dialyzer: Correct a parameterized opaque types bug

See also https://bugs.erlang.org/browse/ERL-565.

To avoid loops, erl_types:t_is_subtype checks for equality using
unopaqued types, but in (at least) one case something is lost:

This fix makes sure that when forwarding arguments in dataflow, types
with different parameters but equal when unopaqued are considered
different.

For example, dict:dict(0, {}) and dict:dict(0, []) are equal when
unopaqued (due to how dict(_, _) is declared in module dict), but
should be considered different when forwarding args.

2 files changed, 28 insertions, 0 deletions

diff --git a/lib/dialyzer/test/opaque_SUITE_data/src/para_bug/same.erl b/lib/dialyzer/test/opaque_SUITE_data/src/para_bug/same.erl
new file mode 100644
index 0000000000..44149f4199
--- /dev/null
+++ b/lib/dialyzer/test/opaque_SUITE_data/src/para_bug/same.erl
@@ -0,0 +1,15 @@
+-module(same).
+
+-export([baz/1]).
+
+-record(bar, {
+          a :: same_type:st(integer()),
+          b :: same_type:st(atom())
+         }).
+
+baz(Bar) ->
+    _ = wrap_find(0, Bar#bar.a),
+    wrap_find(0, Bar#bar.b).
+
+wrap_find(K, D) ->
+  same_type:t(K, D).
diff --git a/lib/dialyzer/test/opaque_SUITE_data/src/para_bug/same_type.erl b/lib/dialyzer/test/opaque_SUITE_data/src/para_bug/same_type.erl
new file mode 100644
index 0000000000..855a5d30be
--- /dev/null
+++ b/lib/dialyzer/test/opaque_SUITE_data/src/para_bug/same_type.erl
@@ -0,0 +1,13 @@
+-module(same_type).
+
+-export([t/2]).
+
+-export_type([st/1]).
+
+%% When unopaqued all specializations of st/1 are equal.
+-opaque st(_A) :: {st, tuple()}.
+
+-spec t(_, st(_)) -> _.
+
+t(K, V) ->
+    {K, V}.