Add special fn case to signature_to_binary (#8429)

2 files changed, 11 insertions, 0 deletions

diff --git a/lib/elixir/src/elixir_erl.erl b/lib/elixir/src/elixir_erl.erl
index 9623df65c..f8ea91032 100644
--- a/lib/elixir/src/elixir_erl.erl
+++ b/lib/elixir/src/elixir_erl.erl
@@ -531,6 +531,9 @@ get_type_docs(Set, Types) ->
 signature_to_binary(_Module, Name, _Signature) when Name == '__aliases__'; Name == '__block__' ->
   <<(atom_to_binary(Name, utf8))/binary, "(args)">>;
 
+signature_to_binary(_Module, fn, _Signature) -> 
+  <<"fn">>;
+
 signature_to_binary(_Module, Name, _Signature)
     when Name == '__CALLER__'; Name == '__DIR__'; Name == '__ENV__';
          Name == '__MODULE__'; Name == '__STACKTRACE__'; Name == '%{}' ->
diff --git a/lib/elixir/test/elixir/kernel/docs_test.exs b/lib/elixir/test/elixir/kernel/docs_test.exs
index b5209a21d..fd26dd2a5 100644
--- a/lib/elixir/test/elixir/kernel/docs_test.exs
+++ b/lib/elixir/test/elixir/kernel/docs_test.exs
@@ -307,4 +307,12 @@ defmodule Kernel.DocsTest do
              {{:fuz, 0}, :none}
            ] = Enum.sort(function_docs)
   end
+
+  describe "special signatures" do
+    test "fn" do
+      {:docs_v1, _, _, _, _, _, docs} = Code.fetch_docs(Kernel.SpecialForms)
+      {_, _, fn_docs, _, _} = Enum.find(docs, &match?({_, :fn, 1}, elem(&1, 0)))
+      assert fn_docs == ["fn"]
+    end
+  end
 end