Add meta generated to for/1 clauses with bitstrings (#7560)

Closes #7508.

Signed-off-by: José Valim <jose.valim@plataformatec.com.br>

Author: ggcampinho

lib/elixir/src/elixir_erl_for.erl

@@ -104,30 +104,31 @@ build_inline_each(Ann, Clauses, Expr, {nil, _} = Into, Uniq, S) ->
   {elixir_erl:remote(Ann, lists, reverse, [ReduceExpr]), S};
 build_inline_each(Ann, Clauses, Expr, {bin, _, []}, Uniq, S) ->
   {InnerValue, SV} = build_var(Ann, S),
+  Generated = erl_anno:set_generated(true, Ann),
 
   InnerFun = fun(InnerExpr, InnerAcc) ->
     {'case', Ann, InnerExpr, [
-      {clause, Ann,
+      {clause, Generated,
        [InnerValue],
        [[elixir_erl:remote(Ann, erlang, is_binary, [InnerValue]),
          elixir_erl:remote(Ann, erlang, is_list, [InnerAcc])]],
-       [{cons, Ann, InnerAcc, InnerValue}]},
-      {clause, Ann,
+       [{cons, Generated, InnerAcc, InnerValue}]},
+      {clause, Generated,
        [InnerValue],
        [[elixir_erl:remote(Ann, erlang, is_bitstring, [InnerValue]),
          elixir_erl:remote(Ann, erlang, is_bitstring, [InnerAcc])]],
        [{bin, Ann, [
           {bin_element, Ann, InnerAcc, default, [bitstring]},
           {bin_element, Ann, InnerValue, default, [bitstring]}
        ]}]},
-      {clause, Ann,
+      {clause, Generated,
        [InnerValue],
        [[elixir_erl:remote(Ann, erlang, is_bitstring, [InnerValue])]],
        [{bin, Ann, [
           {bin_element, Ann, elixir_erl:remote(Ann, erlang, iolist_to_binary, [InnerAcc]), default, [bitstring]},
           {bin_element, Ann, InnerValue, default, [bitstring]}
        ]}]},
-      {clause, Ann,
+      {clause, Generated,
        [InnerValue],
        [],
        [elixir_erl:remote(Ann, erlang, error, [{tuple, Ann, [{atom, Ann, badarg}, InnerValue]}])]}

lib/elixir/test/elixir/fixtures/dialyzer/for_bitstring.ex

@@ -0,0 +1,5 @@
+defmodule Dialyzer.ForBitstring do
+  def foo() do
+    for a <- 1..3, into: "", do: <<a>>
+  end
+end

lib/elixir/test/elixir/kernel/dialyzer_test.exs

@@ -120,6 +120,11 @@ defmodule Kernel.DialyzerTest do
     assert_dialyze_no_warnings!(context)
   end
 
+  test "no warnings on for comprehensions with bitstrings", context do
+    copy_beam!(context, Dialyzer.ForBitstring)
+    assert_dialyze_no_warnings!(context)
+  end
+
   test "no warnings on for falsy check that always boolean", context do
     copy_beam!(context, Dialyzer.ForBooleanCheck)
     assert_dialyze_no_warnings!(context)