vim-patch:8.2.4929: off-by-one error in in statusline item

Problem:    Off-by-one error in in statusline item.
Solution:   Subtrace one less. (closes vim/vim#10394, closes vim/vim#5599)
57ff52677b

src/nvim/buffer.c

@@ -3635,7 +3635,8 @@ int build_stl_str_hl(win_T *wp, char *out, size_t outlen, char *fmt, int use_san
         // correct the start of the items for the truncation
         for (int idx = stl_groupitems[groupdepth] + 1; idx < curitem; idx++) {
           // Shift everything back by the number of removed bytes
-          stl_items[idx].start -= n;
+          // Minus one for the leading '<' added above.
+          stl_items[idx].start -= n - 1;
 
           // If the item was partially or completely truncated, set its
           // start to the start of the group

src/nvim/testdir/test_statusline.vim

@@ -461,7 +461,6 @@ func Test_statusline_removed_group()
   call writefile(lines, 'XTest_statusline')
 
   let buf = RunVimInTerminal('-S XTest_statusline', {'rows': 10, 'cols': 50})
-  call term_wait(buf, 100)
   call VerifyScreenDump(buf, 'Test_statusline_1', {})
 
   " clean up
@@ -535,4 +534,22 @@ func Test_statusline_verylong_filename()
   bwipe!
 endfunc
 
+func Test_statusline_highlight_truncate()
+  CheckScreendump
+
+  let lines =<< trim END
+    set laststatus=2
+    hi! link User1 Directory
+    hi! link User2 ErrorMsg
+    set statusline=%.5(%1*ABC%2*DEF%1*GHI%)
+  END
+  call writefile(lines, 'XTest_statusline')
+
+  let buf = RunVimInTerminal('-S XTest_statusline', {'rows': 6})
+  call VerifyScreenDump(buf, 'Test_statusline_hl', {})
+
+  call StopVimInTerminal(buf)
+  call delete('XTest_statusline')
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab