vim-patch:9.0.0138: not enough characters accepted for 'spellfile'

Problem:    Not enough characters accepted for 'spellfile'.
Solution:   Add vim_is_fname_char() and use it for 'spellfile'.

bc49c5f48f

Cherry-pick related doc update from Vim runtime.

Co-authored-by: Bram Moolenaar <Bram@vim.org>

src/nvim/charset.c

@@ -858,8 +858,10 @@ bool vim_iswordp_buf(const char *const p, buf_T *const buf)
   return vim_iswordc_buf(c, buf);
 }
 
-/// Check that "c" is a valid file-name character.
+/// Check that "c" is a valid file-name character as specified with the
+/// 'isfname' option.
 /// Assume characters above 0x100 are valid (multi-byte).
+/// To be used for commands like "gf".
 ///
 /// @param  c  character to check
 bool vim_isfilec(int c)
@@ -868,6 +870,14 @@ bool vim_isfilec(int c)
   return c >= 0x100 || (c > 0 && (g_chartab[c] & CT_FNAME_CHAR));
 }
 
+/// Check if "c" is a valid file-name character, including characters left
+/// out of 'isfname' to make "gf" work, such as comma, space, '@', etc.
+bool vim_is_fname_char(int c)
+  FUNC_ATTR_PURE FUNC_ATTR_WARN_UNUSED_RESULT
+{
+  return vim_isfilec(c) || c == ',' || c == ' ' || c == '@';
+}
+
 /// Check that "c" is a valid file-name character or a wildcard character
 /// Assume characters above 0x100 are valid (multi-byte).
 /// Explicitly interpret ']' as a wildcard character as path_has_wildcard("]")

src/nvim/spell.c

@@ -3621,7 +3621,7 @@ bool valid_spellfile(const char *val)
   FUNC_ATTR_NONNULL_ALL FUNC_ATTR_PURE FUNC_ATTR_WARN_UNUSED_RESULT
 {
   for (const char *s = val; *s != NUL; s++) {
-    if (!vim_isfilec((uint8_t)(*s)) && *s != ',' && *s != ' ') {
+    if (!vim_is_fname_char((uint8_t)(*s))) {
       return false;
     }
   }