Extract correct implied wildcards for Java classes and @JvmSuppressWildcards-annotated entities

For Java classes this means following the structure of the underlying Java type to determine where the wildcard was really present and where the Java signature ruled it out. The annotation tracking simply means looking for @JvmSuppressWildcards on any surrounding class or function to turn off wildcard introduction by default.

java/kotlin-extractor/src/main/kotlin/KotlinFileExtractor.kt

@@ -497,9 +497,9 @@ open class KotlinFileExtractor(
                 else
                     null
             } ?: vp.type
-            val typeWithWildcards = addJavaLoweringWildcards(maybeErasedType, true)
+            val javaType = ((vp.parent as? IrFunction)?.let { getJavaMethod(it) })?.valueParameters?.getOrNull(idx)?.type
+            val typeWithWildcards = addJavaLoweringWildcards(maybeErasedType, !hasWildcardSuppressionAnnotation(vp), javaType)
             val substitutedType = typeSubstitution?.let { it(typeWithWildcards, TypeContext.OTHER, pluginContext) } ?: typeWithWildcards
-
             val id = useValueParameter(vp, parent)
             if (extractTypeAccess) {
                 extractTypeAccessRecursive(substitutedType, location, id, -1)
@@ -533,7 +533,9 @@ open class KotlinFileExtractor(
                     extensionReceiverParameter = null,
                     functionTypeParameters = listOf(),
                     classTypeArgsIncludingOuterClasses = listOf(),
-                    overridesCollectionsMethod = false
+                    overridesCollectionsMethod = false,
+                    javaSignature = null,
+                    addParameterWildcardsByDefault = false
                 )
                 val clinitId = tw.getLabelFor<DbMethod>(clinitLabel)
                 val returnType = useType(pluginContext.irBuiltIns.unitType, TypeContext.RETURN)
@@ -706,7 +708,7 @@ open class KotlinFileExtractor(
 
                 val paramsSignature = allParamTypes.joinToString(separator = ",", prefix = "(", postfix = ")") { it.javaResult.signature!! }
 
-                val adjustedReturnType = addJavaLoweringWildcards(getAdjustedReturnType(f), false)
+                val adjustedReturnType = addJavaLoweringWildcards(getAdjustedReturnType(f), false, getJavaMethod(f)?.returnType)
                 val substReturnType = typeSubstitution?.let { it(adjustedReturnType, TypeContext.RETURN, pluginContext) } ?: adjustedReturnType
 
                 val locId = locOverride ?: getLocation(f, classTypeArgsIncludingOuterClasses)

java/kotlin-extractor/src/main/kotlin/KotlinUsesExtractor.kt

@@ -7,6 +7,7 @@ import com.semmle.extractor.java.OdasaOutput
 import org.jetbrains.kotlin.backend.common.extensions.IrPluginContext
 import org.jetbrains.kotlin.backend.common.ir.allOverridden
 import org.jetbrains.kotlin.backend.common.ir.isFinalClass
+import org.jetbrains.kotlin.backend.common.lower.parents
 import org.jetbrains.kotlin.backend.common.lower.parentsWithSelf
 import org.jetbrains.kotlin.backend.jvm.ir.getJvmNameFromAnnotation
 import org.jetbrains.kotlin.backend.jvm.ir.propertyIfAccessor
@@ -21,6 +22,8 @@ import org.jetbrains.kotlin.ir.types.impl.*
 import org.jetbrains.kotlin.ir.util.*
 import org.jetbrains.kotlin.load.java.BuiltinMethodsWithSpecialGenericSignature
 import org.jetbrains.kotlin.load.java.JvmAbi
+import org.jetbrains.kotlin.load.java.sources.JavaSourceElement
+import org.jetbrains.kotlin.load.java.structure.*
 import org.jetbrains.kotlin.name.FqName
 import org.jetbrains.kotlin.name.Name
 import org.jetbrains.kotlin.name.SpecialNames
@@ -852,23 +855,30 @@ open class KotlinUsesExtractor(
                 (f.name.asString() == "addAll" && overridesFunctionDefinedOn(f, "kotlin.collections", "MutableList"))
 
 
-    private fun wildcardAdditionAllowed(v: Variance, t: IrType, inParameterContext: Boolean) =
+    private val jvmWildcardAnnotation = FqName("kotlin.jvm.JvmWildcard")
+    private val jvmWildcardSuppressionAnnotaton = FqName("kotlin.jvm.JvmSuppressWildcards")
+
+    private fun wildcardAdditionAllowed(v: Variance, t: IrType, addByDefault: Boolean) =
         when {
-            t.hasAnnotation(FqName("kotlin.jvm.JvmWildcard")) -> true
-            !inParameterContext -> false // By default, wildcards are only automatically added for method parameters.
-            t.hasAnnotation(FqName("kotlin.jvm.JvmSuppressWildcards")) -> false
+            t.hasAnnotation(jvmWildcardAnnotation) -> true
+            !addByDefault -> false
+            t.hasAnnotation(jvmWildcardSuppressionAnnotaton) -> false
             v == Variance.IN_VARIANCE -> !(t.isNullableAny() || t.isAny())
             v == Variance.OUT_VARIANCE -> ((t as? IrSimpleType)?.classOrNull?.owner?.isFinalClass) != true
             else -> false
         }
 
-    private fun addJavaLoweringArgumentWildcards(p: IrTypeParameter, t: IrTypeArgument, inParameterContext: Boolean): IrTypeArgument =
+    private fun addJavaLoweringArgumentWildcards(p: IrTypeParameter, t: IrTypeArgument, addByDefault: Boolean, javaType: JavaType?): IrTypeArgument =
         (t as? IrTypeProjection)?.let {
-            val newBase = addJavaLoweringWildcards(it.type, inParameterContext)
+            val newBase = addJavaLoweringWildcards(it.type, addByDefault, javaType)
             val newVariance =
                 if (it.variance == Variance.INVARIANT &&
                     p.variance != Variance.INVARIANT &&
-                    wildcardAdditionAllowed(p.variance, it.type, inParameterContext))
+                    // The next line forbids inferring a wildcard type when we have a corresponding Java type with conflicting variance.
+                    // For example, Java might declare f(Comparable<CharSequence> cs), in which case we shouldn't add a `? super ...`
+                    // wildcard. Note if javaType is unknown (e.g. this is a Kotlin source element), we assume wildcards should be added.
+                    (javaType?.let { jt -> jt is JavaWildcardType && jt.isExtends == (p.variance == Variance.OUT_VARIANCE) } != false) &&
+                    wildcardAdditionAllowed(p.variance, it.type, addByDefault))
                     p.variance
                 else
                     it.variance
@@ -878,14 +888,22 @@ open class KotlinUsesExtractor(
                 null
         } ?: t
 
-    fun addJavaLoweringWildcards(t: IrType, inParameterContext: Boolean): IrType =
+    fun getJavaTypeArgument(jt: JavaType, idx: Int) =
+        when(jt) {
+            is JavaClassifierType -> jt.typeArguments.getOrNull(idx)
+            is JavaArrayType -> if (idx == 0) jt.componentType else null
+            else -> null
+        }
+
+    fun addJavaLoweringWildcards(t: IrType, addByDefault: Boolean, javaType: JavaType?): IrType =
         (t as? IrSimpleType)?.let {
             val typeParams = it.classOrNull?.owner?.typeParameters ?: return t
-            val newArgs = typeParams.zip(it.arguments).map { pair ->
+            val newArgs = typeParams.zip(it.arguments).mapIndexed { idx, pair ->
                 addJavaLoweringArgumentWildcards(
                     pair.first,
                     pair.second,
-                    inParameterContext
+                    addByDefault,
+                    javaType?.let { jt -> getJavaTypeArgument(jt, idx) }
                 )
             }
             return if (newArgs.zip(it.arguments).all { pair -> pair.first === pair.second })
@@ -927,6 +945,14 @@ open class KotlinUsesExtractor(
         return otherKeySet.returnType.codeQlWithHasQuestionMark(false)
     }
 
+    @OptIn(ObsoleteDescriptorBasedAPI::class)
+    fun getJavaMethod(f: IrFunction) = (f.descriptor.source as? JavaSourceElement)?.javaElement as? JavaMethod
+
+    fun hasWildcardSuppressionAnnotation(d: IrDeclaration) =
+        d.hasAnnotation(jvmWildcardSuppressionAnnotaton) ||
+        // Note not using `parentsWithSelf` as that only works if `d` is an IrDeclarationParent
+        d.parents.any { (it as? IrAnnotationContainer)?.hasAnnotation(jvmWildcardSuppressionAnnotaton) == true }
+
     /*
      * There are some pairs of classes (e.g. `kotlin.Throwable` and
      * `java.lang.Throwable`) which are really just 2 different names
@@ -947,7 +973,9 @@ open class KotlinUsesExtractor(
             f.extensionReceiverParameter,
             getFunctionTypeParameters(f),
             classTypeArgsIncludingOuterClasses,
-            overridesCollectionsMethodWithAlteredParameterTypes(f)
+            overridesCollectionsMethodWithAlteredParameterTypes(f),
+            getJavaMethod(f),
+            !hasWildcardSuppressionAnnotation(f)
         )
 
     /*
@@ -977,6 +1005,11 @@ open class KotlinUsesExtractor(
         // If true, this method implements a Java Collections interface (Collection, Map or List) and may need
         // parameter erasure to match the way this class will appear to an external consumer of the .class file.
         overridesCollectionsMethod: Boolean,
+        // The Java signature of this callable, if known.
+        javaSignature: JavaMethod?,
+        // If true, Java wildcards implied by Kotlin type parameter variance should be added by default to this function's value parameters' types.
+        // (Return-type wildcard addition is always off by default)
+        addParameterWildcardsByDefault: Boolean,
         // The prefix used in the label. "callable", unless a property label is created, then it's "property".
         prefix: String = "callable"
     ): String {
@@ -1001,7 +1034,7 @@ open class KotlinUsesExtractor(
             // If this has happened, erase the type again to get the correct Java signature.
             val maybeAmendedForCollections = if (overridesCollectionsMethod) eraseCollectionsMethodParameterType(it.value.type, name, it.index) else it.value.type
             // Add any wildcard types that the Kotlin compiler would add in the Java lowering of this function:
-            val withAddedWildcards = addJavaLoweringWildcards(maybeAmendedForCollections, true)
+            val withAddedWildcards = addJavaLoweringWildcards(maybeAmendedForCollections, addParameterWildcardsByDefault, javaSignature?.let { sig -> sig.valueParameters[it.index].type })
             // Now substitute any class type parameters in:
             val maybeSubbed = withAddedWildcards.substituteTypeAndArguments(substitutionMap, TypeContext.OTHER, pluginContext)
             // Finally, mimic the Java extractor's behaviour by naming functions with type parameters for their erased types;
@@ -1473,7 +1506,7 @@ open class KotlinUsesExtractor(
             val returnType = getter?.returnType ?: setter?.valueParameters?.singleOrNull()?.type ?: pluginContext.irBuiltIns.unitType
             val typeParams = getFunctionTypeParameters(func)
 
-            getFunctionLabel(p.parent, parentId, p.name.asString(), listOf(), returnType, ext, typeParams, classTypeArgsIncludingOuterClasses, overridesCollectionsMethod = false, prefix = "property")
+            getFunctionLabel(p.parent, parentId, p.name.asString(), listOf(), returnType, ext, typeParams, classTypeArgsIncludingOuterClasses, overridesCollectionsMethod = false, javaSignature = null, addParameterWildcardsByDefault = false, prefix = "property")
         }
     }