patch 9.0.1578: SpellCap highlight not always updated when needed

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 #12428,
            closes #12420)

src/drawline.c

@@ -1062,7 +1062,7 @@ win_line(
     linenr_T	lnum,
     int		startrow,
     int		endrow,
-    int		nochange UNUSED,	// not updating for changed text
+    int		mod_top UNUSED,	        // top line updated for changed text
     int		number_only)		// only update the number column
 {
     winlinevars_T	wlv;		// variables passed between functions
@@ -1314,11 +1314,18 @@ win_line(
 
 	    // 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
+#ifdef FEAT_FOLDING
+			|| hasFoldingWin(wp, lnum - 1, NULL, NULL, TRUE, NULL)
+#endif
+			) && check_need_cap(wp, lnum, 0)))
 		cap_col = 0;
+	    else if (lnum != capcol_lnum)
+		cap_col = -1;
 	    capcol_lnum = 0;
 	}
 #endif
@@ -2787,7 +2794,7 @@ win_line(
 			    p = prev_ptr;
 			cap_col -= (int)(prev_ptr - line);
 			len = spell_check(wp, p, &spell_hlf, &cap_col,
-								    nochange);
+								mod_top == 0);
 			word_end = v + len;
 
 			// In Insert mode only highlight a word that

src/drawscreen.c

@@ -2487,8 +2487,7 @@ win_update(win_T *wp)
 #endif
 
 		// Display one line.
-		row = win_line(wp, lnum, srow, wp->w_height,
-							  mod_top == 0, FALSE);
+		row = win_line(wp, lnum, srow, wp->w_height, mod_top, FALSE);
 
 #ifdef FEAT_FOLDING
 		wp->w_lines[idx].wl_folded = FALSE;
@@ -2535,7 +2534,7 @@ win_update(win_T *wp)
 		    fold_line(wp, fold_count, &win_foldinfo, lnum, row);
 		else
 #endif
-		    (void)win_line(wp, lnum, srow, wp->w_height, TRUE, TRUE);
+		    (void)win_line(wp, lnum, srow, wp->w_height, mod_top, TRUE);
 	    }
 
 	    // This line does not need to be drawn, advance to the next one.

src/proto/spell.pro

@@ -28,7 +28,7 @@ void init_spell_chartab(void);
 int spell_iswordp(char_u *p, win_T *wp);
 int spell_iswordp_nmw(char_u *p, win_T *wp);
 int spell_casefold(win_T *wp, char_u *str, int len, char_u *buf, int buflen);
-int check_need_cap(linenr_T lnum, colnr_T col);
+int check_need_cap(win_T *wp, linenr_T lnum, colnr_T col);
 void ex_spellrepall(exarg_T *eap);
 void onecap_copy(char_u *word, char_u *wcopy, int upper);
 void allcap_copy(char_u *word, char_u *wcopy);

src/spell.c

@@ -1342,7 +1342,7 @@ spell_move_to(
 	{
 	    // For spellbadword(): check if first word needs a capital.
 	    col = getwhitecols(line);
-	    if (check_need_cap(lnum, col))
+	    if (check_need_cap(curwin, lnum, col))
 		capcol = col;
 
 	    // Need to get the line again, may have looked at the previous
@@ -2815,24 +2815,20 @@ spell_casefold(
 
 /*
  * Check if the word at line "lnum" column "col" is required to start with a
- * capital.  This uses 'spellcapcheck' of the current buffer.
+ * capital.  This uses 'spellcapcheck' of the buffer in window "wp".
  */
     int
-check_need_cap(linenr_T lnum, colnr_T col)
+check_need_cap(win_T *wp, linenr_T lnum, colnr_T col)
 {
-    int		need_cap = FALSE;
-    char_u	*line;
-    char_u	*line_copy = NULL;
-    char_u	*p;
-    colnr_T	endcol;
-    regmatch_T	regmatch;
-
-    if (curwin->w_s->b_cap_prog == NULL)
+    if (wp->w_s->b_cap_prog == NULL)
 	return FALSE;
 
-    line = ml_get_curline();
-    endcol = 0;
-    if (getwhitecols(line) >= (int)col)
+    int		need_cap = FALSE;
+    char_u	*line = col ? ml_get_buf(wp->w_buffer, lnum, FALSE) : NULL;
+    char_u	*line_copy = NULL;
+    colnr_T	endcol = 0;
+
+    if (col == 0 || getwhitecols(line) >= col)
     {
 	// At start of line, check if previous line is empty or sentence
 	// ends there.
@@ -2840,13 +2836,16 @@ check_need_cap(linenr_T lnum, colnr_T col)
 	    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
 	    {
 		// Append a space in place of the line break.
 		line_copy = concat_str(line, (char_u *)" ");
+		if (line_copy == NULL)
+		    return FALSE;
+
 		line = line_copy;
 		endcol = (colnr_T)STRLEN(line);
 	    }
@@ -2858,13 +2857,14 @@ check_need_cap(linenr_T lnum, colnr_T col)
     if (endcol > 0)
     {
 	// Check if sentence ends before the bad word.
-	regmatch.regprog = curwin->w_s->b_cap_prog;
+	regmatch_T	regmatch;
+	regmatch.regprog = wp->w_s->b_cap_prog;
 	regmatch.rm_ic = FALSE;
-	p = line + endcol;
+	char_u *p = line + endcol;
 	for (;;)
 	{
 	    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)
 					 && regmatch.endp[0] == line + endcol)
@@ -2873,7 +2873,7 @@ 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;
     }
 
     vim_free(line_copy);
@@ -4340,7 +4340,7 @@ static int 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);
 }
 
 /*

src/spellsuggest.c

@@ -538,7 +538,8 @@ spell_suggest(int count)
     // Get the word and its length.
 
     // Figure out if the word should be capitalised.
-    need_cap = check_need_cap(curwin->w_cursor.lnum, curwin->w_cursor.col);
+    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 = vim_strsave(ml_get_curline());

src/testdir/dumps/Test_spell_6.dump

@@ -0,0 +1,8 @@
+| +0&#ffffff0@2|T|h|i|s| |l|i|n|e| |h|a|s| |a| |s+0&#ffd7d7255|e|p|l@1| +0&#ffffff0|e|r@1|o|r|.| |a+0&#5fd7ff255|n|d| +0&#ffffff0|m|i|s@1|i|n|g| |c|a|p|s| |a|n|d| |t|r|a|i|l|i|n|g| |s|p|a|c|e|s|.| @5
+|a+0&#5fd7ff255|n|o|t|h|e|r| +0&#ffffff0|m|i|s@1|i|n|g| |c|a|p| |h|e|r|e|.| @49
+|N|o|t| @71
+>++0#0000e05#a8a8a8255|-@1| @1|2| |l|i|n|e|s|:| |a|n|d| |h|e|r|e|.|-@51
+|a+0#0000000#5fd7ff255|n|d| +0&#ffffff0|h|e|r|e|.| @65
+|~+0#4040ff13&| @73
+|~| @73
+| +0#0000000&@56|4|,|4|-|1| @8|A|l@1| 

src/testdir/dumps/Test_spell_7.dump

@@ -0,0 +1,8 @@
+| +0&#ffffff0@2|T|h|i|s| |l|i|n|e| |h|a|s| |a| |s+0&#ffd7d7255|e|p|l@1| +0&#ffffff0|e|r@1|o|r|.| |a+0&#5fd7ff255|n|d| +0&#ffffff0|m|i|s@1|i|n|g| |c|a|p|s| |a|n|d| |t|r|a|i|l|i|n|g| |s|p|a|c|e|s|.| @5
+|a+0&#5fd7ff255|n|o|t|h|e|r| +0&#ffffff0|m|i|s@1|i|n|g| |c|a|p| |h|e|r>e| @50
+|++0#0000e05#a8a8a8255|-@1| @1|2| |l|i|n|e|s|:| |N|o|t|-@57
+|a+0#0000000#5fd7ff255|n|d| +0&#ffffff0|h|e|r|e|.| @65
+|~+0#4040ff13&| @73
+|~| @73
+|~| @73
+| +0#0000000&@56|2|,|2|4| @9|A|l@1| 

src/testdir/dumps/Test_spell_8.dump

@@ -0,0 +1,8 @@
+|a+0&#5fd7ff255|n|o|t|h|e|r| +0&#ffffff0|m|i|s@1|i|n|g| |c|a|p| |h|e|r|e| @50
+|++0#0000e05#a8a8a8255|-@1| @1|2| |l|i|n|e|s|:| |N|o|t|-@57
+|a+0#0000000#5fd7ff255|n|d| +0&#ffffff0|h|e|r|e>.| @65
+|~+0#4040ff13&| @73
+|~| @73
+|~| @73
+|~| @73
+| +0#0000000&@56|5|,|9| @10|B|o|t| 

src/testdir/test_spell.vim

@@ -999,13 +999,26 @@ func Test_spell_screendump_spellcap()
   call VerifyScreenDump(buf, 'Test_spell_3', {})
 
   " Deleting a full stop removes missing Cap in next line
-  call term_sendkeys(buf, "5Gddk$x")
+  call term_sendkeys(buf, "5Gdd\<C-L>k$x")
   call VerifyScreenDump(buf, 'Test_spell_4', {})
 
   " Undo also updates the next line (go to command line to remove message)
   call term_sendkeys(buf, "u:\<Esc>")
   call VerifyScreenDump(buf, 'Test_spell_5', {})
 
+  " Folding an empty line does not remove Cap in next line
+  call term_sendkeys(buf, "uzfk:\<Esc>")
+  call VerifyScreenDump(buf, 'Test_spell_6', {})
+
+  " Folding the end of a sentence does not remove Cap in next line
+  " and editing a line does not remove Cap in current line
+  call term_sendkeys(buf, "Jzfkk$x")
+  call VerifyScreenDump(buf, 'Test_spell_7', {})
+
+  " Cap is correctly applied in the first row of a window
+  call term_sendkeys(buf, "\<C-E>\<C-L>")
+  call VerifyScreenDump(buf, 'Test_spell_8', {})
+
   " clean up
   call StopVimInTerminal(buf)
 endfunc

src/version.c

@@ -695,6 +695,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1578,
 /**/
     1577,
 /**/