if 'MakeNormalDelete.deleteLine' deletes to the end of the file such that there is no newline at the end, then append a newline. This makes one of the tests we have pass.

fcore/normal-mode/make-normal-delete.sml

@@ -354,11 +354,31 @@ struct
       val finishIdx = Cursor.viDlr (buffer, cursorIdx, count) + 2
       val length = finishIdx - startIdx
 
+      val textLengthBeforeDelete = #textLength buffer
+
       val buffer = LineGap.goToIdx (startIdx, buffer)
       val initialMsg = Fn.initMsgs (startIdx, length, buffer)
       val buffer = LineGap.delete (startIdx, length, buffer)
     in
-      finishAfterDeletingBuffer (app, startIdx, buffer, time, initialMsg)
+      if finishIdx >= textLengthBeforeDelete - 1 then
+        (* we deleted to the end of the buffer.
+         * Let's check if there is a newline at the end
+         * and insert one if there isn't. *)
+        let
+          val lastPosAfterDelete = #textLength buffer - 1
+          val buffer = LineGap.goToIdx (lastPosAfterDelete, buffer)
+          val buffer =
+            if lastPosAfterDelete < 0 then
+              LineGap.append ("\n", buffer)
+            else if Cursor.isCursorAtStartOfLine (buffer, lastPosAfterDelete) then
+              buffer
+            else
+              LineGap.append ("\n", buffer)
+        in
+          finishAfterDeletingBuffer (app, startIdx, buffer, time, initialMsg)
+        end
+      else
+        finishAfterDeletingBuffer (app, startIdx, buffer, time, initialMsg)
     end
 
   fun finishDeleteLineBack (app, buffer, lineIdx, length, endOfLine, time) =

temp.txt

@@ -1,2 +1,3 @@
 hello
 world
+

test/normal-delete.sml

@@ -312,6 +312,30 @@ struct
         in
           Expect.isTrue (stringIsExpected andalso cursorIdxIsExpected)
         end)
+    , test
+        "deletes when cursor is on first line and there are at least two lines"
+        (fn _ =>
+           let
+             (* arrange *)
+             val originalString = "hello\nworld\n"
+             val originalIdx = 0
+
+             val app = TestUtils.init originalString
+             val app = AppWith.idx (app, originalIdx)
+
+             (* act *)
+             val {cursorIdx, buffer, ...} = TestUtils.updateMany (app, "dj")
+
+             (* assert *)
+             val expectedString = "\n"
+             val actualString = LineGap.toString buffer
+             val stringIsExpected = expectedString = actualString
+
+             val expectedCursorIdx = 0
+             val cursorIdxIsExpected = expectedCursorIdx = cursorIdx
+           in
+             Expect.isTrue (stringIsExpected andalso cursorIdxIsExpected)
+           end)
     , test
         "deletes first two lines when there are three lines \
         \and cursor is on first line"