Dialyzer should not throw away spec information because of overspec

1 files changed, 59 insertions, 0 deletions

diff --git a/lib/dialyzer/test/small_SUITE_data/src/extra_range.erl b/lib/dialyzer/test/small_SUITE_data/src/extra_range.erl
new file mode 100644
index 0000000000..9d6ba89c95
--- /dev/null
+++ b/lib/dialyzer/test/small_SUITE_data/src/extra_range.erl
@@ -0,0 +1,59 @@
+%% Test that a spec containing more items than actually returned
+%% (whether by accident or by benign overspeccing) does not prevent
+%% detection of impossible matches.
+
+-module(extra_range).
+
+-export([t1/2, t2/2, t3/2, t4/2]).
+
+-dialyzer([no_return]).
+
+%% this spec matches the behaviour of the code
+-spec normal(integer()) -> ok | error.
+normal(1) -> ok;
+normal(2) -> error.
+
+t1(X, Y) when is_integer(X), is_integer(Y) ->
+    ok = normal(X),
+    error = normal(Y),
+    ok.
+
+
+%% this spec has a typo, which should cause anyone trying to match on
+%% `ok = typo(X)' to get a warning, because `ok' is not in the spec
+-spec typo(integer()) -> ook | error.
+typo(1) -> ok;
+typo(2) -> error.
+
+t2(X, Y) when is_integer(X), is_integer(Y) ->
+    ok = typo(X),  % warning expected - not allowed according to spec
+    error = typo(Y),
+    ok.
+
+
+%% this is overspecified, and should cause a warning for trying
+%% to match on `no = over(X)', because it cannot succeed and either
+%% the spec should be updated or the code should be extended
+-spec over(integer()) -> yes | no | maybe.
+over(1) -> yes;
+over(_) -> maybe.
+
+t3(X, Y) when is_integer(X), is_integer(Y) ->
+    yes = over(X),
+    no = over(Y),  % warning expected - spec or code needs fixing
+    maybe = over(X + Y),
+    ok.
+
+
+%% this is underspecified, which should cause anyone trying to match on
+%% `maybe = under(X)' to get a warning, because `maybe' is not in the spec
+-spec under(integer()) -> yes | no.
+under(1) -> yes;
+under(2) -> no;
+under(_) -> maybe.
+
+t4(X, Y) when is_integer(X), is_integer(Y) ->
+    yes = under(X),
+    no = under(Y),
+    maybe = under(X + Y), % warning expected - not in spec
+    ok.