The else clause in with supports guards (#4960)

Signed-off-by: José Valim <[email protected]>

Author: ericentin

lib/elixir/src/elixir_with.erl

@@ -107,9 +107,14 @@ build_else(Meta, ElseClauses) ->
     each_clause_to_error_match(ElseClauses)] ++ [build_raise(Meta)].
 
 each_clause_to_error_match(Clauses) ->
-  [{match, Meta, [{error, Match}], Expr} ||
+  [{match, Meta, [error_match_for_match(Match)], Expr} ||
     {'->', Meta, [[Match], Expr]} <- Clauses].
 
+error_match_for_match({'when', Meta, [Left, Right]}) ->
+  {'when', Meta, [{error, Left}, Right]};
+error_match_for_match(Match) ->
+  {error, Match}.
+
 build_raise(Meta) ->
   Other = {other, Meta, ?MODULE},
   {match, ?generated, [{error, Other}], {{'.', Meta, [erlang, error]}, Meta, [{with_clause, Other}]}}.

lib/elixir/test/elixir/kernel/with_test.exs

@@ -66,6 +66,7 @@ defmodule Kernel.WithTest do
 
   test "else conditions" do
     assert with({:ok, res} <- 41, do: res, else: ({:error, error} -> error; res -> res + 1)) == 42
+    assert with({:ok, res} <- 41, do: res, else: (res when res == 41 -> res + 1; res -> res)) == 42
     assert with({:ok, res} <- 41, do: res, else: (_ -> :error)) == :error
   end