Support nullable callable references in FIR resolve

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/FirCallResolver.kt

@@ -207,7 +207,9 @@ class FirCallResolver(
         when {
             referencedSymbol is FirClassLikeSymbol<*> -> {
                 val classId = referencedSymbol.classId
-                return FirResolvedQualifierImpl(nameReference.source, classId.packageFqName, classId.relativeClassName).apply {
+                return FirResolvedQualifierImpl(
+                    nameReference.source, classId.packageFqName, classId.relativeClassName, safe = false
+                ).apply {
                     typeArguments.addAll(qualifiedAccess.typeArguments)
                     resultType = if (classId.isLocal) {
                         typeForQualifierByDeclaration(referencedSymbol.fir, resultType, session)

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/FirQualifiedNameResolver.kt

@@ -65,7 +65,8 @@ class FirQualifiedNameResolver(components: BodyResolveComponents) : BodyResolveC
             return FirResolvedQualifierImpl(
                 source,
                 resolved.packageFqName,
-                resolved.relativeClassFqName
+                resolved.relativeClassFqName,
+                safe = false
             ).apply { resultType = typeForQualifier(this) }
         }
 

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/FirDoubleColonExpressionResolver.kt

@@ -69,7 +69,7 @@ class FirDoubleColonExpressionResolver(
 
     private fun shouldTryResolveLHSAsExpression(expression: FirCallableReferenceAccess): Boolean {
         val lhs = expression.explicitReceiver ?: return false
-        return lhs.canBeConsideredProperExpression() /* && !expression.hasQuestionMarks */
+        return lhs.canBeConsideredProperExpression() && !expression.safe
     }
 
     private fun shouldTryResolveLHSAsType(expression: FirCallableReferenceAccess): Boolean {
@@ -168,7 +168,7 @@ class FirDoubleColonExpressionResolver(
                     else -> ConeStarProjection
                 }
             },
-            isNullable = false // TODO: Use org.jetbrains.kotlin.psi.KtDoubleColonExpression.getHasQuestionMarks
+            isNullable = expression.safe
         )
 
         return DoubleColonLHS.Type(type)

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/transformers/body/resolve/FirExpressionsResolveTransformer.kt

@@ -13,6 +13,7 @@ import org.jetbrains.kotlin.fir.diagnostics.FirSimpleDiagnostic
 import org.jetbrains.kotlin.fir.expressions.*
 import org.jetbrains.kotlin.fir.expressions.impl.FirErrorExpressionImpl
 import org.jetbrains.kotlin.fir.expressions.impl.FirFunctionCallImpl
+import org.jetbrains.kotlin.fir.expressions.impl.FirResolvedQualifierImpl
 import org.jetbrains.kotlin.fir.expressions.impl.FirVariableAssignmentImpl
 import org.jetbrains.kotlin.fir.references.*
 import org.jetbrains.kotlin.fir.references.impl.FirErrorNamedReferenceImpl
@@ -357,8 +358,12 @@ class FirExpressionsResolveTransformer(transformer: FirBodyResolveTransformer) :
         }
 
         callableReferenceAccess.annotations.forEach { it.accept(this, data) }
-        val transformedLHS =
-            callableReferenceAccess.explicitReceiver?.transformSingle(this, ResolutionMode.ContextIndependent)
+        val explicitReceiver = callableReferenceAccess.explicitReceiver
+        val transformedLHS = explicitReceiver?.transformSingle(this, ResolutionMode.ContextIndependent)?.apply {
+            if (this is FirResolvedQualifierImpl && callableReferenceAccess.safe) {
+                this.safe = true
+            }
+        }
 
         val callableReferenceAccessWithTransformedLHS =
             if (transformedLHS != null)

compiler/fir/resolve/testData/resolve/stdlib/getOnKProperty.kt

@@ -3,6 +3,6 @@ val Any?.meaning: Int
 
 fun test() {
     val f = Any?::meaning
-    f.<!INAPPLICABLE_CANDIDATE!>get<!>(null)
+    f.get(null)
     f.get("")
 }

compiler/fir/resolve/testData/resolve/stdlib/getOnKProperty.txt

@@ -4,7 +4,7 @@ FILE: getOnKProperty.kt
             ^ Int(42)
         }
     public final fun test(): R|kotlin/Unit| {
-        lval f: R|kotlin/reflect/KProperty1<kotlin/Any, kotlin/Int>| = Q|kotlin/Any|?::R|/meaning|
-        R|<local>/f|.<Inapplicable(INAPPLICABLE): [kotlin/reflect/KProperty1.get]>#(Null(null))
+        lval f: R|kotlin/reflect/KProperty1<kotlin/Any?, kotlin/Int>| = Q|kotlin/Any?|::R|/meaning|
+        R|<local>/f|.R|FakeOverride<kotlin/reflect/KProperty1.get: R|kotlin/Int|>|(Null(null))
         R|<local>/f|.R|FakeOverride<kotlin/reflect/KProperty1.get: R|kotlin/Int|>|(String())
     }

compiler/fir/tree/gen/org/jetbrains/kotlin/fir/expressions/FirResolvedQualifier.kt

@@ -25,6 +25,7 @@ abstract class FirResolvedQualifier : FirPureAbstractElement(), FirExpression {
     abstract val packageFqName: FqName
     abstract val relativeClassFqName: FqName?
     abstract val classId: ClassId?
+    abstract val safe: Boolean
     abstract val typeArguments: List<FirTypeProjection>
 
     override fun <R, D> accept(visitor: FirVisitor<R, D>, data: D): R = visitor.visitResolvedQualifier(this, data)

compiler/fir/tree/gen/org/jetbrains/kotlin/fir/expressions/impl/FirResolvedQualifierImpl.kt

@@ -24,7 +24,8 @@ import org.jetbrains.kotlin.fir.visitors.*
 class FirResolvedQualifierImpl(
     override val source: FirSourceElement?,
     override var packageFqName: FqName,
-    override var relativeClassFqName: FqName?
+    override var relativeClassFqName: FqName?,
+    override var safe: Boolean
 ) : FirResolvedQualifier(), FirAbstractAnnotatedElement {
     override var typeRef: FirTypeRef = FirImplicitTypeRefImpl(null)
     override val annotations: MutableList<FirAnnotationCall> = mutableListOf()

compiler/fir/tree/src/org/jetbrains/kotlin/fir/FirRenderer.kt

@@ -944,7 +944,7 @@ class FirRenderer(builder: StringBuilder) : FirVisitorVoid() {
     override fun visitCallableReferenceAccess(callableReferenceAccess: FirCallableReferenceAccess) {
         callableReferenceAccess.annotations.renderAnnotations()
         callableReferenceAccess.explicitReceiver?.accept(this)
-        if (callableReferenceAccess.safe) {
+        if (callableReferenceAccess.safe && callableReferenceAccess.explicitReceiver !is FirResolvedQualifier) {
             print("?")
         }
         print("::")
@@ -1052,6 +1052,9 @@ class FirRenderer(builder: StringBuilder) : FirVisitorVoid() {
         } else {
             print(resolvedQualifier.packageFqName.asString().replace(".", "/"))
         }
+        if (resolvedQualifier.safe) {
+            print("?")
+        }
         print("|")
     }
 

compiler/fir/tree/tree-generator/src/org/jetbrains/kotlin/fir/tree/generator/ImplementationConfigurator.kt

@@ -323,7 +323,7 @@ object ImplementationConfigurator : AbstractFirTreeImplementationConfigurator()
         }
 
         impl(resolvedQualifier) {
-            isMutable("packageFqName", "relativeClassFqName")
+            isMutable("packageFqName", "relativeClassFqName", "safe")
             default("classId") {
                 value = """
                     |relativeClassFqName?.let {

compiler/fir/tree/tree-generator/src/org/jetbrains/kotlin/fir/tree/generator/NodeConfigurator.kt

@@ -435,6 +435,7 @@ object NodeConfigurator : AbstractFieldConfigurator<FirTreeBuilder>(FirTreeBuild
             +field("packageFqName", fqNameType)
             +field("relativeClassFqName", fqNameType, nullable = true)
             +field("classId", classIdType, nullable = true)
+            +booleanField("safe")
             +typeArguments.withTransform()
         }