fix(normal): fix segfault with bracket command jumping to a mark

vim-patch:9.0.0043: insufficient testing for bracket commands

Problem:    Insufficient testing for bracket commands.
Solution:   Add a few more tests. (closes vim/vim#10668)
cf34434b5e

Cherry-pick a change from patch 8.2.0369.

src/nvim/normal.c

@@ -5011,8 +5011,6 @@ static void nv_bracket_block(cmdarg_T *cap, const pos_T *old_pos)
 /// cap->arg is BACKWARD for "[" and FORWARD for "]".
 static void nv_brackets(cmdarg_T *cap)
 {
-  pos_T prev_pos;
-  pos_T *pos = NULL;          // init for GCC
   pos_T old_pos;                    // cursor position before command
   int flag;
   long n;
@@ -5091,19 +5089,19 @@ static void nv_brackets(cmdarg_T *cap)
     nv_put_opt(cap, true);
   } else if (cap->nchar == '\'' || cap->nchar == '`') {
     // "['", "[`", "]'" and "]`": jump to next mark
-    fmark_T *fm = NULL;
+    fmark_T *fm = pos_to_mark(curbuf, NULL, curwin->w_cursor);
-    pos = &curwin->w_cursor;
+    fmark_T *prev_fm;
     for (n = cap->count1; n > 0; n--) {
-      prev_pos = *pos;
+      prev_fm = fm;
-      fm = getnextmark(pos, cap->cmdchar == '[' ? BACKWARD : FORWARD,
+      fm = getnextmark(&fm->mark, cap->cmdchar == '[' ? BACKWARD : FORWARD,
                        cap->nchar == '\'');
-      if (pos == NULL) {
+      if (fm == NULL) {
         break;
-      } else {
-        pos = fm != NULL ? &fm->mark : NULL;  // Adjust for the next iteration.
       }
     }
-    fm = fm == NULL ? pos_to_mark(curbuf, NULL, curwin->w_cursor) : fm;
+    if (fm == NULL) {
+      fm = prev_fm;
+    }
     MarkMove flags = kMarkContext;
     flags |= cap->nchar == '\'' ? kMarkBeginLine: 0;
     nv_mark_move_to(cap, flags, fm);

src/nvim/testdir/test_normal.vim

@@ -1422,9 +1422,16 @@ func Test_normal27_bracket()
   call assert_equal(5, line('.'))
   call assert_equal(3, col('.'))
 
-  " No mark after line 21, cursor moves to first non blank on current line
+  " No mark before line 1, cursor moves to first non-blank on current line
+  1
+  norm! 5|['
+  call assert_equal('  1   b', getline('.'))
+  call assert_equal(1, line('.'))
+  call assert_equal(3, col('.'))
+
+  " No mark after line 21, cursor moves to first non-blank on current line
   21
-  norm! $]'
+  norm! 5|]'
   call assert_equal('  21   b', getline('.'))
   call assert_equal(21, line('.'))
   call assert_equal(3, col('.'))
@@ -1441,12 +1448,40 @@ func Test_normal27_bracket()
   call assert_equal(20, line('.'))
   call assert_equal(8, col('.'))
 
+  " No mark before line 1, cursor does not move
+  1
+  norm! 5|[`
+  call assert_equal('  1   b', getline('.'))
+  call assert_equal(1, line('.'))
+  call assert_equal(5, col('.'))
+
+  " No mark after line 21, cursor does not move
+  21
+  norm! 5|]`
+  call assert_equal('  21   b', getline('.'))
+  call assert_equal(21, line('.'))
+  call assert_equal(5, col('.'))
+
+  " Count too large for [`
+  " cursor moves to first lowercase mark
+  norm! 99[`
+  call assert_equal('  1   b', getline('.'))
+  call assert_equal(1, line('.'))
+  call assert_equal(7, col('.'))
+
+  " Count too large for ]`
+  " cursor moves to last lowercase mark
+  norm! 99]`
+  call assert_equal('  20   b', getline('.'))
+  call assert_equal(20, line('.'))
+  call assert_equal(8, col('.'))
+
   " clean up
   bw!
 endfunc
 
+" Test for ( and ) sentence movements
 func Test_normal28_parenthesis()
-  " basic testing for ( and )
   new
   call append(0, ['This is a test. With some sentences!', '', 'Even with a question? And one more. And no sentence here'])