Add mix help Mod, mix help Mod.fun and mix help Mod.fun/arity

Author: renanroberto

lib/mix/lib/mix/tasks/help.ex

@@ -94,13 +94,22 @@ defmodule Mix.Tasks.Help do
     Mix.raise("Unexpected arguments, expected \"mix help --search PATTERN\"")
   end
 
-  def run([task]) do
-    loadpaths!()
-    opts = Application.get_env(:mix, :colors)
-    opts = [width: width(), enabled: ansi_docs?(opts)] ++ opts
-
-    for doc <- verbose_doc(task) do
-      print_doc(task, doc, opts)
+  def run([task_or_module]) do
+    if Regex.match?(~r/(:|[A-Z]).*/, task_or_module) do
+      task_or_module
+      |> Code.string_to_quoted!()
+      |> IEx.Introspection.decompose(__ENV__)
+      |> Code.eval_quoted()
+      |> elem(0)
+      |> IEx.Introspection.h()
+    else
+      loadpaths!()
+      opts = Application.get_env(:mix, :colors)
+      opts = [width: width(), enabled: ansi_docs?(opts)] ++ opts
+
+      for doc <- verbose_doc(task_or_module) do
+        print_doc(task_or_module, doc, opts)
+      end
     end
 
     :ok

lib/mix/test/mix/tasks/help_test.exs

@@ -191,6 +191,52 @@ defmodule Mix.Tasks.HelpTest do
     end)
   end
 
+  test "help Elixir MODULE", context do
+    in_tmp(context.test, fn ->
+      output =
+        capture_io(fn ->
+          Mix.Tasks.Help.run(["Mix"])
+        end)
+
+      assert output =~
+               "Mix is a build tool that provides tasks for creating, compiling, and testing\nElixir projects, managing its dependencies, and more."
+    end)
+  end
+
+  test "help Erlang MODULE", context do
+    in_tmp(context.test, fn ->
+      output =
+        capture_io(fn ->
+          Mix.Tasks.Help.run([":math"])
+        end)
+
+      assert output =~ "This module provides an interface to a number of mathematical functions."
+    end)
+  end
+
+  test "help FUNCTION/0", context do
+    in_tmp(context.test, fn ->
+      output =
+        capture_io(fn ->
+          Mix.Tasks.Help.run(["DateTime.utc_now()"])
+        end)
+
+      assert output =~ "Returns the current datetime in UTC"
+    end)
+  end
+
+  test "help FUNCTION/1", context do
+    in_tmp(context.test, fn ->
+      output =
+        capture_io(fn ->
+          Mix.Tasks.Help.run(["Enum.all?/1"])
+        end)
+
+      assert output =~
+               "Returns \e[36mtrue\e[0m if all elements in \e[36menumerable\e[0m are truthy"
+    end)
+  end
+
   test "help --search PATTERN", context do
     in_tmp(context.test, fn ->
       Mix.Tasks.Help.run(["--search", "deps"])