1 files changed, 72 insertions, 0 deletions
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..263fe63e79 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
@@ -15,6 +15,7 @@
 package com.google.devtools.build.lib.packages;
 
 import com.google.common.annotations.VisibleForTesting;
+import com.google.common.base.Preconditions;
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableMap;
 import com.google.common.collect.ImmutableSet;
@@ -22,6 +23,7 @@ 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;
 import com.google.devtools.build.lib.packages.License.LicenseParsingException;
+import com.google.devtools.build.lib.syntax.Printer;
 import com.google.devtools.build.lib.syntax.Runtime;
 import com.google.devtools.build.lib.syntax.SelectorValue;
 import com.google.devtools.build.lib.syntax.Type;
@@ -29,6 +31,7 @@ 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.ArrayList;
 import java.util.Collections;
 import java.util.LinkedHashMap;
 import java.util.List;
@@ -55,6 +58,11 @@ public final class BuildType {
   public static final DictType<String, Label> LABEL_DICT_UNARY = DictType.create(
       Type.STRING, LABEL);
   /**
+   * The type of a dictionary keyed by {@linkplain #LABEL labels} with string values.
+   */
+  public static final DictType<Label, String> LABEL_KEYED_STRING_DICT =
+      LabelKeyedDictType.create(Type.STRING);
+  /**
    *  The type of a list of {@linkplain #LABEL labels}.
    */
   public static final ListType<Label> LABEL_LIST = ListType.create(LABEL);
@@ -247,6 +255,70 @@ public final class BuildType {
   }
 
   /**
+   * Dictionary type specialized for label keys, which is able to detect collisions caused by the
+   * fact that labels have multiple equivalent representations in Skylark code.
+   */
+  private static class LabelKeyedDictType<ValueT> extends DictType<Label, ValueT> {
+    private LabelKeyedDictType(Type<ValueT> valueType) {
+      super(LABEL, valueType, LabelClass.DEPENDENCY);
+    }
+
+    public static <ValueT> LabelKeyedDictType<ValueT> create(Type<ValueT> valueType) {
+      Preconditions.checkArgument(
+          valueType.getLabelClass() == LabelClass.NONE
+          || valueType.getLabelClass() == LabelClass.DEPENDENCY,
+          "Values associated with label keys must not be labels themselves.");
+      return new LabelKeyedDictType<>(valueType);
+    }
+
+    @Override
+    public Map<Label, ValueT> convert(Object x, Object what, Object context)
+        throws ConversionException {
+      Map<Label, ValueT> result = super.convert(x, what, context);
+      // The input is known to be a map because super.convert succeded; otherwise, a
+      // ConversionException would have been thrown.
+      Map<?, ?> input = (Map<?, ?>) x;
+
+      if (input.size() == result.size()) {
+        // No collisions found. Exit early.
+        return result;
+      }
+      // Look for collisions in order to produce a nicer error message.
+      Map<Label, List<Object>> convertedFrom = new LinkedHashMap<>();
+      for (Object original : input.keySet()) {
+        Label label = LABEL.convert(original, what, context);
+        if (!convertedFrom.containsKey(label)) {
+          convertedFrom.put(label, new ArrayList<Object>());
+        }
+        convertedFrom.get(label).add(original);
+      }
+      StringBuilder errorMessage = new StringBuilder();
+      errorMessage.append("duplicate labels");
+      if (what != null) {
+        errorMessage.append(" in ").append(what);
+      }
+      errorMessage.append(':');
+      boolean isFirstEntry = true;
+      for (Map.Entry<Label, List<Object>> entry : convertedFrom.entrySet()) {
+        if (entry.getValue().size() == 1) {
+          continue;
+        }
+        if (isFirstEntry) {
+          isFirstEntry = false;
+        } else {
+          errorMessage.append(',');
+        }
+        errorMessage.append(' ');
+        errorMessage.append(entry.getKey());
+        errorMessage.append(" (as ");
+        Printer.write(errorMessage, entry.getValue());
+        errorMessage.append(')');
+      }
+      throw new ConversionException(errorMessage.toString());
+    }
+  }
+
+  /**
    * Like Label, LicenseType is a derived type, which is declared specially
    * in order to allow syntax validation. It represents the licenses, as
    * described in {@ref License}.