Don't bound a fresh capture type variable by unresolved inference variables

checker/tests/nullness/Issue8298Nullness.java

@@ -0,0 +1,42 @@
+// Test case for https://github.com/typetools/checker-framework/issues/8298
+
+import org.checkerframework.checker.nullness.qual.NonNull;
+import org.checkerframework.checker.nullness.qual.Nullable;
+
+public class Issue8298Nullness {
+  static class Box<T extends @Nullable Object> {}
+
+  static <T extends @Nullable Object> Box<? extends T> wildcardBox(Box<T> b) {
+    throw new RuntimeException();
+  }
+
+  static <X extends @Nullable Object> X takeExtends(Box<? extends X> x) {
+    throw new RuntimeException();
+  }
+
+  static <U extends @Nullable Object> void nullableBound(Box<U> box) {
+    // :: error: (dereference.of.nullable)
+    takeExtends(wildcardBox(box)).toString();
+    U u = takeExtends(wildcardBox(box));
+  }
+
+  static <U extends @Nullable Object> void nonNullUse(Box<@NonNull U> box) {
+    takeExtends(wildcardBox(box)).toString();
+    @NonNull U u = takeExtends(wildcardBox(box));
+  }
+
+  static <U extends @Nullable Object> void nullableUse(Box<@Nullable U> box) {
+    // :: error: (argument)
+    @NonNull Object o = takeExtends(wildcardBox(box));
+  }
+
+  static <U extends Comparable<U>> void fBounded(Box<U> box, U other) {
+    takeExtends(wildcardBox(box)).compareTo(other);
+  }
+
+  static void string(Box<@Nullable String> box) {
+    // :: error: (dereference.of.nullable)
+    takeExtends(wildcardBox(box)).length();
+    @Nullable String s = takeExtends(wildcardBox(box));
+  }
+}

framework/src/main/java/org/checkerframework/framework/util/typeinference8/util/Resolution.java

@@ -480,6 +480,8 @@ private static BoundSet resolveWithCapture(
       }
 
       Set<AbstractType> upperBounds = ai.getBounds().upperBounds();
+      // Omit bounds that mention variables outside `as`, such as `alpha` in `ai <: alpha`.
+      upperBounds.removeIf(u -> !as.containsAll(u.getInferenceVariables()));
       AbstractType upperBound = context.inferenceTypeFactory.glb(upperBounds);
       if (upperBound != null) {
         // `glb` returns its argument when `upperBounds` is a singleton, and that type is still

framework/tests/all-systems/Issue8298.java

@@ -0,0 +1,35 @@
+// Test case for https://github.com/typetools/checker-framework/issues/8298
+
+import java.util.List;
+
+public class Issue8298 {
+  static class Box<T> {}
+
+  static <T> Box<? extends T> wildcardBox(Box<T> b) {
+    throw new RuntimeException();
+  }
+
+  static <X> X takeExtends(Box<? extends X> x) {
+    throw new RuntimeException();
+  }
+
+  static <X> X takeList(Box<? extends List<X>> x) {
+    throw new RuntimeException();
+  }
+
+  static <U> void m(Box<U> box) {
+    takeExtends(wildcardBox(box));
+  }
+
+  static <U extends Comparable<U>> void fBounded(Box<U> box, U other) {
+    takeExtends(wildcardBox(box)).compareTo(other);
+  }
+
+  static void string(Box<String> box) {
+    takeExtends(wildcardBox(box)).length();
+  }
+
+  static void list(Box<List<String>> box) {
+    String s = takeList(wildcardBox(box));
+  }
+}