feat(extmarks): add virt_text_repeat_linebreak flag (#26625)

Problem:  Unable to predict which byte-offset to place virtual text to
          make it repeat visually in the wrapped part of a line.
Solution: Add a flag to nvim_buf_set_extmark() that causes virtual
          text to repeat in wrapped lines.

5 files changed, 16 insertions, 7 deletions

diff --git a/src/nvim/api/extmark.c b/src/nvim/api/extmark.c
index b2ddef1a43..0cf16294b6 100644
--- a/src/nvim/api/extmark.c
+++ b/src/nvim/api/extmark.c
@@ -391,6 +391,8 @@ Array nvim_buf_get_extmarks(Buffer buffer, Integer ns_id, Object start, Object e
 ///                                  text is selected or hidden because of
 ///                                  scrolling with 'nowrap' or 'smoothscroll'.
 ///                                  Currently only affects "overlay" virt_text.
+///               - virt_text_repeat_linebreak : repeat the virtual text on
+///                                              wrapped lines.
 ///               - hl_mode : control how highlights are combined with the
 ///                           highlights of the text. Currently only affects
 ///                           virt_text highlights, but might affect `hl_group`
@@ -613,7 +615,8 @@ Integer nvim_buf_set_extmark(Buffer buffer, Integer ns_id, Integer line, Integer
   }
 
   hl.flags |= opts->hl_eol ? kSHHlEol : 0;
-  virt_text.flags |= opts->virt_text_hide ? kVTHide : 0;
+  virt_text.flags |= ((opts->virt_text_hide ? kVTHide : 0)
+                      | (opts->virt_text_repeat_linebreak ? kVTRepeatLinebreak : 0));
 
   if (HAS_KEY(opts, set_extmark, hl_mode)) {
     String str = opts->hl_mode;
diff --git a/src/nvim/api/keysets_defs.h b/src/nvim/api/keysets_defs.h
index fa9a2cb013..897d546f3d 100644
--- a/src/nvim/api/keysets_defs.h
+++ b/src/nvim/api/keysets_defs.h
@@ -33,6 +33,7 @@ typedef struct {
   String virt_text_pos;
   Integer virt_text_win_col;
   Boolean virt_text_hide;
+  Boolean virt_text_repeat_linebreak;
   Boolean hl_eol;
   String hl_mode;
   Boolean invalidate;
diff --git a/src/nvim/decoration.c b/src/nvim/decoration.c
index 8766f2ca76..02b95576ea 100644
--- a/src/nvim/decoration.c
+++ b/src/nvim/decoration.c
@@ -1061,11 +1061,11 @@ void decor_to_dict_legacy(Dictionary *dict, DecorInline decor, bool hl_name)
     Array chunks = virt_text_to_array(virt_text->data.virt_text, hl_name);
     PUT(*dict, "virt_text", ARRAY_OBJ(chunks));
     PUT(*dict, "virt_text_hide", BOOLEAN_OBJ(virt_text->flags & kVTHide));
+    PUT(*dict, "virt_text_repeat_linebreak", BOOLEAN_OBJ(virt_text->flags & kVTRepeatLinebreak));
     if (virt_text->pos == kVPosWinCol) {
       PUT(*dict, "virt_text_win_col", INTEGER_OBJ(virt_text->col));
     }
-    PUT(*dict, "virt_text_pos",
-        CSTR_TO_OBJ(virt_text_pos_str[virt_text->pos]));
+    PUT(*dict, "virt_text_pos", CSTR_TO_OBJ(virt_text_pos_str[virt_text->pos]));
     priority = virt_text->priority;
   }
 
diff --git a/src/nvim/decoration_defs.h b/src/nvim/decoration_defs.h
index d75a7bc242..93bc202b94 100644
--- a/src/nvim/decoration_defs.h
+++ b/src/nvim/decoration_defs.h
@@ -77,6 +77,7 @@ enum {
   kVTIsLines = 1,
   kVTHide = 2,
   kVTLinesAbove = 4,
+  kVTRepeatLinebreak = 8,
 };
 
 typedef struct DecorVirtText DecorVirtText;
diff --git a/src/nvim/drawline.c b/src/nvim/drawline.c
index de607e912f..885d308514 100644
--- a/src/nvim/drawline.c
+++ b/src/nvim/drawline.c
@@ -286,10 +286,12 @@ static void draw_virt_text(win_T *wp, buf_T *buf, int col_off, int *end_col, int
       int vcol = item->draw_col - col_off;
       col = draw_virt_text_item(buf, item->draw_col, vt->data.virt_text,
                                 vt->hl_mode, max_col, vcol);
+      if (vt->pos == kVPosEndOfLine && do_eol) {
+        state->eol_col = col + 1;
+      }
     }
-    item->draw_col = INT_MIN;  // deactivate
-    if (vt && vt->pos == kVPosEndOfLine && do_eol) {
-      state->eol_col = col + 1;
+    if (!vt || !(vt->flags & kVTRepeatLinebreak)) {
+      item->draw_col = INT_MIN;  // deactivate
     }
 
     *end_col = MAX(*end_col, col);
@@ -1588,7 +1590,9 @@ int win_line(win_T *wp, linenr_T lnum, int startrow, int endrow, bool number_onl
           && wlv.vcol >= wp->w_virtcol)
          || number_only)
         && wlv.filler_todo <= 0) {
-      draw_virt_text(wp, buf, win_col_offset, &wlv.col, wlv.row);
+      if (!number_only) {
+        draw_virt_text(wp, buf, win_col_offset, &wlv.col, wlv.row);
+      }
       // don't clear anything after wlv.col
       win_put_linebuf(wp, wlv.row, 0, wlv.col, wlv.col, bg_attr, false);
       // Pretend we have finished updating the window.  Except when