dialyzer_contracts: Consider #{} a violation

This is analogous to the case of nil. Since #{} is a base-case of almost
all map types, contract and success typing sharing #{} does not mean
much, and is often sign of a violation.

1 files changed, 29 insertions, 12 deletions

diff --git a/lib/dialyzer/src/dialyzer_contracts.erl b/lib/dialyzer/src/dialyzer_contracts.erl
index e03e4d5bb4..1895a98e96 100644
--- a/lib/dialyzer/src/dialyzer_contracts.erl
+++ b/lib/dialyzer/src/dialyzer_contracts.erl
@@ -277,28 +277,45 @@ check_extraneous_1(Contract, SuccType) ->
   case [CR || CR <- CRngs,
               erl_types:t_is_none(erl_types:t_inf(CR, STRng))] of
     [] ->
-      CRngList = list_part(CRng),
-      STRngList = list_part(STRng),
-      case is_not_nil_list(CRngList) andalso is_not_nil_list(STRngList) of
-        false -> ok;
-        true ->
-          CRngElements = erl_types:t_list_elements(CRngList),
-          STRngElements = erl_types:t_list_elements(STRngList),
-          Inf = erl_types:t_inf(CRngElements, STRngElements),
-          case erl_types:t_is_none(Inf) of
-            true -> {error, invalid_contract};
-            false -> ok
-          end
+      case bad_extraneous_list(CRng, STRng)
+	orelse bad_extraneous_map(CRng, STRng)
+      of
+	true -> {error, invalid_contract};
+	false -> ok
       end;
     CRs -> {error, {extra_range, erl_types:t_sup(CRs), STRng}}
   end.
 
+bad_extraneous_list(CRng, STRng) ->
+  CRngList = list_part(CRng),
+  STRngList = list_part(STRng),
+  case is_not_nil_list(CRngList) andalso is_not_nil_list(STRngList) of
+    false -> false;
+    true ->
+      CRngElements = erl_types:t_list_elements(CRngList),
+      STRngElements = erl_types:t_list_elements(STRngList),
+      Inf = erl_types:t_inf(CRngElements, STRngElements),
+      erl_types:t_is_none(Inf)
+  end.
+
 list_part(Type) ->
   erl_types:t_inf(erl_types:t_list(), Type).
 
 is_not_nil_list(Type) ->
   erl_types:t_is_list(Type) andalso not erl_types:t_is_nil(Type).
 
+bad_extraneous_map(CRng, STRng) ->
+  CRngMap = map_part(CRng),
+  STRngMap = map_part(STRng),
+  (not is_empty_map(CRngMap)) andalso (not is_empty_map(STRngMap))
+    andalso is_empty_map(erl_types:t_inf(CRngMap, STRngMap)).
+
+map_part(Type) ->
+  erl_types:t_inf(erl_types:t_map(), Type).
+
+is_empty_map(Type) ->
+  erl_types:t_is_equal(Type, erl_types:t_from_term(#{})).
+
 %% This is the heart of the "range function"
 -spec process_contracts([contract_pair()], [erl_types:erl_type()]) ->
                            erl_types:erl_type().