Remove ConfigurationTransitionProxy.NULL

PiperOrigin-RevId: 182099803

3 files changed, 42 insertions, 8 deletions

diff --git a/src/main/java/com/google/devtools/build/lib/analysis/config/TransitionResolver.java b/src/main/java/com/google/devtools/build/lib/analysis/config/TransitionResolver.java
index 09fa8a1741..44530445c5 100644
--- a/src/main/java/com/google/devtools/build/lib/analysis/config/TransitionResolver.java
+++ b/src/main/java/com/google/devtools/build/lib/analysis/config/TransitionResolver.java
@@ -19,6 +19,7 @@ import com.google.common.base.Preconditions;
 import com.google.devtools.build.lib.analysis.TargetAndConfiguration;
 import com.google.devtools.build.lib.analysis.config.transitions.ComposingSplitTransition;
 import com.google.devtools.build.lib.analysis.config.transitions.ConfigurationTransitionProxy;
+import com.google.devtools.build.lib.analysis.config.transitions.NullTransition;
 import com.google.devtools.build.lib.analysis.config.transitions.PatchTransition;
 import com.google.devtools.build.lib.analysis.config.transitions.SplitTransition;
 import com.google.devtools.build.lib.analysis.config.transitions.Transition;
@@ -70,7 +71,7 @@ public final class TransitionResolver {
 
     // I. Input files and package groups have no configurations. We don't want to duplicate them.
     if (usesNullConfiguration(toTarget)) {
-      return ConfigurationTransitionProxy.NULL;
+      return NullTransition.INSTANCE;
     }
 
     // II. Host configurations never switch to another. All prerequisites of host targets have the
@@ -166,9 +167,9 @@ public final class TransitionResolver {
       return transition1;
     } else if (transition2 == ConfigurationTransitionProxy.NONE) {
       return transition1;
-    } else if (transition2 == ConfigurationTransitionProxy.NULL) {
+    } else if (transition2 == NullTransition.INSTANCE) {
       // A NULL transition can just replace earlier transitions: no need to compose them.
-      return ConfigurationTransitionProxy.NULL;
+      return NullTransition.INSTANCE;
     } else if (transition2.isHostTransition()) {
       // A HOST transition can just replace earlier transitions: no need to compose them.
       // But it also improves performance: host transitions are common, and
@@ -189,7 +190,7 @@ public final class TransitionResolver {
    * be composed after it.
    */
   private static boolean isFinal(Transition transition) {
-    return (transition == ConfigurationTransitionProxy.NULL
+    return (transition == NullTransition.INSTANCE
         || transition == HostTransition.INSTANCE);
   }
 
@@ -197,7 +198,7 @@ public final class TransitionResolver {
    * Applies the given split and composes it after an existing transition.
    */
   private static Transition split(Transition currentTransition, SplitTransition split) {
-    Preconditions.checkState(currentTransition != ConfigurationTransitionProxy.NULL,
+    Preconditions.checkState(currentTransition != NullTransition.INSTANCE,
         "cannot apply splits after null transitions (null transitions are expected to be final)");
     Preconditions.checkState(currentTransition != HostTransition.INSTANCE,
         "cannot apply splits after host transitions (host transitions are expected to be final)");
diff --git a/src/main/java/com/google/devtools/build/lib/analysis/config/transitions/ConfigurationTransitionProxy.java b/src/main/java/com/google/devtools/build/lib/analysis/config/transitions/ConfigurationTransitionProxy.java
index 3df17bf1af..6a19b36fbb 100644
--- a/src/main/java/com/google/devtools/build/lib/analysis/config/transitions/ConfigurationTransitionProxy.java
+++ b/src/main/java/com/google/devtools/build/lib/analysis/config/transitions/ConfigurationTransitionProxy.java
@@ -25,9 +25,6 @@ public enum ConfigurationTransitionProxy implements Transition {
   /** No transition, i.e., the same configuration as the current. */
   NONE,
 
-  /** Transition to a null configuration (applies to, e.g., input files). */
-  NULL,
-
   /** Transition from the target configuration to the data configuration. */
   // TODO(bazel-team): Move this elsewhere.
   DATA,
diff --git a/src/main/java/com/google/devtools/build/lib/analysis/config/transitions/NullTransition.java b/src/main/java/com/google/devtools/build/lib/analysis/config/transitions/NullTransition.java
new file mode 100644
index 0000000000..2edbb9fb0f
--- /dev/null
+++ b/src/main/java/com/google/devtools/build/lib/analysis/config/transitions/NullTransition.java
@@ -0,0 +1,36 @@
+// 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.analysis.config.transitions;
+
+import com.google.devtools.build.lib.analysis.config.BuildOptions;
+
+/**
+ * A {@link PatchTransition} to a null configuration.
+ */
+public class NullTransition implements PatchTransition {
+
+  public static final NullTransition INSTANCE = new NullTransition();
+
+  private NullTransition() {
+  }
+
+  @Override
+  public BuildOptions apply(BuildOptions options) {
+    throw new UnsupportedOperationException(
+        "This is only referenced in a few places, so it's easier and more efficient to optimize "
+        + "Blaze's transition logic in the presence of null transitions vs. actually call this "
+        + "method to get results we know ahead of time. If there's ever a need to properly "
+        + "implement this method we can always do so.");
+  }
+}