Prohibited comparison of Skylark sets

RELNOTES: Comparing sets (`if set1 < set2:`) is not allowed anymore in Skylark because it didn't work correctly anyway.

--
MOS_MIGRATED_REVID=138408411

1 files changed, 3 insertions, 0 deletions

diff --git a/src/main/java/com/google/devtools/build/lib/syntax/EvalUtils.java b/src/main/java/com/google/devtools/build/lib/syntax/EvalUtils.java
index 29667813ad..f9f2f62a88 100644
--- a/src/main/java/com/google/devtools/build/lib/syntax/EvalUtils.java
+++ b/src/main/java/com/google/devtools/build/lib/syntax/EvalUtils.java
@@ -72,6 +72,9 @@ public final class EvalUtils {
       o1 = SkylarkType.convertToSkylark(o1, /*env=*/ null);
       o2 = SkylarkType.convertToSkylark(o2, /*env=*/ null);
 
+      if (o1 instanceof SkylarkNestedSet && o2 instanceof SkylarkNestedSet) {
+        throw new ComparisonException("Cannot compare sets");
+      }
       if (o1 instanceof SkylarkList && o2 instanceof SkylarkList
           && ((SkylarkList) o1).isTuple() == ((SkylarkList) o2).isTuple()) {
         return compareLists((SkylarkList) o1, (SkylarkList) o2);