shada,functests: Test how ShaDa support code reacts on errors

Some notes:
- Replaced msgpack_unpacker usage with regular xmalloc’ed buffer. Also since
  msgpack_unpack_next (as well as msgpack_unpacker_next) is not ever going to
  return MSGPACK_UNPACK_EXTRA_BYTES this condition was checked manually.
  Function that does return this status is msgpack_unpack, but it is marked as
  obsolete.
- Zero type is checked prior to main switch in shada_read_next_item because
  otherwise check would be skipped.
- Zeroing entry at the start of shada_read_next_item makes it safer.
- dedent('') does not work.
- v:oldfiles list is only replaced with bang, if it is NULL or empty.

1 files changed, 17 insertions, 2 deletions

diff --git a/test/functional/shada/helpers.lua b/test/functional/shada/helpers.lua
index 7e93fcb915..909fcd62e6 100644
--- a/test/functional/shada/helpers.lua
+++ b/test/functional/shada/helpers.lua
@@ -1,6 +1,7 @@
 local helpers = require('test.functional.helpers')
-local spawn, set_session, nvim, nvim_prog =
-  helpers.spawn, helpers.set_session, helpers.nvim, helpers.nvim_prog
+local spawn, set_session, nvim, nvim_prog, nvim_command, nvim_eval =
+  helpers.spawn, helpers.set_session, helpers.nvim, helpers.nvim_prog,
+  helpers.command, helpers.eval
 
 local tmpname = os.tmpname()
 local additional_cmd = ''
@@ -46,8 +47,22 @@ local clear = function()
   set_additional_cmd('')
 end
 
+local exc_exec = function(cmd)
+  nvim_command(([[
+    try
+      execute "%s"
+    catch
+      let g:__exception = v:exception
+    endtry
+  ]]):format(cmd:gsub('\n', '\\n'):gsub('[\\"]', '\\%0')))
+  local ret = nvim_eval('get(g:, "__exception", 0)')
+  nvim_command('unlet! g:__exception')
+  return ret
+end
+
 return {
   reset=reset,
   set_additional_cmd=set_additional_cmd,
   clear=clear,
+  exc_exec=exc_exec,
 }