Merge multi-snippet common field, fix #921

[Bekaboo]

Should fix #921

Currently the common field is replaced as a whole when the passed arg has this field set instead of merging the passed arg and the extend arg, which is not expected.

To clarify, consider the following cases:

I create some luasnip conds and define a new multi-snippet that only expand if ts is not active or ts and active and the cursor is not in a comment or string:

local msc = ls.extend_decorator.apply(ms, {
  common = {
    condition = -conds.ts_active
      + -conds.in_tsnode('comment') * -conds.in_tsnode('string'),
    show_condition = -conds.ts_active
      + -conds.in_tsnode('comment') * -conds.in_tsnode('string'),
  },
})

Then I want to create a multi-snippet with regex trigger and only expand when the cursor is not in a comment or string:

msc(
  {
    common = { regTrig = true },
    { trig = '(%S?)(%s*)%.%.%s*ck' },
    { trig = '(%S?)(%s*)%.%.%s*check' },
  },
  fmta('<spc>.. ", <v>: " .. vim.inspect(<v>)', {
    spc = f(function(_, snip, _)
      return snip.captures[1] == '' and snip.captures[2]
        or snip.captures[1] .. ' '
    end, {}, {}),
    v = i(1),
  }, { repeat_duplicates = true })
)

the original condition field is dropped because I provide the common field in the new snippet, making the original common table completely replaced by the new one i.e. { regTrig = true, condition = nil, show_condition = nil, ... }

I would suggest using vim.tbl_deep_extend to merge the common table, this fixes the issue (in function extend_multisnippet_contexts:

	-- extend ("keep") valid keyword-arguments.
	passed_arg.common = vim.tbl_deep_extend(
		"keep",
		passed_arg.common or {},
		extend_arg.common or {}
	)

[L3MON4D3]

Nice!
common can also be a string, could you take care of that? (node_util.wrap_context handles the conversion iirc)

[Bekaboo]

Sure, will work on this later. Dont know why the test fails, though.

[Bekaboo]

@L3MON4D3 Wrapped common in node_util.wrap_context.

[L3MON4D3]

Looks good 👍
Thank you!