fix(api): only flush nvim__redraw when necessary #31250

Problem:  Not possible to only set a "redraw later" type with
          nvim__redraw, which seems to be desired for the
          treesitter highlighter.
Solution: Do not update the screen when "flush" is explicitly set to
          false and only redraw later types are present. In that case,
          do not call ui_flush() either.

1 files changed, 13 insertions, 1 deletions

diff --git a/src/nvim/api/vim.c b/src/nvim/api/vim.c
index 0d562f2276..83f9aa573d 100644
--- a/src/nvim/api/vim.c
+++ b/src/nvim/api/vim.c
@@ -2396,9 +2396,16 @@ void nvim__redraw(Dict(redraw) *opts, Error *err)
       last = rbuf->b_ml.ml_line_count;
     }
     redraw_buf_range_later(rbuf, first, last);
+  }
+
+  // Redraw later types require update_screen() so call implicitly unless set to false.
+  if (HAS_KEY(opts, redraw, valid) || HAS_KEY(opts, redraw, range)) {
     opts->flush = HAS_KEY(opts, redraw, flush) ? opts->flush : true;
   }
 
+  // When explicitly set to false and only "redraw later" types are present,
+  // don't call ui_flush() either.
+  bool flush_ui = opts->flush;
   if (opts->tabline) {
     // Flush later in case tabline was just hidden or shown for the first time.
     if (redraw_tabline && firstwin->w_lines_valid == 0) {
@@ -2406,6 +2413,7 @@ void nvim__redraw(Dict(redraw) *opts, Error *err)
     } else {
       draw_tabline();
     }
+    flush_ui = true;
   }
 
   bool save_lz = p_lz;
@@ -2422,6 +2430,7 @@ void nvim__redraw(Dict(redraw) *opts, Error *err)
     } else {
       redraw_status(win, opts, &opts->flush);
     }
+    flush_ui = true;
   }
 
   win_T *cwin = win ? win : curwin;
@@ -2438,9 +2447,12 @@ void nvim__redraw(Dict(redraw) *opts, Error *err)
 
   if (opts->cursor) {
     setcursor_mayforce(cwin, true);
+    flush_ui = true;
   }
 
-  ui_flush();
+  if (flush_ui) {
+    ui_flush();
+  }
 
   RedrawingDisabled = save_rd;
   p_lz = save_lz;