Add API for accessing all attribute keys in a color scheme

platform/editor-ui-ex/src/com/intellij/openapi/editor/colors/impl/AbstractColorsScheme.java

-/*
- * Copyright 2000-2017 JetBrains s.r.o.
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- * http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
+// Copyright 2000-2018 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license that can be found in the LICENSE file.
 
 package com.intellij.openapi.editor.colors.impl;
 
@@ -196,6 +182,19 @@ public abstract class AbstractColorsScheme extends EditorFontCacheImpl implement
     return myColorsMap.keySet();
   }
 
+  /**
+   * Returns the collection of text attribute keys for which this color scheme defines attributes.
+   */
+  @SuppressWarnings("unused")
+  @NotNull
+  public Set<TextAttributesKey> getAttributeKeys() {
+    HashSet<TextAttributesKey> result = new HashSet<>(myAttributesMap.keySet());
+    if (myParentScheme instanceof DefaultColorsScheme) {
+      result.addAll(((DefaultColorsScheme) myParentScheme).getAttributeKeys());
+    }
+    return result;
+  }
+
   @Override
   public void setEditorFontName(String fontName) {
     ModifiableFontPreferences currPreferences = ensureEditableFontPreferences();