If there is a typespec in the function, dialyzer will fail 
Example:
defmodule Test do
defstruct a: 0, b: nil, c: nil
@type t :: %__MODULE__{a: non_neg_integer(), b: nil | String.t(), c: atom()}
@spec foo() :: t
def foo do
%Test{
a: 1,
b: "aha",
c: :foo
}
|> Map.put(:bar, "bar")
end
end
$ mix dialyzer
lib/test.ex:6:invalid_contract
The @spec for the function does not match the success typing of the function.
Function:
Test.foo/0
Success typing:
@spec foo() :: %Test{:a => 1, :b => <<_::24>>, :bar => <<_::24>>, :c => :foo}
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