Merge ComposingSplitTransition and ComposingPatchTransition.

Part of https://docs.google.com/document/d/1_UJKmAQ9EE8i3Pl0il3YLTYr-Q9EKYYyLatt2zohfyM/edit#

PiperOrigin-RevId: 198420365

1 files changed, 7 insertions, 0 deletions

diff --git a/src/main/java/com/google/devtools/build/lib/packages/RuleTransitionFactory.java b/src/main/java/com/google/devtools/build/lib/packages/RuleTransitionFactory.java
index e449253fb6..2445ddb955 100644
--- a/src/main/java/com/google/devtools/build/lib/packages/RuleTransitionFactory.java
+++ b/src/main/java/com/google/devtools/build/lib/packages/RuleTransitionFactory.java
@@ -23,6 +23,13 @@ public interface RuleTransitionFactory {
   /**
    * Generates a transition to be used when entering the given rule.
    *
+   * <p>This cannot be a
+   * {@link com.google.devtools.build.lib.analysis.config.transitions.SplitTransition} because
+   * splits are conceptually a property of the <i>parent<i> rule. In other words, it makes sense for
+   * a parent to say "build my deps in configurations A and B". But it doesn't make sense for a dep
+   * to say "build myself in configurations A and B" if its parent doesn't know how to intelligently
+   * handle the results.
+   *
    * <p>If this class determines that no transition should be performed, it should return
    * {@code NoTransition.INSTANCE}.
    */