vim-patch:8.0.0380: with 'linebreak' double wide char wraps badly

Problem:    With 'linebreak' set and 'breakat' includes ">" a double-wide
            character results in "<<" displayed.
Solution:   Check for the character not to be replaced. (Ozaki Kiichi,
            closes vim/vim#1456)

https://github.com/vim/vim/commit/38632faf635f6434441827e136bceb5a930c59ad

2 files changed, 40 insertions, 13 deletions

diff --git a/src/nvim/screen.c b/src/nvim/screen.c
index ed96e98d32..8a29734025 100644
--- a/src/nvim/screen.c
+++ b/src/nvim/screen.c
@@ -3143,14 +3143,15 @@ win_line (
       }
       --n_extra;
     } else {
+      int c0;
+
       if (p_extra_free != NULL) {
         xfree(p_extra_free);
         p_extra_free = NULL;
       }
-      /*
-       * Get a character from the line itself.
-       */
-      c = *ptr;
+
+      // Get a character from the line itself.
+      c0 = c = *ptr;
       if (has_mbyte) {
         mb_c = c;
         if (enc_utf8) {
@@ -3160,11 +3161,12 @@ win_line (
           mb_utf8 = FALSE;
           if (mb_l > 1) {
             mb_c = utfc_ptr2char(ptr, u8cc);
-            /* Overlong encoded ASCII or ASCII with composing char
-             * is displayed normally, except a NUL. */
-            if (mb_c < 0x80)
-              c = mb_c;
-            mb_utf8 = TRUE;
+            // Overlong encoded ASCII or ASCII with composing char
+            // is displayed normally, except a NUL.
+            if (mb_c < 0x80) {
+              c0 = c = mb_c;
+            }
+            mb_utf8 = true;
 
             /* At start of the line we can have a composing char.
              * Draw it as a space with a composing char. */
@@ -3428,10 +3430,8 @@ win_line (
           char_attr = hl_combine_attr(char_attr, term_attrs[vcol]);
         }
 
-        /*
-         * Found last space before word: check for line break.
-         */
-        if (wp->w_p_lbr && vim_isbreak(c) && !vim_isbreak(*ptr)) {
+        // Found last space before word: check for line break.
+        if (wp->w_p_lbr && c0 == c && vim_isbreak(c) && !vim_isbreak(*ptr)) {
           int mb_off = has_mbyte ? (*mb_head_off)(line, ptr - 1) : 0;
           char_u *p = ptr - (mb_off + 1);
           // TODO: is passing p for start of the line OK?
diff --git a/src/nvim/testdir/test_listlbr_utf8.vim b/src/nvim/testdir/test_listlbr_utf8.vim
index 980d67d49d..56a4cc9b31 100644
--- a/src/nvim/testdir/test_listlbr_utf8.vim
+++ b/src/nvim/testdir/test_listlbr_utf8.vim
@@ -194,6 +194,33 @@ func Test_multibyte_sign_and_colorcolumn()
   call s:close_windows()
 endfunc
 
+func Test_illegal_byte_and_breakat()
+  call s:test_windows("setl sbr= brk+=<")
+  vert resize 18
+  call setline(1, repeat("\x80", 6))
+  redraw!
+  let lines = s:screen_lines([1, 2], winwidth(0))
+  let expect = [
+\ "<80><80><80><80><8",
+\ "0><80>            ",
+\ ]
+  call s:compare_lines(expect, lines)
+  call s:close_windows('setl brk&vim')
+endfunc
+
+func Test_multibyte_wrap_and_breakat()
+  call s:test_windows("setl sbr= brk+=>")
+  call setline(1, repeat('a', 17) . repeat('あ', 2))
+  redraw!
+  let lines = s:screen_lines([1, 2], winwidth(0))
+  let expect = [
+\ "aaaaaaaaaaaaaaaaaあ>",
+\ "あ                  ",
+\ ]
+  call s:compare_lines(expect, lines)
+  call s:close_windows('setl brk&vim')
+endfunc
+
 func Test_chinese_char_on_wrap_column()
   call s:test_windows("setl nolbr wrap sbr=")
   syntax off