From ce2c10c10f7750cc726ca480923e50a58c04392d Mon Sep 17 00:00:00 2001
From: "Gregory.Shrago" <gregory.shrago@jetbrains.com>
Date: Thu, 27 Aug 2015 20:49:00 +0300
Subject: [PATCH] Traverser: introduce psiTraverser(root), astTraverser(root)

---
 .../core-api/src/com/intellij/psi/SyntaxTraverser.java | 10 ++++++++++
 .../util/containers/FilteredTraverserBase.java         |  5 ++---
 2 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/platform/core-api/src/com/intellij/psi/SyntaxTraverser.java b/platform/core-api/src/com/intellij/psi/SyntaxTraverser.java
index 785de7e4b5ad..cff07563ccaa 100644
--- a/platform/core-api/src/com/intellij/psi/SyntaxTraverser.java
+++ b/platform/core-api/src/com/intellij/psi/SyntaxTraverser.java
@@ -47,6 +47,11 @@ public class SyntaxTraverser<T> extends FilteredTraverserBase<T, SyntaxTraverser
     return new SyntaxTraverser<PsiElement>(psiApi(), null);
   }
 
+  @NotNull
+  public static SyntaxTraverser<PsiElement> psiTraverser(@Nullable PsiElement root) {
+    return psiTraverser().withRoot(root);
+  }
+
   @NotNull
   public static SyntaxTraverser<PsiElement> revPsiTraverser() {
     return new SyntaxTraverser<PsiElement>(psiApiReversed(), null);
@@ -57,6 +62,11 @@ public class SyntaxTraverser<T> extends FilteredTraverserBase<T, SyntaxTraverser
     return new SyntaxTraverser<ASTNode>(astApi(), null);
   }
 
+  @NotNull
+  public static SyntaxTraverser<ASTNode> astTraverser(@Nullable ASTNode root) {
+    return astTraverser().withRoot(root);
+  }
+
   @NotNull
   public static SyntaxTraverser<LighterASTNode> lightTraverser(@NotNull PsiBuilder builder) {
     LighterASTApi api = new LighterASTApi(builder);
diff --git a/platform/util/src/com/intellij/util/containers/FilteredTraverserBase.java b/platform/util/src/com/intellij/util/containers/FilteredTraverserBase.java
index 86c31037247c..6b721e211ecb 100644
--- a/platform/util/src/com/intellij/util/containers/FilteredTraverserBase.java
+++ b/platform/util/src/com/intellij/util/containers/FilteredTraverserBase.java
@@ -22,7 +22,6 @@ import com.intellij.util.Function;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 
-import java.util.Collections;
 import java.util.Iterator;
 import java.util.List;
 
@@ -108,8 +107,8 @@ public abstract class FilteredTraverserBase<T, Self extends FilteredTraverserBas
   }
 
   @NotNull
-  public Self withRoot(@NotNull T root) {
-    return newInstance(meta.withRoots(Collections.singleton(root)));
+  public Self withRoot(@Nullable T root) {
+    return newInstance(meta.withRoots(ContainerUtil.createMaybeSingletonList(root)));
   }
 
   @NotNull