[platform] add LeftRightRenderer combining two renderers

platform/platform-api/src/com/intellij/ui/list/LeftRightRenderer.kt

@@ -0,0 +1,48 @@
+// Copyright 2000-2019 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.ui.list
+
+import com.intellij.util.ui.JBUI
+import java.awt.BorderLayout
+import java.awt.Component
+import javax.swing.JList
+import javax.swing.JPanel
+import javax.swing.ListCellRenderer
+
+/**
+ * A renderer which combines two renderers.
+ *
+ * [mainRenderer] component is aligned to the left, [rightRenderer] component is aligned to the right.
+ * This renderer uses background from [mainRenderer] component.
+ */
+abstract class LeftRightRenderer<T> : ListCellRenderer<T> {
+
+  protected abstract val mainRenderer: ListCellRenderer<T>
+  protected abstract val rightRenderer: ListCellRenderer<T>
+
+  private val spacer = JPanel().apply {
+    border = JBUI.Borders.empty(0, 2)
+  }
+
+  private val component = JPanel(BorderLayout())
+
+  final override fun getListCellRendererComponent(list: JList<out T>,
+                                                  value: T,
+                                                  index: Int,
+                                                  isSelected: Boolean,
+                                                  cellHasFocus: Boolean): Component {
+    val mainComponent = mainRenderer.getListCellRendererComponent(list, value, index, isSelected, cellHasFocus)
+    val rightComponent = rightRenderer.getListCellRendererComponent(list, value, index, isSelected, cellHasFocus)
+    mainComponent.background.let {
+      component.background = it
+      spacer.background = it
+      rightComponent.background = it
+    }
+    component.apply {
+      removeAll()
+      add(mainComponent, BorderLayout.WEST)
+      add(spacer, BorderLayout.CENTER)
+      add(rightComponent, BorderLayout.EAST)
+    }
+    return component
+  }
+}