Substitute inferred @NonNull types for generic method inference (#1445)

msridhar · web-flow · commit c27f3f494a6b · 2026-01-25T10:14:16.000-05:00
Fixes #1444 In certain cases, like the test from #1444 added here, `javac` adds a `@Nullable` annotation to a type incorrectly as part of its inference. Here, for a call from the test: ```java @NullMarked public class Test { static class DefaultConfiguration { final @nullable Stream<? extends String> children; } final Stream<? extends String> children; Test(DefaultConfiguration configuration) { // relevant call this.children = notNull(configuration.children, "children must not be null"); } public static <T> T notNull(@nullable T object, String message) { throw new RuntimeException("todo"); } } ``` `javac`s inferred type for the return of the `notNull` call matches the inferred parameter type exactly, `@Nullable Stream<...>`. But, when applying JSpecify rules, the return cannot be `@Nullable`. To fix this, add inferred `@NonNull` qualifiers along with `@Nullable` when doing a substitution inside a type.  ## Summary by CodeRabbit * **Bug Fixes** * Simplified printing of error/unknown generic types to show only the simple type name. * Improved type-variable substitution so inferred nullability is applied for both nullable and non-null cases. * **Tests** * Added/updated tests covering generic method type inference and JSpecify/Nullability behaviors (includes a new scenario for issue1444). <sub>✏️ Tip: You can customize this high-level summary in your review settings.</sub>
diff --git a/nullaway/src/main/java/com/uber/nullaway/generics/GenericTypePrettyPrintingVisitor.java b/nullaway/src/main/java/com/uber/nullaway/generics/GenericTypePrettyPrintingVisitor.java
@@ -89,6 +89,13 @@ public String visitArrayType(Type.ArrayType t, @Nullable Void unused) {
     return sb.append(" []").toString();
   }
 
+  @Override
+  public String visitErrorType(Type.ErrorType t, @Nullable Void unused) {
+    // this arises for our synthetic @Nullable and @NonNull annotations; we just return the simple
+    // name
+    return t.tsym.getSimpleName().toString();
+  }
+
   @Override
   public String visitType(Type t, @Nullable Void s) {
     return t.toString();
diff --git a/nullaway/src/main/java/com/uber/nullaway/generics/TypeSubstitutionUtils.java b/nullaway/src/main/java/com/uber/nullaway/generics/TypeSubstitutionUtils.java
@@ -224,18 +224,20 @@ private static Type substituteInferredNullabilityForTypeVariables(
     ListBuffer<Type> inferredTypes = new ListBuffer<>();
     for (Map.Entry<Element, ConstraintSolver.InferredNullability> entry :
         typeVarNullability.entrySet()) {
-      if (entry.getValue() == NULLABLE) {
-        // find all TypeVars occurring in targetType with the same symbol and substitute for those.
-        // we can have multiple such TypeVars due to previous substitutions that modified the type
-        // in some way, e.g., by changing its bounds
-        Element symbol = entry.getKey();
-        TypeVarWithSymbolCollector tvc = new TypeVarWithSymbolCollector(symbol);
-        targetType.accept(tvc, null);
-        for (Type.TypeVar tv : tvc.getMatches()) {
-          typeVars.append(tv);
-          inferredTypes.append(
-              typeWithAnnot(tv, GenericsChecks.getSyntheticNullableAnnotType(state)));
-        }
+      // find all TypeVars occurring in targetType with the same symbol and substitute for those.
+      // we can have multiple such TypeVars due to previous substitutions that modified the type
+      // in some way, e.g., by changing its bounds
+      Element symbol = entry.getKey();
+      TypeVarWithSymbolCollector tvc = new TypeVarWithSymbolCollector(symbol);
+      targetType.accept(tvc, null);
+      for (Type.TypeVar tv : tvc.getMatches()) {
+        typeVars.append(tv);
+        inferredTypes.append(
+            typeWithAnnot(
+                tv,
+                entry.getValue() == NULLABLE
+                    ? GenericsChecks.getSyntheticNullableAnnotType(state)
+                    : GenericsChecks.getSyntheticNonNullAnnotType(state)));
       }
     }
     List<Type> typeVarsToReplace = typeVars.toList();
diff --git a/nullaway/src/test/java/com/uber/nullaway/jspecify/GenericMethodTests.java b/nullaway/src/test/java/com/uber/nullaway/jspecify/GenericMethodTests.java
@@ -425,7 +425,7 @@ abstract class TestCase {
                 static class Bar<T extends @Nullable Object> {}
                 abstract <U> Bar<U> make(Bar<U> other);
                 void test(Bar<Bar<String>> other) {
-                    // BUG: Diagnostic contains: incompatible types: Bar<Bar<String>> cannot be converted to Bar<Bar<@Nullable String>>
+                    // BUG: Diagnostic contains: incompatible types: Bar<@NonNull Bar<String>> cannot be converted to Bar<Bar<@Nullable String>>
                     Bar<Bar<@Nullable String>> unused = make(other);
                 }
             }
@@ -1498,6 +1498,36 @@ void test(String s1, String s2, List<Object> l) {
         .doTest();
   }
 
+  @Test
+  public void issue1444() {
+    makeHelper()
+        .addSourceLines(
+            "Test.java",
+            """
+            import org.jspecify.annotations.NullMarked;
+            import org.jspecify.annotations.Nullable;
+            import java.util.stream.Stream;
+            @NullMarked
+            public class Test {
+                static class DefaultConfiguration {
+                    final @Nullable Stream<? extends String> children;
+
+                    DefaultConfiguration(Stream<? extends String> children) {
+                        this.children = children;
+                    }
+                }
+                final Stream<? extends String> children;
+                Test(DefaultConfiguration configuration) {
+                    this.children = notNull(configuration.children, "children must not be null");
+                }
+                public static <T> T notNull(@Nullable T object, String message) {
+                    throw new RuntimeException("todo");
+                }
+            }
+            """)
+        .doTest();
+  }
+
   private CompilationTestHelper makeHelper() {
     return makeTestHelperWithArgs(
         JSpecifyJavacConfig.withJSpecifyModeArgs(
