Add info about protocols in the i/1 IEx Helpers (#5241)

With this commit, we show info about the protocols that a given data
structure implements and in case that data structure is a module that is
also a protocol, we show all the data structures that implement that
protocols as well.

4 files changed, 45 insertions, 9 deletions

diff --git a/lib/iex/lib/iex/helpers.ex b/lib/iex/lib/iex/helpers.ex
index 9dfc97e62..6b6470a3f 100644
--- a/lib/iex/lib/iex/helpers.ex
+++ b/lib/iex/lib/iex/helpers.ex
@@ -429,7 +429,10 @@ defmodule IEx.Helpers do
 
   """
   def i(term) do
-    info = ["Term": inspect(term)] ++ IEx.Info.info(term)
+    info =
+      ["Term": inspect(term)] ++
+      IEx.Info.info(term) ++
+      ["Implemented protocols": all_implemented_protocols_for_term(term)]
 
     for {subject, info} <- info do
       info = info |> to_string() |> String.trim() |> String.replace("\n", "\n  ")
@@ -440,6 +443,17 @@ defmodule IEx.Helpers do
     dont_display_result()
   end
 
+  # Given any "term", this function returns all the protocols in
+  # :code.get_path() implemented by the data structure of such term, in the form
+  # of a binary like "Protocol1, Protocol2, Protocol3".
+  defp all_implemented_protocols_for_term(term) do
+    :code.get_path()
+    |> Protocol.extract_protocols()
+    |> Enum.uniq()
+    |> Enum.reject(fn(protocol) -> is_nil(protocol.impl_for(term)) end)
+    |> Enum.map_join(", ", &inspect/1)
+  end
+
   @doc """
   Flushes all messages sent to the shell and prints them out.
   """
diff --git a/lib/iex/lib/iex/info.ex b/lib/iex/lib/iex/info.ex
index b7e6b32b0..517ba740c 100644
--- a/lib/iex/lib/iex/info.ex
+++ b/lib/iex/lib/iex/info.ex
@@ -35,13 +35,27 @@ defimpl IEx.Info, for: Atom do
       end
 
     mod_info = mod.module_info()
-    ["Module bytecode": module_object_file(mod),
-     "Source": module_source_file(mod_info),
-     "Version": module_version(mod_info),
-     "Compile options": module_compile_options(mod_info),
-     "Description": "#{extra}Call #{inspect mod}.module_info() to access metadata.",
-     "Raw representation": ":" <> inspect(Atom.to_string(mod)),
-     "Reference modules": "Module, Atom"]
+    generic_info =
+      ["Module bytecode": module_object_file(mod),
+       "Source": module_source_file(mod_info),
+       "Version": module_version(mod_info),
+       "Compile options": module_compile_options(mod_info),
+       "Description": "#{extra}Call #{inspect mod}.module_info() to access metadata."]
+
+    specific_info =
+      if function_exported?(mod, :__protocol__, 1) do
+        impls =
+          mod
+          |> Protocol.extract_impls(:code.get_path())
+          |> Enum.map_join(", ", &inspect/1)
+        ["Protocol": "This module is a protocol. These data structures implement it:\n  #{impls}"]
+      else
+        []
+      end
+
+    generic_info ++ specific_info ++
+      ["Raw representation": ":" <> inspect(Atom.to_string(mod)),
+       "Reference modules": "Module, Atom"]
   end
 
   defp info_module_like_atom(atom) do
diff --git a/lib/iex/test/iex/helpers_test.exs b/lib/iex/test/iex/helpers_test.exs
index 96da4f6ce..16338d6ae 100644
--- a/lib/iex/test/iex/helpers_test.exs
+++ b/lib/iex/test/iex/helpers_test.exs
@@ -493,7 +493,7 @@ defmodule IEx.HelpersTest do
 
   test "i helper" do
     output = capture_iex ~s[i(:ok)]
-    assert output == String.trim_trailing("""
+    assert output =~ String.trim_trailing("""
     Term
       :ok
     Data type
diff --git a/lib/iex/test/iex/info_test.exs b/lib/iex/test/iex/info_test.exs
index 8974e6fc4..a9daece59 100644
--- a/lib/iex/test/iex/info_test.exs
+++ b/lib/iex/test/iex/info_test.exs
@@ -29,6 +29,14 @@ defmodule IEx.InfoTest do
     assert info[:"Description"] == description
   end
 
+  test "atoms: module that is also a protocol" do
+    info = Info.info(String.Chars)
+    description = info[:"Protocol"]
+    assert description =~ "This module is a protocol"
+    assert description =~ "Atom"
+    assert description =~ "BitString"
+  end
+
   test "atoms: module-like atom (Foo)" do
     info = Info.info(NonexistentModuleAtom)
     assert info[:"Raw representation"] == ~s(:"Elixir.NonexistentModuleAtom")