IDEA-67172 "Empty text" feature in EditorTextField

Added ability to specify editor's 'placeholder text'

platform/lang-impl/src/com/intellij/injected/editor/EditorWindow.java

@@ -625,4 +625,9 @@ public class EditorWindow extends UserDataHolderBase implements EditorEx {
   public void setSoftWrapAppliancePlace(@NotNull SoftWrapAppliancePlaces place) {
     myDelegate.setSoftWrapAppliancePlace(place);
   }
+
+  @Override
+  public void setPlaceholder(@Nullable CharSequence text) {
+    myDelegate.setPlaceholder(text);
+  }
 }

platform/platform-impl/src/com/intellij/openapi/editor/ex/EditorEx.java

@@ -164,4 +164,15 @@ public interface EditorEx extends Editor {
    * @param place   soft wraps appliance appliance use-case
    */
   void setSoftWrapAppliancePlace(@NotNull SoftWrapAppliancePlaces place);
+
+  /**
+   * Allows to define <code>'placeholder text'</code> for the current editor, i.e. virtual text that will be represented until
+   * any user data is entered and current editor is not focused.
+   * <p/>
+   * Feel free to see the detailed feature
+   * definition <a href="http://dev.w3.org/html5/spec/Overview.html#the-placeholder-attribute">here</a>.
+   * 
+   * @param text    virtual text to show until user data is entered or the editor is focused
+   */
+  void setPlaceholder(@Nullable CharSequence text);
 }

platform/platform-impl/src/com/intellij/openapi/editor/impl/EditorImpl.java

@@ -259,6 +259,10 @@ public final class EditorImpl extends UserDataHolderBase implements EditorEx, Hi
   private char[] myPrefixText;
   private TextAttributes myPrefixAttributes;
   private final IndentsModel myIndentsModel;
+  
+  @Nullable
+  private CharSequence myPlaceholderText;
+  private int myLastPaintedPlaceholderWidth;
 
   static {
     ourCaretBlinkingCommand = new RepaintCursorCommand();
@@ -1549,6 +1553,7 @@ public final class EditorImpl extends UserDataHolderBase implements EditorEx, Hi
     paintLineMarkersSeparators(g, clip, docMarkup);
     paintLineMarkersSeparators(g, clip, myMarkupModel);
     paintText(g, clip);
+    paintPlaceholderText(g, clip);
     paintSegmentHighlightersBorderAndAfterEndOfLine(g, clip);
     BorderEffect borderEffect = new BorderEffect(this, g);
     borderEffect.paintHighlighters(getHighlighter());
@@ -1625,6 +1630,11 @@ public final class EditorImpl extends UserDataHolderBase implements EditorEx, Hi
     return myTextDrawingCallback;
   }
 
+  @Override
+  public void setPlaceholder(@Nullable CharSequence text) {
+    myPlaceholderText = text;
+  }
+
   private Color getBackgroundColor(final TextAttributes attributes) {
     final Color attrColor = attributes.getBackgroundColor();
     return attrColor == myScheme.getDefaultBackground() ? getBackgroundColor() : attrColor;
@@ -2331,6 +2341,29 @@ public final class EditorImpl extends UserDataHolderBase implements EditorEx, Hi
     flushCachedChars(g);
   }
 
+  private void paintPlaceholderText(Graphics g, Rectangle clip) {
+    CharSequence hintText = myPlaceholderText;
+    if (myDocument.getTextLength() > 0 || hintText == null || hintText.length() == 0) {
+      return;
+    }
+
+    if (KeyboardFocusManager.getCurrentKeyboardFocusManager().getFocusOwner() == myEditorComponent) {
+      // There is a possible case that placeholder text was painted and the editor gets focus now. We want to over-paint previuosly
+      // used placeholder text then.
+      myLastBackgroundColor = getBackgroundColor();
+      myLastBackgroundPosition = new Point(0, 0);
+      myLastBackgroundWidth = myLastPaintedPlaceholderWidth;
+      flushBackground(g, clip);
+    }
+    else {
+      myLastPaintedPlaceholderWidth = drawString(
+        g, CharArrayUtil.fromSequence(hintText), 0, hintText.length(), new Point(0, 0), clip, null, null, Font.PLAIN,
+        myFoldingModel.getPlaceholderAttributes().getForegroundColor()
+      );
+      flushCachedChars(g);
+    }
+  }
+  
   private boolean paintSelection() {
     return !isOneLineMode() || IJSwingUtilities.hasFocus(getContentComponent());
   }

platform/platform-impl/src/com/intellij/ui/EditorTextField.java

@@ -76,6 +76,7 @@ public class EditorTextField extends NonOpaquePanel implements DocumentListener,
   private boolean myCenterByHeight = true;
   private boolean myEnsureWillComputePreferredSize;
   private Dimension myPassivePreferredSize;
+  private CharSequence myHintText;
 
   public EditorTextField() {
     this("");
@@ -250,6 +251,20 @@ public class EditorTextField extends NonOpaquePanel implements DocumentListener,
     });
   }
 
+  /**
+   * Allows to define {@link EditorEx#setPlaceholder(CharSequence) editor's placeholder}. The trick here is that the editor
+   * is instantiated lazily by the editor text field and provided placeholder text is applied to the editor during its
+   * actual construction then.
+   *
+   * @param text    {@link EditorEx#setPlaceholder(CharSequence) editor's placeholder} text to use
+   */
+  public void setPlaceholder(@Nullable CharSequence text) {
+    myHintText = text;
+    if (myEditor != null) {
+      myEditor.setPlaceholder(text);
+    }
+  }
+  
   public void selectAll() {
     if (myEditor != null) {
       myEditor.getSelectionModel().setSelection(0, myDocument.getTextLength());
@@ -485,6 +500,8 @@ public class EditorTextField extends NonOpaquePanel implements DocumentListener,
 
     editor.putUserData(SUPPLEMENTARY_KEY, myIsSupplementary);
     editor.getContentComponent().setFocusCycleRoot(false);
+    
+    editor.setPlaceholder(myHintText);
 
     initOneLineMode(editor);