Optimize how null configurations get created and add test infrastructure for Bazel's dep configuration creation logic.

This essentially implements the following TODOs:

https://github.com/bazelbuild/bazel/blob/bc6045dcc8fa33d4241d231138020ac4bdecc14f/src/main/java/com/google/devtools/build/lib/skyframe/ConfiguredTargetFunction.java#L599
https://github.com/bazelbuild/bazel/blob/bc6045dcc8fa33d4241d231138020ac4bdecc14f/src/test/java/com/google/devtools/build/lib/skyframe/ConfigurationsForTargetsTest.java#L42

--
MOS_MIGRATED_REVID=134607049

1 files changed, 7 insertions, 1 deletions

diff --git a/src/main/java/com/google/devtools/build/lib/analysis/config/BuildConfiguration.java b/src/main/java/com/google/devtools/build/lib/analysis/config/BuildConfiguration.java
index 7b89d6f142..e00a95edef 100644
--- a/src/main/java/com/google/devtools/build/lib/analysis/config/BuildConfiguration.java
+++ b/src/main/java/com/google/devtools/build/lib/analysis/config/BuildConfiguration.java
@@ -1742,7 +1742,13 @@ public final class BuildConfiguration {
     public Iterable<Dependency> getDependencies(
         Label label, ImmutableSet<AspectDescriptor> aspects) {
       return ImmutableList.of(
-          Dependency.withTransitionAndAspects(label, currentTransition, aspects));
+          isNull()
+              // We can trivially set the final value for null-configured targets now. This saves
+              // us from having to recreate a new Dependency object for the final value later. Since
+              // there are lots of null-configured targets (e.g. all source files), this can add up
+              // over the course of a build.
+              ? Dependency.withNullConfiguration(label)
+              : Dependency.withTransitionAndAspects(label, currentTransition, aspects));
     }
   }