screen: Adjust buffer sizes for multiple sign columns #10314

* screen: Fix to draw signs with combining characters.
The buffer size for signs can be too small, because the upper length
limit of a sign can be 56 bytes. If combining characters are only two
bytes in size, this reduces to 32 bytes.

* screen: Adjust buffer size to maximal sign column count

1 files changed, 16 insertions, 4 deletions

diff --git a/src/nvim/screen.c b/src/nvim/screen.c
index 45c82d70d1..f349304468 100644
--- a/src/nvim/screen.c
+++ b/src/nvim/screen.c
@@ -1775,7 +1775,9 @@ static void fold_line(win_T *wp, long fold_count, foldinfo_T *foldinfo, linenr_T
           if (len > len_max) {
               len = len_max;
           }
-          copy_text_attr(off + col, (char_u *)"  ", len,
+          char_u space_buf[18] = "                  ";
+          assert((size_t)len_max <= sizeof(space_buf));
+          copy_text_attr(off + col, space_buf, len,
                          win_hl_attr(wp, HLF_FL));
           col += len;
       }
@@ -2061,7 +2063,8 @@ win_line (
   int row;                            // row in the window, excl w_winrow
   ScreenGrid *grid = &wp->w_grid;     // grid specfic to the window
 
-  char_u extra[18];                   // line number and 'fdc' must fit in here
+  char_u extra[57];                   // sign, line number and 'fdc' must
+                                      // fit in here
   int n_extra = 0;                    // number of extra chars
   char_u      *p_extra = NULL;        // string of extra chars, plus NUL
   char_u      *p_extra_free = NULL;   // p_extra needs to be freed
@@ -2712,15 +2715,24 @@ win_line (
                                               sign_idx, count);
                   if (text_sign != 0) {
                       p_extra = sign_get_text(text_sign);
-                      int symbol_blen = (int)STRLEN(p_extra);
                       if (p_extra != NULL) {
+                          int symbol_blen = (int)STRLEN(p_extra);
+
                           c_extra = NUL;
                           c_final = NUL;
+
+                          // TODO(oni-link): Is sign text already extended to
+                          // full cell width?
+                          assert((size_t)win_signcol_width(wp)
+                                 >= mb_string2cells(p_extra));
                           // symbol(s) bytes + (filling spaces) (one byte each)
                           n_extra = symbol_blen +
                             (win_signcol_width(wp) - mb_string2cells(p_extra));
+
+                          assert(sizeof(extra) > (size_t)symbol_blen);
                           memset(extra, ' ', sizeof(extra));
-                          STRNCPY(extra, p_extra, STRLEN(p_extra));
+                          memcpy(extra, p_extra, symbol_blen);
+
                           p_extra = extra;
                           p_extra[n_extra] = NUL;
                       }