From da6cbce4ef35cd4f30e26d9ed126d86df367da99 Mon Sep 17 00:00:00 2001
From: maralorn <mail@maralorn.de>
Date: Thu, 28 Nov 2024 23:12:48 +0100
Subject: [PATCH] Try to prevent more flickering

---
 lib/NOM/IO.hs | 63 +++++++++++++++++++++++++++++----------------------
 1 file changed, 36 insertions(+), 27 deletions(-)

diff --git a/lib/NOM/IO.hs b/lib/NOM/IO.hs
index c8271c3..82a159c 100644
--- a/lib/NOM/IO.hs
+++ b/lib/NOM/IO.hs
@@ -54,6 +54,13 @@ runUpdate output_builder_var state_var refresh_display_var updater input = do
       modifyTVar' output_builder_var (log_output :)
     modifyTVar' refresh_display_var (|| display_changed)
 
+-- https://gitlab.com/gnachman/iterm2/-/wikis/synchronized-updates-spec
+startAtomicUpdate :: Builder.Builder
+startAtomicUpdate = "\x1b[?2026h"
+
+endAtomicUpdate :: Builder.Builder
+endAtomicUpdate = "\x1b[?2026l"
+
 writeStateToScreen ::
   forall state.
   Bool ->
@@ -126,34 +133,36 @@ writeStateToScreen pad printed_lines_var nom_state_var nix_output_buffer_var ref
       output =
         toStrict
           . Builder.toLazyByteString
-          $
-          -- when we clear the line, but don‘t use cursorUpLine, the cursor needs to be moved to the start for printing.
-          -- we do that before clearing because we can
-          memptyIfFalse (last_printed_line_count == 1) (Builder.stringUtf8 $ Terminal.setCursorColumnCode 0)
-          <>
-          -- Clear last output from screen.
-          -- First we clear the current line, if we have written on it.
-          memptyIfFalse (last_printed_line_count > 0) (Builder.stringUtf8 Terminal.clearLineCode)
-          <>
-          -- Then, if necessary we, move up and clear more lines.
-          stimesMonoid
-            (max (last_printed_line_count - 1) 0)
-            ( Builder.stringUtf8 (Terminal.cursorUpLineCode 1) -- Moves cursor one line up and to the beginning of the line.
-                <> Builder.stringUtf8 Terminal.clearLineCode -- We are avoiding to use clearFromCursorToScreenEnd
-                -- because it apparently triggers a flush on some terminals.
-            )
-          <>
-          -- Insert the output to write to the screen.
-          ( output_to_print_with_newline_annotations & foldMap \(newline, line) ->
-              ( case newline of
-                  StayInLine -> mempty
-                  MoveToNextLine -> Builder.stringUtf8 (Terminal.cursorDownLineCode 1)
-                  PrintNewLine -> Builder.byteString "\n"
+          $ startAtomicUpdate
+            <>
+            -- when we clear the line, but don‘t use cursorUpLine, the cursor needs to be moved to the start for printing.
+            -- we do that before clearing because we can
+            memptyIfFalse (last_printed_line_count == 1) (Builder.stringUtf8 $ Terminal.setCursorColumnCode 0)
+            <>
+            -- Clear last output from screen.
+            -- First we clear the current line, if we have written on it.
+            memptyIfFalse (last_printed_line_count > 0) (Builder.stringUtf8 Terminal.clearLineCode)
+            <>
+            -- Then, if necessary we, move up and clear more lines.
+            stimesMonoid
+              (max (last_printed_line_count - 1) 0)
+              ( Builder.stringUtf8 (Terminal.cursorUpLineCode 1) -- Moves cursor one line up and to the beginning of the line.
+                  <> Builder.stringUtf8 Terminal.clearLineCode -- We are avoiding to use clearFromCursorToScreenEnd
+                  -- because it apparently triggers a flush on some terminals.
               )
-                <> Builder.byteString line
-          )
-          -- Corner case: If nom is not outputting anything but we are printing output from nix, then we want to append a newline
-          <> memptyIfFalse (nom_output_length == 0 && nix_output_length > 0) Builder.byteString "\n"
+            <>
+            -- Insert the output to write to the screen.
+            ( output_to_print_with_newline_annotations & foldMap \(newline, line) ->
+                ( case newline of
+                    StayInLine -> mempty
+                    MoveToNextLine -> Builder.stringUtf8 (Terminal.cursorDownLineCode 1)
+                    PrintNewLine -> Builder.byteString "\n"
+                )
+                  <> Builder.byteString line
+            )
+            -- Corner case: If nom is not outputting anything but we are printing output from nix, then we want to append a newline
+            <> memptyIfFalse (nom_output_length == 0 && nix_output_length > 0) Builder.byteString "\n"
+            <> endAtomicUpdate
 
   -- Actually write to the buffer. We do this all in one step and with a strict
   -- ByteString so that everything is precalculated and the actual put is