[dialyzer] Re-work the handling of opaque types

It is now OK to inspect and modify the internals of opaque types within
the scope of the module.

The contracts are used for decorating types with opaqueness when it is
harmless to do so. The opaqueness is propagated by the typesig module
and also by the dataflow module.

A lot of details have been fixed or updated. In particular the modules
erl_types and erl_bif_types have been modified extensively.

The version in vsn.mk has been updated to 2.7. The reason is a
modification of #opaque{} in erl_types.

Dialyzer seems to be about five percent slower than it used to be.

13 files changed, 105 insertions, 9 deletions

diff --git a/lib/dialyzer/test/opaque_SUITE_data/results/crash b/lib/dialyzer/test/opaque_SUITE_data/results/crash
index 1ddae5149f..69bdc00257 100644
--- a/lib/dialyzer/test/opaque_SUITE_data/results/crash
+++ b/lib/dialyzer/test/opaque_SUITE_data/results/crash
@@ -1,6 +1,6 @@
 
 crash_1.erl:45: Record construction #targetlist{list::[]} violates the declared type of field list::'undefined' | crash_1:target()
-crash_1.erl:48: The call crash_1:get_using_branch2(Branch::maybe_improper_list(),L::'undefined' | crash_1:target()) contains an opaque term as 2nd argument when terms of different types are expected in these positions
+crash_1.erl:48: The call crash_1:get_using_branch2(Branch::maybe_improper_list(),L::'undefined' | crash_1:target()) will never return since it differs in the 2nd argument from the success typing arguments: (any(),maybe_improper_list())
 crash_1.erl:50: The pattern <_Branch, []> can never match the type <maybe_improper_list(),'undefined' | crash_1:target()>
 crash_1.erl:52: The pattern <Branch, [H = {'target', _, _} | _T]> can never match the type <maybe_improper_list(),'undefined' | crash_1:target()>
 crash_1.erl:54: The pattern <Branch, [{'target', _, _} | T]> can never match the type <maybe_improper_list(),'undefined' | crash_1:target()>
diff --git a/lib/dialyzer/test/opaque_SUITE_data/results/ets b/lib/dialyzer/test/opaque_SUITE_data/results/ets
index 5498ba1538..e79696bc30 100644
--- a/lib/dialyzer/test/opaque_SUITE_data/results/ets
+++ b/lib/dialyzer/test/opaque_SUITE_data/results/ets
@@ -1,3 +1,4 @@
 
 ets_use.erl:12: Guard test is_integer(T::atom() | tid()) breaks the opaqueness of its argument
+ets_use.erl:20: The type test is_integer(atom() | tid()) breaks the opaqueness of the term atom() | tid()
 ets_use.erl:7: Guard test is_integer(T::tid()) breaks the opaqueness of its argument
diff --git a/lib/dialyzer/test/opaque_SUITE_data/results/ewgi b/lib/dialyzer/test/opaque_SUITE_data/results/ewgi
index 3c8cfb59f8..5bc6b87fbb 100644
--- a/lib/dialyzer/test/opaque_SUITE_data/results/ewgi
+++ b/lib/dialyzer/test/opaque_SUITE_data/results/ewgi
@@ -1,4 +1,4 @@
 
 ewgi_api.erl:55: The call gb_trees:to_list({non_neg_integer(),'nil' | {_,_,_,_}}) does not have an opaque term of type gb_tree() as 1st argument
-ewgi_testapp.erl:35: The call ewgi_testapp:htmlise_data("request_data",{non_neg_integer(),'nil' | {_,_,_,_}}) will never return since it differs in the 2nd argument from the success typing arguments: ([95 | 97 | 100 | 101 | 104 | 112 | 113 | 114 | 115 | 116 | 117,...],[{_,_}])
+ewgi_testapp.erl:35: The call ewgi_testapp:htmlise_data("request_data",{non_neg_integer(),'nil' | {_,_,_,_}}) does not have a term of type [{_,_}] | gb_tree() (with opaque subterms) as 2nd argument
 ewgi_testapp.erl:43: The call gb_trees:to_list(T::{non_neg_integer(),'nil' | {_,_,_,_}}) does not have an opaque term of type gb_tree() as 1st argument
diff --git a/lib/dialyzer/test/opaque_SUITE_data/results/inf_loop1 b/lib/dialyzer/test/opaque_SUITE_data/results/inf_loop1
index eb8f304905..4fe5fcfe2d 100644
--- a/lib/dialyzer/test/opaque_SUITE_data/results/inf_loop1
+++ b/lib/dialyzer/test/opaque_SUITE_data/results/inf_loop1
@@ -2,4 +2,4 @@
 inf_loop1.erl:119: The pattern [{_, LNorms}] can never match the type []
 inf_loop1.erl:121: The pattern [{LinksA, LNormA}, {LinksB, LNormB}] can never match the type []
 inf_loop1.erl:129: The pattern [{_, Norm} | _] can never match the type []
-inf_loop1.erl:71: The call gb_trees:get(Edge::any(),Etab::array()) contains an opaque term as 2nd argument when terms of different types are expected in these positions
+inf_loop1.erl:71: The call gb_trees:get(Edge::any(),Etab::array()) does not have an opaque term of type gb_tree() as 2nd argument
diff --git a/lib/dialyzer/test/opaque_SUITE_data/results/inf_loop2 b/lib/dialyzer/test/opaque_SUITE_data/results/inf_loop2
new file mode 100644
index 0000000000..4f0b79eb35
--- /dev/null
+++ b/lib/dialyzer/test/opaque_SUITE_data/results/inf_loop2
@@ -0,0 +1,5 @@
+
+inf_loop2.erl:122: The pattern [{_, LNorms}] can never match the type []
+inf_loop2.erl:124: The pattern [{LinksA, LNormA}, {LinksB, LNormB}] can never match the type []
+inf_loop2.erl:132: The pattern [{_, Norm} | _] can never match the type []
+inf_loop2.erl:74: The call gb_trees:get(Edge::any(),Etab::array()) does not have an opaque term of type gb_tree() as 2nd argument
diff --git a/lib/dialyzer/test/opaque_SUITE_data/results/int b/lib/dialyzer/test/opaque_SUITE_data/results/int
index 3ee4def34b..dc806fa12c 100644
--- a/lib/dialyzer/test/opaque_SUITE_data/results/int
+++ b/lib/dialyzer/test/opaque_SUITE_data/results/int
@@ -1,3 +1,3 @@
 
-int_adt.erl:28: Invalid type specification for function int_adt:add_f/2. The success typing is (number(),float()) -> number()
-int_adt.erl:32: Invalid type specification for function int_adt:div_f/2. The success typing is (number(),number()) -> float()
+int_adt.erl:28: Invalid type specification for function int_adt:add_f/2. The success typing is (number() | int_adt:int(),float()) -> number() | int_adt:int()
+int_adt.erl:32: Invalid type specification for function int_adt:div_f/2. The success typing is (number() | int_adt:int(),number() | int_adt:int()) -> float()
diff --git a/lib/dialyzer/test/opaque_SUITE_data/results/mixed_opaque b/lib/dialyzer/test/opaque_SUITE_data/results/mixed_opaque
index ab850b613e..0363be544d 100644
--- a/lib/dialyzer/test/opaque_SUITE_data/results/mixed_opaque
+++ b/lib/dialyzer/test/opaque_SUITE_data/results/mixed_opaque
@@ -1,2 +1,2 @@
 
-mixed_opaque_use.erl:31: The call mixed_opaque_rec_adt:get_a(Q::mixed_opaque_queue_adt:my_queue()) contains an opaque term as 1st argument when an opaque term of type mixed_opaque_rec_adt:rec() is expected
+mixed_opaque_use.erl:31: The call mixed_opaque_rec_adt:get_a(Q::mixed_opaque_queue_adt:my_queue()) does not have an opaque term of type mixed_opaque_rec_adt:rec() as 1st argument
diff --git a/lib/dialyzer/test/opaque_SUITE_data/results/modules b/lib/dialyzer/test/opaque_SUITE_data/results/modules
new file mode 100644
index 0000000000..f71334b9de
--- /dev/null
+++ b/lib/dialyzer/test/opaque_SUITE_data/results/modules
@@ -0,0 +1,3 @@
+
+opaque_digraph.erl:353: Cons will produce an improper list since its 2nd argument is number()
+opaque_digraph.erl:365: Cons will produce an improper list since its 2nd argument is number()
diff --git a/lib/dialyzer/test/opaque_SUITE_data/results/my_queue b/lib/dialyzer/test/opaque_SUITE_data/results/my_queue
index 2860b91084..1f25a6f9c3 100644
--- a/lib/dialyzer/test/opaque_SUITE_data/results/my_queue
+++ b/lib/dialyzer/test/opaque_SUITE_data/results/my_queue
@@ -4,4 +4,4 @@ my_queue_use.erl:19: The call my_queue_adt:add(42,Q0::[]) does not have an opaqu
 my_queue_use.erl:24: The attempt to match a term of type my_queue_adt:my_queue() against the pattern [42 | Q2] breaks the opaqueness of the term
 my_queue_use.erl:30: Attempt to test for equality between a term of type [] and a term of opaque type my_queue_adt:my_queue()
 my_queue_use.erl:34: Cons will produce an improper list since its 2nd argument is my_queue_adt:my_queue()
-my_queue_use.erl:34: The call my_queue_adt:dequeue(nonempty_improper_list(42,my_queue_adt:my_queue())) does not have an opaque term of type my_queue_adt:my_queue() as 1st argument
+my_queue_use.erl:34: The call my_queue_adt:dequeue(nonempty_maybe_improper_list(42,my_queue_adt:my_queue())) does not have an opaque term of type my_queue_adt:my_queue() as 1st argument
diff --git a/lib/dialyzer/test/opaque_SUITE_data/results/opaque b/lib/dialyzer/test/opaque_SUITE_data/results/opaque
index ca76f57b54..5747f9061f 100644
--- a/lib/dialyzer/test/opaque_SUITE_data/results/opaque
+++ b/lib/dialyzer/test/opaque_SUITE_data/results/opaque
@@ -1,2 +1,3 @@
 
+opaque_bug3.erl:19: The pattern 'a' can never match the type #c{}
 opaque_bug4.erl:20: The attempt to match a term of type opaque_adt:abc() against the pattern 'a' breaks the opaqueness of the term
diff --git a/lib/dialyzer/test/opaque_SUITE_data/results/queue b/lib/dialyzer/test/opaque_SUITE_data/results/queue
index c3f04ea64d..59ce33f098 100644
--- a/lib/dialyzer/test/opaque_SUITE_data/results/queue
+++ b/lib/dialyzer/test/opaque_SUITE_data/results/queue
@@ -5,7 +5,6 @@ queue_use.erl:27: The attempt to match a term of type queue() against the patter
 queue_use.erl:33: Attempt to test for equality between a term of type {[42,...],[]} and a term of opaque type queue()
 queue_use.erl:36: The attempt to match a term of type queue() against the pattern {F, _R} breaks the opaqueness of the term
 queue_use.erl:40: The call queue:out({[42,...],[]}) does not have an opaque term of type queue() as 1st argument
-queue_use.erl:48: The call queue_use:add_unique(42,#db{p::[],q::queue()}) contains an opaque term as 2nd argument when terms of different types are expected in these positions
 queue_use.erl:51: The call queue_use:is_in_queue(E::42,DB::#db{p::[],q::queue()}) contains an opaque term as 2nd argument when terms of different types are expected in these positions
 queue_use.erl:56: The attempt to match a term of type #db{p::[],q::queue()} against the pattern {'db', _, {L1, L2}} breaks the opaqueness of queue()
 queue_use.erl:62: The call queue_use:tuple_queue({42,'gazonk'}) does not have a term of type {_,queue()} (with opaque subterms) as 1st argument
diff --git a/lib/dialyzer/test/opaque_SUITE_data/results/simple b/lib/dialyzer/test/opaque_SUITE_data/results/simple
new file mode 100644
index 0000000000..f55b384cbe
--- /dev/null
+++ b/lib/dialyzer/test/opaque_SUITE_data/results/simple
@@ -0,0 +1,87 @@
+
+exact_api.erl:17: The call exact_api:set_type(A::#digraph{vtab::'notable',etab::'notable',ntab::'notable',cyclic::'true'}) does not have an opaque term of type digraph() as 1st argument
+exact_api.erl:23: The call digraph:delete(G::#digraph{vtab::'notable',etab::'notable',ntab::'notable',cyclic::'true'}) does not have an opaque term of type digraph() as 1st argument
+exact_api.erl:55: The attempt to match a term of type exact_adt:exact_adt() against the pattern {'exact_adt'} breaks the opaqueness of the term
+exact_api.erl:59: The call exact_adt:exact_adt_set_type2(A::#exact_adt{}) does not have an opaque term of type exact_adt:exact_adt() as 1st argument
+is_rec.erl:10: The call erlang:is_record(simple1_adt:d1(),'r',2) contains an opaque term as 1st argument when terms of different types are expected in these positions
+is_rec.erl:15: The call erlang:is_record(A::simple1_adt:d1(),'r',I::1 | 2 | 3) contains an opaque term as 1st argument when terms of different types are expected in these positions
+is_rec.erl:19: Guard test is_record(A::simple1_adt:d1(),'r',2) breaks the opaqueness of its argument
+is_rec.erl:23: Guard test is_record({simple1_adt:d1(),1},'r',2) breaks the opaqueness of its argument
+is_rec.erl:41: The call erlang:is_record(A::simple1_adt:d1(),R::'a') contains an opaque term as 1st argument when terms of different types are expected in these positions
+is_rec.erl:45: The call erlang:is_record(A::simple1_adt:d1(),A::simple1_adt:d1(),1) contains an opaque term as 2nd argument when terms of different types are expected in these positions
+is_rec.erl:49: The call erlang:is_record(A::simple1_adt:d1(),any(),1) contains an opaque term as 1st argument when terms of different types are expected in these positions
+is_rec.erl:53: The call erlang:is_record(A::simple1_adt:d1(),A::simple1_adt:d1(),any()) contains an opaque term as 2nd argument when terms of different types are expected in these positions
+is_rec.erl:57: Guard test is_record(A::simple1_adt:d1(),'r',2) breaks the opaqueness of its argument
+is_rec.erl:61: The record #r{f1::simple1_adt:d1()} violates the declared type for #r{}
+is_rec.erl:65: The call erlang:is_record({simple1_adt:d1(),1},'r',2) contains an opaque term as 1st argument when terms of different types are expected in these positions
+rec_api.erl:22: Record construction #r1{f1::10} violates the declared type of field f1::'undefined' | rec_api:a()
+rec_api.erl:23: The pattern {'r1', 10} violates the declared type for #r1{}
+rec_api.erl:27: The attempt to match a term of type rec_adt:r1() against the pattern {'r1', 'a'} breaks the opaqueness of the term
+rec_api.erl:29: Invalid type specification for function rec_api:adt_t1/1. The success typing is (#r1{f1::'a'}) -> #r1{f1::'a'}
+rec_api.erl:34: Invalid type specification for function rec_api:adt_r1/0. The success typing is () -> #r1{f1::'a'}
+rec_api.erl:77: The attempt to match a term of type rec_api:f() against the variable _ breaks the opaqueness of the term
+simple1_api.erl:113: The test simple1_api:d1() =:= simple1_api:d2() can never evaluate to 'true'
+simple1_api.erl:118: Guard test simple1_api:d2() =:= A::simple1_api:d1() can never succeed
+simple1_api.erl:142: Attempt to test for equality between a term of type simple1_adt:o2() and a term of opaque type simple1_adt:o1()
+simple1_api.erl:148: Guard test simple1_adt:o2() =:= A::simple1_adt:o1() contains an opaque term as 1st argument
+simple1_api.erl:154: Attempt to test for inequality between a term of type simple1_adt:o2() and a term of opaque type simple1_adt:o1()
+simple1_api.erl:160: Attempt to test for inequality between a term of type simple1_adt:o2() and a term of opaque type simple1_adt:o1()
+simple1_api.erl:165: Attempt to test for equality between a term of type simple1_adt:c2() and a term of opaque type simple1_adt:c1()
+simple1_api.erl:181: Guard test A::simple1_adt:d1() =< B::simple1_adt:d2() contains an opaque term as 1st argument
+simple1_api.erl:185: Guard test 'a' =< B::simple1_adt:d2() contains an opaque term as 2nd argument
+simple1_api.erl:189: Guard test A::simple1_adt:d1() =< 'd' contains an opaque term as 1st argument
+simple1_api.erl:197: The type test is_integer(A::simple1_adt:d1()) breaks the opaqueness of the term A::simple1_adt:d1()
+simple1_api.erl:221: Guard test A::simple1_api:i1() > 3 can never succeed
+simple1_api.erl:225: Guard test A::simple1_adt:i1() > 3 contains an opaque term as 1st argument
+simple1_api.erl:233: Guard test A::simple1_adt:i1() < 3 contains an opaque term as 1st argument
+simple1_api.erl:239: Guard test A::1 > 3 can never succeed
+simple1_api.erl:243: Guard test A::1 > 3 can never succeed
+simple1_api.erl:257: Guard test is_function(T::simple1_api:o1()) can never succeed
+simple1_api.erl:265: Guard test is_function(T::simple1_adt:o1()) breaks the opaqueness of its argument
+simple1_api.erl:269: The type test is_function(T::simple1_adt:o1()) breaks the opaqueness of the term T::simple1_adt:o1()
+simple1_api.erl:274: Guard test is_function(T::simple1_api:o1(),A::simple1_api:i1()) can never succeed
+simple1_api.erl:284: Guard test is_function(T::simple1_adt:o1(),A::simple1_adt:i1()) breaks the opaqueness of its argument
+simple1_api.erl:289: The type test is_function(T::simple1_adt:o1(),A::simple1_adt:i1()) breaks the opaqueness of the term T::simple1_adt:o1()
+simple1_api.erl:294: The call erlang:is_function(T::simple1_api:o1(),A::simple1_adt:i1()) contains an opaque term as 2nd argument when terms of different types are expected in these positions
+simple1_api.erl:300: The type test is_function(T::simple1_adt:o1(),A::simple1_api:i1()) breaks the opaqueness of the term T::simple1_adt:o1()
+simple1_api.erl:306: Guard test B::simple1_api:b2() =:= 'true' can never succeed
+simple1_api.erl:315: Guard test A::simple1_api:b1() =:= 'false' can never succeed
+simple1_api.erl:319: Guard test not('and'('true','true')) can never succeed
+simple1_api.erl:337: Clause guard cannot succeed.
+simple1_api.erl:342: Guard test B::simple1_adt:b2() =:= 'true' contains an opaque term as 1st argument
+simple1_api.erl:347: Guard test A::simple1_adt:b1() =:= 'true' contains an opaque term as 1st argument
+simple1_api.erl:355: Invalid type specification for function simple1_api:bool_adt_t6/1. The success typing is ('true') -> 1
+simple1_api.erl:365: Clause guard cannot succeed.
+simple1_api.erl:368: Invalid type specification for function simple1_api:bool_adt_t8/2. The success typing is (boolean(),boolean()) -> 1
+simple1_api.erl:378: Clause guard cannot succeed.
+simple1_api.erl:381: Invalid type specification for function simple1_api:bool_adt_t9/2. The success typing is ('false','false') -> 1
+simple1_api.erl:407: The size simple1_adt:i1() breaks the opaqueness of A
+simple1_api.erl:418: The attempt to match a term of type non_neg_integer() against the variable A breaks the opaqueness of simple1_adt:i1()
+simple1_api.erl:425: The attempt to match a term of type non_neg_integer() against the variable B breaks the opaqueness of simple1_adt:i1()
+simple1_api.erl:432: The attempt to match a term of type non_neg_integer() against the variable B breaks the opaqueness of simple1_api:o1()
+simple1_api.erl:448: The attempt to match a term of type non_neg_integer() against the variable Sz breaks the opaqueness of simple1_adt:i1()
+simple1_api.erl:460: The attempt to match a term of type simple1_adt:bit1() against the pattern <<_/binary-unit:8>> breaks the opaqueness of the term
+simple1_api.erl:478: The call 'foo':A(A::simple1_adt:a()) breaks the opaqueness of the term A :: simple1_adt:a()
+simple1_api.erl:486: The call A:'foo'(A::simple1_adt:a()) breaks the opaqueness of the term A :: simple1_adt:a()
+simple1_api.erl:499: The call 'foo':A(A::simple1_api:i()) requires that A is of type atom() not simple1_api:i()
+simple1_api.erl:503: The call 'foo':A(A::simple1_adt:i()) requires that A is of type atom() not simple1_adt:i()
+simple1_api.erl:507: The call A:'foo'(A::simple1_api:i()) requires that A is of type atom() | tuple() not simple1_api:i()
+simple1_api.erl:511: The call A:'foo'(A::simple1_adt:i()) requires that A is of type atom() | tuple() not simple1_adt:i()
+simple1_api.erl:519: Guard test A::simple1_adt:d2() == B::simple1_adt:d1() contains an opaque term as 1st argument
+simple1_api.erl:534: Guard test A::simple1_adt:d1() >= 3 contains an opaque term as 1st argument
+simple1_api.erl:536: Guard test A::simple1_adt:d1() == 3 contains an opaque term as 1st argument
+simple1_api.erl:538: Guard test A::simple1_adt:d1() =:= 3 contains an opaque term as 1st argument
+simple1_api.erl:548: The call erlang:'<'(A::simple1_adt:d1(),3) contains an opaque term as 1st argument when terms of different types are expected in these positions
+simple1_api.erl:558: The call erlang:'=<'(A::simple1_adt:d1(),B::simple1_adt:d2()) contains an opaque term as 1st argument when terms of different types are expected in these positions
+simple1_api.erl:565: Guard test {digraph(),3} > {digraph(),atom() | tid()} contains an opaque term as 2nd argument
+simple1_api.erl:91: Invalid type specification for function simple1_api:tup/0. The success typing is () -> {'a','b'}
+simple2_api.erl:100: The call lists:flatten(A::simple1_adt:tuple1()) contains an opaque term as 1st argument when a structured term of type [any()] is expected
+simple2_api.erl:116: The call lists:flatten({simple1_adt:tuple1()}) will never return since it differs in the 1st argument from the success typing arguments: ([any()])
+simple2_api.erl:121: Guard test {simple1_adt:d1(),3} > {simple1_adt:d1(),simple1_adt:tuple1()} contains an opaque term as 2nd argument
+simple2_api.erl:125: The call erlang:tuple_to_list(B::simple1_adt:tuple1()) contains an opaque term as 1st argument when a structured term of type tuple() is expected
+simple2_api.erl:31: The call erlang:'!'(A::simple1_adt:d1(),'foo') contains an opaque term as 1st argument when terms of different types are expected in these positions
+simple2_api.erl:35: The call erlang:send(A::simple1_adt:d1(),'foo') contains an opaque term as 1st argument when terms of different types are expected in these positions
+simple2_api.erl:51: The call erlang:'<'(A::simple1_adt:d1(),3) contains an opaque term as 1st argument when terms of different types are expected in these positions
+simple2_api.erl:59: The call lists:keysearch(1,A::simple1_adt:d1(),[]) contains an opaque term as 2nd argument when terms of different types are expected in these positions
+simple2_api.erl:67: The call lists:keysearch('key',1,A::simple1_adt:tuple1()) contains an opaque term as 3rd argument when terms of different types are expected in these positions
+simple2_api.erl:96: The call lists:keyreplace('a',1,[{1, 2}],A::simple1_adt:tuple1()) contains an opaque term as 4th argument when terms of different types are expected in these positions
diff --git a/lib/dialyzer/test/opaque_SUITE_data/results/wings b/lib/dialyzer/test/opaque_SUITE_data/results/wings
index a9571441f8..0ca91ae331 100644
--- a/lib/dialyzer/test/opaque_SUITE_data/results/wings
+++ b/lib/dialyzer/test/opaque_SUITE_data/results/wings
@@ -4,7 +4,7 @@ wings_dissolve.erl:19: Guard test is_list(Faces::gb_set()) breaks the opaqueness
 wings_dissolve.erl:272: Guard test is_list(Faces::gb_set()) breaks the opaqueness of its argument
 wings_dissolve.erl:31: The call gb_sets:is_empty(Faces::[any(),...]) does not have an opaque term of type gb_set() as 1st argument
 wings_edge.erl:205: The pattern <Edge, 'hard', Htab> can never match the type <_,'soft',_>
-wings_edge_cmd.erl:30: The call gb_trees:size(P::gb_set()) contains an opaque term as 1st argument when an opaque term of type gb_tree() is expected
+wings_edge_cmd.erl:30: The call gb_trees:size(P::gb_set()) does not have an opaque term of type gb_tree() as 1st argument
 wings_edge_cmd.erl:32: The pattern [_ | Parts] can never match the type []
 wings_edge_cmd.erl:32: The pattern [{_, P} | _] can never match the type []
 wings_io.erl:30: The attempt to match a term of type {'empty',queue()} against the pattern {'empty', {In, Out}} breaks the opaqueness of queue()