Non-preprocessor assertion results in compiler failing its own assertions

[IcedQuinn]

Accidentally discovered this one during a two-week Nelua challenge. Minimized with picire (delta debugger.)

Bug description

An assert statement which is not in a preprocessor line causes the compiler to crash internally.

/usr/local/bin/nelua-lua: /usr/local/lib/nelua/lualib/nelua/cbuiltins.lua:1453: assertion failed!
stack traceback:
	[C]: in function 'assert'
	/usr/local/lib/nelua/lualib/nelua/cbuiltins.lua:1453: in local 'builtin'
	/usr/local/lib/nelua/lualib/nelua/cgenerator.lua:1575: in local 'visit'
	/usr/local/lib/nelua/lualib/nelua/visitorcontext.lua:171: in function 'nelua.visitorcontext.traverse_node'
	/usr/local/lib/nelua/lualib/nelua/emitter.lua:160: in function 'nelua.emitter.add_value'
	/usr/local/lib/nelua/lualib/nelua/cemitter.lua:186: in function 'nelua.cemitter.add_converted_val'
	/usr/local/lib/nelua/lualib/nelua/cgenerator.lua:660: in upvalue 'visitor_Call'
	/usr/local/lib/nelua/lualib/nelua/cgenerator.lua:706: in local 'visit'
	/usr/local/lib/nelua/lualib/nelua/visitorcontext.lua:171: in function 'nelua.visitorcontext.traverse_node'
	/usr/local/lib/nelua/lualib/nelua/emitter.lua:160: in function 'nelua.emitter.add_value'
	...	(skipping 10 levels)
	/usr/local/lib/nelua/lualib/nelua/cgenerator.lua:1709: in function 'nelua.cgenerator.emit_nelua_main'
	/usr/local/lib/nelua/lualib/nelua/cgenerator.lua:1739: in function 'nelua.cgenerator.emit_entrypoint'
	/usr/local/lib/nelua/lualib/nelua/cgenerator.lua:1761: in function 'nelua.cgenerator.generate'
	/usr/local/lib/nelua/lualib/nelua/runner.lua:206: in upvalue 'run'
	/usr/local/lib/nelua/lualib/nelua/runner.lua:262: in function </usr/local/lib/nelua/lualib/nelua/runner.lua:261>
	[C]: in function 'xpcall'
	/usr/local/lib/nelua/lualib/nelua/utils/except.lua:135: in function 'nelua.utils.except.try'
	/usr/local/lib/nelua/lualib/nelua/runner.lua:261: in function 'nelua.runner.run'
	/usr/local/lib/nelua/lualib/nelua.lua:4: in main chunk
	[C]: in function 'require'
	[C]: in ?
stack traceback:
	[C]: in function 'error'
	/usr/local/lib/nelua/lualib/nelua/utils/except.lua:108: in function 'nelua.utils.except.reraise'
	/usr/local/lib/nelua/lualib/nelua/utils/except.lua:146: in function 'nelua.utils.except.try'
	/usr/local/lib/nelua/lualib/nelua/runner.lua:261: in function 'nelua.runner.run'
	/usr/local/lib/nelua/lualib/nelua.lua:4: in main chunk
	[C]: in function 'require'
	[C]: in ?

Code example

local State = @record{
  acc: [4]uint64,
  buffer: [32]uint8,
  buffered_size: uint32,
}
function State:consume_long(input: pointer, len: isize): pointer
  assert(self.acc ~= nil)
  return input
end
function State:update(input: pointer, len: isize)
  do
    if self.buffered_size > 0 then
      self:consume_long(&self.buffer, #self.buffer)
    end
  end
end
local fart: State
local data = "i am the egg man"
fart:update(&data, #data)

Expected behavior

A runtime assertion to be in the program, or, an intentional error from the compiler that this function does not exist.

Workaround

Removing the assert statement.

[cpaybcho]

Just a quick note on your bug description and code example.
self.acc is an array, not a pointer, so it will be zero-initialized when the fart variable is created. This means the check assert(self.acc ~= nil) is a bit unusual, since the array itself can't be nil.
However, a compiler crash is not the expected behavior. I was able to reproduce it.
I've also found that it can be reproduced with a more minimal example:

local arr: [4]uint64
assert(arr ~= nil)

Looking at the code in cbuiltins.lua:1453, the assertion failed occurs because the Nelua compiler requires the right-hand operand of the ~= operator to also be an array if the left-hand operand is an array.