Unused require, as: warning suggest alias

lib/elixir/src/elixir_lexical.erl

@@ -99,7 +99,17 @@ warn_unused_imports(Pid, E) ->
   ok.
 
 warn_unused_requires(Pid, E) ->
-  [elixir_errors:file_warn(Meta, ?key(E, file), ?MODULE, {unused_require, Module})
+  [case lists:keyfind(opts, 1, Meta) of
+     {opts, Opts} ->
+       case lists:keyfind(as, 1, Opts) of
+         {as, Alias} when is_atom(Alias) ->
+           elixir_errors:file_warn(Meta, ?key(E, file), ?MODULE, {unused_require, Module, Alias});
+         _ ->
+           elixir_errors:file_warn(Meta, ?key(E, file), ?MODULE, {unused_require, Module})
+       end;
+     _ ->
+       elixir_errors:file_warn(Meta, ?key(E, file), ?MODULE, {unused_require, Module})
+   end
    || {Module, Meta} <- ?tracker:collect_unused_requires(Pid)],
   ok.
 
@@ -121,4 +131,7 @@ format_error({unused_import, {Module, Function, Arity}}) ->
 format_error({unused_import, Module}) ->
   io_lib:format("unused import ~ts", [elixir_aliases:inspect(Module)]);
 format_error({unused_require, Module}) ->
-  io_lib:format("unused require ~ts", [elixir_aliases:inspect(Module)]).
+  io_lib:format("unused require ~ts", [elixir_aliases:inspect(Module)]);
+format_error({unused_require, Module, Alias}) ->
+  io_lib:format("unused require ~ts. Consider using alias ~ts, as: ~ts instead", 
+                [elixir_aliases:inspect(Module), elixir_aliases:inspect(Module), elixir_aliases:inspect(Alias)]).

lib/elixir/test/elixir/kernel/lexical_tracker_test.exs

@@ -138,6 +138,22 @@ defmodule Kernel.LexicalTrackerTest do
     assert D.collect_unused_requires(config[:pid]) == [{String, [module: TestModule, opts: []]}]
   end
 
+  test "unused require with as option - module not used", config do
+    D.add_require(config[:pid], Application, module: TestModule, opts: [as: Foo])
+
+    assert D.collect_unused_requires(config[:pid]) == [
+             {Application, [module: TestModule, opts: [as: Foo]]}
+           ]
+  end
+
+  test "unused require with as option - module used via alias", config do
+    D.add_require(config[:pid], Application, module: TestModule, opts: [as: Foo])
+
+    assert D.collect_unused_requires(config[:pid]) == [
+             {Application, [module: TestModule, opts: [as: Foo]]}
+           ]
+  end
+
   test "imports with no warn are not unused", config do
     D.add_import(config[:pid], String, [], 1, false)
     assert D.collect_unused_imports(config[:pid]) == []

lib/elixir/test/elixir/kernel/warning_test.exs

@@ -2290,6 +2290,23 @@ defmodule Kernel.WarningTest do
     purge(Sample)
   end
 
+  test "unused require with as: suggest alias" do
+    assert_warn_compile(
+      [
+        "nofile:2:3",
+        "unused require Application. Consider using alias Application, as: Foo instead"
+      ],
+      """
+      defmodule Sample do
+        require Application, as: Foo
+        def a, do: Foo.app_dir(:bar)
+      end
+      """
+    )
+  after
+    purge(Sample)
+  end
+
   defp purge(module) when is_atom(module) do
     :code.purge(module)
     :code.delete(module)