Ensure -> does not pass line lengths, closes #7279

Author: José Valim

lib/elixir/lib/code/formatter.ex

@@ -1549,10 +1549,16 @@ defmodule Code.Formatter do
     {args_doc, state} = clause_args_to_algebra(args, min_line, state)
     {body_doc, state} = block_to_algebra(body, min_line, max_line, state)
 
+    head =
+      args_doc
+      |> ungroup_if_group()
+      |> concat(" ->")
+      |> nest(:cursor)
+      |> group()
+
     doc =
       "fn "
-      |> concat(group(nest(args_doc, :cursor)))
-      |> concat(" ->")
+      |> concat(head)
       |> glue(body_doc)
       |> nest(2)
       |> glue("end")
@@ -1598,15 +1604,12 @@ defmodule Code.Formatter do
     {args_doc, state} = clause_args_to_algebra(args, min_line, state)
     {body_doc, state} = block_to_algebra(body, min_line, max_line, state)
 
-    clause_doc =
-      " ->"
-      |> glue(body_doc)
-      |> nest(2)
-
     doc =
       args_doc
+      |> ungroup_if_group()
+      |> concat(" ->")
       |> group()
-      |> concat(clause_doc)
+      |> concat(break() |> concat(body_doc) |> nest(2))
       |> wrap_in_parens()
       |> maybe_force_clauses(clauses)
       |> group()
@@ -1674,7 +1677,15 @@ defmodule Code.Formatter do
 
     state = %{state | operand_nesting: nesting}
     {body_doc, state} = block_to_algebra(body, min_line, end_line(meta), state)
-    {concat(args_doc, " ->" |> glue(body_doc) |> nest(2)), state}
+
+    doc =
+      args_doc
+      |> ungroup_if_group()
+      |> concat(" ->")
+      |> group()
+      |> concat(break() |> concat(body_doc) |> nest(2))
+
+    {doc, state}
   end
 
   defp add_max_line_to_last_clause([{op, meta, args}], max_line) do

lib/elixir/lib/gen_event/stream.ex

@@ -161,7 +161,8 @@ defimpl Enumerable, for: GenEvent.Stream do
 
   defp flush_events(ref) do
     receive do
-      {_from, {_pid, ^ref}, {notify, _event}} when notify in [:notify, :ack_notify, :sync_notify] ->
+      {_from, {_pid, ^ref}, {notify, _event}}
+      when notify in [:notify, :ack_notify, :sync_notify] ->
         flush_events(ref)
     after
       0 -> :ok

lib/elixir/test/elixir/code_formatter/general_test.exs

@@ -329,6 +329,46 @@ defmodule Code.Formatter.GeneralTest do
       end
       """
     end
+
+    test "with -> on line limit" do
+      bad = """
+      fn ab, cd ->
+        ab + cd
+      end
+      """
+
+      good = """
+      fn ab,
+         cd ->
+        ab + cd
+      end
+      """
+
+      assert_format bad, good, @short_length
+
+      bad = """
+      fn
+        ab, cd ->
+          1
+        xy, zw ->
+          2
+      end
+      """
+
+      good = """
+      fn
+        ab,
+        cd ->
+          1
+
+        xy,
+        zw ->
+          2
+      end
+      """
+
+      assert_format bad, good, @short_length
+    end
   end
 
   describe "anonymous functions types" do