correctly handle matching in injected trees.

lua/luasnip/extras/_treesitter.lua

@@ -281,41 +281,39 @@ function TSParser:get_node_at_pos(pos)
 	return self.parser:named_node_for_range(range)
 end
 
----@param root TSNode?
-function TSParser:get_range(root)
-	if root == nil then
-		-- try first tree's root
-		local first_tree = self.parser:trees()[1]
-		if first_tree then
-			root = first_tree:root()
-		end
-	end
-	if root == nil then
-		return
+---Get the root for the smallest tree containing `pos`.
+---@param pos { [1]: number, [2]: number }
+---@return TSNode?
+function TSParser:root_at(pos)
+	local tree = self.parser:tree_for_range({pos[1], pos[2], pos[1], pos[2]}, {ignore_injections = false})
+	if not tree then
+		return nil
 	end
 
-	local range = { root:range() }
-
-	return {
-		root = root,
-		start = range[1],
-		stop = range[3] + 1,
-	}
+	return tree:root()
 end
 
 ---@param match_opts LuaSnip.extra.EffectiveMatchTSNodeOpts
 ---@param pos { [1]: number, [2]: number }
 ---@return LuaSnip.extra.NamedTSMatch?, TSNode?
 function TSParser:match_at(match_opts, pos)
-	local info = self:get_range()
-	if info == nil then
+	-- Since we want to find a match to the left of pos, and if we accept there
+	-- has to be at least one character (I assume), we should probably not look
+	-- for the tree containing `pos`, since that might be the wrong one (if
+	-- injected languages are in play).
+	local root = self:root_at({pos[1], pos[2]-1})
+	if root == nil then
 		return nil, nil
 	end
+	local root_from_line, _, root_to_line, _ = root:range()
 
 	local query = match_opts.query
 	local selector = match_opts.selector()
 	local next_ts_match =
-		query:iter_matches(info.root, self.source, info.start, info.stop)
+		-- end-line is excluded by iter_matches, if the column of root_to
+		-- greater than 0, we would erroneously ignore a line that could
+		-- contain our match.
+		query:iter_matches(root, self.source, root_from_line, root_to_line+1)
 
 	for match, node in match_opts.generator(query, next_ts_match) do
 		-- false: don't include bytes.