Avoid NPEs when providers are not found in JavaInfo.

Fixes #4173.

RELNOTES: None.
PiperOrigin-RevId: 177582228

src/main/java/com/google/devtools/build/lib/rules/java/JavaInfo.java

@@ -49,6 +49,8 @@ public final class JavaInfo extends NativeInfo {
   public static final NativeProvider<JavaInfo> PROVIDER =
       new NativeProvider<JavaInfo>(JavaInfo.class, "JavaInfo") {};
 
+  public static final JavaInfo EMPTY = JavaInfo.Builder.create().build();
+
   private static final ImmutableSet<Class<? extends TransitiveInfoProvider>> ALLOWED_PROVIDERS =
       ImmutableSet.of(
         JavaCompilationArgsProvider.class,
@@ -207,10 +209,11 @@ private JavaInfo(TransitiveInfoProviderMap providers) {
       structField = true
   )
   public SkylarkNestedSet getTransitiveRuntimeJars() {
-    return SkylarkNestedSet.of(
-        Artifact.class,
-        providers.getProvider(JavaCompilationArgsProvider.class)
-            .getRecursiveJavaCompilationArgs().getRuntimeJars());
+    JavaCompilationArgsProvider provider = getProvider(JavaCompilationArgsProvider.class);
+    NestedSet<Artifact> runtimeJars = provider == null
+        ? NestedSetBuilder.<Artifact>stableOrder().build()
+        : provider.getRecursiveJavaCompilationArgs().getRuntimeJars();
+    return SkylarkNestedSet.of(Artifact.class, runtimeJars);
   }
 
   @SkylarkCallable(
@@ -220,10 +223,11 @@ public SkylarkNestedSet getTransitiveRuntimeJars() {
       structField = true
   )
   public SkylarkNestedSet getTransitiveCompileTimeJars() {
-    return SkylarkNestedSet.of(
-        Artifact.class,
-        providers.getProvider(JavaCompilationArgsProvider.class)
-            .getRecursiveJavaCompilationArgs().getCompileTimeJars());
+    JavaCompilationArgsProvider provider = getProvider(JavaCompilationArgsProvider.class);
+    NestedSet<Artifact> compileTimeJars = provider == null
+        ? NestedSetBuilder.<Artifact>stableOrder().build()
+        : provider.getRecursiveJavaCompilationArgs().getCompileTimeJars();
+    return SkylarkNestedSet.of(Artifact.class, compileTimeJars);
   }
 
   @SkylarkCallable(
@@ -238,10 +242,11 @@ public SkylarkNestedSet getTransitiveCompileTimeJars() {
       structField = true
   )
   public SkylarkNestedSet getCompileTimeJars() {
-    return SkylarkNestedSet.of(
-        Artifact.class,
-        providers.getProvider(JavaCompilationArgsProvider.class)
-            .getJavaCompilationArgs().getCompileTimeJars());
+    JavaCompilationArgsProvider provider = getProvider(JavaCompilationArgsProvider.class);
+    NestedSet<Artifact> compileTimeJars = provider == null
+        ? NestedSetBuilder.<Artifact>stableOrder().build()
+        : provider.getJavaCompilationArgs().getCompileTimeJars();
+    return SkylarkNestedSet.of(Artifact.class, compileTimeJars);
   }
 
   @SkylarkCallable(
@@ -255,10 +260,11 @@ public SkylarkNestedSet getCompileTimeJars() {
       structField = true
   )
   public SkylarkNestedSet getFullCompileTimeJars() {
-    return SkylarkNestedSet.of(
-        Artifact.class,
-        providers.getProvider(JavaCompilationArgsProvider.class)
-            .getJavaCompilationArgs().getFullCompileTimeJars());
+    JavaCompilationArgsProvider provider = getProvider(JavaCompilationArgsProvider.class);
+    NestedSet<Artifact> fullCompileTimeJars = provider == null
+        ? NestedSetBuilder.<Artifact>stableOrder().build()
+        : provider.getJavaCompilationArgs().getFullCompileTimeJars();
+    return SkylarkNestedSet.of(Artifact.class, fullCompileTimeJars);
   }
 
   @SkylarkCallable(
@@ -269,8 +275,10 @@ public SkylarkNestedSet getFullCompileTimeJars() {
       structField = true
   )
   public SkylarkList<Artifact> getSourceJars() {
-    return SkylarkList.createImmutable(
-        providers.getProvider(JavaSourceJarsProvider.class).getSourceJars());
+    JavaSourceJarsProvider provider = providers.getProvider(JavaSourceJarsProvider.class);
+    ImmutableList<Artifact> sourceJars =
+        provider == null ? ImmutableList.of() : provider.getSourceJars();
+    return SkylarkList.createImmutable(sourceJars);
   }
 
   @SkylarkCallable(

src/test/java/com/google/devtools/build/lib/rules/java/JavaInfoTest.java

@@ -0,0 +1,53 @@
+// Copyright 2017 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.java;
+
+import static com.google.common.truth.Truth.assertThat;
+
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.JUnit4;
+
+/**
+ * Unit tests for {@link JavaInfo}.
+ */
+@RunWith(JUnit4.class)
+public class JavaInfoTest {
+
+  @Test
+  public void getTransitiveRuntimeJars_noJavaCompilationArgsProvider() {
+    assertThat(JavaInfo.EMPTY.getTransitiveRuntimeJars().isEmpty()).isTrue();
+  }
+
+  @Test
+  public void getTransitiveCompileTimeJarsJars_noJavaCompilationArgsProvider() {
+    assertThat(JavaInfo.EMPTY.getTransitiveCompileTimeJars().isEmpty()).isTrue();
+  }
+
+  @Test
+  public void getCompileTimeJarsJars_noJavaCompilationArgsProvider() {
+    assertThat(JavaInfo.EMPTY.getCompileTimeJars().isEmpty()).isTrue();
+  }
+
+  @Test
+  public void getFullCompileTimeJarsJars_noJavaCompilationArgsProvider() {
+    assertThat(JavaInfo.EMPTY.getFullCompileTimeJars().isEmpty()).isTrue();
+  }
+
+  @Test
+  public void getSourceJars_noJavaSourceJarsProvider() {
+    assertThat(JavaInfo.EMPTY.getSourceJars()).isEmpty();
+  }
+}