vim-patch:8.1.2294: cursor pos wrong with concealing and search causes a scroll

Problem:    Cursor position wrong when characters are concealed and asearch
            causes a scroll.
Solution:   Fix the cursor column in a concealed line after window scroll.
            (closes vim/vim#5215, closes vim/vim#5012)
cbee635eee

src/nvim/screen.c

@@ -698,8 +698,10 @@ static void win_update(win_T *wp)
   int didline = FALSE;           /* if TRUE, we finished the last line */
   int i;
   long j;
-  static int recursive = FALSE;         /* being called recursively */
-  int old_botline = wp->w_botline;
+  static bool recursive = false;  // being called recursively
+  const linenr_T old_botline = wp->w_botline;
+  const int old_wrow = wp->w_wrow;
+  const int old_wcol = wp->w_wcol;
   // Remember what happened to the previous line.
 #define DID_NONE 1      // didn't update a line
 #define DID_LINE 2      // updated a normal line
@@ -1639,18 +1641,51 @@ static void win_update(win_T *wp)
     wp->w_valid |= VALID_BOTLINE;
     wp->w_viewport_invalid = true;
     if (wp == curwin && wp->w_botline != old_botline && !recursive) {
-      recursive = TRUE;
+      const linenr_T old_topline = wp->w_topline;
+      const int new_wcol = wp->w_wcol;
+      recursive = true;
       curwin->w_valid &= ~VALID_TOPLINE;
-      update_topline();         /* may invalidate w_botline again */
-      if (must_redraw != 0) {
-        /* Don't update for changes in buffer again. */
+      update_topline();  // may invalidate w_botline again
+
+      if (old_wcol != new_wcol
+          && (wp->w_valid & (VALID_WCOL|VALID_WROW))
+          != (VALID_WCOL|VALID_WROW)) {
+        // A win_line() call applied a fix to screen cursor column to
+        // accomodate concealment of cursor line, but in this call to
+        // update_topline() the cursor's row or column got invalidated.
+        // If they are left invalid, setcursor() will recompute them
+        // but there won't be any further win_line() call to re-fix the
+        // column and the cursor will end up misplaced.  So we call
+        // cursor validation now and reapply the fix again (or call
+        // win_line() to do it for us).
+        validate_cursor();
+        if (wp->w_wcol == old_wcol
+            && wp->w_wrow == old_wrow
+            && old_topline == wp->w_topline) {
+          wp->w_wcol = new_wcol;
+        } else {
+          redrawWinline(wp, wp->w_cursor.lnum);
+        }
+      }
+      // New redraw either due to updated topline or due to wcol fix.
+      if (wp->w_redr_type != 0) {
+        // Don't update for changes in buffer again.
         i = curbuf->b_mod_set;
         curbuf->b_mod_set = false;
+        j = curbuf->b_mod_xlines;
+        curbuf->b_mod_xlines = 0;
         win_update(curwin);
-        must_redraw = 0;
         curbuf->b_mod_set = i;
+        curbuf->b_mod_xlines = j;
       }
-      recursive = FALSE;
+      // Other windows might have w_redr_type raised in update_topline().
+      must_redraw = 0;
+      FOR_ALL_WINDOWS_IN_TAB(wwp, curtab) {
+        if (wwp->w_redr_type > must_redraw) {
+          must_redraw = wwp->w_redr_type;
+        }
+      }
+      recursive = false;
     }
   }
 

src/nvim/testdir/test_matchadd_conceal.vim

@@ -1,9 +1,11 @@
 " Test for matchadd() and conceal feature
-if !has('conceal')
-  finish
-endif
+
+source check.vim
+CheckFeature conceal
 
 source shared.vim
+source term_util.vim
+source view_util.vim
 
 function! Test_simple_matchadd()
   new
@@ -273,3 +275,40 @@ function! Test_matchadd_and_syn_conceal()
   call assert_notequal(screenattr(1, 11) , screenattr(1, 12))
   call assert_equal(screenattr(1, 11) , screenattr(1, 32))
 endfunction
+
+func Test_cursor_column_in_concealed_line_after_window_scroll()
+  CheckRunVimInTerminal
+
+  " Test for issue #5012 fix.
+  " For a concealed line with cursor, there should be no window's cursor
+  " position invalidation during win_update() after scrolling attempt that is
+  " not successful and no real topline change happens. The invalidation would
+  " cause a window's cursor position recalc outside of win_line() where it's
+  " not possible to take conceal into account.
+  let lines =<< trim END
+    3split
+    let m = matchadd('Conceal', '=')
+    setl conceallevel=2 concealcursor=nc
+    normal gg
+    "==expr==
+  END
+  call writefile(lines, 'Xcolesearch')
+  let buf = RunVimInTerminal('Xcolesearch', {})
+
+  " Jump to something that is beyond the bottom of the window,
+  " so there's a scroll down.
+  call term_sendkeys(buf, ":so %\<CR>")
+  call term_sendkeys(buf, "/expr\<CR>")
+  call term_wait(buf)
+
+  " Are the concealed parts of the current line really hidden?
+  let cursor_row = term_scrape(buf, '.')->map({_, e -> e.chars})->join('')
+  call assert_equal('"expr', cursor_row)
+
+  " BugFix check: Is the window's cursor column properly updated for hidden
+  " parts of the current line?
+  call assert_equal(2, term_getcursor(buf)[1])
+
+  call StopVimInTerminal(buf)
+  call delete('Xcolesearch')
+endfunc