Add support of empty target to LateBoundAlias.

RELNOTES:none
PiperOrigin-RevId: 197132230

2 files changed, 137 insertions, 6 deletions

diff --git a/src/main/java/com/google/devtools/build/lib/rules/LateBoundAlias.java b/src/main/java/com/google/devtools/build/lib/rules/LateBoundAlias.java
index 3e309c338b..176411b7f6 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/LateBoundAlias.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/LateBoundAlias.java
@@ -18,13 +18,17 @@ import static com.google.devtools.build.lib.packages.BuildType.LABEL;
 
 import com.google.common.base.Preconditions;
 import com.google.common.collect.ImmutableMap;
+import com.google.devtools.build.lib.actions.MutableActionGraph.ActionConflictException;
 import com.google.devtools.build.lib.analysis.AliasProvider;
 import com.google.devtools.build.lib.analysis.BaseRuleClasses;
 import com.google.devtools.build.lib.analysis.ConfiguredTarget;
+import com.google.devtools.build.lib.analysis.RuleConfiguredTargetBuilder;
 import com.google.devtools.build.lib.analysis.RuleConfiguredTargetFactory;
 import com.google.devtools.build.lib.analysis.RuleContext;
 import com.google.devtools.build.lib.analysis.RuleDefinition;
 import com.google.devtools.build.lib.analysis.RuleDefinitionEnvironment;
+import com.google.devtools.build.lib.analysis.Runfiles;
+import com.google.devtools.build.lib.analysis.RunfilesProvider;
 import com.google.devtools.build.lib.analysis.VisibilityProvider;
 import com.google.devtools.build.lib.analysis.VisibilityProviderImpl;
 import com.google.devtools.build.lib.analysis.config.BuildConfiguration;
@@ -36,14 +40,19 @@ import com.google.devtools.build.lib.packages.RuleClass;
 import java.util.function.Function;
 
 /** Implements template for creating custom alias rules. */
-public class LateBoundAlias implements RuleConfiguredTargetFactory {
+public final class LateBoundAlias implements RuleConfiguredTargetFactory {
 
   private static final String ATTRIBUTE_NAME = ":alias";
 
   @Override
-  public ConfiguredTarget create(RuleContext ruleContext) {
+  public ConfiguredTarget create(RuleContext ruleContext)
+      throws ActionConflictException {
     ConfiguredTarget actual =
         (ConfiguredTarget) ruleContext.getPrerequisite(ATTRIBUTE_NAME, Mode.TARGET);
+    if (actual == null) {
+      return createEmptyConfiguredTarget(ruleContext);
+    }
+
     return new AliasConfiguredTarget(
         ruleContext,
         actual,
@@ -54,10 +63,15 @@ public class LateBoundAlias implements RuleConfiguredTargetFactory {
             new VisibilityProviderImpl(ruleContext.getVisibility())));
   }
 
-  /**
-   *  Rule definition for custom alias rules"
-   */
-  public static class CommonAliasRule implements RuleDefinition {
+  private ConfiguredTarget createEmptyConfiguredTarget(RuleContext ruleContext)
+      throws ActionConflictException {
+    return new RuleConfiguredTargetBuilder(ruleContext)
+        .addProvider(RunfilesProvider.class, RunfilesProvider.simple(Runfiles.EMPTY))
+        .build();
+  }
+
+  /** Rule definition for custom alias rules */
+  public abstract static class CommonAliasRule implements RuleDefinition {
 
     private static final String ATTRIBUTE_NAME = ":alias";
 
diff --git a/src/test/java/com/google/devtools/build/lib/rules/LateBoundAliasTest.java b/src/test/java/com/google/devtools/build/lib/rules/LateBoundAliasTest.java
new file mode 100644
index 0000000000..4da5bb3f98
--- /dev/null
+++ b/src/test/java/com/google/devtools/build/lib/rules/LateBoundAliasTest.java
@@ -0,0 +1,117 @@
+// Copyright 2018 The Bazel Authors. 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.rules;
+
+import static com.google.common.truth.Truth.assertThat;
+
+import com.google.common.collect.ImmutableSet;
+import com.google.devtools.build.lib.analysis.ConfiguredRuleClassProvider;
+import com.google.devtools.build.lib.analysis.ConfiguredTarget;
+import com.google.devtools.build.lib.analysis.config.BuildConfiguration.Fragment;
+import com.google.devtools.build.lib.analysis.config.BuildOptions;
+import com.google.devtools.build.lib.analysis.config.ConfigurationFragmentFactory;
+import com.google.devtools.build.lib.analysis.config.FragmentOptions;
+import com.google.devtools.build.lib.analysis.util.BuildViewTestCase;
+import com.google.devtools.build.lib.cmdline.Label;
+import com.google.devtools.build.lib.cmdline.LabelSyntaxException;
+import com.google.devtools.build.lib.packages.Attribute.LateBoundDefault;
+import com.google.devtools.build.lib.packages.AttributeMap;
+import com.google.devtools.build.lib.packages.Rule;
+import com.google.devtools.build.lib.rules.LateBoundAlias.CommonAliasRule;
+import com.google.devtools.build.lib.testutil.TestRuleClassProvider;
+import java.io.IOException;
+import javax.annotation.Nullable;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.JUnit4;
+
+/**
+ * Tests that LateBoundAlias can resolve null actual reference.
+ */
+@RunWith(JUnit4.class)
+public class LateBoundAliasTest extends BuildViewTestCase {
+
+  private static final class TestFragment extends Fragment {}
+
+  private static final class TestFragmentOptionFactory implements ConfigurationFragmentFactory {
+
+    @Override
+    public Class<? extends Fragment> creates() {
+      return TestFragment.class;
+    }
+
+    @Override
+    public ImmutableSet<Class<? extends FragmentOptions>> requiredOptions() {
+      return ImmutableSet.of();
+    }
+
+    @Nullable
+    @Override
+    public Fragment create(BuildOptions buildOptions) {
+      return new TestFragment();
+    }
+  }
+
+  private static final class TestLateBoundDefault extends LateBoundDefault<TestFragment, Label> {
+
+    private TestLateBoundDefault() {
+      super(false, TestFragment.class, null);
+    }
+
+    @Override
+    public Label resolve(Rule rule, AttributeMap attributes, TestFragment input) {
+      return null;
+    }
+  }
+
+  private static final class MyTestRule extends CommonAliasRule {
+    public MyTestRule() {
+      super("test_rule_name", env -> new TestLateBoundDefault(), TestFragment.class);
+    }
+  }
+
+  @Override
+  protected ConfiguredRuleClassProvider getRuleClassProvider() {
+    ConfiguredRuleClassProvider.Builder builder = new ConfiguredRuleClassProvider.Builder();
+    TestRuleClassProvider.addStandardRules(builder);
+    builder.addConfigurationFragment(new TestFragmentOptionFactory());
+    builder.addRuleDefinition(new MyTestRule());
+    return builder.build();
+  }
+
+  @Test
+  public void testResolveNullTarget() throws IOException, LabelSyntaxException {
+    scratch.file("a/BUILD", "test_rule_name(name='alias')");
+
+    ConfiguredTarget alias = getConfiguredTarget("//a:alias");
+
+    assertThat(alias).isNotNull();
+  }
+
+  @Test
+  public void testNullTargetCanBeDependant() throws IOException, LabelSyntaxException {
+    scratch.file(
+        "a/BUILD",
+        "test_rule_name(name='alias')",
+        "filegroup(",
+        "    name = 'my_filegroup',",
+        "    srcs = [':alias']",
+        ")");
+
+    ConfiguredTarget myFilegroup = getConfiguredTarget("//a:my_filegroup");
+
+    assertThat(myFilegroup).isNotNull();
+  }
+}