"Function call without opaqueness type mismatch" under OTP 28

hez

With this code under OTP 27 dialyzer ran cleanly:

defmodule Test do
  @base_uribase_uri URI.new!(“`https://google.ca`”)

  def our_base do
    @base_uri |> URI.append_path(“/foo”)
  end
end

But in OTP 28 we are getting the following error:


> mix dialyzer
…

---

lib/app/test.ex:5:call_without_opaque
Function call without opaqueness type mismatch.

Call does not have expected term of type %URI{
:authority => URI.authority(),
:fragment => nil | binary(),
:host => nil | binary(),
:path => nil | binary(),
:port => nil | char(),
:query => nil | binary(),
:scheme => nil | binary(),
:userinfo => nil | binary()
} (with opaque subterms) in the 1st position.

URI.append_path(
%URI{
:authority => nil,
:fragment => nil,
:host => <<103, 111, 111, 103, 108, 101, 46, 99, 97>>,
:path => nil,
:port => 443,
:query => nil,
:scheme => <<104, 116, 116, 112, 115>>,
:userinfo => nil
},
<<47, 102, 111, 111>>
)

12 comments

#dialyzer #uri

1 1681 12

2026-06-19 11:11:45 UTC

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LostKobrakai

This looks like something to report to the elixir repo.

Post #1

sabiwara

Elixir Core Team

I think it should be fixed on the next 1.19rc: Mark inlined function call result as generated by sabiwara · Pull Request #14581 · elixir-lang/elixir · GitHub

Post #2

sabiwara

Elixir Core Team

OK I tried it out and it seems the error is still present on the v1.19 branch

Will open an issue.

Edit: issue link: Opaqueness warning on OTP28 · Issue #14750 · elixir-lang/elixir · GitHub

Post #3

hez

Thank you!

Post #4

lud

Hello,

Running into that tonight, and I’m not sure how to fix it without a dialyzer ignore.

I’m not sure I really understand the problem. Is dialyzer complaining that the given authority is not somehow inheriting the opaqueness? I tried to add nil which corresponds to the type, but I still have the error.

If I understand correctly, instead of this:

URI.to_string(%URI{scheme: scheme, host: host, port: port, authority: nil})

We should have something like this?:

URI.to_string(%URI{scheme: scheme, host: host, port: port, authority: URI.nil_authority()})

# module URI

@spec nil_authority :: authority
def nil_authority, do: nil

(When I say “we should” it’s only about making dialyzer happy again, I know it’s otherwise useless to specify the authority key to its default).

Currently my workaround is to use URI.parse which is more fragile because it involves string manipulation, or @dialyzer {:no_opaque, ...}. Is there a real proper solution to build URI structs from known data (scheme,host,etc)

Erlang/OTP 28 [erts-16.3] [source] [64-bit] [smp:12:12] [ds:12:12:10] [async-threads:1] [jit:ns]

Elixir 1.19.5 (compiled with Erlang/OTP 28)

Post #5

sabiwara

Elixir Core Team

For what it’s worth, we removed the opaqueness on authority (PR) on main/1.20rc but there hasn’t been a version after 1.19.5 to backport these changes.

So :no_opaque as a temporary stop-gap makes sense.

Post #6

lud

Thank you

Post #7

grossvogel

I’m wondering if I’m doing something wrong, b/c I’m still seeing errors in my project despite the related Elixir issues being closed as fixed. To test, I created a brand new mix project with this code

defmodule TmpDialyzerProject do
  @spec produce() :: MapSet.t(integer())
  def produce, do: MapSet.new([1, 2, 3])

  @spec consume(MapSet.t(integer())) :: list(integer())
  def consume(deleted) do
    MapSet.new([4, 5, 6])
    |> MapSet.difference(deleted)
    |> MapSet.to_list()
  end

  def driver, do: consume(produce())
end

and the result of mix dialyzer in Elixir 1.20.1 and OTP 28.4 is

lib/tmp_dialyzer_project.ex:12:27:call_without_opaque
Function call without opaqueness type mismatch.

Call does not have expected term of type %MapSet{:map => :sets.set(_)} (with opaque subterms) in the 1st position.

TmpDialyzerProject.consume(%MapSet{:map => %{1 => [], 2 => [], 3 => []}})

________________________________________________________________________________

Are folks still using the opaque exclusions, or is there something else I can do to resolve these?

Post #8

sabiwara

Elixir Core Team

Thanks for sharing @grossvogel. This issue is un-killable

You’re not doing anything wrong. But unfortunately I fear we’re getting out of options here to deal with it in the language itself.

I managed to silence it using the following two workarounds:

def produce do
 # option 1: un-inline the MapSet creation so it's not a literal anymore
 list = [1, 2, 3])
 MapSet.new(list)
end

# option 2: replace produce/0 by a module attr
@produce MapSet.new([1, 2, 3])
def driver, do: consume(@produce)

But honestly it might be better to just explicitly disable opaqueness checks when working with MapSet rather than jumping through hoops and try to trick dialyzer.

Post #9