Introduce a compiler X flag to enable enhancing not null annotated type parameter's types to definitely not null types

compiler/cli/cli-common/src/org/jetbrains/kotlin/cli/common/arguments/K2JVMCompilerArguments.kt

@@ -505,6 +505,12 @@ default: `indy-with-constants` for JVM target 9 or greater, `inline` otherwise""
     )
     var validateBytecode: Boolean by FreezableVar(false)
 
+    @Argument(
+        value = "-Xenhance-type-parameter-types-to-def-not-null",
+        description = "Enhance not null annotated type parameter's types to definitely not null types (@NotNull T => T & Any)"
+    )
+    var enhanceTypeParameterTypesToDefNotNull: Boolean by FreezableVar(false)
+
     override fun configureAnalysisFlags(collector: MessageCollector, languageVersion: LanguageVersion): MutableMap<AnalysisFlag<*>, Any> {
         val result = super.configureAnalysisFlags(collector, languageVersion)
         result[JvmAnalysisFlags.strictMetadataVersionSemantics] = strictMetadataVersionSemantics
@@ -533,6 +539,10 @@ default: `indy-with-constants` for JVM target 9 or greater, `inline` otherwise""
         if (typeEnhancementImprovementsInStrictMode) {
             result[LanguageFeature.TypeEnhancementImprovementsInStrictMode] = LanguageFeature.State.ENABLED
         }
+        if (enhanceTypeParameterTypesToDefNotNull) {
+            result[LanguageFeature.ProhibitUsingNullableTypeParameterAgainstNotNullAnnotated] = LanguageFeature.State.ENABLED
+        }
+
         return result
     }
 

compiler/testData/cli/jvm/extraHelp.out

@@ -27,6 +27,8 @@ where advanced options include:
   -Xemit-jvm-type-annotations Emit JVM type annotations in bytecode
   -Xjvm-enable-preview       Allow using features from Java language that are in preview phase.
                              Works as `--enable-preview` in Java. All class files are marked as preview-generated thus it won't be possible to use them in release environment
+  -Xenhance-type-parameter-types-to-def-not-null
+                             Enhance not null annotated type parameter's types to definitely not null types (@NotNull T => T & Any)
   -Xfriend-paths=<path>      Paths to output directories for friend modules (whose internals should be visible)
   -Xmultifile-parts-inherit  Compile multifile classes as a hierarchy of parts and facade
   -Xmodule-path=<path>       Paths where to find Java 9+ modules

compiler/testData/cli/jvm/kt49209.args

@@ -0,0 +1,6 @@
+-Xenhance-type-parameter-types-to-def-not-null
+$TESTDATA_DIR$/kt49209.kt
+$TESTDATA_DIR$/kt49209
+$FOREIGN_JAVA8_ANNOTATIONS_DIR$
+-d
+$TEMP_DIR$

compiler/testData/cli/jvm/kt49209.kt

@@ -0,0 +1,2 @@
+fun usingMethod(java : Java<String?>) : String = java.getFoo()
+fun usingProperty(java : Java<String?>) : String = java.foo

compiler/testData/cli/jvm/kt49209.out

@@ -0,0 +1 @@
+OK

compiler/testData/cli/jvm/kt49209/Java.java

@@ -0,0 +1,6 @@
+import org.checkerframework.checker.nullness.qual.NonNull;
+import org.checkerframework.checker.nullness.qual.Nullable;
+
+public interface Java<T extends @Nullable Object> {
+    @NonNull T getFoo();
+}

compiler/tests-common/tests/org/jetbrains/kotlin/cli/AbstractCliTest.java

@@ -263,6 +263,10 @@ public abstract class AbstractCliTest extends TestCaseWithTmpdir {
                 .replace(
                         "$FOREIGN_ANNOTATIONS_DIR$",
                         new File(ThirdPartyAnnotationPathsKt.FOREIGN_ANNOTATIONS_SOURCES_PATH).getPath()
+                )
+                .replace(
+                        "$FOREIGN_JAVA8_ANNOTATIONS_DIR$",
+                        new File(ThirdPartyAnnotationPathsKt.FOREIGN_JDK8_ANNOTATIONS_SOURCES_PATH).getPath()
                 ).replace(
                         "$JDK_17$",
                         KtTestUtil.getJdk17Home().getPath()

compiler/tests-gen/org/jetbrains/kotlin/cli/CliTestGenerated.java

@@ -631,6 +631,11 @@ public class CliTestGenerated extends AbstractCliTest {
             runTest("compiler/testData/cli/jvm/kt22304.args");
         }
 
+        @TestMetadata("kt49209.args")
+        public void testKt49209() throws Exception {
+            runTest("compiler/testData/cli/jvm/kt49209.args");
+        }
+
         @TestMetadata("languageVersion.args")
         public void testLanguageVersion() throws Exception {
             runTest("compiler/testData/cli/jvm/languageVersion.args");