a = a :: type should be free.

[ghost]

Right now, code such as

local function(a: number?)
  a = a :: number
end

will generate an unneccessary bytecode operation, the code above generates MOVE R0 R0 which is redundant.

[vegorov-rbx]

Extra info - same happens without type assertion:

local function f(a: number?)
  a = a
end

[vegorov-rbx]

We should have a fix for this soon.