From 8d241366a1fd1eedcb7579fa12f63f9c25923bf9 Mon Sep 17 00:00:00 2001
From: Humza Shahid <humzasaur@gmail.com>
Date: Sat, 6 Sep 2025 10:05:06 +0100
Subject: [PATCH] handle edge cases in line-break removal function ('J'
 command). If the newline we find is the last character in the file, we don't
 delete it, because of Unix convention that text files always end with
 newlines.

---
 fcore/normal-mode/make-normal-delete.sml | 79 +++++++++++++++++++-----
 1 file changed, 65 insertions(+), 14 deletions(-)

diff --git a/fcore/normal-mode/make-normal-delete.sml b/fcore/normal-mode/make-normal-delete.sml
index ac3e942..54d4d9d 100644
--- a/fcore/normal-mode/make-normal-delete.sml
+++ b/fcore/normal-mode/make-normal-delete.sml
@@ -100,34 +100,85 @@ struct
    * 1J delettes 1 line break, 2J deletes 2, and so on. *)
   fun helpRemoveLineBreaks (app, buffer, cursorIdx, count, time) =
     if count = 0 then
-      finishAfterDeletingBuffer (app, cursorIdx, buffer, time, [])
+      (* we don't use Fn.initMsgs in this function.
+       * Removing line breaks is a discrete action which doesn't operate
+       * as a range the way that motions like 'dw' or 'diw'.
+       * Instead, a single character is deleted at different places. 
+       * So it doesn't make any sense to use Fn.initMsgs 
+       * which expects a range. *)
+      let
+        val buffer = LineGap.goToStart buffer
+        val searchString = #searchString app
+        val initialMsg = [SEARCH (buffer, searchString)]
+      in
+        finishAfterDeletingBuffer (app, cursorIdx, buffer, time, initialMsg)
+      end
     else
       let
         val buffer = LineGap.goToIdx (cursorIdx, buffer)
-        val newCursorIdx = Cursor.toNextChr (buffer, cursorIdx, #"\n")
-
-        val buffer = LineGap.delete (newCursorIdx, 1, buffer)
-        val buffer = LineGap.insert (newCursorIdx, " ", buffer)
-        val newCount = if newCursorIdx = cursorIdx then 0 else count - 1
       in
-        helpRemoveLineBreaks (app, buffer, newCursorIdx, newCount, time)
+        if Cursor.isCursorAtStartOfLine (buffer, cursorIdx) then
+          (* if the cursor is at a linebreak, delete the linebreak
+           * and don't insert a space. *)
+          let val buffer = LineGap.delete (cursorIdx, 1, buffer)
+          in helpRemoveLineBreaks (app, buffer, cursorIdx, count - 1, time)
+          end
+        else
+          let
+            val newCursorIdx = Cursor.toNextChr (buffer, cursorIdx, #"\n")
+            val buffer = LineGap.goToIdx (newCursorIdx, buffer)
+            val clippedIdx = Cursor.clipIdx (buffer, newCursorIdx)
+
+            val buffer =
+              if clippedIdx = newCursorIdx then
+                let val buffer = LineGap.delete (newCursorIdx, 1, buffer)
+                in LineGap.insert (newCursorIdx, " ", buffer)
+                end
+              else
+                (* if clippedIdx and newCursorIdx are different,
+                * that means our previous search brought us past
+                * the ending #"\n" in the file.
+                * We don't want to delete the last newline in the file
+                * because of Unix convention
+                * so don't modify the buffer. *)
+                buffer
+            val newCount = if clippedIdx = cursorIdx then 0 else count - 1
+          in
+            helpRemoveLineBreaks (app, buffer, clippedIdx, newCount, time)
+          end
       end
 
   fun removeLineBreaks (app: app_type, count, time) =
     let
       val {buffer, cursorIdx, ...} = app
       val buffer = LineGap.goToIdx (cursorIdx, buffer)
-      val newCursorIdx = Cursor.toNextChr (buffer, cursorIdx, #"\n")
     in
-      if cursorIdx = newCursorIdx then
-        (* no change *)
-        NormalFinish.clearMode app
+      if Cursor.isCursorAtStartOfLine (buffer, cursorIdx) then
+        let val buffer = LineGap.delete (cursorIdx, 1, buffer)
+        in helpRemoveLineBreaks (app, buffer, cursorIdx, count - 1, time)
+        end
       else
         let
-          val buffer = LineGap.delete (newCursorIdx, 1, buffer)
-          val buffer = LineGap.insert (newCursorIdx, " ", buffer)
+          val buffer = LineGap.goToIdx (cursorIdx, buffer)
+          val newCursorIdx = Cursor.toNextChr (buffer, cursorIdx, #"\n")
+          val buffer = LineGap.goToIdx (newCursorIdx, buffer)
+          val clippedIdx = Cursor.clipIdx (buffer, newCursorIdx)
         in
-          helpRemoveLineBreaks (app, buffer, newCursorIdx, count - 1, time)
+          if cursorIdx = newCursorIdx orelse newCursorIdx <> clippedIdx then
+            (* no change, either because no #"\n" was found
+             * or because the next #"\n" found is the last character in the
+             * file.
+             * We don't delete the last #"\n" in the file
+             * because Unix convention is that text files always
+             * end with newlines. *)
+            NormalFinish.clearMode app
+          else
+            let
+              val buffer = LineGap.delete (newCursorIdx, 1, buffer)
+              val buffer = LineGap.insert (newCursorIdx, " ", buffer)
+            in
+              helpRemoveLineBreaks (app, buffer, newCursorIdx, count - 1, time)
+            end
         end
     end