vim-patch:9.0.1578: SpellCap highlight not always updated when needed (#23755)

Problem:    SpellCap highlight not always updated when needed.
Solution:   Handle updating line below closed fold and other situations where
            only part of the window is redrawn. (Luuk van Baal, closes vim/vim#12428,
            closes vim/vim#12420)

https://github.com/vim/vim/commit/2ac6497f0ef186f0e3ba67d7f0a485bfb612bb08

4 files changed, 29 insertions, 27 deletions

diff --git a/src/nvim/drawline.c b/src/nvim/drawline.c
index f3332dc8a2..016a25b9d5 100644
--- a/src/nvim/drawline.c
+++ b/src/nvim/drawline.c
@@ -1028,7 +1028,7 @@ static void win_line_continue(winlinevars_T *wlv)
 /// @param lnum         line to display
 /// @param startrow     first row relative to window grid
 /// @param endrow       last grid row to be redrawn
-/// @param nochange     not updating for changed text
+/// @param mod_top      top line updated for changed text
 /// @param number_only  only update the number column
 /// @param foldinfo     fold info for this line
 /// @param[in, out] providers  decoration providers active this line
@@ -1036,7 +1036,7 @@ static void win_line_continue(winlinevars_T *wlv)
 ///                            or explicitly return `false`.
 ///
 /// @return             the number of last row the line occupies.
-int win_line(win_T *wp, linenr_T lnum, int startrow, int endrow, bool nochange, bool number_only,
+int win_line(win_T *wp, linenr_T lnum, int startrow, int endrow, int mod_top, bool number_only,
              foldinfo_T foldinfo, DecorProviders *providers, char **provider_err)
 {
   winlinevars_T wlv;                  // variables passed between functions
@@ -1227,12 +1227,16 @@ int win_line(win_T *wp, linenr_T lnum, int startrow, int endrow, bool nochange,
 
       // When there was a sentence end in the previous line may require a
       // word starting with capital in this line.  In line 1 always check
-      // the first word.
-      if (lnum != capcol_lnum) {
-        cap_col = -1;
-      }
-      if (lnum == 1) {
+      // the first word.  Also check for sentence end in the line above
+      // when updating the first row in a window, the top line with
+      // changed text in a window, or if the previous line is folded.
+      if (lnum == 1
+          || ((startrow == 0 || mod_top == lnum
+               || hasFoldingWin(wp, lnum - 1, NULL, NULL, true, NULL))
+              && check_need_cap(wp, lnum, 0))) {
         cap_col = 0;
+      } else if (lnum != capcol_lnum) {
+        cap_col = -1;
       }
       capcol_lnum = 0;
     }
@@ -2207,7 +2211,7 @@ int win_line(win_T *wp, linenr_T lnum, int startrow, int endrow, bool nochange,
               p = prev_ptr;
             }
             cap_col -= (int)(prev_ptr - line);
-            size_t tmplen = spell_check(wp, p, &spell_hlf, &cap_col, nochange);
+            size_t tmplen = spell_check(wp, p, &spell_hlf, &cap_col, mod_top == 0);
             assert(tmplen <= INT_MAX);
             int len = (int)tmplen;
             word_end = (int)v + len;
diff --git a/src/nvim/drawscreen.c b/src/nvim/drawscreen.c
index 7f7c721379..4f79ba87af 100644
--- a/src/nvim/drawscreen.c
+++ b/src/nvim/drawscreen.c
@@ -2222,9 +2222,8 @@ static void win_update(win_T *wp, DecorProviders *providers)
         }
 
         // Display one line
-        row = win_line(wp, lnum, srow,
-                       foldinfo.fi_lines ? srow : wp->w_grid.rows,
-                       mod_top == 0, false, foldinfo, &line_providers, &provider_err);
+        row = win_line(wp, lnum, srow, foldinfo.fi_lines ? srow : wp->w_grid.rows,
+                       mod_top, false, foldinfo, &line_providers, &provider_err);
 
         if (foldinfo.fi_lines == 0) {
           wp->w_lines[idx].wl_folded = false;
@@ -2261,7 +2260,7 @@ static void win_update(win_T *wp, DecorProviders *providers)
         // text doesn't need to be drawn, but the number column does.
         foldinfo_T info = wp->w_p_cul && lnum == wp->w_cursor.lnum ?
                           cursorline_fi : fold_info(wp, lnum);
-        (void)win_line(wp, lnum, srow, wp->w_grid.rows, true, true,
+        (void)win_line(wp, lnum, srow, wp->w_grid.rows, mod_top, true,
                        info, &line_providers, &provider_err);
       }
 
@@ -2359,7 +2358,7 @@ static void win_update(win_T *wp, DecorProviders *providers)
         // for ml_line_count+1 and only draw filler lines
         foldinfo_T info = { 0 };
         row = win_line(wp, wp->w_botline, row, wp->w_grid.rows,
-                       false, false, info, &line_providers, &provider_err);
+                       mod_top, false, info, &line_providers, &provider_err);
       }
     } else if (dollar_vcol == -1) {
       wp->w_botline = lnum;
diff --git a/src/nvim/spell.c b/src/nvim/spell.c
index 498bd56b9e..778266e5ac 100644
--- a/src/nvim/spell.c
+++ b/src/nvim/spell.c
@@ -1312,7 +1312,7 @@ size_t spell_move_to(win_T *wp, int dir, bool allwords, bool curline, hlf_T *att
     } else if (curline && wp == curwin) {
       // For spellbadword(): check if first word needs a capital.
       col = (colnr_T)getwhitecols(line);
-      if (check_need_cap(lnum, col)) {
+      if (check_need_cap(curwin, lnum, col)) {
         capcol = col;
       }
 
@@ -2536,25 +2536,24 @@ int spell_casefold(const win_T *wp, char *str, int len, char *buf, int buflen)
 }
 
 // Check if the word at line "lnum" column "col" is required to start with a
-// capital.  This uses 'spellcapcheck' of the current buffer.
-bool check_need_cap(linenr_T lnum, colnr_T col)
+// capital.  This uses 'spellcapcheck' of the buffer in window "wp".
+bool check_need_cap(win_T *wp, linenr_T lnum, colnr_T col)
 {
-  bool need_cap = false;
-
-  if (curwin->w_s->b_cap_prog == NULL) {
+  if (wp->w_s->b_cap_prog == NULL) {
     return false;
   }
 
-  char *line = get_cursor_line_ptr();
+  bool need_cap = false;
+  char *line = col ? ml_get_buf(wp->w_buffer, lnum, false) : NULL;
   char *line_copy = NULL;
   colnr_T endcol = 0;
-  if (getwhitecols(line) >= (int)col) {
+  if (col == 0 || getwhitecols(line) >= col) {
     // At start of line, check if previous line is empty or sentence
     // ends there.
     if (lnum == 1) {
       need_cap = true;
     } else {
-      line = ml_get(lnum - 1);
+      line = ml_get_buf(wp->w_buffer, lnum - 1, false);
       if (*skipwhite(line) == NUL) {
         need_cap = true;
       } else {
@@ -2571,13 +2570,13 @@ bool check_need_cap(linenr_T lnum, colnr_T col)
   if (endcol > 0) {
     // Check if sentence ends before the bad word.
     regmatch_T regmatch = {
-      .regprog = curwin->w_s->b_cap_prog,
+      .regprog = wp->w_s->b_cap_prog,
       .rm_ic = false
     };
     char *p = line + endcol;
     while (true) {
       MB_PTR_BACK(line, p);
-      if (p == line || spell_iswordp_nmw(p, curwin)) {
+      if (p == line || spell_iswordp_nmw(p, wp)) {
         break;
       }
       if (vim_regexec(&regmatch, p, 0)
@@ -2586,7 +2585,7 @@ bool check_need_cap(linenr_T lnum, colnr_T col)
         break;
       }
     }
-    curwin->w_s->b_cap_prog = regmatch.regprog;
+    wp->w_s->b_cap_prog = regmatch.regprog;
   }
 
   xfree(line_copy);
@@ -3601,7 +3600,7 @@ static bool spell_expand_need_cap;
 
 void spell_expand_check_cap(colnr_T col)
 {
-  spell_expand_need_cap = check_need_cap(curwin->w_cursor.lnum, col);
+  spell_expand_need_cap = check_need_cap(curwin, curwin->w_cursor.lnum, col);
 }
 
 // Get list of spelling suggestions.
diff --git a/src/nvim/spellsuggest.c b/src/nvim/spellsuggest.c
index 84be88be7b..1c34c2487f 100644
--- a/src/nvim/spellsuggest.c
+++ b/src/nvim/spellsuggest.c
@@ -509,7 +509,7 @@ void spell_suggest(int count)
   // Get the word and its length.
 
   // Figure out if the word should be capitalised.
-  int need_cap = check_need_cap(curwin->w_cursor.lnum, curwin->w_cursor.col);
+  int need_cap = check_need_cap(curwin, curwin->w_cursor.lnum, curwin->w_cursor.col);
 
   // Make a copy of current line since autocommands may free the line.
   line = xstrdup(get_cursor_line_ptr());