Merge branch 'bjorn/lc-warnings/OTP-11626'

* bjorn/lc-warnings/OTP-11626:
  dialyzer: Silence useless warnings about list comprehensions

4 files changed, 110 insertions, 0 deletions

diff --git a/lib/dialyzer/test/unmatched_returns_SUITE_data/dialyzer_options b/lib/dialyzer/test/unmatched_returns_SUITE_data/dialyzer_options
new file mode 100644
index 0000000000..49ac917f61
--- /dev/null
+++ b/lib/dialyzer/test/unmatched_returns_SUITE_data/dialyzer_options
@@ -0,0 +1 @@
+{dialyzer_options, [{warnings, [unmatched_returns]}]}.
diff --git a/lib/dialyzer/test/unmatched_returns_SUITE_data/results/lc_warnings b/lib/dialyzer/test/unmatched_returns_SUITE_data/results/lc_warnings
new file mode 100644
index 0000000000..2784f2119e
--- /dev/null
+++ b/lib/dialyzer/test/unmatched_returns_SUITE_data/results/lc_warnings
@@ -0,0 +1,5 @@
+
+lc_warnings.erl:32: Expression produces a value of type [opaque_atom_adt:opaque_atom()], but this value is unmatched
+lc_warnings.erl:43: Expression produces a value of type [array()], but this value is unmatched
+lc_warnings.erl:65: Expression produces a value of type [lc_warnings:opaque_tuple()], but this value is unmatched
+lc_warnings.erl:7: Expression produces a value of type ['ok' | {'error',atom()}], but this value is unmatched
diff --git a/lib/dialyzer/test/unmatched_returns_SUITE_data/src/lc_warnings/lc_warnings.erl b/lib/dialyzer/test/unmatched_returns_SUITE_data/src/lc_warnings/lc_warnings.erl
new file mode 100644
index 0000000000..cb01a8fde3
--- /dev/null
+++ b/lib/dialyzer/test/unmatched_returns_SUITE_data/src/lc_warnings/lc_warnings.erl
@@ -0,0 +1,95 @@
+-module(lc_warnings).
+-compile([export_all]).
+
+close(Fs) ->
+    %% There should be a warning since we ignore a potential
+    %% {error,Error} return from file:close/1.
+    [file:close(F) || F <- Fs],
+
+    %% No warning because the type of unmatched return will be ['ok']
+    %% (which is a list of a simple type).
+    [ok = file:close(F) || F <- Fs],
+
+    %% Suppressed.
+    _ = [file:close(F) || F <- Fs],
+    ok.
+
+format(X) ->
+    %% No warning since the result of the list comprehension is
+    %% a list of simple.
+    [io:format("~p\n", [E]) || E <- X],
+
+    %% Warning explicitly suppressed.
+    _ = [io:format("~p\n", [E]) || E <- X],
+    ok.
+
+opaque1() ->
+    List = gen_atom(),
+    %% This is a list of an externally defined opaque type. Since
+    %% we are not allowed to peek inside opaque types, there should
+    %% be a warning (even though the type in this case happens to be
+    %% an atom).
+    [E || E <- List],
+
+    %% Suppressed.
+    _ = [E || E <- List],
+    ok.
+
+opaque2() ->
+    List = gen_array(),
+    %% This is an list of an externally defined opaque type. Since
+    %% we are not allowed to peek inside opaque types, there should
+    %% be a warning.
+    [E || E <- List],
+
+    %% Suppressed.
+    _ = [E || E <- List],
+    ok.
+
+opaque3() ->
+    List = gen_int(),
+
+    %% No warning, since we are allowed to look into the type and can
+    %% see that it is a simple type.
+    [E || E <- List],
+
+    %% Suppressed.
+    _ = [E || E <- List],
+    ok.
+
+opaque4() ->
+    List = gen_tuple(),
+
+    %% There should be a warning, since we are allowed to look inside
+    %% the opaque type and see that it is a tuple (non-simple).
+    [E || E <- List],
+
+    %% Suppressed.
+    _ = [E || E <- List],
+    ok.
+
+gen_atom() ->
+    [opaque_atom_adt:atom(ok)].
+
+gen_array() ->
+    [array:new()].
+
+
+gen_int() ->
+    [opaque_int(42)].
+
+gen_tuple() ->
+    [opaque_tuple(x, 25)].
+
+-opaque opaque_int() :: integer().
+
+-spec opaque_int(integer()) -> opaque_int().
+
+opaque_int(Int) -> Int.
+
+-opaque opaque_tuple() :: {any(),any()}.
+
+-spec opaque_tuple(any(), any()) -> opaque_tuple().
+
+opaque_tuple(X, Y) ->
+    {X,Y}.
diff --git a/lib/dialyzer/test/unmatched_returns_SUITE_data/src/lc_warnings/opaque_atom_adt.erl b/lib/dialyzer/test/unmatched_returns_SUITE_data/src/lc_warnings/opaque_atom_adt.erl
new file mode 100644
index 0000000000..b5b51fe75b
--- /dev/null
+++ b/lib/dialyzer/test/unmatched_returns_SUITE_data/src/lc_warnings/opaque_atom_adt.erl
@@ -0,0 +1,9 @@
+-module(opaque_atom_adt).
+-export([atom/1]).
+
+-opaque opaque_atom() :: atom().
+
+-spec atom(atom()) -> opaque_atom().
+
+atom(Atom) ->
+    Atom.