vim-patch:9.0.1595: line pointer becomes invalid when using spell checking

Problem:    Line pointer becomes invalid when using spell checking.
Solution:   Call ml_get() at the right places. (Luuk van Baal, closes vim/vim#12456)

e84c773d42

src/nvim/drawline.c

@@ -1377,9 +1377,6 @@ int win_line(win_T *wp, linenr_T lnum, int startrow, int endrow, bool number_onl
     line_attr_lowprio_save = wlv.line_attr_lowprio;
   }
 
-  line = end_fill ? "" : ml_get_buf(wp->w_buffer, lnum, false);
-  ptr = line;
-
   if (spv->spv_has_spell && !number_only) {
     // Prepare for spell checking.
     extra_check = true;
@@ -1389,28 +1386,36 @@ int win_line(win_T *wp, linenr_T lnum, int startrow, int endrow, bool number_onl
     if (lnum == spv->spv_checked_lnum) {
       cur_checked_col = spv->spv_checked_col;
     }
-    if (lnum != spv->spv_capcol_lnum) {
+    // Previous line was not spell checked, check for capital. This happens
+    // for the first line in an updated region or after a closed fold.
+    if (spv->spv_capcol_lnum == 0 && check_need_cap(wp, lnum, 0)) {
+      spv->spv_cap_col = 0;
+    } else if (lnum != spv->spv_capcol_lnum) {
       spv->spv_cap_col = -1;
     }
     spv->spv_checked_lnum = 0;
 
-    // For checking first word with a capital skip white space.
-    if (spv->spv_cap_col == 0) {
-      spv->spv_cap_col = (int)getwhitecols(line);
-    } else if (*skipwhite(line) == NUL) {
-      // If current line is empty, check first word in next line for capital.
-      spv->spv_cap_col = 0;
-      spv->spv_capcol_lnum = lnum + 1;
-    }
-
     // Get the start of the next line, so that words that wrap to the
     // next line are found too: "et<line-break>al.".
     // Trick: skip a few chars for C/shell/Vim comments
     nextline[SPWORDLEN] = NUL;
     if (lnum < wp->w_buffer->b_ml.ml_line_count) {
-      spell_cat_line(nextline + SPWORDLEN,
-                     ml_get_buf(wp->w_buffer, lnum + 1, false), SPWORDLEN);
+      line = ml_get_buf(wp->w_buffer, lnum + 1, false);
+      spell_cat_line(nextline + SPWORDLEN, line, SPWORDLEN);
     }
+    line = end_fill ? "" : ml_get_buf(wp->w_buffer, lnum, false);
+
+    // If current line is empty, check first word in next line for capital.
+    ptr = skipwhite(line);
+    if (*ptr == NUL) {
+      spv->spv_cap_col = 0;
+      spv->spv_capcol_lnum = lnum + 1;
+    }
+    // For checking first word with a capital skip white space.
+    else if (spv->spv_cap_col == 0) {
+      spv->spv_cap_col = (int)(ptr - line);
+    }
+
     // Copy the end of the current line into nextline[].
     if (nextline[SPWORDLEN] == NUL) {
       // No next line or it is empty.
@@ -1434,6 +1439,9 @@ int win_line(win_T *wp, linenr_T lnum, int startrow, int endrow, bool number_onl
     }
   }
 
+  line = end_fill ? "" : ml_get_buf(wp->w_buffer, lnum, false);
+  ptr = line;
+
   colnr_T trailcol = MAXCOL;  // start of trailing spaces
   colnr_T leadcol = 0;        // start of leading spaces
 

src/nvim/drawscreen.c

@@ -1995,11 +1995,9 @@ static void win_update(win_T *wp, DecorProviders *providers)
   spellvars_T spv = { 0 };
   linenr_T lnum = wp->w_topline;  // first line shown in window
   // Initialize spell related variables for the first drawn line.
-  spv.spv_has_spell = spell_check_window(wp);
-  if (spv.spv_has_spell) {
+  if (spell_check_window(wp)) {
+    spv.spv_has_spell = true;
     spv.spv_unchanged = mod_top == 0;
-    spv.spv_capcol_lnum = mod_top ? mod_top : lnum;
-    spv.spv_cap_col = check_need_cap(wp, spv.spv_capcol_lnum, 0) ? 0 : -1;
   }
 
   // Update all the window rows.
@@ -2242,16 +2240,10 @@ static void win_update(win_T *wp, DecorProviders *providers)
           syntax_last_parsed = lnum;
         } else {
           foldinfo.fi_lines--;
-          linenr_T lnume = lnum + foldinfo.fi_lines;
           wp->w_lines[idx].wl_folded = true;
-          wp->w_lines[idx].wl_lastlnum = lnume;
-
-          // Check if the line after this fold requires a capital.
-          if (spv.spv_has_spell && check_need_cap(wp, lnume + 1, 0)) {
-            spv.spv_cap_col = 0;
-            spv.spv_capcol_lnum = lnume + 1;
-          }
+          wp->w_lines[idx].wl_lastlnum = lnum + foldinfo.fi_lines;
           did_update = DID_FOLD;
+          spv.spv_capcol_lnum = 0;
         }
       }
 
@@ -2288,6 +2280,7 @@ static void win_update(win_T *wp, DecorProviders *providers)
       }
       lnum = wp->w_lines[idx - 1].wl_lastlnum + 1;
       did_update = DID_NONE;
+      spv.spv_capcol_lnum = 0;
     }
 
     // 'statuscolumn' width has changed or errored, start from the top.

test/functional/ui/spell_spec.lua

@@ -178,6 +178,30 @@ describe("'spell'", function()
       {0:~                                                                               }|
                                                                                       |
     ]])
+    -- Adding an empty line does not remove Cap in "mod_bot" area
+    feed('zbO<Esc>')
+    screen:expect([[
+         This line has a {1:sepll} error. {2:and} missing caps and trailing spaces.           |
+      ^                                                                                |
+      {2:another} missing cap here                                                        |
+      {10:+--  2 lines: Not·······························································}|
+      {2:and} here.                                                                       |
+      {0:~                                                                               }|
+      {0:~                                                                               }|
+                                                                                      |
+    ]])
+    -- Multiple empty lines does not remove Cap in the line after
+    feed('O<Esc><C-L>')
+    screen:expect([[
+         This line has a {1:sepll} error. {2:and} missing caps and trailing spaces.           |
+      ^                                                                                |
+                                                                                      |
+      {2:another} missing cap here                                                        |
+      {10:+--  2 lines: Not·······························································}|
+      {2:and} here.                                                                       |
+      {0:~                                                                               }|
+                                                                                      |
+    ]])
   end)
 
   -- oldtest: Test_spell_compatible()

test/old/testdir/test_spell.vim

@@ -962,6 +962,7 @@ func Test_spell_screendump()
   CheckScreendump
 
   let lines =<< trim END
+       call test_override('alloc_lines', 1)
        call setline(1, [
              \ "This is some text without any spell errors.  Everything",
              \ "should just be black, nothing wrong here.",
@@ -984,6 +985,7 @@ func Test_spell_screendump_spellcap()
   CheckScreendump
 
   let lines =<< trim END
+       call test_override('alloc_lines', 1)
        call setline(1, [
              \ "   This line has a sepll error. and missing caps and trailing spaces.   ",
              \ "another missing cap here.",
@@ -1023,6 +1025,14 @@ func Test_spell_screendump_spellcap()
   call term_sendkeys(buf, "\<C-E>\<C-L>")
   call VerifyScreenDump(buf, 'Test_spell_8', {})
 
+  " Adding an empty line does not remove Cap in "mod_bot" area
+  call term_sendkeys(buf, "zbO\<Esc>")
+  call VerifyScreenDump(buf, 'Test_spell_9', {})
+
+  " Multiple empty lines does not remove Cap in the line after
+  call term_sendkeys(buf, "O\<Esc>\<C-L>")
+  call VerifyScreenDump(buf, 'Test_spell_10', {})
+
   " clean up
   call StopVimInTerminal(buf)
 endfunc
@@ -1031,6 +1041,7 @@ func Test_spell_compatible()
   CheckScreendump
 
   let lines =<< trim END
+       call test_override('alloc_lines', 1)
        call setline(1, [
              \ "test "->repeat(20),
              \ "",