Fix arithmetic for scrolling columns

src/com/maddyhome/idea/vim/helper/EditorHelper.java

@@ -231,7 +231,7 @@ public class EditorHelper {
    */
   public static int getVisualColumnAtRightOfScreen(final @NotNull Editor editor, int visualLine) {
     final Rectangle area = getVisibleArea(editor);
-    return getFullVisualColumn(editor, area.x + area.width, editor.visualLineToY(visualLine), area.x, area.x + area.width);
+    return getFullVisualColumn(editor, area.x + area.width - 1, editor.visualLineToY(visualLine), area.x, area.x + area.width);
   }
 
   /**
@@ -707,16 +707,18 @@ public class EditorHelper {
     // of columns. It also works with inline inlays and folds. It is slightly inaccurate for proportional fonts, but is
     // still a good solution. Besides, what kind of monster uses Vim with proportional fonts?
     final int standardColumnWidth = EditorUtil.getPlainSpaceWidth(editor);
-    final int something = ((point.x - (screenWidth / 2)) / standardColumnWidth) * standardColumnWidth;
-    EditorHelper.scrollHorizontally(editor, something);
+    final int x = point.x - (screenWidth / standardColumnWidth / 2 * standardColumnWidth);
+    EditorHelper.scrollHorizontally(editor, x);
   }
 
   public static void scrollColumnToRightOfScreen(@NotNull Editor editor, int visualLine, int visualColumn) {
     var inlay = editor.getInlayModel().getInlineElementAt(new VisualPosition(visualLine, visualColumn + 1));
     int inlayWidth = inlay != null && inlay.isRelatedToPrecedingText() ? inlay.getWidthInPixels() : 0;
-    final int columnRightX = editor.visualPositionToXY(new VisualPosition(visualLine, visualColumn + 1)).x;
+
+    // Scroll to the start of the next column, minus a screenwidth
+    final int nextColumnX = editor.visualPositionToXY(new VisualPosition(visualLine, visualColumn + 1)).x;
     final int screenWidth = EditorHelper.getVisibleArea(editor).width;
-    EditorHelper.scrollHorizontally(editor, columnRightX + inlayWidth - 1 - screenWidth);
+    EditorHelper.scrollHorizontally(editor, nextColumnX + inlayWidth - screenWidth);
   }
 
   /**

test/org/jetbrains/plugins/ideavim/action/scroll/ScrollLastScreenColumnActionTest.kt

@@ -111,10 +111,8 @@ class ScrollLastScreenColumnActionTest : VimTestCase() {
     assertVisibleLineBounds(0, 99 - availableColumns + 1, 99)
 
     // We have to assert the location of the inlay
-    Assert.assertTrue("Inlay bounds must be greater than last text location",
-      inlay.bounds!!.x > (visibleArea.x + textWidth))
-    Assert.assertTrue("Inlay bounds must be less than width of screen",
-      inlay.bounds!!.x + inlay.bounds!!.width <= (visibleArea.x + visibleArea.width + 1))
+    Assert.assertEquals(visibleArea.x + textWidth, inlay.bounds!!.x)
+    Assert.assertEquals(visibleArea.x + visibleArea.width, inlay.bounds!!.x + inlay.bounds!!.width)
   }
 
   fun `test last screen column does not include subsequent inline inlay associated with following text`() {

test/org/jetbrains/plugins/ideavim/helper/EditorHelperTest.kt

@@ -0,0 +1,65 @@
+/*
+ * IdeaVim - Vim emulator for IDEs based on the IntelliJ platform
+ * Copyright (C) 2003-2020 The IdeaVim authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <https://www.gnu.org/licenses/>.
+ */
+
+package org.jetbrains.plugins.ideavim.helper
+
+import com.maddyhome.idea.vim.helper.EditorHelper
+import org.jetbrains.plugins.ideavim.VimTestCase
+import org.junit.Assert
+
+class EditorHelperTest : VimTestCase() {
+  fun `test scroll column to left of screen`() {
+    configureByColumns(100)
+    EditorHelper.scrollColumnToLeftOfScreen(myFixture.editor, 0, 2)
+    val visibleArea = myFixture.editor.scrollingModel.visibleArea
+    val columnWidth = visibleArea.width / screenWidth
+    Assert.assertEquals(2 * columnWidth, visibleArea.x)
+  }
+
+  fun `test scroll column to right of screen`() {
+    configureByColumns(100)
+    val column = screenWidth + 2
+    EditorHelper.scrollColumnToRightOfScreen(myFixture.editor, 0, column)
+    val visibleArea = myFixture.editor.scrollingModel.visibleArea
+    val columnWidth = visibleArea.width / screenWidth
+    Assert.assertEquals((column - screenWidth + 1) * columnWidth, visibleArea.x)
+  }
+
+  fun `test scroll column to middle of screen with even number of columns`() {
+    configureByColumns(200)
+    // For an 80 column screen, moving a column to the centre should position it in column 41 (1 based) - 40 columns on
+    // the left, mid point, 39 columns on the right
+    // Put column 100 into position 41 -> offset is 59 columns
+    EditorHelper.scrollColumnToMiddleOfScreen(myFixture.editor, 0, 99)
+    val visibleArea = myFixture.editor.scrollingModel.visibleArea
+    val columnWidth = visibleArea.width / screenWidth
+    Assert.assertEquals(59 * columnWidth, visibleArea.x)
+  }
+
+  fun `test scroll column to middle of screen with odd number of columns`() {
+    configureByColumns(200)
+    setEditorVisibleSize(81, 25)
+    // For an 81 column screen, moving a column to the centre should position it in column 41 (1 based) - 40 columns on
+    // the left, mid point, 40 columns on the right
+    // Put column 100 into position 41 -> offset is 59 columns
+    EditorHelper.scrollColumnToMiddleOfScreen(myFixture.editor, 0, 99)
+    val visibleArea = myFixture.editor.scrollingModel.visibleArea
+    val columnWidth = visibleArea.width / screenWidth
+    Assert.assertEquals(59 * columnWidth, visibleArea.x)
+  }
+}