From 6b2501317748eaf3ac5c61ad290d7569e637237d Mon Sep 17 00:00:00 2001
From: Suzanne Millstein <smillst@cs.washington.edu>
Date: Thu, 10 Oct 2024 11:27:19 -0700
Subject: [PATCH] Fix crash.

---
 .../framework/util/AnnotatedTypes.java                | 11 +++++++++++
 framework/tests/all-systems/Issue6810.java            | 11 +++++++++++
 2 files changed, 22 insertions(+)
 create mode 100644 framework/tests/all-systems/Issue6810.java

diff --git a/framework/src/main/java/org/checkerframework/framework/util/AnnotatedTypes.java b/framework/src/main/java/org/checkerframework/framework/util/AnnotatedTypes.java
index 0ea32d0cdea..8a32cb9f7f7 100644
--- a/framework/src/main/java/org/checkerframework/framework/util/AnnotatedTypes.java
+++ b/framework/src/main/java/org/checkerframework/framework/util/AnnotatedTypes.java
@@ -893,6 +893,17 @@ public static AnnotatedTypeMirror annotatedGLB(
     TypeMirror tm1 = type1.getUnderlyingType();
     TypeMirror tm2 = type2.getUnderlyingType();
     TypeMirror glbJava = TypesUtils.greatestLowerBound(tm1, tm2, atypeFactory.getProcessingEnv());
+    if (glbJava.getKind() == TypeKind.ERROR) {
+      if (type1.getKind() == TypeKind.TYPEVAR) {
+        return type1;
+      }
+      if (type2.getKind() == TypeKind.TYPEVAR) {
+        return type2;
+      }
+      // I think the only way error happens is when one of the types is a typevarible, but just in
+      // case, just return type1.
+      return type1;
+    }
     Types types = atypeFactory.types;
     QualifierHierarchy qualHierarchy = atypeFactory.getQualifierHierarchy();
     if (types.isSubtype(tm1, tm2)) {
diff --git a/framework/tests/all-systems/Issue6810.java b/framework/tests/all-systems/Issue6810.java
new file mode 100644
index 00000000000..2f19cb67677
--- /dev/null
+++ b/framework/tests/all-systems/Issue6810.java
@@ -0,0 +1,11 @@
+import java.util.Set;
+
+public class Issue6810 {
+  static class Box<T extends Box<T>> {}
+
+  abstract static class BoxSet<T extends Box<T>> implements Set<T> {}
+
+  static <E extends Box<E>> void intersect2(BoxSet<? extends E> intersect, Set<E> set2) {
+    intersect.retainAll(set2);
+  }
+}