feat(statusline): support multibyte fillchar

This includes a partial port of Vim patch 8.2.2569 and some changes to
nvim_eval_statusline() to allow a multibyte fillchar. Literally every
line of C code touched by that patch has been refactored in Nvim, and
that patch contains some irrelevant foldcolumn tests I'm not sure how to
port (as Nvim's foldcolumn behavior has diverged from Vim's).

1 files changed, 8 insertions, 7 deletions

diff --git a/src/nvim/api/vim.c b/src/nvim/api/vim.c
index 59db12f2c0..7ef8faa67e 100644
--- a/src/nvim/api/vim.c
+++ b/src/nvim/api/vim.c
@@ -19,6 +19,7 @@
 #include "nvim/ascii.h"
 #include "nvim/buffer.h"
 #include "nvim/buffer_defs.h"
+#include "nvim/charset.h"
 #include "nvim/context.h"
 #include "nvim/decoration.h"
 #include "nvim/edit.h"
@@ -2234,7 +2235,7 @@ Dictionary nvim_eval_statusline(String str, Dict(eval_statusline) *opts, Error *
   Dictionary result = ARRAY_DICT_INIT;
 
   int maxwidth;
-  char fillchar = 0;
+  int fillchar = 0;
   Window window = 0;
   bool use_tabline = false;
   bool highlights = false;
@@ -2249,12 +2250,12 @@ Dictionary nvim_eval_statusline(String str, Dict(eval_statusline) *opts, Error *
   }
 
   if (HAS_KEY(opts->fillchar)) {
-    if (opts->fillchar.type != kObjectTypeString || opts->fillchar.data.string.size > 1) {
-      api_set_error(err, kErrorTypeValidation, "fillchar must be an ASCII character");
+    if (opts->fillchar.type != kObjectTypeString || opts->fillchar.data.string.size == 0
+        || char2cells(fillchar = utf_ptr2char((char_u *)opts->fillchar.data.string.data)) != 1
+        || (size_t)utf_char2len(fillchar) != opts->fillchar.data.string.size) {
+      api_set_error(err, kErrorTypeValidation, "fillchar must be a single-width character");
       return result;
     }
-
-    fillchar = opts->fillchar.data.string.data[0];
   }
 
   if (HAS_KEY(opts->highlights)) {
@@ -2285,7 +2286,7 @@ Dictionary nvim_eval_statusline(String str, Dict(eval_statusline) *opts, Error *
 
     if (fillchar == 0) {
       int attr;
-      fillchar = (char)fillchar_status(&attr, wp);
+      fillchar = fillchar_status(&attr, wp);
     }
   }
 
@@ -2313,7 +2314,7 @@ Dictionary nvim_eval_statusline(String str, Dict(eval_statusline) *opts, Error *
                                sizeof(buf),
                                (char_u *)str.data,
                                false,
-                               (char_u)fillchar,
+                               fillchar,
                                maxwidth,
                                hltab_ptr,
                                NULL);