JSpecify: assume NONNULL in generic method inference for unconstrained type variables

nullaway/src/main/java/com/uber/nullaway/generics/GenericsChecks.java

@@ -729,7 +729,14 @@ private MethodInferenceResult runInferenceForCall(
           methodSymbol,
           invocationTree,
           allInvocations);
-      typeVarNullability = solver.solve();
+      typeVarNullability = new HashMap<>(solver.solve());
+      // The solver only computes a solution for variables that appear in constraints. For
+      // unconstrained variables, treat them as NONNULL, consistent with solver behavior for
+      // unconstrained variables that do appear in the constraint graph.
+      for (int i = 0; i < methodSymbol.getTypeParameters().size(); i++) {
+        Symbol.TypeVariableSymbol typeVar = methodSymbol.getTypeParameters().get(i);
+        typeVarNullability.putIfAbsent(typeVar, ConstraintSolver.InferredNullability.NONNULL);
+      }
 
       // Store inferred types for lambda arguments
       new InvocationArguments(invocationTree, methodSymbol.type.asMethodType())

nullaway/src/test/java/com/uber/nullaway/jspecify/GenericMethodTests.java

@@ -1528,6 +1528,46 @@ public static <T> T notNull(@Nullable T object, String message) {
         .doTest();
   }
 
+  @Test
+  public void issue1453() {
+    makeHelper()
+        .addSourceLines(
+            "NullUtil.java",
+            """
+            package com.uber;
+            import org.jspecify.annotations.NullMarked;
+            import org.jspecify.annotations.Nullable;
+            import org.jetbrains.annotations.Contract;
+            @NullMarked
+            public class NullUtil {
+              @SuppressWarnings("NullAway")
+              public static <T> T assumeNonNull(@Nullable T object) {
+                return object;
+              }
+            }
+            """)
+        .addSourceLines(
+            "Test.java",
+            """
+            package com.uber;
+            import java.util.List;
+            import org.jspecify.annotations.NullMarked;
+            import org.jspecify.annotations.Nullable;
+            import static com.uber.NullUtil.assumeNonNull;
+            import java.util.concurrent.atomic.AtomicReference;
+            @NullMarked
+            class Test {
+              private final AtomicReference<@Nullable List<String>> ref = new AtomicReference<>();
+              void test() {
+                for (String s: assumeNonNull(ref.get())) {
+                  System.out.println(s);
+                }
+              }
+            }
+            """)
+        .doTest();
+  }
+
   private CompilationTestHelper makeHelper() {
     return makeTestHelperWithArgs(
         JSpecifyJavacConfig.withJSpecifyModeArgs(