buffer.selection_n_anchor doesn't check keys and causes crash

[tmewett]

I want to apply changes to all selections, so I was trying to iterate over buffer.selection_n_anchor. However, using ipairs on it causes Textadept to crash.

1. Open Command Entry and enter for i,p in ipairs(buffer.selection_n_anchor) do end
2. Textadept crashes

Also, for k,v in pairs(buffer.selection_n_anchor) do print(k,v) end prints

_self	ta_buffer: 0000017FE97C5C20
_iface	table: 0000017FE48CD770

Meaning pairs and ipairs are inconsistent.

It seems I can access arbitrary memory via this too; buffer.selection_n_anchor[150] gives e.g. 1648849914305 even though I have only one selection in an empty buffer.

[orbitalquark]

Textadept uses Scintilla (https://scintilla.org) as its editing component and provides a Lua interface for making Scintilla API calls (https://scintilla.org/ScintillaDoc.html) to do things like iterate over selections. This interface does not have many guardrails, so if you're not careful you can do unintended things like out-of-bounds memory access. I'd classify that as user error, though crashing is certainly not ideal.

To iterate over selections, you'll do something like this:

for i = 1, buffer.selections do
  local s, e = buffer.selection_n_start[i], buffer.selection_n_end[i]
  -- ... do something with the selection
end

There are a number of examples in Textadept's source for iterating over selections and doing things with them. For example:

textadept/modules/textadept/editing.lua

Lines 153 to 173 in cef331d

	--- Encloses the selected text within delimiters, or encloses the current word if no text is
	-- selected.
	-- If there are multiple selections, each one will be enclosed.
	-- @param left String left delimiter to enclose with.
	-- @param right String right delimiter to enclose with.
	-- @param[opt=false] select Keep enclosed text selected.
	function M.enclose(left, right, select)
	assert_type(left, 'string', 1)
	assert_type(right, 'string', 2)
	assert_type(select, 'boolean/nil', 3)
	buffer:begin_undo_action()
	for i = 1, buffer.selections do
	local s, e = buffer.selection_n_start[i], buffer.selection_n_end[i]
	if s == e then s, e = buffer:word_start_position(s, true), buffer:word_end_position(e, true) end
	buffer:set_target_range(s, e)
	buffer:replace_target(left .. buffer.target_text .. right)
	buffer.selection_n_start[i] = not select and buffer.target_end or buffer.target_start + #left
	buffer.selection_n_end[i] = buffer.target_end - (not select and 0 or #right)
	end
	buffer:end_undo_action()
	end