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Unify :empty_list and :list domains in maps #14955

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Unify :empty_list and :list domains in maps #14955

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3caa8ba
Unify :empty_list and :list domains in maps
gldubc Nov 24, 2025
3f8881f
Add test for domain instantiation
gldubc Nov 24, 2025
47b58b2
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gldubc Nov 24, 2025
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3 changes: 1 addition & 2 deletions lib/elixir/lib/module/types/descr.ex
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Original file line number Diff line number Diff line change
Expand Up @@ -32,7 +32,6 @@ defmodule Module.Types.Descr do

@domain_key_types [
{:domain_key, :binary},
{:domain_key, :empty_list},
{:domain_key, :integer},
{:domain_key, :float},
{:domain_key, :pid},
Expand Down Expand Up @@ -3031,7 +3030,7 @@ defmodule Module.Types.Descr do
defp bitmap_to_domain_keys(bitmap) do
[
if((bitmap &&& @bit_binary) != 0, do: domain_key(:binary)),
if((bitmap &&& @bit_empty_list) != 0, do: domain_key(:empty_list)),
if((bitmap &&& @bit_empty_list) != 0, do: domain_key(:list)),
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@josevalim josevalim Nov 24, 2025

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Now we can include :list twice. I think we need to handle that a bit upstream. :S

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@gldubc gldubc Nov 24, 2025

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I believe this gets handled gracefully thanks to

  # TODO: Double check if we indeed want the union here
  # when we start using domain types from Elixir itself
  defp map_put_domain(domain, key, value) do
    Map.update(domain, key, if_set(value), &union(&1, value))
  end

So when we instantiate say, empty_list() to integer() and non_empty_list() to atom() from Elixir, this will be split into two pairs of bindings passed to the constructor closed_map or open_map, with twice the same key domain_key(:list). Then, the map will have :list bound to integer() or atom(). I just added a test for that. A typing test would be nice too perhaps.

if((bitmap &&& @bit_integer) != 0, do: domain_key(:integer)),
if((bitmap &&& @bit_float) != 0, do: domain_key(:float)),
if((bitmap &&& @bit_pid) != 0, do: domain_key(:pid)),
Expand Down
25 changes: 25 additions & 0 deletions lib/elixir/test/elixir/module/types/descr_test.exs
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Expand Up @@ -1702,6 +1702,31 @@ defmodule Module.Types.DescrTest do
t2 = closed_map([{domain_key(:tuple), float()}])
t3 = union(t1, t2)
assert map_get(t3, tuple()) == {:ok, number() |> nil_or_type()}

# Verify that empty_list() bitmap type maps to :list domain (not :empty_list domain)
map_with_list_domain = closed_map([{domain_key(:list), atom([:empty])}])

# empty_list() should access the :list domain
assert map_get(map_with_list_domain, empty_list()) == {:ok, atom([:empty]) |> nil_or_type()}

# non_empty_list() should also access the :list domain
assert map_get(map_with_list_domain, non_empty_list(integer())) ==
{:ok, atom([:empty]) |> nil_or_type()}

# list() should also access the :list domain
assert map_get(map_with_list_domain, list(integer())) ==
{:ok, atom([:empty]) |> nil_or_type()}

# If I create a map and instantiate both empty_list() and non_empty_list(integer()), it should return the union of the two types
map =
closed_map([{domain_key(:list), atom([:empty])}, {domain_key(:list), atom([:non_empty])}])

assert map_get(map, empty_list()) == {:ok, atom([:empty, :non_empty]) |> nil_or_type()}

assert map_get(map, non_empty_list(integer())) ==
{:ok, atom([:empty, :non_empty]) |> nil_or_type()}

assert map_get(map, list(integer())) == {:ok, atom([:empty, :non_empty]) |> nil_or_type()}
end

test "map_get with dynamic" do
Expand Down