import com.google.devtools.build.lib.util.FileTypeSet;
 import com.google.devtools.build.lib.util.Preconditions;
@@ -508,7 +507,7 @@ public final class Attribute implements Comparable<Attribute> {
      * Makes the built attribute producing a single artifact.
      */
     public Builder<TYPE> singleArtifact() {
-      Preconditions.checkState(type.getLabelClass() == LabelClass.DEPENDENCY,
+      Preconditions.checkState((type == BuildType.LABEL) || (type == BuildType.LABEL_LIST),
           "attribute '%s' must be a label-valued type", name);
       return setPropertyFlag(PropertyFlag.SINGLE_ARTIFACT, "single_artifact");
     }
@@ -518,7 +517,7 @@ public final class Attribute implements Comparable<Attribute> {
      * This flag is introduced to handle plugins, do not use it in other cases.
      */
     public Builder<TYPE> silentRuleClassFilter() {
-      Preconditions.checkState(type.getLabelClass() == LabelClass.DEPENDENCY,
+      Preconditions.checkState((type == BuildType.LABEL) || (type == BuildType.LABEL_LIST),
           "must be a label-valued type");
       return setPropertyFlag(PropertyFlag.SILENT_RULECLASS_FILTER, "silent_ruleclass_filter");
     }
@@ -527,7 +526,7 @@ public final class Attribute implements Comparable<Attribute> {
      * Skip analysis time filetype check. Don't use it if avoidable.
      */
     public Builder<TYPE> skipAnalysisTimeFileTypeCheck() {
-      Preconditions.checkState(type.getLabelClass() == LabelClass.DEPENDENCY,
+      Preconditions.checkState((type == BuildType.LABEL) || (type == BuildType.LABEL_LIST),
           "must be a label-valued type");
       return setPropertyFlag(PropertyFlag.SKIP_ANALYSIS_TIME_FILETYPE_CHECK,
           "skip_analysis_time_filetype_check");
@@ -802,7 +801,7 @@ public final class Attribute implements Comparable<Attribute> {
      * other words, it works for 'deps' attributes, but not 'srcs' attributes.
      */
     public Builder<TYPE> allowedRuleClasses(Predicate<RuleClass> allowedRuleClasses) {
-      Preconditions.checkState(type.getLabelClass() == LabelClass.DEPENDENCY,
+      Preconditions.checkState((type == BuildType.LABEL) || (type == BuildType.LABEL_LIST),
           "must be a label-valued type");
       propertyFlags.add(PropertyFlag.STRICT_LABEL_CHECKING);
       allowedRuleClassesForLabels = allowedRuleClasses;
@@ -832,7 +831,7 @@ public final class Attribute implements Comparable<Attribute> {
      * other words, it works for 'deps' attributes, but not 'srcs' attributes.
      */
     public Builder<TYPE> allowedFileTypes(FileTypeSet allowedFileTypes) {
-      Preconditions.checkState(type.getLabelClass() == LabelClass.DEPENDENCY,
+      Preconditions.checkState((type == BuildType.LABEL) || (type == BuildType.LABEL_LIST),
           "must be a label-valued type");
       propertyFlags.add(PropertyFlag.STRICT_LABEL_CHECKING);
       allowedFileTypesForLabels = Preconditions.checkNotNull(allowedFileTypes);
@@ -887,7 +886,7 @@ public final class Attribute implements Comparable<Attribute> {
      * other words, it works for 'deps' attributes, but not 'srcs' attributes.
      */
     public Builder<TYPE> allowedRuleClassesWithWarning(Predicate<RuleClass> allowedRuleClasses) {
-      Preconditions.checkState(type.getLabelClass() == LabelClass.DEPENDENCY,
+      Preconditions.checkState((type == BuildType.LABEL) || (type == BuildType.LABEL_LIST),
           "must be a label-valued type");
       propertyFlags.add(PropertyFlag.STRICT_LABEL_CHECKING);
       allowedRuleClassesForLabelsWarning = allowedRuleClasses;
@@ -915,7 +914,7 @@ public final class Attribute implements Comparable<Attribute> {
      */
     public final Builder<TYPE> mandatoryNativeProvidersList(
         Iterable<? extends Iterable<Class<? extends TransitiveInfoProvider>>> providersList) {
-      Preconditions.checkState(type.getLabelClass() == LabelClass.DEPENDENCY,
+      Preconditions.checkState((type == BuildType.LABEL) || (type == BuildType.LABEL_LIST),
           "must be a label-valued type");
       ImmutableList.Builder<ImmutableList<Class<? extends TransitiveInfoProvider>>> listBuilder
           = ImmutableList.builder();
@@ -942,7 +941,7 @@ public final class Attribute implements Comparable<Attribute> {
      */
     public Builder<TYPE> mandatoryProvidersList(
         Iterable<? extends Iterable<SkylarkProviderIdentifier>> providersList){
-      Preconditions.checkState(type.getLabelClass() == LabelClass.DEPENDENCY,
+      Preconditions.checkState((type == BuildType.LABEL) || (type == BuildType.LABEL_LIST),
           "must be a label-valued type");
       ImmutableList.Builder<ImmutableSet<SkylarkProviderIdentifier>> listBuilder
           = ImmutableList.builder();
@@ -1087,13 +1086,13 @@ public final class Attribute implements Comparable<Attribute> {
 
       // do not modify this.allowedFileTypesForLabels, instead create a copy.
       FileTypeSet allowedFileTypesForLabels = this.allowedFileTypesForLabels;
-      if (type.getLabelClass() == LabelClass.DEPENDENCY) {
+      if ((type == BuildType.LABEL) || (type == BuildType.LABEL_LIST)) {
         if (isPrivateAttribute(name) && allowedFileTypesForLabels == null) {
           allowedFileTypesForLabels = FileTypeSet.ANY_FILE;
         }
         Preconditions.checkNotNull(
             allowedFileTypesForLabels, "allowedFileTypesForLabels not set for %s", name);
-      } else if (type.getLabelClass() == LabelClass.OUTPUT) {
+      } else if ((type == BuildType.OUTPUT) || (type == BuildType.OUTPUT_LIST)) {
         // TODO(bazel-team): Set the default to no file type and make explicit calls instead.
         if (allowedFileTypesForLabels == null) {
           allowedFileTypesForLabels = FileTypeSet.ANY_FILE;
@@ -1770,8 +1769,8 @@ public final class Attribute implements Comparable<Attribute> {
     Preconditions.checkNotNull(configTransition);
     Preconditions.checkArgument(
         (configTransition == ConfigurationTransition.NONE && configurator == null)
-        || type.getLabelClass() == LabelClass.DEPENDENCY
-        || type.getLabelClass() == LabelClass.NONDEP_REFERENCE,
+        || type == BuildType.LABEL || type == BuildType.LABEL_LIST
+        || type == BuildType.NODEP_LABEL || type == BuildType.NODEP_LABEL_LIST,
         "Configuration transitions can only be specified for label or label list attributes");
     Preconditions.checkArgument(
         isLateBound(name) == (defaultValue instanceof LateBoundDefault),
@@ -1976,8 +1975,8 @@ public final class Attribute implements Comparable<Attribute> {
    * Returns true if this attribute's value can be influenced by the build configuration.
    */
   public boolean isConfigurable() {
-    // Output types are excluded because of Rule#populateExplicitOutputFiles.
-    return !(type.getLabelClass() == LabelClass.OUTPUT
+    return !(type == BuildType.OUTPUT      // Excluded because of Rule#populateExplicitOutputFiles.
+        || type == BuildType.OUTPUT_LIST
         || getPropertyFlag(PropertyFlag.NONCONFIGURABLE));
   }
 
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 051b7e033f..ae3b1214ed 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
@@ -27,7 +27,6 @@ import com.google.devtools.build.lib.syntax.SelectorValue;
 import com.google.devtools.build.lib.syntax.Type;
 import com.google.devtools.build.lib.syntax.Type.ConversionException;
 import com.google.devtools.build.lib.syntax.Type.DictType;
-import com.google.devtools.build.lib.syntax.Type.LabelClass;
 import com.google.devtools.build.lib.syntax.Type.ListType;
 import java.util.Collections;
 import java.util.LinkedHashMap;
@@ -48,7 +47,7 @@ public final class BuildType {
    * attributes that it's worth treating them specially (and providing support
    * for resolution of relative-labels in the <code>convert()</code> method).
    */
-  public static final Type<Label> LABEL = new LabelType(LabelClass.DEPENDENCY);
+  public static final Type<Label> LABEL = new LabelType();
   /**
    * The type of a dictionary of {@linkplain #LABEL labels}.
    */
@@ -63,7 +62,7 @@ public final class BuildType {
    * certain rules want to verify the type of a target referenced by one of their attributes, but
    * if there was a dependency edge there, it would be a circular dependency.
    */
-  public static final Type<Label> NODEP_LABEL = new LabelType(LabelClass.NONDEP_REFERENCE);
+  public static final Type<Label> NODEP_LABEL = new LabelType();
   /**
    *  The type of a list of {@linkplain #NODEP_LABEL labels} that do not cause
    *  dependencies.
@@ -137,7 +136,8 @@ public final class BuildType {
    * Returns whether the specified type is a label type or not.
    */
   public static boolean isLabelType(Type<?> type) {
-    return type.getLabelClass() != LabelClass.NONE;
+    return type == LABEL || type == LABEL_LIST || type == LABEL_DICT_UNARY
+        || type == NODEP_LABEL || type == NODEP_LABEL_LIST || type == FILESET_ENTRY_LIST;
   }
 
   /**
@@ -182,11 +182,6 @@ public final class BuildType {
     }
 
     @Override
-    public LabelClass getLabelClass() {
-      return LabelClass.FILESET_ENTRY;
-    }
-
-    @Override
     public FilesetEntry getDefaultValue() {
       return null;
     }
@@ -200,12 +195,6 @@ public final class BuildType {
   }
 
   private static class LabelType extends Type<Label> {
-    private final LabelClass labelClass;
-
-    LabelType(LabelClass labelClass) {
-      this.labelClass = labelClass;
-    }
-
     @Override
     public Label cast(Object value) {
       return (Label) value;
@@ -227,11 +216,6 @@ public final class BuildType {
     }
 
     @Override
-    public LabelClass getLabelClass() {
-      return labelClass;
-    }
-
-    @Override
     public Label convert(Object x, Object what, Object context)
         throws ConversionException {
       if (x instanceof Label) {
@@ -343,11 +327,6 @@ public final class BuildType {
     }
 
     @Override
-    public LabelClass getLabelClass() {
-      return LabelClass.OUTPUT;
-    }
-
-    @Override
     public String toString() {
       return "output";
     }
diff --git a/src/main/java/com/google/devtools/build/lib/packages/DependencyFilter.java b/src/main/java/com/google/devtools/build/lib/packages/DependencyFilter.java
index 88fe6d4157..a5d41ee631 100644
--- a/src/main/java/com/google/devtools/build/lib/packages/DependencyFilter.java
+++ b/src/main/java/com/google/devtools/build/lib/packages/DependencyFilter.java
@@ -15,7 +15,6 @@ package com.google.devtools.build.lib.packages;
 
 import com.google.devtools.build.lib.packages.Attribute.ConfigurationTransition;
 import com.google.devtools.build.lib.packages.DependencyFilter.AttributeInfoProvider;
-import com.google.devtools.build.lib.syntax.Type.LabelClass;
 import com.google.devtools.build.lib.util.BinaryPredicate;
 
 /**
@@ -39,8 +38,8 @@ public abstract class DependencyFilter
       new DependencyFilter() {
     @Override
     public boolean apply(AttributeInfoProvider infoProvider, Attribute attribute) {
-      // getConfigurationTransition() is only defined for labels which introduce a dependency.
-      if (attribute.getType().getLabelClass() != LabelClass.DEPENDENCY) {
+      // isHostConfiguration() is only defined for labels and label lists.
+      if (attribute.getType() != BuildType.LABEL && attribute.getType() != BuildType.LABEL_LIST) {
         return true;
       }
 
@@ -63,7 +62,8 @@ public abstract class DependencyFilter
       new DependencyFilter() {
     @Override
     public boolean apply(AttributeInfoProvider infoProvider, Attribute attribute) {
-      return attribute.getType().getLabelClass() != LabelClass.NONDEP_REFERENCE;
+      return attribute.getType() != BuildType.NODEP_LABEL
+          && attribute.getType() != BuildType.NODEP_LABEL_LIST;
     }
   };
   /**
diff --git a/src/main/java/com/google/devtools/build/lib/rules/SkylarkAttr.java b/src/main/java/com/google/devtools/build/lib/rules/SkylarkAttr.java
index 08113b6f20..abec031476 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/SkylarkAttr.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/SkylarkAttr.java
@@ -46,7 +46,6 @@ import com.google.devtools.build.lib.syntax.SkylarkSignatureProcessor;
 import com.google.devtools.build.lib.syntax.SkylarkType;
 import com.google.devtools.build.lib.syntax.Type;
 import com.google.devtools.build.lib.syntax.Type.ConversionException;
-import com.google.devtools.build.lib.syntax.Type.LabelClass;
 import com.google.devtools.build.lib.syntax.UserDefinedFunction;
 import com.google.devtools.build.lib.util.FileType;
 import com.google.devtools.build.lib.util.FileTypeSet;
@@ -236,7 +235,7 @@ public final class SkylarkAttr {
       Object fileTypesObj = arguments.get(ALLOW_SINGLE_FILE_ARG);
       setAllowedFileTypes(ALLOW_SINGLE_FILE_ARG, fileTypesObj, ast, builder);
       builder.setPropertyFlag("SINGLE_ARTIFACT");
-    } else if (type.getLabelClass() == LabelClass.DEPENDENCY) {
+    } else if (type.equals(BuildType.LABEL) || type.equals(BuildType.LABEL_LIST)) {
       builder.allowedFileTypes(FileTypeSet.NO_FILE);
     }
 
diff --git a/src/main/java/com/google/devtools/build/lib/rules/SkylarkRuleContext.java b/src/main/java/com/google/devtools/build/lib/rules/SkylarkRuleContext.java
index 76ee3c9253..7e7b69cda1 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/SkylarkRuleContext.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/SkylarkRuleContext.java
@@ -64,7 +64,6 @@ import com.google.devtools.build.lib.syntax.SkylarkDict;
 import com.google.devtools.build.lib.syntax.SkylarkList;
 import com.google.devtools.build.lib.syntax.SkylarkType;
 import com.google.devtools.build.lib.syntax.Type;
-import com.google.devtools.build.lib.syntax.Type.LabelClass;
 import com.google.devtools.build.lib.util.Preconditions;
 import com.google.devtools.build.lib.vfs.PathFragment;
 import java.util.ArrayList;
@@ -207,7 +206,7 @@ public final class SkylarkRuleContext {
       for (Attribute a : attributes) {
         String attrName = a.getName();
         Type<?> type = a.getType();
-        if (type.getLabelClass() != LabelClass.OUTPUT) {
+        if (type != BuildType.OUTPUT && type != BuildType.OUTPUT_LIST) {
           continue;
         }
         ImmutableList.Builder<Artifact> artifactsBuilder = ImmutableList.builder();
@@ -291,7 +290,7 @@ public final class SkylarkRuleContext {
     for (Attribute a : attributes) {
       Type<?> type = a.getType();
       Object val = attributeValueExtractor.apply(a);
-      if (type.getLabelClass() != LabelClass.DEPENDENCY) {
+      if (type != BuildType.LABEL && type != BuildType.LABEL_LIST) {
         attrBuilder.put(a.getPublicName(), val == null ? Runtime.NONE
             // Attribute values should be type safe
             : SkylarkType.convertToSkylark(val, null));
@@ -337,14 +336,10 @@ public final class SkylarkRuleContext {
           prereq = Runtime.NONE;
         }
         attrBuilder.put(skyname, prereq);
-      } else if (type == BuildType.LABEL_LIST
-          || (type == BuildType.LABEL && a.hasSplitConfigurationTransition())) {
+      } else {
+        // Type.LABEL_LIST
         List<?> allPrereq = ruleContext.getPrerequisites(a.getName(), Mode.DONT_CHECK);
         attrBuilder.put(skyname, SkylarkList.createImmutable(allPrereq));
-      } else {
-        throw new IllegalArgumentException(
-            "Can't transform attribute " + a.getName() + " of type " + type
-            + " to a Skylark object");
       }
     }
 
diff --git a/src/main/java/com/google/devtools/build/lib/rules/cpp/CcToolchainSuiteRule.java b/src/main/java/com/google/devtools/build/lib/rules/cpp/CcToolchainSuiteRule.java
index 55244b470a..a08e6e0930 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/cpp/CcToolchainSuiteRule.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/cpp/CcToolchainSuiteRule.java
@@ -22,7 +22,6 @@ import com.google.devtools.build.lib.packages.BuildType;
 import com.google.devtools.build.lib.packages.RuleClass;
 import com.google.devtools.build.lib.packages.RuleClass.Builder;
 import com.google.devtools.build.lib.syntax.Type;
-import com.google.devtools.build.lib.util.FileTypeSet;
 
 /**
  * Definition of the {@code cc_toolchain_suite} rule.
@@ -35,7 +34,6 @@ public final class CcToolchainSuiteRule implements RuleDefinition {
         .setUndocumented()
         .add(attr("toolchains", BuildType.LABEL_DICT_UNARY)
             .mandatory()
-            .allowedFileTypes(FileTypeSet.NO_FILE)
             .nonconfigurable("Used during configuration creation"))
         .add(attr("proto", Type.STRING)
             .nonconfigurable("Used during configuration creation"))
diff --git a/src/main/java/com/google/devtools/build/lib/rules/java/JavaRuntimeSuiteRule.java b/src/main/java/com/google/devtools/build/lib/rules/java/JavaRuntimeSuiteRule.java
index 22de4df4a3..8b28e91c29 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/java/JavaRuntimeSuiteRule.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/java/JavaRuntimeSuiteRule.java
@@ -35,7 +35,7 @@ public final class JavaRuntimeSuiteRule implements RuleDefinition {
         /* <!-- #BLAZE_RULE(java_runtime_suite).ATTRIBUTE(runtimes) -->
         A map from each supported architecture to the corresponding <code>java_runtime</code>.
         <!-- #END_BLAZE_RULE.ATTRIBUTE --> */
-        .add(attr("runtimes", BuildType.LABEL_DICT_UNARY).allowedFileTypes(FileTypeSet.NO_FILE))
+        .add(attr("runtimes", BuildType.LABEL_DICT_UNARY))
         /* <!-- #BLAZE_RULE(java_runtime_suite).ATTRIBUTE(default) -->
         The default <code>java_runtime</code>, used if
         <a href="${link java_runtime_suite.runtimes}"><code>runtimes</code></a>
diff --git a/src/main/java/com/google/devtools/build/lib/syntax/Type.java b/src/main/java/com/google/devtools/build/lib/syntax/Type.java
index 387794b40f..dbbfc79c42 100644
--- a/src/main/java/com/google/devtools/build/lib/syntax/Type.java
+++ b/src/main/java/com/google/devtools/build/lib/syntax/Type.java
@@ -15,7 +15,6 @@
 package com.google.devtools.build.lib.syntax;
 
 import com.google.common.base.Joiner;
-import com.google.common.base.Preconditions;
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableMap;
 import com.google.common.collect.ImmutableSet;
@@ -140,31 +139,6 @@ public abstract class Type<T> {
    */
   public abstract void visitLabels(LabelVisitor visitor, Object value) throws InterruptedException;
 
-  /** Classifications of labels by their usage. */
-  public enum LabelClass {
-    /** Used for types which are not labels. */
-    NONE,
-    /** Used for types which use labels to declare a dependency. */
-    DEPENDENCY,
-    /**
-     * Used for types which use labels to reference another target but do not declare a dependency,
-     * in cases where doing so would cause a dependency cycle.
-     */
-    NONDEP_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. */
-  public LabelClass getLabelClass() {
-    return LabelClass.NONE;
-  }
-
   /**
    * Implementation of concatenation for this type (e.g. "val1 + val2"). Returns null to
    * indicate concatenation isn't supported.
@@ -449,8 +423,6 @@ public abstract class Type<T> {
 
     private final Map<KeyT, ValueT> empty = ImmutableMap.of();
 
-    private final LabelClass labelClass;
-
     @Override
     public void visitLabels(LabelVisitor visitor, Object value) throws InterruptedException {
       for (Entry<KeyT, ValueT> entry : cast(value).entrySet()) {
@@ -461,24 +433,12 @@ public abstract class Type<T> {
 
     public static <KEY, VALUE> DictType<KEY, VALUE> create(
         Type<KEY> keyType, Type<VALUE> valueType) {
-      LabelClass keyLabelClass = keyType.getLabelClass();
-      LabelClass valueLabelClass = valueType.getLabelClass();
-      Preconditions.checkArgument(
-          keyLabelClass == LabelClass.NONE
-              || valueLabelClass == LabelClass.NONE
-              || keyLabelClass == valueLabelClass,
-          "A DictType's keys and values must be the same class of label if both contain labels, "
-          + "but the key type " + keyType + " contains " + keyLabelClass + " labels, while "
-          + "the value type " + valueType + " contains " + valueLabelClass + " labels.");
-      LabelClass labelClass = (keyLabelClass != LabelClass.NONE) ? keyLabelClass : valueLabelClass;
-
-      return new DictType<>(keyType, valueType, labelClass);
+      return new DictType<>(keyType, valueType);
     }
 
-    private DictType(Type<KeyT> keyType, Type<ValueT> valueType, LabelClass labelClass) {
+    private DictType(Type<KeyT> keyType, Type<ValueT> valueType) {
       this.keyType = keyType;
       this.valueType = valueType;
-      this.labelClass = labelClass;
     }
 
     public Type<KeyT> getKeyType() {
@@ -489,11 +449,6 @@ public abstract class Type<T> {
       return valueType;
     }
 
-    @Override
-    public LabelClass getLabelClass() {
-      return labelClass;
-    }
-
     @SuppressWarnings("unchecked")
     @Override
     public Map<KeyT, ValueT> cast(Object value) {
@@ -556,11 +511,6 @@ public abstract class Type<T> {
     }
 
     @Override
-    public LabelClass getLabelClass() {
-      return elemType.getLabelClass();
-    }
-
-    @Override
     public List<ElemT> getDefaultValue() {
       return empty;
     }
diff --git a/src/test/java/com/google/devtools/build/lib/testutil/BuildRuleWithDefaultsBuilder.java b/src/test/java/com/google/devtools/build/lib/testutil/BuildRuleWithDefaultsBuilder.java
index e0e6b77407..7db103eba3 100644
--- a/src/test/java/com/google/devtools/build/lib/testutil/BuildRuleWithDefaultsBuilder.java
+++ b/src/test/java/com/google/devtools/build/lib/testutil/BuildRuleWithDefaultsBuilder.java
@@ -20,8 +20,6 @@ import com.google.devtools.build.lib.packages.Attribute.AllowedValueSet;
 import com.google.devtools.build.lib.packages.BuildType;
 import com.google.devtools.build.lib.packages.RuleClass;
 import com.google.devtools.build.lib.syntax.Type;
-import com.google.devtools.build.lib.syntax.Type.LabelClass;
-import com.google.devtools.build.lib.syntax.Type.ListType;
 import com.google.devtools.build.lib.util.FileTypeSet;
 import com.google.devtools.build.lib.util.Preconditions;
 
@@ -59,8 +57,8 @@ public class BuildRuleWithDefaultsBuilder extends BuildRuleBuilder {
    */
   private String getDummyFileLabel(String rulePkg, String filePkg, String extension,
       Type<?> attrType) {
-    boolean isOutput = attrType.getLabelClass() == LabelClass.OUTPUT;
-    String fileName = (isOutput ? "dummy_output" : "dummy_input") + extension;
+    boolean isInput = (attrType == BuildType.LABEL || attrType == BuildType.LABEL_LIST);
+    String fileName = (isInput ? "dummy_input" : "dummy_output") + extension;
     generateFiles.add(filePkg + "/" + fileName);
     if (rulePkg.equals(filePkg)) {
       return ":" + fileName;
@@ -124,7 +122,7 @@ public class BuildRuleWithDefaultsBuilder extends BuildRuleBuilder {
       }
     }
     if (label != null) {
-      if (attrType instanceof ListType<?>) {
+      if (attrType == BuildType.LABEL_LIST || attrType == BuildType.OUTPUT_LIST) {
         addMultiValueAttributes(attribute.getName(), label);
       } else {
         setSingleValueAttribute(attribute.getName(), label);
@@ -177,10 +175,17 @@ public class BuildRuleWithDefaultsBuilder extends BuildRuleBuilder {
   public BuildRuleWithDefaultsBuilder populateAttributes(String rulePkg, boolean heuristics) {
     for (Attribute attribute : ruleClass.getAttributes()) {
       if (attribute.isMandatory()) {
-        if (BuildType.isLabelType(attribute.getType())) {
-          // TODO(bazel-team): actually an empty list would be fine in the case where
-          // attribute instanceof ListType && !attribute.isNonEmpty(), but BuildRuleBuilder
-          // doesn't support that, and it makes little sense anyway
+        if (attribute.getType() == BuildType.LABEL_LIST
+            || attribute.getType() == BuildType.OUTPUT_LIST) {
+          if (attribute.isNonEmpty()) {
+            populateLabelAttribute(rulePkg, attribute);
+          } else {
+            // TODO(bazel-team): actually here an empty list would be fine, but BuildRuleBuilder
+            // doesn't support that, and it makes little sense anyway
+            populateLabelAttribute(rulePkg, attribute);
+          }
+        } else if (attribute.getType() == BuildType.LABEL
+            || attribute.getType() == BuildType.OUTPUT) {
           populateLabelAttribute(rulePkg, attribute);
         } else {
           // Non label type attributes