try to send a uniform to a shader without getting blocking errors when it's been optimised away

shader_try_send.lua

--[[
	try to send a uniform to a shader
	prints a warning once for the lifetime of the shader for missing uniforms
	otherwise succeeds or fails silently
]]
do
	local _warned = setmetatable({}, {__mode = "k"})
	local function _warn(s, u)
		local already_warned = _warned[s]
		if not already_warned then
			_warned[s] = {}
			return _warn(s, u)
		end
		if already_warned[u] then
			return
		end
		already_warned[u] = true
		print(
			debug.traceback(
				("warning: attempted to send uniform '%s'")
					:format(u),
				2
			)
		)
	end
	function shader_try_send(shader, uniform, ...)
		if shader:hasUniform(uniform) then
			return shader:send(uniform, ...)
		end
		return _warn(shader, uniform)
	end
end

--[[
	example;

	one uniform is used, one is not
]]

local shader = love.graphics.newShader([[
uniform float is_used;
uniform float not_used;

vec4 effect(vec4 c, Image t, vec2 uv, vec2 px) {
	return vec4(is_used);
}
]])

--[[
	sending both in a loop results in just one print
]]

for i = 1, 100 do
	shader_try_send(shader, "is_used", 1.0)
	shader_try_send(shader, "not_used", 1.0)
end

--[[
example output:

warning: attempted to send uniform 'not_used'
stack traceback:
        main.lua:55: in main chunk
        [C]: in function 'require'
        [string "boot.lua"]:570: in function <[string "boot.lua"]:380>
        [C]: in function 'xpcall'
        [string "boot.lua"]:787: in function <[string "boot.lua"]:780>
        [C]: in function 'xpcall'
        [string "boot.lua"]:802: in function <[string "boot.lua"]:769>

]]