feat: allow modifying expand-position in pre_expand-callback (#1219).

DOC.md

@@ -3400,6 +3400,8 @@ The node and `event_args` can be accessed through `require("luasnip").session`:
  `event_args`:
  * `expand_pos`: `{<row>, <column>}`, position at which the snippet will be
  expanded. `<row>` and `<column>` are both 0-indexed.
+ * `expand_pos_mark_id`: `number`, the id of the extmark luasnip uses to track
+ `expand_pos`. This may be moved around freely.
  `event_res`:
  * `env_override`: `map string->(string[]|string)`, override or extend the
  snippet's environment (`snip.env`).

lua/luasnip/nodes/snippet.lua

@@ -632,6 +632,12 @@ end
 function Snippet:trigger_expand(current_node, pos_id, env, indent_nodes)
  local pos = vim.api.nvim_buf_get_extmark_by_id(0, session.ns_id, pos_id, {})
 
+ local pre_expand_res = self:event(events.pre_expand, { expand_pos = pos, expand_pos_mark_id = pos_id })
+ or {}
+
+ -- update pos, event-callback might have moved the extmark.
+ pos = vim.api.nvim_buf_get_extmark_by_id(0, session.ns_id, pos_id, {})
+
  -- find tree-node the snippet should be inserted at (could be before another node).
  local _, sibling_snippets, own_indx, parent_node =
  node_util.snippettree_find_undamaged_node(pos, {
@@ -697,11 +703,6 @@ function Snippet:trigger_expand(current_node, pos_id, env, indent_nodes)
  end
  end
 
- local pre_expand_res = self:event(events.pre_expand, { expand_pos = pos })
- or {}
- -- update pos, event-callback might have moved the extmark.
- pos = vim.api.nvim_buf_get_extmark_by_id(0, session.ns_id, pos_id, {})
-
  Environ:override(env, pre_expand_res.env_override or {})
 
  if indent_nodes then

tests/integration/snippet_basics_spec.lua

@@ -1626,4 +1626,24 @@ describe("snippets_basic", function()
  {2:-- INSERT --} |]],
  })
  end)
+
+ it("expand-position may be moved in pre_expand.", function()
+ feed("i.")
+
+ exec_lua[[
+ snip = s("foo", {
+ t"asdf"
+ }, {callbacks = {[-1] = { [events.pre_expand] = function(node, event_args)
+ vim.api.nvim_buf_set_extmark(0, ls.session.ns_id, 0,0, {id = event_args.expand_pos_mark_id})
+ end}} } )
+
+ ls.snip_expand(snip)
+ ]]
+
+ screen:expect({
+ grid = [[
+ asdf^. |
+ {0:~ }|
+ {2:-- INSERT --} |]]})
+ end)
 end)