Report spec discrepancy on mismatching lists

This patch enables Dialyzer to detect cases where a function has a specification
for a return type containing some list with elements different than the ones
Dialyzer's own algorithm can infer e.g. a function specified to return [atom()]
when actually [[atom()]] is returned.

Previously Dialyzer remained silent, under normal operation, seeing that these
two types have the empty list as a common element, so they were not 'completely
irrelevant'.

2 files changed, 59 insertions, 0 deletions

diff --git a/lib/dialyzer/test/small_SUITE_data/results/empty_list_infimum b/lib/dialyzer/test/small_SUITE_data/results/empty_list_infimum
new file mode 100644
index 0000000000..a59986cba5
--- /dev/null
+++ b/lib/dialyzer/test/small_SUITE_data/results/empty_list_infimum
@@ -0,0 +1,2 @@
+
+empty_list_infimum.erl:39: Invalid type specification for function empty_list_infimum:list_vhost_permissions/1. The success typing is (_) -> [[{_,_}]]
diff --git a/lib/dialyzer/test/small_SUITE_data/src/empty_list_infimum.erl b/lib/dialyzer/test/small_SUITE_data/src/empty_list_infimum.erl
new file mode 100644
index 0000000000..b58fa732cb
--- /dev/null
+++ b/lib/dialyzer/test/small_SUITE_data/src/empty_list_infimum.erl
@@ -0,0 +1,57 @@
+%%
+%% The Original Code is RabbitMQ.
+%%
+%% The Initial Developer of the Original Code is VMware, Inc.
+%%
+
+-module(empty_list_infimum).
+
+-record(permission, {configure, write, read}).
+-record(user_vhost, {username, virtual_host}).
+-record(user_permission, {user_vhost, permission}).
+
+%%----------------------------------------------------------------------------
+
+-export([i_delete/1]).
+
+-type(vhost() :: binary()).
+
+-type(info_key() :: atom()).
+-type(info_keys() :: [info_key()]).
+
+-type(info() :: {info_key(), any()}).
+-type(infos() :: [info()]).
+
+%%----------------------------------------------------------------------------
+
+-spec i_delete(vhost()) -> 'ok'.
+
+i_delete(VHostPath) ->
+    [ok || _ <- list_vhost_permissions(VHostPath)],
+    ok.
+
+%%----------------------------------------------------------------------------
+
+vhost_perms_info_keys() ->
+    [user, configure, write, read].
+
+-spec list_vhost_permissions(vhost()) -> infos().
+
+list_vhost_permissions(VHostPath) ->
+    list_permissions(vhost_perms_info_keys(), rabbit_foo:some_list()).
+
+filter_props(Keys, Props) ->
+    [T || T = {K, _} <- Props, lists:member(K, Keys)].
+
+list_permissions(Keys, SomeList) ->
+    [filter_props(Keys, [{user,      Username},
+                         {vhost,     VHostPath},
+                         {configure, ConfigurePerm},
+                         {write,     WritePerm},
+                         {read,      ReadPerm}]) ||
+        #user_permission{user_vhost = #user_vhost{username     = Username,
+                                                  virtual_host = VHostPath},
+                         permission = #permission{configure = ConfigurePerm,
+						  write     = WritePerm,
+						  read      = ReadPerm}} <-
+           SomeList].