option: Use different default value for &runtimepath

src/nvim/option.c

@@ -301,6 +301,89 @@ static char *(p_cot_values[]) = {"menu", "menuone", "longest", "preview",
 # include "option.c.generated.h"
 #endif
 
+/// Set &runtimepath to default value
+static void set_runtimepath_default(void)
+{
+  size_t rtp_size = 0;
+  char *const data_home = vim_getenv("XDG_DATA_HOME");
+  char *const config_home = vim_getenv("XDG_CONFIG_HOME");
+  char *const vimruntime = vim_getenv("VIMRUNTIME");
+  char *const data_dirs = vim_getenv("XDG_DATA_DIRS");
+  char *const config_dirs = vim_getenv("XDG_CONFIG_DIRS");
+  assert(data_home != NULL);
+  assert(config_home != NULL);
+  assert(vimruntime != NULL);
+  assert(data_dirs != NULL);
+  assert(config_dirs != NULL);
+#define NVIM_SIZE (sizeof("/nvim") - 1)
+#define AFTER_SIZE (sizeof("/after") - 1)
+  const size_t data_len = strlen(data_home);
+  const size_t config_len = strlen(config_home);
+  const size_t vimruntime_len = strlen(vimruntime);
+  rtp_size += ((data_len + NVIM_SIZE) * 2 + AFTER_SIZE) + 2;
+  rtp_size += ((config_len + NVIM_SIZE) * 2 + AFTER_SIZE) + 2;
+  rtp_size += vimruntime_len;
+#define COMPUTE_COLON_LEN(rtp_size, val) \
+  do { \
+    const void *iter = NULL; \
+    do { \
+      size_t dir_len; \
+      const char *dir; \
+      iter = vim_colon_env_iter(val, iter, &dir, &dir_len); \
+      if (dir != NULL && dir_len > 0) { \
+        rtp_size += ((dir_len + NVIM_SIZE) * 2 + AFTER_SIZE) + 2; \
+      } \
+    } while (iter != NULL); \
+  } while (0)
+  COMPUTE_COLON_LEN(rtp_size, data_dirs);
+  COMPUTE_COLON_LEN(rtp_size, config_dirs);
+#undef COMPUTE_COLON_LEN
+  char *const rtp = xmallocz(rtp_size);
+  char *rtp_cur = rtp;
+#define ADD_STRING(tgt, src, len) \
+  do { memmove(tgt, src, len); tgt += len; } while (0)
+#define ADD_STATIC_STRING(tgt, str) \
+  ADD_STRING(tgt, str, sizeof(str) - 1)
+#define ADD_COLON_DIRS(tgt, val, suffix, revsuffix) \
+  do { \
+    const void *iter = NULL; \
+    do { \
+      size_t dir_len; \
+      const char *dir; \
+      iter = vim_colon_env_iter##revsuffix(val, iter, &dir, &dir_len); \
+      if (dir != NULL && dir_len > 0) { \
+        ADD_STRING(rtp_cur, dir, dir_len); \
+        ADD_STATIC_STRING(rtp_cur, "/nvim" suffix ","); \
+      } \
+    } while (iter != NULL); \
+  } while (0)
+  ADD_STRING(rtp_cur, config_home, config_len);
+  ADD_STATIC_STRING(rtp_cur, "/nvim,");
+  ADD_STRING(rtp_cur, data_home, data_len);
+  ADD_STATIC_STRING(rtp_cur, "/nvim,");
+  ADD_COLON_DIRS(rtp_cur, config_dirs, "", );
+  ADD_COLON_DIRS(rtp_cur, data_dirs, "", );
+  ADD_STRING(rtp_cur, vimruntime, vimruntime_len);
+  *rtp_cur++ = ',';
+  ADD_COLON_DIRS(rtp_cur, data_dirs, "/after", _rev);
+  ADD_COLON_DIRS(rtp_cur, config_dirs, "/after", _rev);
+  ADD_STRING(rtp_cur, data_home, data_len);
+  ADD_STATIC_STRING(rtp_cur, "/nvim/after,");
+  ADD_STRING(rtp_cur, config_home, config_len);
+  ADD_STATIC_STRING(rtp_cur, "/nvim/after");
+#undef ADD_COLON_DIRS
+#undef ADD_STATIC_STRING
+#undef ADD_STRING
+#undef NVIM_SIZE
+#undef AFTER_SIZE
+  set_string_default("runtimepath", (char_u *)rtp);
+  xfree(data_dirs);
+  xfree(config_dirs);
+  xfree(data_home);
+  xfree(config_home);
+  xfree(vimruntime);
+}
+
 /*
  * Initialize the options, first part.
  *
@@ -437,6 +520,10 @@ void set_init_1(void)
       "system('lpr' . (&printdevice == '' ? '' : ' -P' . &printdevice) . ' ' . v:fname_in) . delete(v:fname_in) + v:shell_error"
       );
 
+  // Set default for &runtimepath. All necessary expansions are performed in 
+  // this function.
+  set_runtimepath_default();
+
   /*
    * Set all the options (except the terminal options) to their default
    * value.  Also set the global value for local options.

src/nvim/options.lua

@@ -1910,7 +1910,7 @@ return {
       vi_def=true,
       expand=true,
       varname='p_rtp',
-      defaults={if_true={vi=macros('DFLT_RUNTIMEPATH')}}
+      defaults={if_true={vi=''}}
     },
     {
       full_name='scroll', abbreviation='scr',

src/nvim/os/unix_defs.h

@@ -70,13 +70,4 @@
 # define DFLT_VDIR    "$XDG_DATA_HOME/nvim/view/"
 #endif
 
-#ifdef RUNTIME_GLOBAL
-# define DFLT_RUNTIMEPATH NVIM_CONF_DIR "," RUNTIME_GLOBAL ",$VIMRUNTIME," \
-                          RUNTIME_GLOBAL "/after," NVIM_CONF_DIR "/after"
-#else
-# define DFLT_RUNTIMEPATH \
-  NVIM_CONF_DIR ",$VIM/vimfiles,$VIMRUNTIME,$VIM/vimfiles/after,"\
-  NVIM_CONF_DIR "/after"
-#endif
-
 #endif  // NVIM_OS_UNIX_DEFS_H

src/nvim/os/win_defs.h

@@ -13,7 +13,6 @@
 // - DFLT_DIR
 // - DFLT_BDIR
 // - DFLT_VDIR
-// - DFLT_RUNTIMEPATH
 // - EXRC_FILE
 // - VIMRC_FILE
 // - SYNTAX_FNAME