Initial subtype checking for wildcards

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

@@ -1,6 +1,7 @@
 package com.uber.nullaway.generics;
 
 import com.google.errorprone.VisitorState;
+import com.sun.tools.javac.code.BoundKind;
 import com.sun.tools.javac.code.Symbol;
 import com.sun.tools.javac.code.Type;
 import com.sun.tools.javac.code.Types;
@@ -63,18 +64,7 @@ public Boolean visitClassType(Type.ClassType lhsType, Type rhsType) {
     for (int i = 0; i < lhsTypeArguments.size(); i++) {
       Type lhsTypeArgument = lhsTypeArguments.get(i);
       Type rhsTypeArgument = rhsTypeArguments.get(i);
-      if (lhsTypeArgument.getKind().equals(TypeKind.WILDCARD)
-          || rhsTypeArgument.getKind().equals(TypeKind.WILDCARD)) {
-        // TODO Handle wildcard types
-        continue;
-      }
-      boolean isLHSNullableAnnotated = genericsChecks.isNullableAnnotated(lhsTypeArgument);
-      boolean isRHSNullableAnnotated = genericsChecks.isNullableAnnotated(rhsTypeArgument);
-      if (isLHSNullableAnnotated != isRHSNullableAnnotated) {
-        return false;
-      }
-      // nested generics
-      if (!lhsTypeArgument.accept(this, rhsTypeArgument)) {
+      if (!typeArgumentContainedBy(lhsTypeArgument, rhsTypeArgument)) {
         return false;
       }
     }
@@ -116,4 +106,80 @@ public Boolean visitArrayType(Type.ArrayType lhsType, Type rhsType) {
   public Boolean visitType(Type t, Type type) {
     return true;
   }
+
+  /**
+   * Returns whether the actual type argument on the right is contained by the formal type argument
+   * on the left, following the JLS 4.5.1 notion of type-argument containment but interpreted with
+   * NullAway's nullability-aware subtype relation. Non-wildcard pairs require matching nullability
+   * annotations and recursively matching nested type arguments. Wildcard formals are delegated to
+   * {@link #wildcardContains}.
+   */
+  private boolean typeArgumentContainedBy(Type lhsTypeArgument, Type rhsTypeArgument) {
+    if (lhsTypeArgument.getKind().equals(TypeKind.WILDCARD)) {
+      return wildcardContains((Type.WildcardType) lhsTypeArgument, rhsTypeArgument);
+    }
+    if (rhsTypeArgument.getKind().equals(TypeKind.WILDCARD)) {
+      // Treat wildcard actual arguments as accepted here until we add more complete support.
+      return true;
+    }
+    boolean isLHSNullableAnnotated = genericsChecks.isNullableAnnotated(lhsTypeArgument);
+    boolean isRHSNullableAnnotated = genericsChecks.isNullableAnnotated(rhsTypeArgument);
+    if (isLHSNullableAnnotated != isRHSNullableAnnotated) {
+      return false;
+    }
+    return lhsTypeArgument.accept(this, rhsTypeArgument);
+  }
+
+  /**
+   * Handles a narrow slice of the JLS type-argument containment rules from JLS 4.5.1 for wildcard
+   * type arguments. In particular, for a formal argument {@code ? extends S}, we accept either a
+   * concrete actual argument {@code T} or a wildcard actual argument {@code ? extends T} whenever
+   * {@code T <: S}, using NullAway's nullability-aware subtype check in place of plain Java
+   * subtyping. This covers the JLS cases behind both {@code T <= ? extends S} and {@code ? extends
+   * T <= ? extends S}. For now, this method intentionally leaves {@code super} wildcards and other
+   * more complex cases to existing fallback behavior.
+   */
+  private boolean wildcardContains(Type.WildcardType lhsWildcard, Type rhsTypeArgument) {
+    if (lhsWildcard.kind == BoundKind.UNBOUND) {
+      return true;
+    }
+    if (lhsWildcard.kind != BoundKind.EXTENDS) {
+      // Treat non-extends wildcards as accepted here until we add more complete support.
+      return true;
+    }
+    Type lhsBound = lhsWildcard.getExtendsBound();
+    if (lhsBound == null) {
+      return true;
+    }
+    if (rhsTypeArgument.getKind().equals(TypeKind.WILDCARD)) {
+      Type.WildcardType rhsWildcard = (Type.WildcardType) rhsTypeArgument;
+      if (rhsWildcard.kind != BoundKind.EXTENDS) {
+        // Treat non-extends wildcard actual arguments as accepted here until we add more complete
+        // support.
+        return true;
+      }
+      Type rhsBound = rhsWildcard.getExtendsBound();
+      if (rhsBound == null) {
+        return true;
+      }
+      return typeArgumentSubtype(lhsBound, rhsBound);
+    }
+    return typeArgumentSubtype(lhsBound, rhsTypeArgument);
+  }
+
+  /**
+   * Returns whether the actual type argument on the right is a nullability-aware subtype of the
+   * formal type argument on the left. This check first rejects flows from nullable to non-null at
+   * the top level of the type argument, then delegates to {@link
+   * GenericsChecks#subtypeParameterNullability(Type, Type, VisitorState)} for recursive nested
+   * checks.
+   */
+  private boolean typeArgumentSubtype(Type lhsType, Type rhsType) {
+    boolean isLHSNullableAnnotated = genericsChecks.isNullableAnnotated(lhsType);
+    boolean isRHSNullableAnnotated = genericsChecks.isNullableAnnotated(rhsType);
+    if (isRHSNullableAnnotated && !isLHSNullableAnnotated) {
+      return false;
+    }
+    return genericsChecks.subtypeParameterNullability(lhsType, rhsType, state);
+  }
 }

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

@@ -1450,7 +1450,7 @@ private boolean identicalTypeParameterNullability(
    * @param rhsType type for the rhs of the assignment
    * @param state the visitor state
    */
-  private boolean subtypeParameterNullability(Type lhsType, Type rhsType, VisitorState state) {
+  boolean subtypeParameterNullability(Type lhsType, Type rhsType, VisitorState state) {
     if (lhsType.isRaw()) {
       return true;
     }

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

@@ -9,7 +9,34 @@
 
 public class WildcardTests extends NullAwayTestsBase {
 
-  @Ignore("https://github.com/uber/NullAway/issues/1360")
+  @Test
+  public void simpleWildcardNoInference() {
+    makeHelper()
+        .addSourceLines(
+            "Test.java",
+            """
+            import org.jspecify.annotations.*;
+            @NullMarked
+            class Test {
+              class Foo<T extends @Nullable Object> {}
+              String nullableWildcard(Foo<? extends @Nullable String> foo) { throw new RuntimeException(); }
+              String nonnullWildcard(Foo<? extends String> foo) { throw new RuntimeException(); }
+              void testNegative(Foo<@Nullable String> f) {
+                // this is legal since the wildcard upper bound is @Nullable
+                String s = nullableWildcard(f);
+                s.hashCode();
+              }
+              void testPositive(Foo<@Nullable String> f) {
+                // not legal since the wildcard upper bound is non-null
+                // BUG: Diagnostic contains: incompatible types: Test.Foo<@Nullable String> cannot be converted to Test.Foo<? extends String>
+                String s = nonnullWildcard(f);
+                s.hashCode();
+              }
+            }
+            """)
+        .doTest();
+  }
+
   @Test
   public void simpleWildcard() {
     makeHelper()
@@ -29,7 +56,70 @@ void testNegative(Foo<@Nullable String> f) {
               }
               void testPositive(Foo<@Nullable String> f) {
                 // not legal since the wildcard upper bound is non-null
-                // BUG: Diagnostic contains: something about how f cannot be passed here
+                // BUG: Diagnostic contains: incompatible types: Test.Foo<@Nullable String> cannot be converted to Test.Foo<? extends String>
+                String s = nonnullWildcard(f);
+                s.hashCode();
+              }
+            }
+            """)
+        .doTest();
+  }
+
+  @Test
+  public void nestedTypeArgsInWildcardBoundNoInference() {
+    makeHelper()
+        .addSourceLines(
+            "Test.java",
+            """
+            import org.jspecify.annotations.*;
+            @NullMarked
+            class Test {
+              class Foo<T extends @Nullable Object> {}
+              class Bar<T extends @Nullable Object> {}
+              String nullableWildcard(Foo<? extends Bar<@Nullable String>> foo) {
+                throw new RuntimeException();
+              }
+              String nonnullWildcard(Foo<? extends Bar<String>> foo) {
+                throw new RuntimeException();
+              }
+              void testNegative(Foo<Bar<@Nullable String>> f) {
+                String s = nullableWildcard(f);
+                s.hashCode();
+              }
+              void testPositive(Foo<Bar<@Nullable String>> f) {
+                // BUG: Diagnostic contains: incompatible types: Test.Foo<Test.Bar<@Nullable String>> cannot be converted to Test.Foo<? extends Test.Bar<String>>
+                String s = nonnullWildcard(f);
+                s.hashCode();
+              }
+            }
+            """)
+        .doTest();
+  }
+
+  @Test
+  public void deeplyNestedTypeArgsInWildcardBoundNoInference() {
+    makeHelper()
+        .addSourceLines(
+            "Test.java",
+            """
+            import org.jspecify.annotations.*;
+            @NullMarked
+            class Test {
+              class Foo<T extends @Nullable Object> {}
+              class Bar<T extends @Nullable Object> {}
+              class Baz<T extends @Nullable Object> {}
+              String nullableWildcard(Foo<? extends Bar<Baz<@Nullable String>>> foo) {
+                throw new RuntimeException();
+              }
+              String nonnullWildcard(Foo<? extends Bar<Baz<String>>> foo) {
+                throw new RuntimeException();
+              }
+              void testNegative(Foo<Bar<Baz<@Nullable String>>> f) {
+                String s = nullableWildcard(f);
+                s.hashCode();
+              }
+              void testPositive(Foo<Bar<Baz<@Nullable String>>> f) {
+                // BUG: Diagnostic contains: incompatible types: Test.Foo<Test.Bar<Test.Baz<@Nullable String>>> cannot be converted to Test.Foo<? extends Test.Bar<Test.Baz<String>>>
                 String s = nonnullWildcard(f);
                 s.hashCode();
               }
@@ -38,6 +128,102 @@ void testPositive(Foo<@Nullable String> f) {
         .doTest();
   }
 
+  @Test
+  public void intermediateNestedTypeArgsInWildcardBoundNoInference() {
+    makeHelper()
+        .addSourceLines(
+            "Test.java",
+            """
+            import org.jspecify.annotations.*;
+            @NullMarked
+            class Test {
+              class Foo<T extends @Nullable Object> {}
+              class Bar<T extends @Nullable Object> {}
+              class Baz<T extends @Nullable Object> {}
+              String nullableWildcard(Foo<? extends @Nullable Bar<Baz<String>>> foo) {
+                throw new RuntimeException();
+              }
+              String nonnullWildcard(Foo<? extends Bar<Baz<String>>> foo) {
+                throw new RuntimeException();
+              }
+              void testNegative(Foo<@Nullable Bar<Baz<String>>> f) {
+                String s = nullableWildcard(f);
+                s.hashCode();
+              }
+              void testPositive(Foo<@Nullable Bar<Baz<String>>> f) {
+                // BUG: Diagnostic contains: incompatible types: Test.Foo<Test.@Nullable Bar<Test.Baz<String>>> cannot be converted to Test.Foo<? extends Test.Bar<Test.Baz<String>>>
+                String s = nonnullWildcard(f);
+                s.hashCode();
+              }
+            }
+            """)
+        .doTest();
+  }
+
+  @Test
+  public void wildcardActualArgumentNoInference() {
+    makeHelper()
+        .addSourceLines(
+            "Test.java",
+            """
+            import org.jspecify.annotations.*;
+            @NullMarked
+            class Test {
+              class Foo<T extends @Nullable Object> {}
+              String nullableWildcard(Foo<? extends @Nullable String> foo) {
+                throw new RuntimeException();
+              }
+              String nonnullWildcard(Foo<? extends String> foo) {
+                throw new RuntimeException();
+              }
+              void testNegative(Foo<? extends @Nullable String> f) {
+                String s = nullableWildcard(f);
+                s.hashCode();
+              }
+              void testPositive(Foo<? extends @Nullable String> f) {
+                // BUG: Diagnostic contains: incompatible types: Test.Foo<? extends @Nullable String> cannot be converted to Test.Foo<? extends String>
+                String s = nonnullWildcard(f);
+                s.hashCode();
+              }
+            }
+            """)
+        .doTest();
+  }
+
+  @Test
+  public void wildcardCheckingForReturnsAndAssignments() {
+    makeHelper()
+        .addSourceLines(
+            "Test.java",
+            """
+            import org.jspecify.annotations.*;
+            @NullMarked
+            class Test {
+              class Foo<T extends @Nullable Object> {}
+              Foo<? extends String> nonnullField;
+              Foo<? extends @Nullable String> nullableField;
+              Test(Foo<? extends @Nullable String> f) {
+                nullableField = f;
+                // BUG: Diagnostic contains: incompatible types: Test.Foo<? extends @Nullable String> cannot be converted to Test.Foo<? extends String>
+                nonnullField = f;
+              }
+              Foo<? extends @Nullable String> nullableReturn(Foo<? extends @Nullable String> f) {
+                return f;
+              }
+              Foo<? extends String> nonnullReturn(Foo<? extends @Nullable String> f) {
+                // BUG: Diagnostic contains: incompatible types: Test.Foo<? extends @Nullable String> cannot be converted to Test.Foo<? extends String>
+                return f;
+              }
+              void testLocal(Foo<? extends @Nullable String> f) {
+                Foo<? extends @Nullable String> ok = f;
+                // BUG: Diagnostic contains: incompatible types: Test.Foo<? extends @Nullable String> cannot be converted to Test.Foo<? extends String>
+                Foo<? extends String> bad = f;
+              }
+            }
+            """)
+        .doTest();
+  }
+
   @Ignore("https://github.com/uber/NullAway/issues/1350")
   @Test
   public void genericMethodLambdaArgWildCard() {