FIR checker: report unresolved reference in imports

Compared to FE1.0, instead of using UNRESOLVED_REFERENCE, a new
UNRESOLVED_IMPORT diagnostic is introduced. This is so that we can use a
different positioning strategy to highlight the last part of the import
if the entire import is passed.

Also, this change fixed some incorrectly rejected imports in FIR. Such
cases are covered the newly added test file staticFunAndPropertyImport.kt

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/transformers/FirImportResolveTransformer.kt

@@ -13,9 +13,11 @@ import org.jetbrains.kotlin.fir.declarations.FirRegularClass
 import org.jetbrains.kotlin.fir.declarations.FirResolvePhase
 import org.jetbrains.kotlin.fir.declarations.builder.buildErrorImport
 import org.jetbrains.kotlin.fir.declarations.builder.buildResolvedImport
+import org.jetbrains.kotlin.fir.diagnostics.ConeDiagnostic
 import org.jetbrains.kotlin.fir.lookupTracker
 import org.jetbrains.kotlin.fir.resolve.ScopeSession
 import org.jetbrains.kotlin.fir.resolve.diagnostics.ConeImportFromSingleton
+import org.jetbrains.kotlin.fir.resolve.diagnostics.ConeUnresolvedParentInImport
 import org.jetbrains.kotlin.fir.resolve.providers.FirSymbolProvider
 import org.jetbrains.kotlin.fir.resolve.providers.symbolProvider
 import org.jetbrains.kotlin.fir.symbols.impl.FirClassLikeSymbol
@@ -73,7 +75,13 @@ open class FirImportResolveTransformer protected constructor(
         get() = true
 
     private fun transformImportForFqName(fqName: FqName, delegate: FirImport): FirImport {
-        val (packageFqName, relativeClassFqName, classSymbol) = resolveToPackageOrClass(symbolProvider, fqName) ?: return delegate
+        val (packageFqName, relativeClassFqName, classSymbol) = when (val result = resolveToPackageOrClass(symbolProvider, fqName)) {
+            is PackageResolutionResult.Error -> return buildErrorImport {
+                this.delegate = delegate
+                this.diagnostic = result.diagnostic
+            }
+            is PackageResolutionResult.PackageOrClass -> result
+        }
         val firClass = classSymbol?.fir as? FirRegularClass
         if (delegate.isAllUnder && firClass?.classKind?.isSingleton == true) {
             return buildErrorImport {
@@ -89,7 +97,7 @@ open class FirImportResolveTransformer protected constructor(
     }
 }
 
-fun resolveToPackageOrClass(symbolProvider: FirSymbolProvider, fqName: FqName): PackageOrClass? {
+fun resolveToPackageOrClass(symbolProvider: FirSymbolProvider, fqName: FqName): PackageResolutionResult {
     var currentPackage = fqName
 
     val pathSegments = fqName.pathSegments()
@@ -102,14 +110,21 @@ fun resolveToPackageOrClass(symbolProvider: FirSymbolProvider, fqName: FqName):
         prefixSize--
     }
 
-    if (currentPackage == fqName) return PackageOrClass(currentPackage, null, null)
-    val relativeClassFqName =
-        FqName.fromSegments((prefixSize until pathSegments.size).map { pathSegments[it].asString() })
+    if (currentPackage == fqName) return PackageResolutionResult.PackageOrClass(currentPackage, null, null)
+    val relativeClassFqName = FqName.fromSegments((prefixSize until pathSegments.size).map { pathSegments[it].asString() })
 
     val classId = ClassId(currentPackage, relativeClassFqName, false)
-    val symbol = symbolProvider.getClassLikeSymbolByClassId(classId) ?: return null
+    val symbol = symbolProvider.getClassLikeSymbolByClassId(classId) ?: return PackageResolutionResult.Error(
+        ConeUnresolvedParentInImport(classId)
+    )
 
-    return PackageOrClass(currentPackage, relativeClassFqName, symbol)
+    return PackageResolutionResult.PackageOrClass(currentPackage, relativeClassFqName, symbol)
 }
 
-data class PackageOrClass(val packageFqName: FqName, val relativeClassFqName: FqName?, val classSymbol: FirClassLikeSymbol<*>?)
+sealed class PackageResolutionResult {
+    data class PackageOrClass(
+        val packageFqName: FqName, val relativeClassFqName: FqName?, val classSymbol: FirClassLikeSymbol<*>?
+    ) : PackageResolutionResult()
+
+    class Error(val diagnostic: ConeDiagnostic) : PackageResolutionResult()
+}