Test capture glb with a non-top type-parameter bound

framework/tests/nontopdefault/CaptureGlbWildcardBound.java

@@ -0,0 +1,41 @@
+import org.checkerframework.framework.testchecker.nontopdefault.qual.NTDMiddle;
+import org.checkerframework.framework.testchecker.nontopdefault.qual.NTDTop;
+
+// Capture conversion of Foo<? extends Bar> where Foo<T extends @NTDTop Object> must give the
+// captured type variable an upper bound equal to the glb of the wildcard's extends bound and the
+// type parameter's bound -- not the type parameter's bound wholesale.  Here the wildcard's extends
+// bound (the type-use default @NTDMiddle, or an explicit qualifier) is more precise than the
+// @NTDTop parameter bound, so the glb is the wildcard's qualifier.
+//
+// This fills the coverage gap noted in framework/tests/h1h2checker/WildcardBounds.java ("We could
+// add an OuterS1 to also test with a non-top upper bound."): the existing wildcard-capture tests
+// use a top parameter bound, for which the glb trivially equals the wildcard's bound.  See also
+// cf-tasks/task-3-findings.md.
+@SuppressWarnings("inconsistent.constructor.type") // not the point of this test
+class CaptureGlbWildcardBound {
+    interface Bar {}
+
+    interface Foo<T extends @NTDTop Object> {
+        T get();
+    }
+
+    // Implicit wildcard extends bound: Bar defaults to the type-use default @NTDMiddle, which is
+    // below the @NTDTop parameter bound.  glb(@NTDMiddle Bar, @NTDTop Object) == @NTDMiddle Bar, so
+    // x.get() is @NTDMiddle.
+    void implicitBound(Foo<? extends Bar> x) {
+        @NTDMiddle Object m = x.get();
+    }
+
+    // Explicit @NTDMiddle wildcard extends bound: same glb, @NTDMiddle.
+    void explicitMiddleBound(Foo<? extends @NTDMiddle Bar> x) {
+        @NTDMiddle Object m = x.get();
+    }
+
+    // Discriminating control: an explicit @NTDTop wildcard extends bound equals the parameter
+    // bound, so the glb is @NTDTop, which is not assignable to @NTDMiddle.  This confirms the glb
+    // machinery actually varies with the wildcard's extends bound.
+    void explicitTopBound(Foo<? extends @NTDTop Bar> x) {
+        // :: error: (assignment.type.incompatible)
+        @NTDMiddle Object m = x.get();
+    }
+}