K2: Replicate K1 enhancement behavior for warning-mode top-level types

^KT-56657 Fixed
^KT-57307 Related

compiler/fir/analysis-tests/tests-gen/org/jetbrains/kotlin/test/runners/FirPsiOldFrontendForeignAnnotationsCompiledJavaTestGenerated.java

@@ -630,6 +630,12 @@ public class FirPsiOldFrontendForeignAnnotationsCompiledJavaTestGenerated extend
             runTest("compiler/testData/diagnostics/foreignAnnotationsTests/java8Tests/typeUseOnObject.kt");
         }
 
+        @Test
+        @TestMetadata("warningModeForHeadType.kt")
+        public void testWarningModeForHeadType() throws Exception {
+            runTest("compiler/testData/diagnostics/foreignAnnotationsTests/java8Tests/warningModeForHeadType.kt");
+        }
+
         @Nested
         @TestMetadata("compiler/testData/diagnostics/foreignAnnotationsTests/java8Tests/jspecify")
         @TestDataPath("$PROJECT_ROOT")

compiler/fir/analysis-tests/tests-gen/org/jetbrains/kotlin/test/runners/FirPsiOldFrontendForeignAnnotationsCompiledJavaWithPsiClassReadingTestGenerated.java

@@ -630,6 +630,12 @@ public class FirPsiOldFrontendForeignAnnotationsCompiledJavaWithPsiClassReadingT
             runTest("compiler/testData/diagnostics/foreignAnnotationsTests/java8Tests/typeUseOnObject.kt");
         }
 
+        @Test
+        @TestMetadata("warningModeForHeadType.kt")
+        public void testWarningModeForHeadType() throws Exception {
+            runTest("compiler/testData/diagnostics/foreignAnnotationsTests/java8Tests/warningModeForHeadType.kt");
+        }
+
         @Nested
         @TestMetadata("compiler/testData/diagnostics/foreignAnnotationsTests/java8Tests/jspecify")
         @TestDataPath("$PROJECT_ROOT")

compiler/fir/analysis-tests/tests-gen/org/jetbrains/kotlin/test/runners/FirPsiOldFrontendForeignAnnotationsSourceJavaTestGenerated.java

@@ -630,6 +630,12 @@ public class FirPsiOldFrontendForeignAnnotationsSourceJavaTestGenerated extends
             runTest("compiler/testData/diagnostics/foreignAnnotationsTests/java8Tests/typeUseOnObject.kt");
         }
 
+        @Test
+        @TestMetadata("warningModeForHeadType.kt")
+        public void testWarningModeForHeadType() throws Exception {
+            runTest("compiler/testData/diagnostics/foreignAnnotationsTests/java8Tests/warningModeForHeadType.kt");
+        }
+
         @Nested
         @TestMetadata("compiler/testData/diagnostics/foreignAnnotationsTests/java8Tests/jspecify")
         @TestDataPath("$PROJECT_ROOT")

compiler/fir/java/src/org/jetbrains/kotlin/fir/java/enhancement/javaTypeUtils.kt

@@ -40,6 +40,14 @@ private fun ConeKotlinType.enhanceConeKotlinType(
 ): ConeKotlinType? {
     return when (this) {
         is ConeFlexibleType -> {
+            // Currently, the warnings are left unsupported in K2 (see KT-57307)
+            // But modulo information for warnings, we reproduce the K1 behavior: if head type qualifier is for warnings, we totally ignore
+            // enhancement on its arguments, too (see JavaTypeEnhancement.enhancePossiblyFlexible).
+            // It's not totally correct, but tolerable since we would like to avoid excessive breaking changes and the warnings should be
+            // anyway reported.
+            // TODO: support not loosing information for warnings here, too
+            if (qualifiers(index).isNullabilityQualifierForWarning) return null
+
             val lowerResult = lowerBound.enhanceInflexibleType(
                 session, TypeComponentPosition.FLEXIBLE_LOWER, qualifiers, index, subtreeSizes
             )
@@ -88,7 +96,7 @@ private fun ConeSimpleKotlinType.enhanceInflexibleType(
     val effectiveQualifiers = qualifiers(index)
     val enhancedTag = lookupTag.enhanceMutability(effectiveQualifiers, position)
 
-    // TODO: implement warnings
+    // TODO: implement warnings (see KT-57307)
     val nullabilityFromQualifiers = effectiveQualifiers.nullability
         .takeIf { shouldEnhance && !effectiveQualifiers.isNullabilityQualifierForWarning }
     val enhancedIsNullable = when (nullabilityFromQualifiers) {

compiler/testData/diagnostics/foreignAnnotationsTests/java8Tests/warningModeForHeadType.kt

@@ -0,0 +1,38 @@
+// FIR_IDENTICAL
+// FULL_JDK
+// !DIAGNOSTICS: -UNUSED_VARIABLE -UNUSED_PARAMETER
+
+// FILE: ElementTypesAreNonnullByDefault.java
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+import javax.annotation.Nonnull;
+import javax.annotation.meta.TypeQualifierDefault;
+
+@Retention(RetentionPolicy.RUNTIME)
+@Target({ElementType.TYPE})
+@TypeQualifierDefault({ElementType.FIELD, ElementType.METHOD, ElementType.PARAMETER})
+@Nonnull
+@interface ElementTypesAreNonnullByDefault {
+}
+
+// FILE: Maps.java
+import org.checkerframework.checker.nullness.qual.Nullable;
+// Here it's important that @ElementTypesAreNonnullByDefault is a JSR-305 default qualifier and disabled by default (resulting in warnings-only)
+// Thus return type (head type) is considered as warningly-annotated as not-nullable and that makes annotations on bounds for K and V
+// be effectively ignored on non-warnings level.
+@ElementTypesAreNonnullByDefault
+public final class Maps {
+    public static <K extends @Nullable Object, V extends @Nullable Object> java.util.HashMap<K,V> newHashMap() { return null; }
+}
+
+// FILE: main.kt
+
+fun foo() {
+    val x = Maps.newHashMap<String, Int>()
+    x.put("", 1)
+    // If there were no @ElementTypesAreNonnullByDefault on the Maps class, there would be an error on `null` argument because the type of `x`
+    // would be `HashMap<String, Int>!`, i.e. with non-flexible type arguments, thus not allowing nulls.
+    x.put("", null)
+}

compiler/tests-common-new/tests-gen/org/jetbrains/kotlin/test/runners/ForeignAnnotationsCompiledJavaTestGenerated.java

@@ -630,6 +630,12 @@ public class ForeignAnnotationsCompiledJavaTestGenerated extends AbstractForeign
             runTest("compiler/testData/diagnostics/foreignAnnotationsTests/java8Tests/typeUseOnObject.kt");
         }
 
+        @Test
+        @TestMetadata("warningModeForHeadType.kt")
+        public void testWarningModeForHeadType() throws Exception {
+            runTest("compiler/testData/diagnostics/foreignAnnotationsTests/java8Tests/warningModeForHeadType.kt");
+        }
+
         @Nested
         @TestMetadata("compiler/testData/diagnostics/foreignAnnotationsTests/java8Tests/jspecify")
         @TestDataPath("$PROJECT_ROOT")

compiler/tests-common-new/tests-gen/org/jetbrains/kotlin/test/runners/ForeignAnnotationsCompiledJavaWithPsiClassReadingTestGenerated.java

@@ -630,6 +630,12 @@ public class ForeignAnnotationsCompiledJavaWithPsiClassReadingTestGenerated exte
             runTest("compiler/testData/diagnostics/foreignAnnotationsTests/java8Tests/typeUseOnObject.kt");
         }
 
+        @Test
+        @TestMetadata("warningModeForHeadType.kt")
+        public void testWarningModeForHeadType() throws Exception {
+            runTest("compiler/testData/diagnostics/foreignAnnotationsTests/java8Tests/warningModeForHeadType.kt");
+        }
+
         @Nested
         @TestMetadata("compiler/testData/diagnostics/foreignAnnotationsTests/java8Tests/jspecify")
         @TestDataPath("$PROJECT_ROOT")

compiler/tests-common-new/tests-gen/org/jetbrains/kotlin/test/runners/ForeignAnnotationsSourceJavaTestGenerated.java

@@ -630,6 +630,12 @@ public class ForeignAnnotationsSourceJavaTestGenerated extends AbstractForeignAn
             runTest("compiler/testData/diagnostics/foreignAnnotationsTests/java8Tests/typeUseOnObject.kt");
         }
 
+        @Test
+        @TestMetadata("warningModeForHeadType.kt")
+        public void testWarningModeForHeadType() throws Exception {
+            runTest("compiler/testData/diagnostics/foreignAnnotationsTests/java8Tests/warningModeForHeadType.kt");
+        }
+
         @Nested
         @TestMetadata("compiler/testData/diagnostics/foreignAnnotationsTests/java8Tests/jspecify")
         @TestDataPath("$PROJECT_ROOT")