dialyzer: Extend the map implementation's handling of ?unit

The Maps implementation handles ?unit in more cases.

Exactly when t_is_none_or_unit() is to be called is not clear to me.
The added cases are about a map type being ?unit, but the key or the
value of an association can also be ?unit, but that is not always
checked.

2 files changed, 11 insertions, 0 deletions

diff --git a/lib/dialyzer/test/map_SUITE_data/results/map_anon_fun b/lib/dialyzer/test/map_SUITE_data/results/map_anon_fun
new file mode 100644
index 0000000000..cfca5b1407
--- /dev/null
+++ b/lib/dialyzer/test/map_SUITE_data/results/map_anon_fun
@@ -0,0 +1,2 @@
+
+map_anon_fun.erl:4: Function g/1 will never be called
diff --git a/lib/dialyzer/test/map_SUITE_data/src/map_anon_fun.erl b/lib/dialyzer/test/map_SUITE_data/src/map_anon_fun.erl
new file mode 100644
index 0000000000..e77016d68a
--- /dev/null
+++ b/lib/dialyzer/test/map_SUITE_data/src/map_anon_fun.erl
@@ -0,0 +1,9 @@
+-module(map_anon_fun).
+
+%% Not exported.
+g(A) ->
+    maps:map(fun F(K, {V, _C}) ->
+                    F(K, V);
+                 F(_K, _V) ->
+                    #{ system => {A} }
+            end, #{}).