A couple utility methods

PsiCodegenPredictor.getFileForCodegenNamedClass() returns JetFile which
contains a declaration which will produce a class with a given name.
PsiCodegenPredictor.getFileForNamespacePartName() returns JetFile which
produces a namespace part with the given name.

BindingContextUtils.getContainingFile() returns JetFile which contains a
declaration which is matched to a given descriptor.

DescriptorUtils.findTopLevelParent() finds a top-level (i.e. its containing
declaration is NamespaceDescriptor) parent for a descriptor.

Also DescriptorUtils.isTopLevelFunction() is changed a little to accept not
only a function, but any descriptor

compiler/backend/src/org/jetbrains/jet/codegen/binding/PsiCodegenPredictor.java

@@ -16,19 +16,26 @@
 
 package org.jetbrains.jet.codegen.binding;
 
+import com.intellij.openapi.util.Ref;
 import com.intellij.psi.PsiElement;
 import com.intellij.psi.util.PsiTreeUtil;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
+import org.jetbrains.jet.codegen.NamespaceCodegen;
 import org.jetbrains.jet.lang.descriptors.ClassDescriptor;
 import org.jetbrains.jet.lang.descriptors.DeclarationDescriptor;
 import org.jetbrains.jet.lang.psi.*;
 import org.jetbrains.jet.lang.resolve.BindingContext;
+import org.jetbrains.jet.lang.resolve.BindingContextUtils;
 import org.jetbrains.jet.lang.resolve.BindingTrace;
+import org.jetbrains.jet.lang.resolve.DelegatingBindingTrace;
 import org.jetbrains.jet.lang.resolve.java.JvmAbi;
 import org.jetbrains.jet.lang.resolve.java.JvmClassName;
 import org.jetbrains.jet.lang.resolve.name.FqName;
 import org.jetbrains.jet.lang.resolve.name.Name;
+import org.jetbrains.jet.util.slicedmap.WritableSlice;
+
+import java.util.List;
 
 import static org.jetbrains.jet.lang.resolve.BindingContextUtils.descriptorToDeclaration;
 
@@ -175,4 +182,42 @@ public final class PsiCodegenPredictor {
 
         return null;
     }
+
+    @Nullable
+    public static JetFile getFileForNamespacePartName(@NotNull List<JetFile> allNamespaceFiles, @NotNull JvmClassName className) {
+        for (JetFile file : allNamespaceFiles) {
+            String internalName = NamespaceCodegen.getNamespacePartInternalName(file);
+            JvmClassName jvmClassName = JvmClassName.byInternalName(internalName);
+            if (jvmClassName.equals(className)) {
+                return file;
+            }
+        }
+        return null;
+    }
+
+    @Nullable
+    public static JetFile getFileForCodegenNamedClass(
+            @NotNull BindingContext context,
+            @NotNull List<JetFile> allNamespaceFiles,
+            @NotNull final JvmClassName className
+    ) {
+        final Ref<DeclarationDescriptor> resultingDescriptor = Ref.create();
+
+        DelegatingBindingTrace trace = new DelegatingBindingTrace(context) {
+            @Override
+            public <K, V> void record(WritableSlice<K, V> slice, K key, V value) {
+                super.record(slice, key, value);
+                if (slice == CodegenBinding.FQN && key instanceof DeclarationDescriptor) {
+                    if (className.equals(value)) {
+                        resultingDescriptor.set((DeclarationDescriptor) key);
+                    }
+                }
+            }
+        };
+
+        CodegenBinding.initTrace(trace, allNamespaceFiles);
+
+        return resultingDescriptor.isNull() ? null
+               : BindingContextUtils.getContainingFile(trace.getBindingContext(), resultingDescriptor.get());
+    }
 }

compiler/frontend/src/org/jetbrains/jet/lang/resolve/BindingContextUtils.java

@@ -112,6 +112,19 @@ public class BindingContextUtils {
         return null;
     }
 
+    @Nullable
+    public static JetFile getContainingFile(@NotNull BindingContext context, @NotNull DeclarationDescriptor declarationDescriptor) {
+        // declarationDescriptor may describe a synthesized element which doesn't have PSI
+        // To workaround that, we find a top-level parent (which is inside a NamespaceDescriptor), which is guaranteed to have PSI
+        DeclarationDescriptor descriptor = DescriptorUtils.findTopLevelParent(declarationDescriptor);
+        if (descriptor == null) return null;
+
+        PsiElement declaration = descriptorToDeclaration(context, descriptor);
+        if (declaration == null) return null;
+
+        return (JetFile) declaration.getContainingFile();
+    }
+
     // TODO these helper methods are added as a workaround to some compiler bugs in Kotlin...
 
     // NOTE this is used by KDoc

compiler/frontend/src/org/jetbrains/jet/lang/resolve/DescriptorUtils.java

@@ -129,8 +129,17 @@ public class DescriptorUtils {
         return getFQName(containingDeclaration).child(descriptor.getName());
     }
 
-    public static boolean isTopLevelFunction(@NotNull SimpleFunctionDescriptor functionDescriptor) {
-        return functionDescriptor.getContainingDeclaration() instanceof NamespaceDescriptor;
+    public static boolean isTopLevelDeclaration(@NotNull DeclarationDescriptor descriptor) {
+        return descriptor.getContainingDeclaration() instanceof NamespaceDescriptor;
+    }
+
+    @Nullable
+    public static DeclarationDescriptor findTopLevelParent(@NotNull DeclarationDescriptor declarationDescriptor) {
+        DeclarationDescriptor descriptor = declarationDescriptor;
+        while (!(descriptor == null || isTopLevelDeclaration(descriptor))) {
+            descriptor = descriptor.getContainingDeclaration();
+        }
+        return descriptor;
     }
 
     @Nullable

idea/src/org/jetbrains/jet/plugin/completion/handlers/JetFunctionInsertHandler.java

@@ -187,7 +187,7 @@ public class JetFunctionInsertHandler implements InsertHandler<LookupElement> {
                             return;
                         }
 
-                        if (DescriptorUtils.isTopLevelFunction(functionDescriptor)) {
+                        if (DescriptorUtils.isTopLevelDeclaration(functionDescriptor)) {
                             ApplicationManager.getApplication().runWriteAction(new Runnable() {
                                 @Override
                                 public void run() {