feat(defaults): store spellfile in stdpath('data') #33048

Problem:
First rtp directory is unpredictable and not in line with XDG
base spec.

Solution:
Use stdpath('data')/spell as directory if 'spellfile' is not set.

Co-authored-by: zeertzjq <zeertzjq@outlook.com>
Co-authored-by: Justin M. Keyes <justinkz@gmail.com>

src/nvim/options.lua

@@ -8158,11 +8158,10 @@ local options = {
         It may also be a comma-separated list of names.  A count before the
         |zg| and |zw| commands can be used to access each.  This allows using
         a personal word list file and a project word list file.
-        When a word is added while this option is empty Vim will set it for
-        you: Using the first directory in 'runtimepath' that is writable.  If
-        there is no "spell" directory yet it will be created.  For the file
-        name the first language name that appears in 'spelllang' is used,
-        ignoring the region.
+        When a word is added while this option is empty Nvim will use
+        (and auto-create) `stdpath('data')/spell/`. For the file name the
+        first language name that appears in 'spelllang' is used, ignoring the
+        region.
         The resulting ".spl" file will be used for spell checking, it does not
         have to appear in 'spelllang'.
         Normally one file is used for all regions, but you can add the region

src/nvim/spellfile.c

@@ -262,6 +262,7 @@
 #include "nvim/os/input.h"
 #include "nvim/os/os.h"
 #include "nvim/os/os_defs.h"
+#include "nvim/os/stdpaths_defs.h"
 #include "nvim/os/time.h"
 #include "nvim/os/time_defs.h"
 #include "nvim/path.h"
@@ -5547,9 +5548,11 @@ void spell_add_word(char *word, int len, SpellAddType what, int idx, bool undo)
 }
 
 // Initialize 'spellfile' for the current buffer.
+//
+// If the location does not exist, create it. Defaults to
+// stdpath("data") + "/spell/{spelllang}.{encoding}.add".
 static void init_spellfile(void)
 {
-  int l;
   char *lend;
   bool aspath = false;
   char *lstart = curbuf->b_s.b_p_spl;
@@ -5558,8 +5561,6 @@ static void init_spellfile(void)
     return;
   }
 
-  char *buf = xmalloc(MAXPATHL);
-
   // Find the end of the language name.  Exclude the region.  If there
   // is a path separator remember the start of the tail.
   for (lend = curwin->w_s->b_p_spl; *lend != NUL
@@ -5570,49 +5571,40 @@ static void init_spellfile(void)
     }
   }
 
-  // Loop over all entries in 'runtimepath'.  Use the first one where we
-  // are allowed to write.
-  char *rtp = p_rtp;
-  while (*rtp != NUL) {
-    if (aspath) {
-      // Use directory of an entry with path, e.g., for
-      // "/dir/lg.utf-8.spl" use "/dir".
-      xmemcpyz(buf, curbuf->b_s.b_p_spl, (size_t)(lstart - curbuf->b_s.b_p_spl - 1));
-    } else {
-      // Copy the path from 'runtimepath' to buf[].
-      copy_option_part(&rtp, buf, MAXPATHL, ",");
-    }
-    if (os_file_is_writable(buf) == 2) {
-      // Use the first language name from 'spelllang' and the
-      // encoding used in the first loaded .spl file.
-      if (aspath) {
-        xmemcpyz(buf, curbuf->b_s.b_p_spl, (size_t)(lend - curbuf->b_s.b_p_spl));
-      } else {
-        // Create the "spell" directory if it doesn't exist yet.
-        l = (int)strlen(buf);
-        vim_snprintf(buf + l, MAXPATHL - (size_t)l, "/spell");
-        if (os_file_is_writable(buf) != 2) {
-          os_mkdir(buf, 0755);
-        }
+  char *buf = xmalloc(MAXPATHL);
+  size_t buf_len = MAXPATHL;
 
-        l = (int)strlen(buf);
-        vim_snprintf(buf + l, MAXPATHL - (size_t)l,
-                     "/%.*s", (int)(lend - lstart), lstart);
-      }
-      l = (int)strlen(buf);
-      char *fname = LANGP_ENTRY(curwin->w_s->b_langp, 0)
-                    ->lp_slang->sl_fname;
-      vim_snprintf(buf + l, MAXPATHL - (size_t)l, ".%s.add",
-                   ((fname != NULL
-                     && strstr(path_tail(fname), ".ascii.") != NULL)
-                    ? "ascii"
-                    : spell_enc()));
-      set_option_value_give_err(kOptSpellfile, CSTR_AS_OPTVAL(buf), OPT_LOCAL);
-      break;
+  if (!aspath) {
+    char *xdg_path = get_xdg_home(kXDGDataHome);
+    xstrlcpy(buf, xdg_path, buf_len);
+    xfree(xdg_path);
+
+    xstrlcat(buf, "/spell", buf_len);
+
+    char *failed_dir;
+    if (os_mkdir_recurse(buf, 0755, &failed_dir, NULL) != 0) {
+      xfree(buf);
+      xfree(failed_dir);
+      return;
     }
-    aspath = false;
+  } else {
+    if ((size_t)(lend - curbuf->b_s.b_p_spl) >= buf_len) {
+      xfree(buf);
+      return;
+    }
+    xmemcpyz(buf, curbuf->b_s.b_p_spl, (size_t)(lend - curbuf->b_s.b_p_spl));
   }
 
+  // Append spelllang
+  vim_snprintf(buf + strlen(buf), buf_len - strlen(buf), "/%.*s", (int)(lend - lstart), lstart);
+
+  // Append ".ascii.add" or ".{enc}.add"
+  char *fname = LANGP_ENTRY(curwin->w_s->b_langp, 0)->lp_slang->sl_fname;
+  const char *enc_suffix =
+    (fname != NULL && strstr(path_tail(fname), ".ascii.") != NULL) ? "ascii" : spell_enc();
+  vim_snprintf(buf + strlen(buf), buf_len - strlen(buf), ".%s.add", enc_suffix);
+
+  set_option_value_give_err(kOptSpellfile, CSTR_AS_OPTVAL(buf), OPT_LOCAL);
   xfree(buf);
 }