Fix inference of open maps with non-singleton keys

Closes #10371.

3 files changed, 41 insertions, 7 deletions

diff --git a/lib/elixir/lib/module/types/of.ex b/lib/elixir/lib/module/types/of.ex
index 5c5b0bd40..ee147a137 100644
--- a/lib/elixir/lib/module/types/of.ex
+++ b/lib/elixir/lib/module/types/of.ex
@@ -16,7 +16,17 @@ defmodule Module.Types.Of do
   """
   def open_map(args, stack, context, fun) do
     with {:ok, pairs, context} <- map_pairs(args, stack, context, fun) do
-      {:ok, {:map, pairs_to_unions(pairs, context) ++ [{:optional, :dynamic, :dynamic}]}, context}
+      pairs =
+        for {key, value} <- pairs, not has_unbound_var?(key, context) do
+          if singleton?(key, context) do
+            {key, value}
+          else
+            {key, to_union([value, :dynamic], context)}
+          end
+        end
+
+      triplets = pairs_to_unions(pairs, [], context) ++ [{:optional, :dynamic, :dynamic}]
+      {:ok, {:map, triplets}, context}
     end
   end
 
@@ -25,7 +35,7 @@ defmodule Module.Types.Of do
   """
   def closed_map(args, stack, context, fun) do
     with {:ok, pairs, context} <- map_pairs(args, stack, context, fun) do
-      {:ok, {:map, pairs_to_unions(pairs, context)}, context}
+      {:ok, {:map, closed_to_unions(pairs, context)}, context}
     end
   end
 
@@ -37,9 +47,9 @@ defmodule Module.Types.Of do
     end)
   end
 
-  defp pairs_to_unions([{key, value}], _context), do: [{:required, key, value}]
+  defp closed_to_unions([{key, value}], _context), do: [{:required, key, value}]
 
-  defp pairs_to_unions(pairs, context) do
+  defp closed_to_unions(pairs, context) do
     case Enum.split_with(pairs, fn {key, _value} -> has_unbound_var?(key, context) end) do
       {[], pairs} -> pairs_to_unions(pairs, [], context)
       {[_ | _], pairs} -> pairs_to_unions([{:dynamic, :dynamic} | pairs], [], context)
diff --git a/lib/elixir/lib/module/types/unify.ex b/lib/elixir/lib/module/types/unify.ex
index bc839199a..df1774530 100644
--- a/lib/elixir/lib/module/types/unify.ex
+++ b/lib/elixir/lib/module/types/unify.ex
@@ -560,13 +560,32 @@ defmodule Module.Types.Unify do
   def has_unbound_var?(_type, _context), do: false
 
   @doc """
+  Returns true if it is a singleton type.
+
+  Only atoms are singleton types. Unbound vars are not
+  considered singleton types.
+  """
+  def singleton?({:var, var}, context) do
+    case context.types do
+      %{^var => :unbound} -> false
+      %{^var => type} -> singleton?(type, context)
+    end
+  end
+
+  def singleton?({:atom, _}, _context), do: true
+  def singleton?(_type, _context), do: false
+
+  @doc """
   Checks if the first argument is a subtype of the second argument.
 
   This function assumes that:
 
-    * dynamic is not considered a subtype of all other types but the top type
     * unbound variables are not subtype of anything
 
+    * dynamic is not considered a subtype of all other types but the top type.
+      This allows this function can be used for ordering, in other cases, you
+      may need to check for both sides
+
   """
   def subtype?(type, type, _context), do: true
 
diff --git a/lib/elixir/test/elixir/module/types/pattern_test.exs b/lib/elixir/test/elixir/module/types/pattern_test.exs
index 5eb336b1b..458d0645e 100644
--- a/lib/elixir/test/elixir/module/types/pattern_test.exs
+++ b/lib/elixir/test/elixir/module/types/pattern_test.exs
@@ -118,13 +118,18 @@ defmodule Module.Types.PatternTest do
                 {:map, [{:required, {:atom, :a}, {:atom, :b}}, {:optional, :dynamic, :dynamic}]}}
 
       assert quoted_pattern(%{123 => a}) ==
-               {:ok, {:map, [{:required, :integer, {:var, 0}}, {:optional, :dynamic, :dynamic}]}}
+               {:ok,
+                {:map,
+                 [
+                   {:required, :integer, {:union, [{:var, 0}, :dynamic]}},
+                   {:optional, :dynamic, :dynamic}
+                 ]}}
 
       assert quoted_pattern(%{123 => :foo, 456 => :bar}) ==
                {:ok,
                 {:map,
                  [
-                   {:required, :integer, {:union, [{:atom, :foo}, {:atom, :bar}]}},
+                   {:required, :integer, :dynamic},
                    {:optional, :dynamic, :dynamic}
                  ]}}