fix(VIM-2432): handle scrolloff with <C-D> and <C-U>

src/main/java/com/maddyhome/idea/vim/group/MotionGroup.java

@@ -270,6 +270,8 @@ else if (caretColumn > rightVisualColumn - sideScrollOffset) {
     return SearchHelper.findParagraphRange(editor, caret, count, isOuter);
   }
 
+  // Get the visual line that will be in the same screen relative location as the current caret line, after the screen
+  // has been scrolled
   private static int getScrollScreenTargetCaretVisualLine(final @NotNull Editor editor, int rawCount, boolean down) {
     final Rectangle visibleArea = getVisibleArea(editor);
     final int caretVisualLine = editor.getCaretModel().getVisualPosition().line;
@@ -285,7 +287,7 @@ private static int getScrollScreenTargetCaretVisualLine(final @NotNull Editor ed
       targetCaretVisualLine = down ? caretVisualLine + scrollOption : caretVisualLine - scrollOption;
     }
 
-    return targetCaretVisualLine;
+    return EditorHelper.normalizeVisualLine(editor, targetCaretVisualLine);
   }
 
   public @Range(from = 0, to = Integer.MAX_VALUE) int moveCaretToNthCharacter(@NotNull Editor editor, int count) {
@@ -1207,6 +1209,8 @@ public boolean scrollScreen(final @NotNull Editor editor, final @NotNull Caret c
 
     final Rectangle visibleArea = getVisibleArea(editor);
 
+    // We want to scroll the screen and keep the caret in the same screen-relative position. Calculate which line will
+    // be at the current caret line and work the offsets out from that
     int targetCaretVisualLine = getScrollScreenTargetCaretVisualLine(editor, rawCount, down);
 
     // Scroll at most one screen height
@@ -1230,12 +1234,11 @@ public boolean scrollScreen(final @NotNull Editor editor, final @NotNull Caret c
       }
     }
     else {
-
       scrollVisualLineToCaretLocation(editor, targetCaretVisualLine);
 
       final int scrollOffset = getNormalizedScrollOffset(editor);
-      final int visualTop = getVisualLineAtTopOfScreen(editor) + scrollOffset;
-      final int visualBottom = getVisualLineAtBottomOfScreen(editor) - scrollOffset;
+      final int visualTop = getVisualLineAtTopOfScreen(editor) + (down ? scrollOffset : 0);
+      final int visualBottom = getVisualLineAtBottomOfScreen(editor) - (down ? 0 : scrollOffset);
 
       targetCaretVisualLine = max(visualTop, min(visualBottom, targetCaretVisualLine));
     }

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

@@ -635,7 +635,8 @@ else if (!Character.isWhitespace(chars.charAt(offset))) {
   }
 
   /**
-   * Scrolls the editor to put the given visual line at the current caret location, relative to the screen.
+   * Scrolls the editor to put the given visual line at the current caret location, relative to the screen, as long as
+   * this doesn't add virtual space to the bottom of the file.
    * <p>
    * Due to block inlays, the caret location is maintained as a scroll offset, rather than the number of lines from the
    * top of the screen. This means the line offset can change if the number of inlays above the caret changes during
@@ -668,7 +669,11 @@ else if (bottomInlayHeight > visibleArea.height - caretScreenOffset + editor.get
       inlayOffset = -bottomInlayHeight;
     }
 
-    scrollVertically(editor, yVisualLine - caretScreenOffset - inlayOffset);
+    // Scroll the given visual line to the caret location, but do not scroll down passed the end of file, or the current
+    // virtual space at the bottom of the screen
+    final int lastVisualLine = EditorHelper.getVisualLineCount(editor) - 1;
+    final int yBottomLineOffset = max(getOffsetToScrollVisualLineToBottomOfScreen(editor, lastVisualLine), visibleArea.y);
+    scrollVertically(editor, min(yVisualLine - caretScreenOffset - inlayOffset, yBottomLineOffset));
   }
 
   /**

src/test/java/org/jetbrains/plugins/ideavim/action/scroll/ScrollHalfPageDownActionTest.kt

@@ -58,9 +58,28 @@ class ScrollHalfPageDownActionTest : VimTestCase() {
   }
 
   @TestWithoutNeovim(SkipNeovimReason.SCROLL)
-  fun`test scroll downwards in bottom half of last page moves to the last line`() {
+  fun`test scroll downwards in bottom half of last page moves caret to the last line without scrolling`() {
     configureByPages(5)
-    setPositionAndScroll(146, 165)
+    setPositionAndScroll(140, 165)
+    typeText(parseKeys("<C-D>"))
+    assertPosition(175, 0)
+    assertVisibleArea(141, 175)
+  }
+
+  @TestWithoutNeovim(SkipNeovimReason.SCROLL)
+  fun`test scroll downwards in bottom half of last page moves caret to the last line with scrolloff`() {
+    OptionsManager.scrolloff.set(10)
+    configureByPages(5)
+    setPositionAndScroll(140, 164)
+    typeText(parseKeys("<C-D>"))
+    assertPosition(175, 0)
+    assertVisibleArea(141, 175)
+  }
+
+  @TestWithoutNeovim(SkipNeovimReason.SCROLL)
+  fun`test scroll downwards at end of file with existing virtual space moves caret without scrolling window`() {
+    configureByPages(5)
+    setPositionAndScroll(146, 165) // 146 at top line means bottom line is 181 (out of 175)
     typeText(parseKeys("<C-D>"))
     assertPosition(175, 0)
     assertVisibleArea(146, 175)

src/test/java/org/jetbrains/plugins/ideavim/action/scroll/ScrollHalfPageUpActionTest.kt

@@ -66,6 +66,16 @@ class ScrollHalfPageUpActionTest : VimTestCase() {
     assertVisibleArea(0, 34)
   }
 
+  @TestWithoutNeovim(SkipNeovimReason.SCROLL)
+  fun`test scroll upwards in first half of first page moves to first line with scrolloff`() {
+    OptionsManager.scrolloff.set(10)
+    configureByPages(5)
+    setPositionAndScroll(5, 15)
+    typeText(parseKeys("<C-U>"))
+    assertPosition(0, 0)
+    assertVisibleArea(0, 34)
+  }
+
   @TestWithoutNeovim(SkipNeovimReason.SCROLL)
   fun`test scroll count lines upwards`() {
     configureByPages(5)