Use correct function to find header for impl in IDE

Also do not call isHeader/isImpl because the returned declarations are
guaranteed to be isHeader in findCompatibleHeaderForImpl and isImpl in
findCompatibleImplForHeader

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

@@ -159,6 +159,9 @@ class HeaderImplDeclarationChecker(val moduleToCheck: ModuleDescriptor? = null)
     fun MemberDescriptor.findCompatibleImplForHeader(): List<MemberDescriptor> =
             findImplForHeader(this, false)?.get(Compatible).orEmpty()
 
+    fun MemberDescriptor.findCompatibleHeaderForImpl(): List<MemberDescriptor> =
+            findHeaderForImpl(this)?.get(Compatible).orEmpty()
+
     private fun CallableMemberDescriptor.findNamesakesFromTheSameModule(): Collection<CallableMemberDescriptor> {
         val packageFqName = (containingDeclaration as? PackageFragmentDescriptor)?.fqName ?: return emptyList()
         val myModule = moduleToCheck ?: module

idea/src/org/jetbrains/kotlin/idea/highlighter/markers/DeclaredHeaderMarker.kt

@@ -17,7 +17,9 @@
 package org.jetbrains.kotlin.idea.highlighter.markers
 
 import org.jetbrains.kotlin.analyzer.ModuleInfo
-import org.jetbrains.kotlin.descriptors.*
+import org.jetbrains.kotlin.descriptors.DeclarationDescriptor
+import org.jetbrains.kotlin.descriptors.MemberDescriptor
+import org.jetbrains.kotlin.descriptors.ModuleDescriptor
 import org.jetbrains.kotlin.idea.caches.resolve.ModuleProductionSourceInfo
 import org.jetbrains.kotlin.idea.caches.resolve.ModuleTestSourceInfo
 import org.jetbrains.kotlin.idea.caches.resolve.findModuleDescriptor
@@ -49,8 +51,8 @@ private enum class SourceKind { NONE, PRODUCTION, TEST }
 fun ModuleDescriptor.hasDeclarationOf(descriptor: MemberDescriptor) = declarationOf(descriptor) != null
 
 private fun ModuleDescriptor.declarationOf(descriptor: MemberDescriptor): DeclarationDescriptor? =
-        with (HeaderImplDeclarationChecker(this)) {
+        with(HeaderImplDeclarationChecker(this)) {
-            descriptor.findCompatibleImplForHeader().firstOrNull { it.isHeader }
+            descriptor.findCompatibleHeaderForImpl().firstOrNull()
         }
 
 fun getHeaderDeclarationTooltip(declaration: KtDeclaration): String? {

idea/src/org/jetbrains/kotlin/idea/highlighter/markers/ImplementedHeaderMarker.kt

@@ -18,7 +18,9 @@ package org.jetbrains.kotlin.idea.highlighter.markers
 
 import com.intellij.codeInsight.daemon.impl.PsiElementListNavigator
 import com.intellij.ide.util.DefaultPsiElementCellRenderer
-import org.jetbrains.kotlin.descriptors.*
+import org.jetbrains.kotlin.descriptors.DeclarationDescriptor
+import org.jetbrains.kotlin.descriptors.MemberDescriptor
+import org.jetbrains.kotlin.descriptors.ModuleDescriptor
 import org.jetbrains.kotlin.idea.caches.resolve.findModuleDescriptor
 import org.jetbrains.kotlin.idea.core.toDescriptor
 import org.jetbrains.kotlin.psi.KtDeclaration
@@ -32,8 +34,8 @@ fun ModuleDescriptor.hasImplementationsOf(descriptor: MemberDescriptor) =
         implementationsOf(descriptor).isNotEmpty()
 
 private fun ModuleDescriptor.implementationsOf(descriptor: MemberDescriptor): List<DeclarationDescriptor> =
-        with (HeaderImplDeclarationChecker(this)) {
+        with(HeaderImplDeclarationChecker(this)) {
-            descriptor.findCompatibleImplForHeader().filter { it.isImpl }
+            descriptor.findCompatibleImplForHeader()
         }
 
 fun getPlatformImplementationTooltip(declaration: KtDeclaration): String? {

idea/testData/multiModuleLineMarker/fromCommonToJvmImpl/jvm/jvm.kt

@@ -1,5 +1,5 @@
 impl class <lineMarker>Header</lineMarker> {
-    impl fun foo() = 42
+    impl fun <lineMarker>foo</lineMarker>() = 42
 }
 
 impl fun <lineMarker>foo</lineMarker>(arg: Int) = arg.toString()