Backport: Bug [#2140]. Move rather than grow selection when insertion at start.

Backport of changeset 7773:20f353cd5507.

1 files changed, 17 insertions, 4 deletions

diff --git a/src/Selection.cxx b/src/Selection.cxx
index 6893ee04e..bd48a2f9f 100644
--- a/src/Selection.cxx
+++ b/src/Selection.cxx
@@ -22,12 +22,16 @@
 
 using namespace Scintilla;
 
-void SelectionPosition::MoveForInsertDelete(bool insertion, Sci::Position startChange, Sci::Position length) noexcept {
+void SelectionPosition::MoveForInsertDelete(bool insertion, Sci::Position startChange, Sci::Position length, bool moveForEqual) noexcept {
 	if (insertion) {
 		if (position == startChange) {
+			// Always consume virtual space
 			const Sci::Position virtualLengthRemove = std::min(length, virtualSpace);
 			virtualSpace -= virtualLengthRemove;
-			position += virtualLengthRemove;
+			if (moveForEqual) {
+				const Sci::Position lengthAfterVirtualRemove = length - virtualLengthRemove;
+				position += lengthAfterVirtualRemove;
+			}
 		} else if (position > startChange) {
 			position += length;
 		}
@@ -84,8 +88,17 @@ Sci::Position SelectionRange::Length() const noexcept {
 }
 
 void SelectionRange::MoveForInsertDelete(bool insertion, Sci::Position startChange, Sci::Position length) noexcept {
-	caret.MoveForInsertDelete(insertion, startChange, length);
-	anchor.MoveForInsertDelete(insertion, startChange, length);
+	// For insertions that occur at the start of the selection move both the start
+	// and end of the selection to preserve the selected length.
+	// The end will automatically move since it is after the insertion, so determine
+	// which position is the start and pass this into
+	// SelectionPosition::MoveForInsertDelete.
+	// There isn't any reason to move an empty selection so don't move it.
+	const bool caretStart = caret < anchor;
+	const bool anchorStart = anchor < caret;
+
+	caret.MoveForInsertDelete(insertion, startChange, length, caretStart);
+	anchor.MoveForInsertDelete(insertion, startChange, length, anchorStart);
 }
 
 bool SelectionRange::Contains(Sci::Position pos) const noexcept {