api/vim: Fix nvim_list_runtimepaths

It used to

1. Always omit last component in runtimepath.
2. Always omit trailing empty item and leave uninitialized memory in place of 
   it.

src/nvim/api/vim.c

@@ -299,7 +299,7 @@ ArrayOf(String) nvim_list_runtime_paths(void)
     FUNC_API_SINCE(1)
 {
   Array rv = ARRAY_DICT_INIT;
-  uint8_t *rtp = p_rtp;
+  char_u *rtp = p_rtp;
 
   if (*rtp == NUL) {
     // No paths
@@ -313,13 +313,14 @@ ArrayOf(String) nvim_list_runtime_paths(void)
     }
     rtp++;
   }
+  rv.size++;
 
   // Allocate memory for the copies
-  rv.items = xmalloc(sizeof(Object) * rv.size);
+  rv.items = xmalloc(sizeof(*rv.items) * rv.size);
   // Reset the position
   rtp = p_rtp;
   // Start copying
-  for (size_t i = 0; i < rv.size && *rtp != NUL; i++) {
+  for (size_t i = 0; i < rv.size; i++) {
     rv.items[i].type = kObjectTypeString;
     rv.items[i].data.string.data = xmalloc(MAXPATHL);
     // Copy the path from 'runtimepath' to rv.items[i]
@@ -708,7 +709,7 @@ void nvim_unsubscribe(uint64_t channel_id, String event)
 Integer nvim_get_color_by_name(String name)
     FUNC_API_SINCE(1)
 {
-  return name_to_color((uint8_t *)name.data);
+  return name_to_color((char_u *)name.data);
 }
 
 Dictionary nvim_get_color_map(void)
@@ -859,7 +860,7 @@ static void write_msg(String message, bool to_err)
 #define PUSH_CHAR(i, pos, line_buf, msg) \
   if (message.data[i] == NL || pos == LINE_BUFFER_SIZE - 1) { \
     line_buf[pos] = NUL; \
-    msg((uint8_t *)line_buf); \
+    msg((char_u *)line_buf); \
     pos = 0; \
     continue; \
   } \

test/functional/api/vim_spec.lua

@@ -327,11 +327,11 @@ describe('api', function()
         {'nvim_get_mode', {}},
         {'nvim_eval',     {'1'}},
       }
-      eq({{{mode='n', blocking=false},
+      eq({ { {mode='n', blocking=false},
-          13,
+             13,
-          {mode='n', blocking=false},  -- TODO: should be blocked=true
+             {mode='n', blocking=false},  -- TODO: should be blocked=true
-          1},
+             1 },
-        NIL}, meths.call_atomic(req))
+           NIL}, meths.call_atomic(req))
       eq({mode='r', blocking=true}, nvim("get_mode"))
     end)
     -- TODO: bug #6166
@@ -588,6 +588,36 @@ describe('api', function()
     end)
   end)
 
+  describe('list_runtime_paths', function()
+    it('returns nothing with empty &runtimepath', function()
+      meths.set_option('runtimepath', '')
+      eq({}, meths.list_runtime_paths())
+    end)
+    it('returns single runtimepath', function()
+      meths.set_option('runtimepath', 'a')
+      eq({'a'}, meths.list_runtime_paths())
+    end)
+    it('returns two runtimepaths', function()
+      meths.set_option('runtimepath', 'a,b')
+      eq({'a', 'b'}, meths.list_runtime_paths())
+    end)
+    it('returns empty strings when appropriate', function()
+      meths.set_option('runtimepath', 'a,,b')
+      eq({'a', '', 'b'}, meths.list_runtime_paths())
+      meths.set_option('runtimepath', ',a,b')
+      eq({'', 'a', 'b'}, meths.list_runtime_paths())
+      meths.set_option('runtimepath', 'a,b,')
+      eq({'a', 'b', ''}, meths.list_runtime_paths())
+    end)
+    it('truncates too long paths', function()
+      local long_path = ('/a'):rep(8192)
+      meths.set_option('runtimepath', long_path)
+      local paths_list = meths.list_runtime_paths()
+      neq({long_path}, paths_list)
+      eq({long_path:sub(1, #(paths_list[1]))}, paths_list)
+    end)
+  end)
+
   it('can throw exceptions', function()
     local status, err = pcall(nvim, 'get_option', 'invalid-option')
     eq(false, status)