Add the ability to title floating windows.

The window title is set using the {title} key on the FloatConfig.

The window title allows for 3 different positions as defined
by the {title_position} key in the FloatConfig:
  - left
  - center
  - right

The title also supports StatusLine-style highlighting using
the %#<HL># keys.

1 files changed, 49 insertions, 2 deletions

diff --git a/src/nvim/screen.c b/src/nvim/screen.c
index 79e960fe8b..0a75e2d09f 100644
--- a/src/nvim/screen.c
+++ b/src/nvim/screen.c
@@ -5567,17 +5567,64 @@ static void win_redr_border(win_T *wp)
   schar_T *chars = wp->w_float_config.border_chars;
   int *attrs = wp->w_float_config.border_attr;
 
-
   int *adj = wp->w_border_adj;
   int irow = wp->w_height_inner, icol = wp->w_width_inner;
 
+  char_u* title = wp->w_float_config.title;
+  size_t n_title = wp->w_float_config.n_title;
+  stl_hlrec_t* title_hl = wp->w_float_config.title_hl;
+
+  int m8[MAX_MCO + 1];
+  int cc;
+  int len;
+  int t_attr = title_hl != NULL && title_hl->userhl
+                  ? syn_id2attr(title_hl->userhl)
+                  : 0;
+  t_attr = hl_combine_attr(attrs[1], t_attr);
+
+  int title_pos = 2;
+  switch (wp->w_float_config.title_pos) {
+    case kTitleLeft:
+      title_pos = 2;
+      break;
+    case kTitleRight:
+      title_pos = icol - 2 - vim_strsize(title);
+      break;
+    case kTitleCenter:
+      title_pos = (icol - vim_strsize(title)) / 2 - 1;
+      break;
+  }
+  title_pos = title_pos < 2 ? 2 : title_pos;
+
   if (adj[0]) {
     grid_puts_line_start(grid, 0);
     if (adj[3]) {
       grid_put_schar(grid, 0, 0, chars[0], attrs[0]);
     }
     for (int i = 0; i < icol; i++) {
-      grid_put_schar(grid, 0, i+adj[3], chars[1], attrs[1]);
+      schar_T ch;
+      int attr;
+      // Draw the title if in the correct position.
+      if (i > title_pos && n_title > 0 && i < icol - 2) {
+        cc = utfc_ptr2char(title, m8);
+        len = utfc_ptr2len(title);
+        n_title -= len;
+        title += len;
+
+        while (title_hl != NULL &&
+               (title_hl + 1)->start != NULL &&
+               (title_hl + 1)->start < title) {
+          ++ title_hl;
+          t_attr = hl_combine_attr(attrs[1], syn_id2attr(-title_hl->userhl));
+        }
+
+        schar_from_cc(ch, cc, m8);
+        attr = t_attr;
+      } else {
+        memcpy(ch, chars[1], sizeof(schar_T));
+        attr = attrs[1];
+      }
+      grid_put_schar(grid, 0, i+adj[3], ch, attr);
     }
     if (adj[1]) {
       grid_put_schar(grid, 0, icol+adj[3], chars[2], attrs[2]);