Move DeclarationDescriptor.substitute to separate interface Substitutable

To get rid of pointless/confusing implementations in ModuleDescriptor,
PackageViewDescriptor, TypeParameterDescriptor and others.

Note that there are still implementations that do not make sense, for
example in those subclasses of VariableDescriptor which are not also
subclasses of CallableMemberDescriptor (e.g. ValueParameterDescriptor).
Those can be removed by making CallableMemberDescriptor (instead of
CallableDescriptor) inherit from Substitutable. However, that would
require more changes in the compiler because CallableDescriptor is used
rather often in places where in fact only CallableMemberDescriptor
instances can appear.

Explicit return types and casts are required in some places now because
there's no single non-trivial supertype for
ClassifierDescriptorWithTypeParameters and CallableDescriptor.
Previously it was DeclarationDescriptorWithVisibility, now it's both
that and Substitutable<...>

idea/idea-analysis/src/org/jetbrains/kotlin/idea/decompiler/navigation/findDecompiledDeclaration.kt

@@ -104,11 +104,12 @@ private fun findCandidateDeclarationsInIndex(
         return KotlinFullClassNameIndex.getInstance().get(containingClass.fqNameSafe.asString(), project, scope)
     }
 
-    val topLevelDeclaration = DescriptorUtils.getParentOfType(referencedDescriptor, PropertyDescriptor::class.java, false)
-                              ?: DescriptorUtils.getParentOfType(referencedDescriptor, TypeAliasConstructorDescriptor::class.java, false)?.typeAliasDescriptor
-                              ?: DescriptorUtils.getParentOfType(referencedDescriptor, FunctionDescriptor::class.java, false)
-                              ?: DescriptorUtils.getParentOfType(referencedDescriptor, TypeAliasDescriptor::class.java, false)
-                              ?: return emptyList()
+    val topLevelDeclaration =
+            DescriptorUtils.getParentOfType(referencedDescriptor, PropertyDescriptor::class.java, false) as DeclarationDescriptor?
+            ?: DescriptorUtils.getParentOfType(referencedDescriptor, TypeAliasConstructorDescriptor::class.java, false)?.typeAliasDescriptor
+            ?: DescriptorUtils.getParentOfType(referencedDescriptor, FunctionDescriptor::class.java, false)
+            ?: DescriptorUtils.getParentOfType(referencedDescriptor, TypeAliasDescriptor::class.java, false)
+            ?: return emptyList()
 
     // filter out synthetic descriptors
     if (!DescriptorUtils.isTopLevelDeclaration(topLevelDeclaration)) return emptyList()

idea/idea-completion/src/org/jetbrains/kotlin/idea/completion/smart/Utils.kt

@@ -208,11 +208,12 @@ fun<TDescriptor: DeclarationDescriptor?> MutableCollection<LookupElement>.addLoo
     }
 }
 
+@Suppress("UNCHECKED_CAST")
 private fun <T : DeclarationDescriptor?> T.substituteFixed(substitutor: TypeSubstitutor): T {
-    if (this is LocalVariableDescriptor || this is ValueParameterDescriptor || this is TypeParameterDescriptor) { // TODO: it's not implemented for them
+    if (this is LocalVariableDescriptor || this is ValueParameterDescriptor || this !is Substitutable<*>) {
         return this
     }
-    return this?.substitute(substitutor) as T
+    return this.substitute(substitutor) as T
 }
 
 private fun MutableCollection<LookupElement>.addLookupElementsForNullable(factory: () -> Collection<LookupElement>, matchedInfos: Collection<ExpectedInfo>) {

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

@@ -47,7 +47,7 @@ private enum class SourceKind { NONE, PRODUCTION, TEST }
 
 fun ModuleDescriptor.hasDeclarationOf(descriptor: MemberDescriptor) = declarationOf(descriptor) != null
 
-private fun ModuleDescriptor.declarationOf(descriptor: MemberDescriptor) =
+private fun ModuleDescriptor.declarationOf(descriptor: MemberDescriptor): DeclarationDescriptor? =
         with (HeaderImplDeclarationChecker(this)) {
             when (descriptor) {
                 is CallableMemberDescriptor ->

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

@@ -32,7 +32,7 @@ import java.awt.event.MouseEvent
 fun ModuleDescriptor.hasImplementationsOf(descriptor: MemberDescriptor) =
         implementationsOf(descriptor).isNotEmpty()
 
-private fun ModuleDescriptor.implementationsOf(descriptor: MemberDescriptor) =
+private fun ModuleDescriptor.implementationsOf(descriptor: MemberDescriptor): List<DeclarationDescriptor> =
         with (HeaderImplDeclarationChecker(this)) {
             when (descriptor) {
                 is CallableMemberDescriptor -> descriptor.findNamesakesFromTheSameModule().filter { it.isImpl }