1 files changed, 109 insertions, 0 deletions
diff --git a/src/main/java/com/google/devtools/build/lib/analysis/LanguageDependentFragment.java b/src/main/java/com/google/devtools/build/lib/analysis/LanguageDependentFragment.java
new file mode 100644
index 0000000000..d42d625620
--- /dev/null
+++ b/src/main/java/com/google/devtools/build/lib/analysis/LanguageDependentFragment.java
@@ -0,0 +1,109 @@
+// Copyright 2014 Google Inc. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.google.devtools.build.lib.analysis;
+
+import com.google.common.collect.ImmutableSet;
+import com.google.devtools.build.lib.analysis.RuleConfiguredTarget.Mode;
+import com.google.devtools.build.lib.concurrent.ThreadSafety.Immutable;
+import com.google.devtools.build.lib.syntax.Label;
+
+import java.util.Set;
+
+/**
+ * Transitive info provider for rules that behave differently when used from
+ * different languages.
+ *
+ * <p>Most rules generate code for a particular language or are totally language independent.
+ * Some rules, however, behave differently when depended upon from different languages.
+ * They might generate different libraries when used from different languages (and with
+ * different API versions). This interface allows code sharing between implementations.
+ *
+ * <p>This provider is not really a roll-up of transitive information.
+ */
+@Immutable
+public final class LanguageDependentFragment implements TransitiveInfoProvider {
+  /**
+   * A language that can be supported by a multi-language configured target.
+   *
+   * <p>Note that no {@code hashCode}/{@code equals} methods are provided, because these
+   * objects are expected to be compared for object identity, which is the default.
+   */
+  public static final class LibraryLanguage {
+    private final String displayName;
+
+    public LibraryLanguage(String displayName) {
+      this.displayName = displayName;
+    }
+
+    @Override
+    public String toString() {
+      return displayName;
+    }
+  }
+
+  private final Label label;
+  private final ImmutableSet<LibraryLanguage> languages;
+
+  public LanguageDependentFragment(Label label, Set<LibraryLanguage> languages) {
+    this.label = label;
+    this.languages = ImmutableSet.copyOf(languages);
+  }
+
+  /**
+   * Returns the label that is associated with this piece of information.
+   *
+   * <p>This is usually the label of the target that provides the information.
+   */
+  public Label getLabel() {
+    return label;
+  }
+
+  /**
+   * Returns a set of the languages the ConfiguredTarget generates output for.
+   * For use only by rules that directly depend on this library via a "deps" attribute.
+   */
+  public ImmutableSet<LibraryLanguage> getSupportedLanguages() {
+    return languages;
+  }
+
+  /**
+   * Routines for verifying that dependency provide the right output.
+   */
+  public static final class Checker {
+    /**
+     * Checks that given dep supports the given language.
+     */
+    public static boolean depSupportsLanguage(
+        RuleContext context, LanguageDependentFragment dep, LibraryLanguage language) {
+      if (dep.getSupportedLanguages().contains(language)) {
+        return true;
+      } else {
+        context.attributeError(
+            "deps", String.format("'%s' does not produce output for %s", dep.getLabel(), language));
+        return false;
+      }
+    }
+
+    /**
+     * Checks that all LanguageDependentFragment support the given language.
+     */
+    public static void depsSupportsLanguage(RuleContext context, LibraryLanguage language) {
+      for (LanguageDependentFragment dep :
+               context.getPrerequisites("deps", Mode.TARGET, LanguageDependentFragment.class)) {
+        depSupportsLanguage(context, dep, language);
+      }
+    }
+  }
+}