instead of clearing the search list when we delete, build a small part of it by searching through a small part that is likely to be visible on the user's screen, which gets rid of flickering effect and makes it look like the search list is not rebuilt from scratch

fcore/app-update.sml

@@ -388,11 +388,16 @@ struct
   fun helpRemoveChr (app: app_type, buffer, cursorIdx, count) =
     if count = 0 then
       let
+        val searchString = #searchString app
         val buffer = LineGap.goToEnd buffer
-        val initialMsg = [SEARCH (buffer, #searchString app)]
+        val initialMsg = [SEARCH (buffer, searchString)]
+
+        val buffer = LineGap.goToIdx (cursorIdx + 777, buffer)
+        val searchList =
+          SearchList.buildRange (buffer, searchString, cursorIdx - 777)
       in
         Finish.buildTextAndClear
-          (app, buffer, cursorIdx, SearchList.empty, initialMsg)
+          (app, buffer, cursorIdx, searchList, initialMsg)
       end
     else
       let
@@ -468,6 +473,10 @@ struct
         val searchString = #searchString app
         val initialMsg = [SEARCH (buffer, searchString)]
 
+        val buffer = LineGap.goToIdx (cursorIdx + 777, buffer)
+        val searchList =
+          SearchList.buildRange (buffer, searchString, cursorIdx - 777)
+
         (* If we have deleted from the buffer so that cursorIdx
         * is no longer a valid idx,
         * clip cursorIdx to the end. *)
@@ -475,7 +484,7 @@ struct
         val cursorIdx = Cursor.clipIdx (buffer, low)
       in
         Finish.buildTextAndClear
-          (app, buffer, cursorIdx, SearchList.empty, initialMsg)
+          (app, buffer, cursorIdx, searchList, initialMsg)
       end
     else
       let
@@ -506,9 +515,13 @@ struct
       val buffer = LineGap.goToEnd buffer
       val initialMsg = [SEARCH (buffer, searchString)]
 
+      val buffer = LineGap.goToIdx (cursorIdx + 777, buffer)
+      val searchList =
+        SearchList.buildRange (buffer, searchString, cursorIdx - 777)
+
       val buffer = LineGap.goToIdx (low, buffer)
     in
-      Finish.buildTextAndClear (app, buffer, low, SearchList.empty, initialMsg)
+      Finish.buildTextAndClear (app, buffer, low, searchList, initialMsg)
     end
 
   fun deleteToEndOfLine (app: app_type) =
@@ -549,10 +562,13 @@ struct
       val buffer = LineGap.goToEnd buffer
       val initialMsg = [SEARCH (buffer, searchString)]
 
+      val buffer = LineGap.goToIdx (cursorIdx + 777, buffer)
+      val searchList =
+        SearchList.buildRange (buffer, searchString, cursorIdx - 777)
+
       val buffer = LineGap.goToIdx (startIdx, buffer)
     in
-      Finish.buildTextAndClear
-        (app, buffer, startIdx, SearchList.empty, initialMsg)
+      Finish.buildTextAndClear (app, buffer, startIdx, searchList, initialMsg)
     end
 
   fun helpDeleteLineBack (app, buffer, low, high, count) =
@@ -566,10 +582,12 @@ struct
         val searchString = #searchString app
         val initialMsg = [SEARCH (buffer, searchString)]
 
+        val buffer = LineGap.goToIdx (low + 777, buffer)
+        val searchList = SearchList.buildRange (buffer, searchString, low - 777)
+
         val buffer = LineGap.goToIdx (low, buffer)
       in
-        Finish.buildTextAndClear
-          (app, buffer, low, SearchList.empty, initialMsg)
+        Finish.buildTextAndClear (app, buffer, low, searchList, initialMsg)
       end
     else
       let
@@ -619,8 +637,12 @@ struct
 
       val buffer = LineGap.goToEnd buffer
       val initialMsg = [SEARCH (buffer, searchString)]
+
+      val buffer = LineGap.goToIdx (cursorIdx + 777, buffer)
+      val searchList =
+        SearchList.buildRange (buffer, searchString, cursorIdx - 777)
     in
-      Finish.buildTextAndClear (app, buffer, low, SearchList.empty, initialMsg)
+      Finish.buildTextAndClear (app, buffer, low, searchList, initialMsg)
     end
 
   fun helpDeleteToChr
@@ -635,9 +657,12 @@ struct
         val buffer = LineGap.goToEnd buffer
         val searchString = #searchString app
         val initialMsg = [SEARCH (buffer, searchString)]
+
+        val buffer = LineGap.goToIdx (cursorIdx + 777, buffer)
+        val searchList =
+          SearchList.buildRange (buffer, searchString, cursorIdx - 777)
       in
-        buildTextAndClearAfterChr
-          (app, buffer, low, SearchList.empty, initialMsg)
+        buildTextAndClearAfterChr (app, buffer, low, searchList, initialMsg)
       end
     else
       let
@@ -668,11 +693,14 @@ struct
         app
 
       val buffer = LineGap.delete (0, cursorIdx, buffer)
-      val searchList = SearchList.empty
 
       val buffer = LineGap.goToEnd buffer
       val initialMsg = [SEARCH (buffer, #searchString app)]
 
+      val buffer = LineGap.goToIdx (cursorIdx + 777, buffer)
+      val searchList =
+        SearchList.buildRange (buffer, searchString, cursorIdx - 777)
+
       val cursorIdx = 0
       val startLine = 0
       val buffer = LineGap.goToIdx (cursorIdx, buffer)
@@ -703,9 +731,12 @@ struct
       val buffer = LineGap.goToEnd buffer
       val initialMsg = [SEARCH (buffer, searchString)]
 
+      val buffer = LineGap.goToIdx (low + 777, buffer)
+      val searchList = SearchList.buildRange (buffer, searchString, low - 777)
+
       val buffer = LineGap.goToIdx (low, buffer)
     in
-      Finish.buildTextAndClear (app, buffer, low, SearchList.empty, initialMsg)
+      Finish.buildTextAndClear (app, buffer, low, searchList, initialMsg)
     end
 
   fun deleteToNextMatch (app: app_type, count) =

fcore/search-list.sml

@@ -159,6 +159,7 @@ struct
 
   fun searchRange (buffer: LineGap.t, searchString, low) =
     let
+      val low = Int.max (low, 0)
       val {rightStrings, leftStrings, idx = absIdx, ...} = buffer
     in
       case rightStrings of