Dialyzer warnings with OTP 19

[aaronjensen]

Brand new phoenix app created with mix phoenix.new on OTP 19 has these warnings.

Here's a repro app: https://github.com/aaronjensen/dialyzer_repro

Irrelevant warnings are omitted. Originally reported at phoenixframework/phoenix#1872

Starting Dialyzer
dialyzer --no_check_plt --plt /Users/aaronjensen/.dialyxir_core_19_1.3.2.plt -Wunmatched_returns -Werror_handling -Wrace_conditions -Wunderspecs /Users/aaronjensen/Source/dialyzer_repro/_build/dev/lib/dialyzer_repro/ebin
  Proceeding with analysis...
repo.ex:2: The inferred type for the 1st argument of insert_or_update/2 (#{'__struct__':='Elixir.Ecto.Changeset', 'data':=#{'__meta__':=#{'state':=_, _=>_}, _=>_}, 'valid?'=>boolean(), _=>_}) is not a supertype of #{'__struct__':='Elixir.Ecto.Changeset', 'action':='delete' | 'insert' | 'nil' | 'replace' | 'update', 'changes':=#{atom()=>_}, 'constraints':=[#{'constraint':=binary(), 'field':=atom(), 'match':='exact' | 'suffix', 'message':={binary(),[{atom(),_}]}, 'type':='unique'}], 'data':='nil' | #{'__struct__':=atom()}, 'errors':=[{atom(),{binary(),[{atom(),_}]}}], 'filters':=#{atom()=>_}, 'params':='nil' | #{binary()=>_}, 'prepare':=[fun((#{'__struct__':='Elixir.Ecto.Changeset', 'action':='delete' | 'insert' | 'nil' | 'replace' | 'update', 'changes':=map(), 'constraints':=[any()], _=>_}) -> #{'__struct__':='Elixir.Ecto.Changeset', 'action':='delete' | 'insert' | 'nil' | 'replace' | 'update', 'changes':=map(), 'constraints':=[any()], _=>_})], 'repo':=atom(), 'required':=[atom()], 'types':='nil' | #{atom()=>atom() | {'array',_} | {'embed',#{'__struct__':='Elixir.Ecto.Embedded', 'cardinality':='many' | 'one', 'field':=atom(), 'on_cast':='nil' | fun(), 'on_replace':='delete' | 'mark_as_invalid' | 'raise', 'owner':=atom(), 'related':=atom()}} | {'in',_} | {'map',_}}, 'valid?':=boolean(), 'validations':=[{atom(),_}]}, which is expected type for this argument in the callback of the 'Elixir.Ecto.Repo' behaviour
repo.ex:2: The inferred type for the 1st argument of 'insert_or_update!'/2 (#{'__struct__':='Elixir.Ecto.Changeset', 'data':=#{'__meta__':=#{'state':=_, _=>_}, _=>_}, 'valid?'=>boolean(), _=>_}) is not a supertype of #{'__struct__':='Elixir.Ecto.Changeset', 'action':='delete' | 'insert' | 'nil' | 'replace' | 'update', 'changes':=#{atom()=>_}, 'constraints':=[#{'constraint':=binary(), 'field':=atom(), 'match':='exact' | 'suffix', 'message':={binary(),[{atom(),_}]}, 'type':='unique'}], 'data':='nil' | #{'__struct__':=atom()}, 'errors':=[{atom(),{binary(),[{atom(),_}]}}], 'filters':=#{atom()=>_}, 'params':='nil' | #{binary()=>_}, 'prepare':=[fun((#{'__struct__':='Elixir.Ecto.Changeset', 'action':='delete' | 'insert' | 'nil' | 'replace' | 'update', 'changes':=map(), 'constraints':=[any()], _=>_}) -> #{'__struct__':='Elixir.Ecto.Changeset', 'action':='delete' | 'insert' | 'nil' | 'replace' | 'update', 'changes':=map(), 'constraints':=[any()], _=>_})], 'repo':=atom(), 'required':=[atom()], 'types':='nil' | #{atom()=>atom() | {'array',_} | {'embed',#{'__struct__':='Elixir.Ecto.Embedded', 'cardinality':='many' | 'one', 'field':=atom(), 'on_cast':='nil' | fun(), 'on_replace':='delete' | 'mark_as_invalid' | 'raise', 'owner':=atom(), 'related':=atom()}} | {'in',_} | {'map',_}}, 'valid?':=boolean(), 'validations':=[{atom(),_}]}, which is expected type for this argument in the callback of the 'Elixir.Ecto.Repo' behaviour
repo.ex:2: Function rollback/1 has no local return
repo.ex:2: The inferred type for the 1st argument of 'update!'/2 (#{'__struct__':='Elixir.Ecto.Changeset', 'action':=_, 'repo':=_, 'valid?':=boolean(), _=>_}) is not a supertype of #{'__struct__':=atom()}, which is expected type for this argument in the callback of the 'Elixir.Ecto.Repo' behaviour
 done in 0m3.37s
done (warnings were emitted)