Fix bugs caused by deleting text with undo collection off when entering IME composition mode.

This deleted text isn't in the undo history and it isn't in the document so can never be recovered
so makes it impossible to correctly perform undo.
Add logging for unexpected situations and throw an exception when undo can't be performed.
Ensure empty marked text range is always in canonical (NSNotFound,0) form.

1 files changed, 5 insertions, 0 deletions

diff --git a/src/CellBuffer.cxx b/src/CellBuffer.cxx
index a770dc335..dfa1350c0 100644
--- a/src/CellBuffer.cxx
+++ b/src/CellBuffer.cxx
@@ -10,6 +10,7 @@
 #include <stdio.h>
 #include <stdarg.h>
 
+#include <stdexcept>
 #include <algorithm>
 
 #include "Platform.h"
@@ -786,6 +787,10 @@ const Action &CellBuffer::GetUndoStep() const {
 void CellBuffer::PerformUndoStep() {
 	const Action &actionStep = uh.GetUndoStep();
 	if (actionStep.at == insertAction) {
+		if (substance.Length() < actionStep.lenData) {
+			throw std::runtime_error(
+				"CellBuffer::PerformUndoStep: deletion must be less than document length.");
+		}
 		BasicDeleteChars(actionStep.position, actionStep.lenData);
 	} else if (actionStep.at == removeAction) {
 		BasicInsertString(actionStep.position, actionStep.data, actionStep.lenData);