K1:report warning on OptIn usages inside SAM constructor #KT-47708 Fixed

compiler/frontend/src/org/jetbrains/kotlin/resolve/checkers/OptInUsageChecker.kt

@@ -52,6 +52,7 @@ import org.jetbrains.kotlin.resolve.deprecation.DeprecationResolver
 import org.jetbrains.kotlin.resolve.deprecation.DeprecationSettings
 import org.jetbrains.kotlin.resolve.descriptorUtil.annotationClass
 import org.jetbrains.kotlin.resolve.descriptorUtil.fqNameSafe
+import org.jetbrains.kotlin.resolve.sam.SamConstructorDescriptor
 import org.jetbrains.kotlin.storage.LockBasedStorageManager
 import org.jetbrains.kotlin.types.AbbreviatedType
 import org.jetbrains.kotlin.types.KotlinType
@@ -97,6 +98,15 @@ class OptInUsageChecker(project: Project) : CallChecker {
                 return
             }
         }
+        if (resultingDescriptor is SamConstructorDescriptor) {
+            // KT-47708 special case (warning only)
+            val methodDescriptor = resultingDescriptor.getSingleAbstractMethod()
+            val samOptIns = methodDescriptor.loadOptIns(moduleAnnotationsResolver, context.languageVersionSettings)
+                .map { (fqName, _, message) ->
+                    OptInDescription(fqName, OptInDescription.Severity.WARNING, message)
+                }
+            reportNotAllowedOptIns(samOptIns, reportOn, context)
+        }
         reportNotAllowedOptIns(optIns, reportOn, context)
     }
 

compiler/testData/diagnostics/testsWithStdLib/experimental/insideSAM.kt

@@ -11,7 +11,7 @@ fun regressionTestOverrides() {
     val anonymous: StableInterface = object : StableInterface {
         override fun <!OPT_IN_OVERRIDE_ERROR!>experimentalMethod<!>() {} // correctly fails check
     }
-    val lambda = StableInterface {} // this does not get flagged
+    val lambda = <!OPT_IN_USAGE!>StableInterface<!> {} // this does not get flagged
 }
 
 @ExperimentalKotlinAnnotation