reimplement 'df' motion as per previous commits, and add a new test for 'df' motion to check that cursor does not land on a 'newline following a non-newline' position, after deleting using 'df<char>'

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

@@ -648,7 +648,7 @@ struct
 
   fun deleteToFirstNonSpaceChr (app: app_type, time) =
     let
-      val {buffer, cursorIdx, windowWidth, windowHeight, startLine, ...} = app
+      val {buffer, cursorIdx, ...} = app
 
       (* move LineGap and buffer to start of line *)
       val buffer = LineGap.goToIdx (cursorIdx, buffer)
@@ -712,6 +712,31 @@ struct
       , time
       )
 
+  fun deleteToNextChr (app: app_type, count, chr, time) =
+    let
+      val {buffer, cursorIdx, ...} = app
+      val buffer = LineGap.goToIdx (cursorIdx, buffer)
+      val newCursorIdx =
+        Cursor.toNextChrNew (buffer, cursorIdx, {findChr = chr, count = count})
+    in
+      if newCursorIdx = ~1 then
+        NormalFinish.clearMode app
+      else
+        let
+          val length = newCursorIdx - cursorIdx + 1
+          val buffer = LineGap.goToIdx (newCursorIdx, buffer)
+          val initialMsg = Fn.initMsgs (cursorIdx, length, buffer)
+          val buffer = LineGap.delete (cursorIdx, length, buffer)
+
+          val buffer = LineGap.goToIdx (cursorIdx, buffer)
+          val cursorIdx =
+            if Cursor.isOnNewlineAfterChr (buffer, cursorIdx) then cursorIdx - 1
+            else cursorIdx
+        in
+          finishAfterDeletingBuffer (app, cursorIdx, buffer, time, initialMsg)
+        end
+    end
+
   fun deleteToStart (app: app_type, time) : AppType.app_type =
     let
       val {cursorIdx, buffer, windowWidth, windowHeight, dfa, ...} = app

fcore/normal-mode/normal-mode.sml

@@ -304,9 +304,7 @@ struct
         | #"T" =>
             NormalDelete.deleteToChr
               (app, 1, Cursor.tillPrevChr, op-, chrCmd, time)
-        | #"f" =>
-            NormalDelete.deleteToChr
-              (app, count, Cursor.toNextChr, op+, chrCmd, time)
+        | #"f" => NormalDelete.deleteToNextChr (app, count, chrCmd, time)
         | #"F" =>
             NormalDelete.deleteToChr
               (app, count, Cursor.toPrevChr, op-, chrCmd, time)
@@ -560,18 +558,13 @@ struct
      * which can be made terminal by adding "w" or "e" at the end. 
      * *)
     case String.sub (str, strPos) of
-      #"t" =>
-        (* to just before char, forward 
-         * tillNextChr with count of 1 has same effect
-         * as tillNextChr with any count above 1
-         * so just hardcode 1 *)
-        NormalMove.tillNextChr (app, count, chrCmd)
+      #"t" => NormalMove.tillNextChr (app, count, chrCmd)
     | #"T" =>
         (* to just before chr, backward *)
         parseMoveToChr (1, app, Cursor.tillPrevChr, chrCmd)
     | #"y" => ParseYank.parseYank (strPos, str, count, app, chrCmd, time)
     | #"d" => ParseDelete.parseDelete (strPos, str, count, app, chrCmd, time)
-    | #"f" => (* to chr, forward *) NormalMove.toNextChr (app, count, chrCmd)
+    | #"f" => NormalMove.toNextChr (app, count, chrCmd)
     | #"F" =>
         (* to chr, backward *)
         parseMoveToChr (count, app, Cursor.toPrevChr, chrCmd)

test/normal-delete.sml

@@ -3576,6 +3576,28 @@ struct
                (actualString = expectedString
                 andalso cursorIdx = expectedCursorIdx)
            end)
+    , test
+        "moves cursor back by one, when deletion range is \
+        \from a newline that follows a non-newline char"
+        (fn _ =>
+           let
+             (* arrange *)
+             val originalString = "hey hello\n"
+             val app = TestUtils.init originalString
+             val app = AppWith.idx (app, 3)
+
+             (* act *)
+             val {buffer, cursorIdx, ...} = TestUtils.updateMany (app, "dfo")
+
+             (* assert *)
+             val actualString = LineGap.toString buffer
+             val expectedString = "hey\n"
+             val expectedCursorIdx = 2
+           in
+             Expect.isTrue
+               (actualString = expectedString
+                andalso cursorIdx = expectedCursorIdx)
+           end)
     ]
 
   val dtDelete = describe "delete motion 'dt<char>'"