feat: #523 allow resizing the error console in the Preview window

Author: bjansen

src/main/java/org/antlr/intellij/plugin/preview/InputPanel.form

@@ -49,6 +49,16 @@
           </grid>
         </children>
       </grid>
+      <component id="57495" class="com.intellij.openapi.ui.Splitter" binding="editorSplitter">
+        <constraints border-constraint="Center"/>
+        <properties>
+          <dividerWidth value="3"/>
+          <firstComponent value="4d6c1"/>
+          <orientation value="true"/>
+          <proportion value="0.8"/>
+          <secondComponent value="37477"/>
+        </properties>
+      </component>
       <component id="4d6c1" class="javax.swing.JTextArea" binding="placeHolder">
         <constraints border-constraint="East"/>
         <properties>

src/main/java/org/antlr/intellij/plugin/preview/InputPanel.java

@@ -17,6 +17,7 @@
 import com.intellij.openapi.fileEditor.FileDocumentManager;
 import com.intellij.openapi.project.Project;
 import com.intellij.openapi.ui.ComponentWithBrowseButton;
+import com.intellij.openapi.ui.Splitter;
 import com.intellij.openapi.ui.TextComponentAccessor;
 import com.intellij.openapi.ui.TextFieldWithBrowseButton;
 import com.intellij.openapi.util.Key;
@@ -70,13 +71,7 @@ public class InputPanel {
 	private JPanel startRuleAndInputPanel;
 	private TextFieldWithBrowseButton fileChooser;
 	private JPanel outerMostPanel;
-
-	/**
-	 * switchToGrammar() was seeing an empty slot instead of a previous
-	 * editor or placeHolder. Figured it was an order of operations thing
-	 * and synchronized add/remove ops. Works now w/o error.
-	 */
-	private final Object swapEditorComponentLock = new Object();
+	private Splitter editorSplitter;
 
 	private final PreviewPanel previewPanel;
 
@@ -266,17 +261,7 @@ public void switchToGrammar(PreviewState previewState, VirtualFile grammarFile)
 	}
 
 	public void setEditorComponent(JComponent editor) {
-		BorderLayout layout = (BorderLayout) outerMostPanel.getLayout();
-		String EDITOR_SPOT_COMPONENT = BorderLayout.CENTER;
-		// atomically remove old
-		synchronized (swapEditorComponentLock) {
-			Component editorSpotComp = layout.getLayoutComponent(EDITOR_SPOT_COMPONENT);
-			if ( editorSpotComp!=null ) {
-				editorSpotComp.setVisible(false);
-				outerMostPanel.remove(editorSpotComp); // remove old editor if it's there
-			}
-			outerMostPanel.add(editor, EDITOR_SPOT_COMPONENT);
-		}
+		editorSplitter.setFirstComponent(editor);
 	}
 
 	public Editor getInputEditor() {